UNIVERSIDADE FEDERAL DO PARANÁ SETOR DE CIÊNCIAS AGRÁRIAS
DEPARTAMENTO DE FITOTECNIA E FITOSSANITARISMO
PROGRAMA DE PÓS GRADUAÇÃO EM AGRONOMIA – PRODUÇÃO VEGETAL
Leonardo Deiss
OAT GROWTH AND GRAIN YIELD UNDER NITROGEN LEVELS IN AGROFORESTRY SYSTEM IN SUBTROPICAL BRAZIL
Leonardo Deiss
OAT GROWTH AND GRAIN YIELD UNDER NITROGEN LEVELS IN AGROFORESTRY SYSTEM IN SUBTROPICAL BRAZIL
Dissertação apresentada ao Programa de Pós-Graduação em Agronomia, Área de Concentração em Produção Vegetal, Departamento de Fitotecnia e Fitossanitarismo, Setor de Ciências Agrárias, Universidade Federal do Paraná, como parte das exigências para obtenção do título de Mestre em Ciências.
Comitê de orientação: Dr. Anibal de Moraes, Dr. Adelino Pelissari, Dr. Francisco Skora Neto, Dr. Edilson Batista de Oliveira e Dr. Vanderley Porfírio da Silva.
AGRADECIMENTO
Agradecimento ao Comitê de orientação: obrigado Prof. Dr. Anibal de Moraes pela aceitação como seu orientado no programa de pós-graduação, confiança depositada ao me encarregar de realizar este trabalho, orientação, amizade e respeito cedidos incondicionalmente. Ao Prof. Dr. Adelino Pelissari pelos ensinamentos de vida e agronomia. Ao Dr. Francisco Skora Neto pelos presentes ensinamentos agronômicos. Ao Dr. Edilson Batista de Oliveira pelo amparo de seu conhecimento estatístico. Ao Dr. Vanderley Porfírio da Silva pelos ensinamentos sobre os sistemas integrados arborizados.
Agradecimento especial: Agradeço a Georgia Bascherotto Kleina pela ajuda nos trabalhos de laboratório e de tabulação de dados e principalmente pela compreensão dos momentos que não podemos ficar juntos, que espero poder retribuí-la pelo resto de nossas vidas.
Agradecimento a outros pesquisadores: Agradeço a Dra. Laíse Silveira Pontes pelas considerações morfológicas e experimentais e amparo financeiro do projeto. A Dra. Raquel Santiago Barro pela imensurável ajuda cedida durante a condução dos experimentos. Ao Prof. Dr. Sebastião Brasil Campos Lustosa e ao Msc. Newton de Lucena Costa pelas considerações feitas à primeira versão desta dissertação.
Agradecimento aos professores da Universidade Federal do Paraná: Especialmente a professora Dra. Maristela Panobianco por permitir a utilização das balanças de precisão do Laboratório de Análise de Sementes, ao professor Dr. Átila Francisco Mógor pelo empréstimo do pulverizador e aos professores Ricardo Augusto de Oliveira e Claudete Reisdorfer Lang pelas considerações científicas feitas ao trabalho.
Agradecimento aos funcionários da Universidade Federal do Paraná: A Técnica do Laboratório de Fitotecnia Maria Emilia Kudla. A secretária do Programa de Pós Graduação Lucimara Antunes. A Técnica do Laboratório de Análise de Sementes Roseli do Rocio Biora.
Agradecimento aos funcionários do Instituto Agronômico do Paraná: Agradeço a todos que participaram de maneira direta e indireta durante a realização deste trabalho. Assim como na incessante busca pelo conhecimento, que possibilitou conviver com vocês, acredito e espero que meu agradecimento fique guardado em seus corações, muito obrigado. Agradecimento aos administradores Renério Ribeiro de Almeida da Estação Experimental Fazenda Modelo e Giovani Luiz Thomaz da Estação Experimental de Ponta Grossa. E a todos os outros funcionários da Estação Experimental Fazenda Modelo do Iapar e aos funcionários Antônio Carlos Campos (mineiro) e Sandoval Carpinelli do Polo Regional de Pesquisa de Ponta Grossa.
Agradecimento aos colegas: Acredito que os novos e os já conhecidos amigos compreenderam os motivos da realização deste trabalho e muito ajudaram para que este pudesse ser concluído. Ana Carolina Oliveira, Gederson Buzzello, Isabel Cristina Bonometti Stieven, Ivan César Furmann Moura, Luciana Helena Kowalski e Sérgio Rodrigues Fernandes.
Agradecimento aos estagiários: Agradeço a ajuda dos estagiários vinculados à Universidade Federal do Paraná: Adriano Gomes Bueno, Leidimara Nascimento, Lurdes Marina Oracz e Marcelo Palazim e vinculado ao Iapar Polo Regional de Ponta Grossa: Erisson Felipe. Agradecimento especial a Mêmora Bitencourt estagiaria da Universidade Federal do Rio Grande do Sul, pela sua grandiosa ajuda.
Na ciência não existe verdade, a ciência é a verdade.
CRESCIMENTO E RENDIMENTO DE GRÃOS DA AVEIA SUBMETIDA A NÍVEIS DE NITROGÊNIO EM SISTEMA AGROFLORESTAL NO SUBTRÓPICO BRASILEIRO
RESUMO
A adequação das práticas agronômicas tem um papel fundamental no desenvolvimento dos sistemas integrados. A hipótese deste trabalho é que a resposta da aveia aos sistemas integrados não é passível de melhoramento, portanto esta é uma cultura que não possui condições morfofisiológicas para coabitar com as árvores, no subtrópico brasileiro. O objetivo geral deste trabalho foi avaliar se a aveia (Avena sativa L. cv. IPR 126) possui características agronômicas que possibilitam o seu cultivo nos sistemas integrados com árvores, utilizando como referência, a forma de agricultura predominante no subtrópico brasileiro e como prática agronômica, a fertilização nitrogenada. O experimento foi realizado em faixas no delineamento de blocos ao acaso com quatro repetições, dois níveis de nitrogênio (12 e 80 kg N ha-1) em cinco posições equidistantes entre faixas adjacentes de linhas duplas [20 m (4 m x 3 m)] de eucaliptos (Eucalyptus dunnii Maiden) em sistema agroflorestal (SAF) e agricultura tradicional em semeadura direta, no subtrópico brasileiro. As variáveis de crescimento avaliadas foram a taxa de crescimento relativo, taxa de assimilação líquida, fração de massa foliar e taxa de enchimento relativo da panícula. As características dos perfilhos avaliadas foram relação de massa seca e de grãos do colmo principal e perfilhos e número de perfilhos por planta. Na colheita as variáveis avaliadas foram o rendimento biológico e de grãos, componentes de rendimento e índice de colheita. O nitrogênio aumentou o crescimento da aveia quando semeada entre faixas de árvores, entretanto os níveis de nitrogênio alteraram o crescimento diferentemente em posições relativas às faixas adjacentes de eucalipto. A persistência do perfilhamento para produção de grãos da aveia foi dependente do nível de nitrogênio em distâncias relativas as faixas de eucaliptos no SAF. Houve compensação do menor número de cariopses por panícula pelo maior número de grãos por cariopse, assim como maior índice de colheita aonde a aveia acumulou menor fitomassa, nos ambientes com alta interação interespecífica. O nitrogênio promoveu mudança na produção da aveia diferentemente em posições relativas às árvores no sistema integrado. O crescimento e rendimento da aveia em SAF pode ser incrementada através da fertilização nitrogenada. As variáveis que descrevem o crescimento, o perfilhamento e o rendimento de grãos da aveia interagem com os níveis de nitrogênio e as posições relativas as árvores dentro do SAF, portanto diferentes níveis de nitrogênio devem ser utilizados nas posições, para aumentar o potencial de rendimento da aveia nos sistemas integrados.
Palavras chave: Avena sativa L., Eucalyptus dunnii Maiden, sistemas integrados, análise do crescimento, perfilhamento, componentes de rendimento
OAT GROWTH AND GRAIN YIELD UNDER NITROGEN LEVELS IN AGROFORESTRY SYSTEM IN SUBTROPICAL BRAZIL
ABSTRACT
The adequacy of agronomic practices plays a key role in the development of integrated systems. The hypothesis of this work is that the oat (Avena sativa L. cv. IPR 126) response to the arborized integrated systems is not amenable to improvement through agronomic practices; therefore it is a crop which has not morphophysiological conditions for cohabitate with trees, in subtropical Brazil. The general objective was evaluate if the oat has agronomic characteristics which allow its cultivation in the arborized integrated systems, using as reference the predominant agriculture form in subtropical Brazil and as agronomic practice, the nitrogen fertilization. The experiment was carried out in a split-block randomized block design with four replicates, two nitrogen levels, in five equidistant positions between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)] in alley cropping agroforestry system (ACS) and traditional no till agriculture in subtropical Brazil. It was evaluated the growth variables relative growth rate, unit leaf rate, leaf weight fraction, panicle relative filling rate and grains to panicle ratio. The tiller traits evaluated was tillers to main shoot phytomass ratio, tillers per main shoot, grain yield and tillers to main shoot grain yield ratio. At harvest was evaluated biological and grain yield, yield compounds and harvest index. The nitrogen increased the oat growth between the tree tracks, however the nitrogen levels altered the growth response differently in positions relative to adjacent eucalyptus tracks. The oat tillering persistence for grains production depended of different nitrogen level in distances relative to adjacent eucalyptus tracks. At the end of oat cycle, there was compensation of the lower number of spikelets per panicle by the greater number of grains per spikelet, as well as higher harvest indexes where less phytomass was accumulated, in environments with high interspecific interaction. The nitrogen levels increased the oat yield differently at positions relative to the trees in the integrated system. The oats growth and yield in ACS can be improved through the nitrogen fertilization. The variables that describe growth, tillering and grain yield of oat interact with nitrogen levels and positions relative to eucalyptus inside ACS, therefore different nitrogen levels should be used in those positions, to improve the oats yield potential inside ACS.
Key words: Avena sativa L., Eucalyptus dunnii Maiden, integrated systems, growth analysis, tillering, yield compounds
SUMMARY
1. General introduction ... 18
1.1 Economical, social and environmental importance of oats ... 18
1.2 Economical, social and environmental importance of the integrated systems ... 19
1.3 Hypothesis ... 21
1.4 Objectives ... 21
2. Bibliographic review ... 21
2.1 Ecological basis of the interactions between species in the integrated systems ... 21
2.2 Microclimate conditions in agroforestry systems ... 22
2.3 Trees interference in the agroforestry systems ... 23
2.4 Small cereals growth and development ... 25
2.5 Morphophysiological responses of small cereals to the light, water, temperature and nutrients as well as its interactions ... 26
3. CHAPTER 1 ... 31
OAT GROWTH UNDER NITROGEN LEVELS IN EUCALYPTUS ALLEY CROPPING SYSTEM IN SUBTROPICAL BRAZIL ... 31
Abstract ... 31
Introduction ... 32
Materials and methods ... 33
Results ... 36 Discussion ... 40 Conclusion ... 42 Acknowledgements ... 43 References ... 43 4. CHAPTER 2 ... 50
TILLERING AND TILLER TRAITS OF OAT UNDER NITROGEN LEVELS IN EUCALYPTUS ALLEY CROPPING SYSTEM IN SUBTROPICAL BRAZIL... 50
Abstract ... 50
Introduction ... 51
Materials and methods ... 51
Results ... 55 Discussion ... 58 Conclusion ... 61 Acknowledgements ... 61 References ... 61 5. CHAPTER 3 ... 69
OAT GRAIN YIELD UNDER NITROGEN LEVELS IN EUCALYPTUS ALLEY CROPPING SYSTEM IN SUBTROPICAL BRAZIL ... 69
Abstract ... 69
Introduction ... 70
Materials and methods ... 71
Results ... 74
Conclusion ... 80 Acknowledgments ... 80 References ... 80 6. General conclusions ... 86 7. Final thoughts ... 86 8. General references ... 86 GENERAL SUPPLEMENT ... 91
LIST OF FIGURES
CHAPTER 1
Fig. 1 Oat (Avena sativa L. cv. IPR 126) growth traits in days after emergence (DAE), relative growth rate (RGR), unit leaf rate (ULR), leaf weight fraction (LWF), panicle phytomass (PDW) panicle relative filling rate (PRFR) from 126 to 152 DAE under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1), in alley cropping agroforestry system, at A: 2.8 m, B: 6.4 m, C: 10.0 m, D: 13.6 m and E: 17.2 m away from track positioned at the lowest elevation of the slope, between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)] in subtropical Brazil. Vertical bars denote standard errors ... 49
CHAPTER 2
Fig. 1 Oat (Avena sativa L. cv. IPR 126) phytomass (a), tillers to main shoot phytomass ratio (b) and tillers number (c) under nitrogen levels (80.0 kg N ha-1 and 12.0 kg N ha-1) in alley cropping agroforestry system, at A: 2.8 m, B: 6.4 m, C: 10.0 m, D: 13.6 m and E: 17.2 m away from track positioned at the lowest elevation of the slope, between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)] and traditional no till agriculture (F), in subtropical Brazil. Vertical bars denote standard errors ... 63
Fig. 2 Oat (Avena sativa L. cv. IPR 126) traits under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in days after emergence (DAE), above ground biological yield, tillers to main shoot phytomass ratio, tillers per main shoot and tillers to main shoot grain yield ratio in alley cropping agroforestry system, at A: 2.8 m, B: 6.4 m, C: 10.0 m, D: 13.6 m and E: 17.2 m away from track positioned at the lowest elevation of the slope, between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)] in subtropical Brazil. Vertical bars denote standard errors ... 64
CHAPTER 3
Fig. 1 Oat (Avena sativa L. cv. IPR 126) above ground biological yield (a), yield compounds spikelets per panicle (b) and grains per spikelet (c), yield (d) and harvest index (e) in alley cropping agroforestry system, at A: 2.8 m, B: 6.4 m, C: 10.0 m, D: 13.6 m and E: 17.2 m away from track positioned at the lowest elevation of the slope, between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)], under levels of nitrogen (12.0 kg N ha-1 and 80.0 kg N ha-1 fertilizer), in subtropical Brazil. Vertical bars denote standard errors ... 82
Supplement 1 Experimental sketch. Oat (Avena sativa L. cv. IPR 126) under nitrogen levels [12.0 kg N ha-1(clear) and 80.0 kg N ha-1 (dark)] in alley cropping agroforestry system (A_E), at A: 2.8 m, B: 6.4 m, C: 10.0 m, D: 13.6 m and E: 17.2 m away from track positioned at the lowest elevation of the slope, between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)] and traditional no till agriculture (F) in subtropical Brazil ...91
LIST OF TABLES
CHAPTER 1
Table 1 Oat (Avena sativa L. cv. IPR 126) relative growth rate under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 45 Table 2 Oat (Avena sativa L. cv. IPR 126) unit leaf rate under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 46 Table 3 Oat (Avena sativa L. cv. IPR 126) leaf weight fraction under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 47 Table 4 Oat (Avena sativa L. cv. IPR 126) panicle phytomass, panicle relative filling rate and grains to panicle ratio, under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 48
CHAPTER 2
Table 1 Oat (Avena sativa L. cv. IPR 126) grains yield per plant and tiller to main shoot grain yield ratio, under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 65
Supplementary Table 1 Oat (Avena sativa L. cv. IPR 126) above ground phytomass under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 66 Supplementary Table 2 Oat (Avena sativa L. cv. IPR 126) tillers to main shoot phytomass ratio under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil... 67 Supplementary Table 3 Oat (Avena sativa L. cv. IPR 126) tillers number per main shoot under nitrogen levels (12.0 kg N ha-1 and 80.0 kg N ha-1) in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 68
CHAPTER 3
Table 1 Biological yield of oat (Avena sativa L. cv. IPR 126) under levels of nitrogen [12.0 kg N ha-1 and 80.0 kg N ha-1] in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 83
Table 2 Yield compounds of oat (Avena sativa L. cv. IPR 126) under levels of nitrogen (N) [12.0 kg N ha-1(-) and 80.0 kg N ha-1 (+)] in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil 84
Table 3 Yield and harvest index of oat (Avena sativa L. cv. IPR 126) under levels of nitrogen (N) [12.0 kg N ha-1(-) and 80.0 kg N ha-1 (+)]in alley cropping agroforestry system (A_E) and traditional no till agriculture (F) in subtropical Brazil ... 85
1. General introduction
Currently in the world, the agriculture is undergoing a time of change, in which the values of high yielding crops, are being replaced by other values that give greater emphasis on the systems performance that consider environmental, social and economic aspects. This new type of agriculture emphasizes the better utilization of the land units, with high yielding components during all seasons of the year, and promotes balanced development in the long term, mainly based on the diversification of the production system.
In Brazil, particularly in the subtropical region, is emerging a proposal to integrate the components crop, livestock and forest, in the same unit of area, for better utilization and greater conservation of the available natural resources. This system concept is fundamentally based on the knowledge more consolidated until then, of the integrated crop-livestock systems (Carvalho et al. 2010). Although the conception of this research is based on the integration of all three components, it will be addressed issues related to the crop and forest components. At world level, the intercropping of trees and crops has already been widely discussed, at the optics of the agroforestry.
The sustainability of an agricultural system is supported by environmental, social, economic, political and cultural issues. The introduction of trees on the annual crop land is bumping in that the cultural issue, because they do not have concrete answers both on the economic response at the system level, as well as the productivity of the components when it is integrated. As the transition from the conventional system to the no tillage system, the agronomic practices should be readapted for the intercropping systems with trees. To take a step to fill this gap, in order to contemplate responses of the crop component, it will be addressed in this research issues related to the oat culture, one of the main crops used in traditional no till agriculture in subtropical Brazil.
1.1 Economical, social and environmental importance of oats
The oats originate from Mediterranean and are domesticated back to the ancient times (Suttie and Reynolds 2004). The white or yellow-hulled is thought to be the progenitor of the common oat (Avena sativa L.) (Stevens et al. 2004) and this is the naked type (6n=42) used in the commerce (Suttie and Reynolds 2004). Avena sativa is self pollinating hexaploid specie, compatible with the hybridizing techniques (Stevens et al. 2004).
Oats are grown principally in cool moist climates around the world, the production for grain, forage, fodder, straw, bedding, hay, haylage, silage and cheaff are concentrated between latitudes 35-65ºN and 20-46ºS, being sensitive to hot and dry weather (Stevens et al. 2004). Oat is a cereal crop used for human food and animal feed throughout the world (Buerstmayr et al. 2007).
For some time oat has been recognized as a kind of healthy food (Cai et al. 2012). Among cereals, oat is considered one of the most nutritious, rich in protein and fiber, with their vitamins and minerals are concentrated in the bran and germ (Stevens et al. 2004). Significant attention was given for oat in recent years due to the human health benefits of consuming it as a whole-grain food (Newell et al. 2011). In contrast, the grain is mainly used as animal feed, because for human consumption need more laborious preparation than wheat, since that has to be milled (Suttie and Reynolds 2004). During the milling process, oat kernels are removed from the husk and other contaminants (White and Watson 2010).
Oat remain the important as a grain crop, for specialist uses in developed economies and for common people in marginal developing world (Stevens et al. 2004). Oats are important crop for the grain transforming industry in Brazil, Argentina and Chile; in addition is an economical and technical alternative crop in many production systems in the region (Federizzi and Mundstock 2004). “Oats are finding new uses and farmers and researchers are finding ways of integrating them into their productions systems” (Suttie and Reynolds 2004). Oats importance for the integrated systems is related to their multiple uses, since the integrated rural proprieties have diversified components, which necessity of agronomic particularities, such as fodder for the livestock or cover crops for the no tillage soil management.
1.2 Economical, social and environmental importance of the integrated systems
In production systems, the agronomic practices (e.g. fertilization and plant arrangement) and the plant species (e.g. additional non-foliar photosynthesis) with improve the capacity for better utilize natural resources (e.g. water, nutrients and light), contribute to the agroecosystems sustainability. The integrated systems importance for the world is related to the following question: how we (rural producers, researchers and government) improve sustainably the production of food, fibers, energy and wood, without the need to opening new
agricultural areas, and to sustain a world population expected by future, in a conservationist way?
Integrating the trees in the agricultural land provide a sustainable land use management (Tsonkova et al. 2012). The agroforestry is a land use practice which combine trees and agricultural crops or livestock in the same field (Quinkenstein et al. 2009). The components combination, on space and time, determine the structure of these systems. The components integration could be made between: crops and trees, livestock (pastures and animals) and trees or crops, livestock (pastures and animals) and trees. These integrated systems provide an array of benefits for the animals or cultivated plants (Quinkenstein et al. 2009), maximizing the provision of ecosystem goods and services (Tsonkova et al. 2012).
In temperate regions, the objectives for establishing agroforestry systems are the production of tree or wood products, agronomic crops or forage, livestock, and improvement of crop quality and quantity, at a scale and magnitude corresponding to the prevailing social as well as economic conditions, and environmental benefits (Jose et al. 2004). One variant of the traditional agroforestry system is the alley cropping, when several crops are cultivated in strips or alleys between hedgerows of trees or shrubs (Quinkenstein et al. 2009). Currently in Brazil, this modality of integrated system is referred to as crop forest integration system (Balbino et al. 2011). The potential application of this modality of integrated system are the biomass production, multipurpose windbreaks, riparian buffer strips, contour planting for erosion control and fertility improvement by nitrogen-fixing trees (Quinkenstein et al. 2009).
Fast growing tree species, planted in high densities (10,000–20,000 trees per hectare) enable, in a period of 20 years, two to ten harvests, when the biomass harvested consists of small diameter stems, twigs and branches, with a large fraction of bark being used for the wood chips production (Quinkenstein et al. 2009). In the alley cropping systems, the harvested biomass of trees is mainly consisted of large diameter stems, with low percentage of bark (Quinkenstein et al. 2009).
Compared to the conventional agriculture, the alley cropping systems with strips of short rotation plantations, have more intensive nutrient cycling, in terms of higher rates of turnover or transfer of nutrients within the system, lower outputs (Tsonkova et al. 2012) and reduced nutrients exportation (Quinkenstein et al. 2009; Tsonkova et al. 2012). The leaching of nutrients below the rooting zone of the crops cause a reduction in the seepage water quality and consequently of the groundwater, and implicate on the temporarily lost of nutrients from the agricultural system (Tsonkova et al. 2012). The trees have the capacity for intercepting
and absorbing the lost nutrients below the annual intercropped rooting zone, and re-deposit on litter form, for subsequent annual crops use.
The correct choice of which annual crop can cohabitate with the selected trees in integrated systems should be based in ecological principles that promote sustainably yield potential of these system. The comparison of the agronomic response of crops, obtained inside the arborized integrated systems, with those obtained in the traditional no till agriculture, should be made taking into consideration that these crops have not gone through breeding programs, to be grown in these types of systems.
1.3 Hypothesis
The hypothesis of this work is that the oat response to the arborized integrated systems is not amenable to improvement through agronomic practices; therefore it is a crop which has not morphophysiological conditions for cohabitate with trees, in subtropical Brazil.
1.4 Objectives
The general objective was to evaluate if the oat has agronomic characteristics which allow its cultivation in arborized integrated systems, using as reference, the predominant agriculture form in subtropical Brazil and as agronomic practice, the nitrogen fertilization.
The specifics objectives were to determine how growth and yield of oat (Avena sativa L. cv. IPR 126) are influenced by nitrogen levels, in eucalyptus (Eucalyptus dunnii Maiden) alley cropping agroforestry system and traditional no till agriculture in subtropical Brazil.
2. Bibliographic review
2.1 Ecological basis of the interactions between species in the integrated systems
The environment utilization by the plant species includes three main components: space, resources and time (Jose et al. 2004). In the integrated systems, the interactions between species include aspects of the water and nutrient cycle, the microclimate and the biodiversity (Quinkenstein et al. 2009). The key for improving the yield potential of the
integrated systems is understand how the biotic and abiotic environmental resources are utilized in the time and the space. Ecological niches are created by the trees planted in alley cropping within the agricultural landscape, for plants with different environmental requirements (Tsonkova et al. 2012).
The interactive relationship between species in the agroforestry systems can occur such as predation, parasitism, amensalism, mutualism, commensalism and neutralism (Jose et al. 2004). When the interaction between components is positive or synergistic, the complementarity results in an overyielding system, when the interaction is negative or antagonistic the species become competitive resulting in an underyielding system (Jose et al. 2004). The net result of synergistic and antagonistic interactions among the components results on the system productivity (Jose et al. 2004).
2.2 Microclimate conditions in agroforestry systems
The enhancement of agricultural sustainability and profitability are benefited by the alley cropping microclimates contribution (Quinkenstein et al. 2009). The microclimate is modified by the trees presence, in terms of temperature, light quality and intensity, wind speed and water vapor content or partial pressure (Jose et al. 2004). The microclimatic site dependant space effect, from close to wide spacing between hedgerows, is modified by increasing temperature extremes, wind speed, soil evaporation, humidity balance and decreasing shading of crops (Quinkenstein et al. 2009). The temperatures in the alley cropping systems have small variation amplitude.
The microclimatic conditions within the agroforestry system, in the time advancement, could be deteriorated or ameliorated, trough the altered interaction patterns between sunrays and tree canopies, resulting from changing solar elevation and angle at various times of the day (Kohli and Saini 2003) and seasons. In addition to sun angle variations during the day, wind induces tree canopy movement, with produces frequent fluctuations in radiation within the agroforestry system (Kohli and Saini 2003). The shading degree is controlled by the hedgerows orientation (Quinkenstein et al. 2009) in relation to the sun pathway. The tree canopies reduce the radiation intensity altering the light wave lengths arriving in the soil surface (Taiz and Zeiger 2010).
Intercropped trees intercept the radiation and reduce the wind speed (Kohli and Saini 2003). The hedgerows are a permeable wind break, the porosity is determinant on wind speed
as well as on the quiet zone size, the height determines the efficiency, and the orientation in relation to the prevailing wind direction, exerts important influence on the wind characteristics inside the system (Quinkenstein et al. 2009).
An increase in the amount of soil water available can be attributed for the reduction in the soil water evaporation, which is related to a decrease in wind speed, promoted by the hedgerows planted in alley cropping (Quinkenstein et al. 2009). In hot and dry environments, the primary effect of trees as windbreak is to reduces the turbulent transfer of heat and water vapor (Kohli and Saini 2003). The evaporation from the bare soil is reduced due to a wind speed reduction, as well as the water vapor transfer away from the surface, helping to conserve soil moisture (Tsonkova et al. 2012).
In agroforestry systems, the spatial distribution of water reaching the soil from the rainfall is determined by its partition between through fall, stem-flow and interception loss by plant canopies (Siles et al. 2010). The tree rows reduce the soil evaporation by shading and “by the creation of a rain shadow on the leeward side or trapping rain fall on the windward side or through the more even distribution” (Quinkenstein et al. 2009).
2.3 Trees interference in the agroforestry systems
The hedgerows in the alley cropping system could enhance or reduce the crop growth and yield, through the microclimate improvement or the interspecific competition for water, nutrients, and light (Tsonkova et al. 2012). The prevalence of benefits or competition is dependent of the site conditions and crop species (Tsonkova et al. 2012). Other benefits can be generated by the trees in the integrated systems, by alteration on the water balance and nutrient cycling. The trees interference can be malefic or benefic. The study of the interactive relationship between species needs to consider all biotic and abiotic elements which can influence that coexistence.
2.3.1 Facilitating conditions in agroforestry systems
Late sown wheat in an agroforestry system, have possibility for grown under higher temperatures during the vegetative stages and lower temperatures during the reproductive stages (Kohli and Saini 2003). Intercropped trees promote alteration on crop energy balance by interception of radiation and reduction of wind speed (Kohli and Saini 2003).
Reduction of the turbulent transfer of heat and water vapor promoted by the windbreaks in the hot and dry environments, modify the crop water use efficiency by reducing evapotranspiration (Kohli and Saini 2003). The trees reduces evaporative stress by slowing the movement of air, and the temperature reduction promoted by the trees can attenuate heat stress of crops (Jose et al. 2004). For ameliorate plant water stress, plant canopies generate cooler and moister atmosphere (Holmgren et al. 2012).
The shade could improve the performance of shade tolerant species for the negative effect of drought, and shade intolerant species have non-linear response along the light gradient increases, more severely affected at higher and lower light availability (Holmgren et al. 2012).
A new component is introduced into the nutrient cycle when trees are integrated on agricultural systems (Quinkenstein et al. 2009). The safety net hypothesis of nutrient capture assumes that the roots of trees retrieve the nutrients below the rooting zone of adjacent crops, and have capacity for recycling these nutrients as litterfall and root turnover in the cropping zone (Jose et al. 2004), implying in a better use of nutrients by the integrated systems. According to Moreno et al. (2007), 80 to 100 years old Holm-oak trees (Quercus ilex L.) promoted a positive effect beneath the tree canopy than beyond the canopy projection, on the soil chemical characteristics organic matter, total nitrogen, exchangeable-K+, cation exchange capacity, sum of exchangeable base cations, nitrate, available P and exchangeable-Ca2+.
In intercropped oat plants, the contents of potassium, nitrogen and calcium, oppositely to the phosphorus and magnesium, were increased by the fertilization, which did not interact with the distances of the trunk of old Holm-oak, in Spanish dehesas (Moreno et al. 2007). These five elements contents decreased with increasing the distance from the oak trunk and significant correlations existed between soil and crop nutrients (Moreno et al. 2007).
Wheat intercropped by poplar (Populus deltoides Bartr.) had grains nutrient concentrations with higher nitrogen followed by potassium and phosphorus, whereas in straw the nutrient concentration of potash was followed by nitrogen and phosphorus, this variation could be due to genetic potential to extract nutrients from the soil (Gill et al. 2009).
Tsonkova et al. (2012) and there cited authors concluded that at post mining sites soil nitrogen of alley cropping systems with the tree species black alder (Alnus glutinosa (L.) Gaertn.), black locust (Robinia pseudoacacia L.), poplar (Populus spp.) and grey alder (Alnus
incana L. Moench) increased in 0-30 cm soil layer with increasing age of trees.
A comprehensive study of nitrogen mineralization from eucalyptus yardwaste mulch, applied to young avocado trees, demonstrate the influence of elevated moisture, in addiction
to higher minimum temperatures and lower maximum temperatures, at lower position of mulch layer (in relation to abstinence), which promote higher rates of nitrogen mineralization and enhancing of microbial decomposition (Valenzuela-Solano et al. 2005).
2.3.2 Competition in agroforestry systems
The plant responses to light quality and intensity is dependent to the carbon fixation mechanism. The photosynthetic rate of C3 plants increases as photosynthetic active radiation increases until 25 % to 50 % of full sunlight, then remains constant, in contrast to C4 plants, that continues to increase the photosynthetic rate up to full sunlight (Jose et al. 2004). Theoretically, C4 plants planted under shade should be able to perform worse than C3 plants in agroforestry systems (Jose et al. 2004), however the shade is not the unique factor which can cause interference on the adjacent crops of these systems.
In terms of water resources, trees planted in hedgerows are competitors for crops (Quinkenstein et al. 2009). The root distribution of the trees and crops species determines the intensity for water competition (Quinkenstein et al. 2009). The root distribution of Eucalyptus and Pinus species in agricultural land adjacent to tree lines, have greater potential for competing for water with annual crops, because the greatest density of roots are distributed in the top 0,5 m of the soil profile and are negatively correlated to soil water content (Sudmeyer et al. 2004). Furthermore, the intensity of water competition is dependent of the site conditions, such as the depth of table water and amount and seasonal distribution of precipitation (Quinkenstein et al. 2009).
Decrease in yield is expected with the absence of fertilization in agroforestry systems (Jose et al. 2004). When fertilizer is applied to annual crops, “some of the nutrients will be intercepted and taken up by tree roots” (Zamora et al. 2009).
The degree to allelochemicals (allelopathic chemicals) negatively affecting the growth of plants depends to their rates and residence times as well as the combinations into the ecosystem (Jose et al. 2004).
2.4 Small cereals growth and development
Small cereals development is categorized into the major phases vegetative, generative and grain filling (Peltonen-Sainio and Rajala, 2007). The earlier development comprises the
vegetative stage, which initiate with the leaf primordia formation and their associated axillary bud, followed by the maturing of the leaf (Klepper et al. 1982). After that, begins the tillering. The tillers origin from the axillary buds (Evers et al. 2006). When the tiller are synchronized with the main stem, a new individual plant is introduced for compose community. The grain filling phase starts post-anthesis (Peltonen-Sainio and Rajala, 2007).
The inflorescence in wheat and barley is a spike rather than a panicle as in oats (Browne et al. 2006). The panicle is a compost inflorescence in oats which is constituted by rachis where at nodes origin branches, and at that ends appear spikelets, which comprises one, two or three grains (Browne et al. 2006). Sheehy et al. (2004) demonstrated that rice has a bi-phasic growth, which comprises the vegetative growth followed by the reproductive growth. In high yielding rice, the heterotrophic growth of panicle had the same maximum growth rate of the autotrophic vegetative component (Sheehy et al. 2004). During the reproductive phase oat panicle and wheat spike promote additional non-foliar photosynthesis (Jennings and Shibles 1968; Maydup et al. 2010).
In grasses the spikelet represents the basic inflorescence, and is constituted by glumes, lemma and palea. The husk, comprises the lemma and palea, and constitutes a quarter of the oat grain weight (Browne et al. 2006), proportion which is principally genetically determined and it‟s not suitable for human consumption, because is fibrous (White and Watson 2010). “Oats comprise two very distinct sub-populations of primary and secondary grain” (Browne et al. 2006). Reduced photoassimilates during oat grain filling promote the abortion of grains, resulting in substantial investment wasted on a per grain basis, because the size and weight dimensions of the husks (Browne et al. 2006).
In the British Isles, oat suitability for milling is derived from screenings (proportion of the grain by weight which passes through a 2.0-mm sieve), hectolitre weight (kg hl−1), kernel content (%), hullability and the content of free kernels (Browne et al. 2006). These characteristics were mainly influenced by variety and little influenced by nitrogen, seed rate and plant regulator, even thought nitrogen largely increases yield (Browne et al. 2006). The hullability is the ease with the kernels is separated from the husks (White and Watson 2010).
2.5 Morphophysiological responses of small cereals to the light, water, temperature and nutrients as well as its interactions
In the agroecosystems, the crops rarely respond to one isolate environmental stimulus. So the environmental resources availability, which could promote benefits or stress on the plant community, must be taking into account. The plants morphophysiological apparatus responds to a natural environment variation (e.g. cumulus cloud cover) or to the anthropic purpose alteration (e.g. sunflecks in agroforestry or agronomic practices).
In oat intact leaves, the quantum yield of photosystem II decreased when photonic flux density increased (between 60 and 1250 µmol−2 s−1 PAR), and was higher in plants grown under low light intensity than in high light intensity (Quiles and López 2004). The photoinhibition occurred when leaves were exposed to more photons than they can utilize for the photosynthesis; the excess promoted the production of reactive oxygen, which can cause damage on the photosystem II (Quiles 2005). In consequence of high light intensity the maximum value of the quantum yield of photosystem II of oat intact leaves was reduced approximately 9% (Quiles and López 2004).
The optimum line between increasing light intensity and the relative electron transport rate, which the last plays in the photoprotection (Quiles and López 2004), occurred when this relationship was linear, and determined the maximum value of quantum yield of photosystem II of oat intact leaves (Tallón and Quiles 2007). When the photosystem II quantum yield decreased, the relative electron transport rate decreased below the values predicted by the optimum line, reflecting a nonradiative dissipation of excitation energy (Tallón and Quiles 2007).
The synergistic effect of high light intensity and moderate heat promoted a severe decrease in the maximal quantum yield of PSII (Quiles 2006), and reduction on the capacity of photosynthetic electron transport, indicating a moderate and chronic inhibition of PS II, in all development stages (young, mature and senescent) of the first leaf of oat (Tallón and Quiles 2007).
A leaf has fast adaptation to shade environments, altering chloroplast protein and pigment composition to optimize light capture and light use efficiency, even though has lower rates of assimilate production (Paul and Foyer 2001). Plant responses to red: far red ratio, due to competition with neighbours under natural conditions, are detrimental for the yield of crops (Ugarte et al. 2010).
The wheat did not produce any secondary tillers under 75 % reduction of full daylight, and the maximal tillers number per plant produced for population densities of 100, 262,3 and 508 plants m-2, were 8,9, 5,7 and 3,7 in full daylight, and 3,0, 1,3 and 0,7 in shaded plants, respectively (Evers et al. 2006). The percentage of mortality of tillers by senescence, after the
wheat reaching a tillering peak, were 44% higher in plants in full daylight than in shade of 25% of full daylight, for population densities of 100 and 262,3 plants m-2 and approximately 12% higher for population of 508 plants m-2 (Evers et al. 2006).
The relationship between the phytochromes and the phytohormones could affect emission and maintaining of the tillers, like that on growth, because alters the apical dominance (Almeida and Mundstock 2001). Induced by far red enriched light, the auxin transport inhibitor abolishes hypocotyl elongation (Stamm and Kumar 2010). The exposition of wheat plants to low red: far red light ratio promoted lower dry matter accumulation at the early stages of the stem (peduncle) and the ear development, which are partially compensated at the later stages of development by the higher rates of dry matter accumulation; stem length was chronically delayed during this period (Ugarte et al. 2010). The reduction in grain yield of wheat, occasioned by the supplemented low red: far red light cannot be regarded, to the resources investment for increase plant stature (Ugarte et al. 2010).
During oat (Avena sativa L. cv. Larry) grain filling, measurements made in variable sun light, at the first or second leaves below the inflorescence, indicated with the rates of net photosynthesis during shade periods showed decline, with insignificant concomitant reductions of the rates of net photosynthesis (~3 µmol m-2 s-1) after periods of shade (steady-state full sun) (Fay and Knapp 1993). Oats has high levels of net photosynthesis, high stomatal conductance to H2O vapor, and moderately low leaf water potential, when is
subjected to a variable light level, and it is species with highly dynamic stomata (Fay and Knapp 1993).
The oat water use efficiency decreased when leaves were shaded, and is partially recovered even during the shade period as stomata closed, than when full day light returned, water use efficiency re-increased above of initial full day light, and returned to steady state as stomata opened (Fay and Knapp 1993). During shade periods their stomata closed slowly or not at all and then reduced water use efficiency (Fay and Knapp 1993). The stomatal conductance to H2O vapor in the variable sun light environment, had insignificant rates of
stomatal opening and closure, with decreases from sun to shade, with progressively lower re-increases in response to sun, and concomitant delays of stomata fully reopen, at beginning of full light periods (Fay and Knapp 1993).
The performance of ecotypes xeric and mesic of Avena barbata in response to moderate drought stress reduce 221% vegetative biomass accumulation and 54% seeds production, despite in the well-watered ambient occurred eight-day delay in flowering time and 146% higher seed abortion (Sherrard et al. 2009). Physiological traits of these ecotypes
under wet conditions compared to the dry ambient, seventy days after germination, increased 39% photosynthetic rate, 303% stomatal conductance, and 69% photosynthetic capacity and decreased 26% chlorophyll concentration (Sherrard et al. 2009). Morphological traits leaf mass per area and stomata longer of well-watered genetic lines had increment of 9% and 8%, respectively, compared to the dry genetic lines (Sherrard et al. 2009).
Plant performance of different species at environmental gradients tend to be non-linear response (humped-back shape) of interactive effects of water availability and light, drought negative effect being lower at intermediate irradiance and more severe at the extremes of light availability (higher and lower) levels (Holmgren et al. 2012). Maximum photosynthetic capacity, maximum photochemical efficiency of photosystem II and stomatal conductance are very sensitive to combined effects of water and light, and lower negatively affected by drought at intermediate light availability (Holmgren et al. 2012).
Oats have a positive correlation between vegetative growth rate and panicle filling rate under a favorable climatic conditions (precipitation and temperature), this association was insignificant and the rates are lower under stress of low precipitation and temperature above normal (Peltonen-Sainio 1993).
The nitrogen could be considered a fundamental nutrient for small cereals, because is determinant for growing, which results in yield, although are highly sensitive to the lodging, which is one main factor that cuts down productivity. Furthermore, in order to optimize economic returns and minimize environmental impacts, improving the agricultural use of nitrogen is needed (Carranca et al. 2009). The nitrogen uses during the plant life cycle are subdivided in the vegetative and reproductive stages. In the vegetative phase, the young leaves and roots are sinks for inorganic N uptake, through the amino acids synthesis and storage, via the nitrate assimilation pathway, which are utilized in the synthesis of proteins and enzymes, involved in biochemical pathways and the photosynthetic apparatus, for conduct plant growth and development (Kant et al. 2011). During the reproductive phase, the leaves and shoot act as a source of nitrogen assimilation and remobilization providing amino acids to flowering and grain filling, than resulting in yield (Kant et al. 2011). In wheat, “during the final stages of grain development, glumes play a major role in feeding grains with nitrogen” (Lopes et al. 2006).
When the nitrogen rate increased the number of panicles and spikelets, greater competition resulted in greater grain mortality (Browne et al. 2006). As the nitrogen rate increased from 40 to 200 kg ha-1, the oat proportion of primary grain relative to secondary grain decrease more in weight than in number, due to a greater increase in weight of
secondary grain compared to the primary grain, even though the mean weight of secondary grain was smaller than primary grain (Browne et al. 2006).
3. CHAPTER 1
OAT GROWTH UNDER NITROGEN LEVELS IN EUCALYPTUS ALLEY CROPPING SYSTEM IN SUBTROPICAL BRAZIL
Leonardo Deiss 1, Anibal de Moraes 1, Adelino Pelissari 1, Francisco Skora Neto 2, Edilson Batista de Oliveira 3 and Vanderley Porfírio da Silva 3
1
Federal University of Paraná, Agricultural Sciences Sector, Phytotechique and Phytosanitary Department, Rua dos Funcionários, 1.540, 80035‑050, Curitiba, Paraná, Brazil. 2 Agronomic Institute of Paraná, Research Regional Center of Ponta Grossa, Rod. do Café, km 496, Av. Presidente Kennedy, s/nº, Post Office Box 129 - 84001-970, Ponta Grossa, Paraná, Brazil. 3 Embrapa Florestas, Post Office Box 319, CEP 83411‑000, Colombo, Paraná, Brazil.
L Deiss
leonardodeiss@ufpr.br 00 55 41 3505633 00 55 41 3505601
Abstract
Plant growth analysis was performed to access how the oat (Avena sativa L. cv. IPR 126) cultivated for grain, responds to the eucalyptus alley cropping system (ACS) in subtropical Brazil. The hypothesis of this work is that the nitrogen does not increase the oat tolerance to the trees interference, then the oat growth response is not modified by the nitrogen in distances relative to the eucalyptus tracks. Thus, the nitrogen can not be utilized to improve the oat growth in ACS. The objective of this study was to determine how the oat growth is influenced by the nitrogen levels (12 and 80 kg N ha-1), in five equidistant positions between two adjacent eucalyptus (Eucalyptus dunnii Maiden) double line tracks [20 m (4 m x 3 m)] in ACS and traditional no till agriculture, in subtropical Brazil. The experiment was carried out in a split-block randomized block design with four replicates. It was evaluated the oat relative growth rate, unit leaf rate, leaf weight fraction, panicle phytomass, panicle relative filling rate and grains to panicle ratio. The nitrogen levels altered the growth response differently in positions relative to adjacent eucalyptus tracks, therefore different nitrogen levels should be used in positions relative to the trees, to improve sustainably the oat yield potential in ACS.
Key words: Avena sativa L., Eucalyptus dunnii Maiden, integrated systems, growth analysis, agroforestry
Abbreviations: ACS, alley cropping agroforestry system; AGR, traditional no till agriculture, RGR, relative growth rate; ULR, unit leaf rate; LWF, leaf weight fraction; DAE, days after emergence
Introduction
The crop yield reflects how the crop expresses its genetic potential, allocating recourses at each stage of development, due to the environmental resources availability. In an agroforestry system, the annual crop growth response is dependent of a range of facilitation and competition relationships, mainly influenced by the trees, which promote biotic and abiotic changes, on the agroecosystem. The growth analysis is a tool that can be used to help understand how these relationships promoted or not promoted changes on the crop cycle, to support the productive responses.
The central parameter in plant growth analysis is relative growth rate (RGR), which is composed by the unit leaf rate (ULR), specific leaf area (SLA) and leaf weight fraction (LWF) (Hunt et al. 2002). The RGR measures the plant growth efficiency, the ULR is a physiological trait which reflects the plant balance between photosynthesis and respiration per unit of leaf area (Useche and Shipley 2010) or mass (Reich et al. 2003), the SLA is a morphological trait which reflects the area for light interception per unit of mass invested in leaves (Useche and Shipley 2010) and the LWF measures the productive investment dealing with the relative expenditure on potentially photosynthesizing organs (Hunt 2003).
The arboreal component of the agroforestry systems promotes interference on the annual crop community, which can be negative or positive. In this sense, the agronomical practices commonly used for the annual crop, must be readapted taking into account, the interaction between species in the integrated systems.
The oats under full daylight compared to partial light availability, reduced leaf area and increased the allocation to roots, and the nutrient stress increased the roots production with concomitant decrease in allocation to leaf mass (Semchenko and Zobel 2005). The response to an intense interspecific competition for nitrogen is positively related with plant ability to minimize plasticity in RGR, when nitrogen availability is reduced (Useche and Shipley 2010). The hypothesis of this work the oat growth response is not modified by the nitrogen in distances relative to the eucalyptus tracks, in ACS. Thus, the nitrogen not can be utilized to improve the oat growth in ACS.
The objective of this study was to determine how the oat (Avena sativa L. cv. IPR 126) growth is influenced by the nitrogen levels, in positions relative to adjacent eucalyptus (Eucalyptus dunnii Maiden) tracks in ACS and traditional no till agriculture (AGR), in subtropical Brazil. The oat IPR 126 is a cultivar with ability for forage and cover crop, however in this work were addressed issues related to the growth until the end of its cycle.
Materials and methods
Study site
The experiment was conducted at the Experimental Station Model Farm of the Agronomic Institute of Paraná (25°06‟19” S 50°02‟38” W, 1020 m above mean sea level) located in Ponta Grossa, Paraná, Brazil. The climate classification of the region, according to the Köppen classification system, is a temperate, with no definite dry season, the average of total annual rainfall, temperature, evapotranspiration and relative humidity are between 1600 to 1800 mm, 17 to 18 °C, 900 to 1000 mm and 70 to 75 %, respectively (http://www.iapar.br/modules/conteudo/conteudo.php?conteudo=677).
The soil classification of the study area according to Santos et al. (2006) is a red-yellow latosol typical dystrophic, moderate, mild medium texture, wavy soft relief phase (4-8% slope). Soil samples were collected at 0-0.20 m depth, at the positions level (described below), and formed a composite sample for the experimental area. The soil analysis resulted in the following characteristics (means ± standard deviation, n = 6): pH (CaCl2) 4.9 ± 0.20,
pH (SMP) 6.2 ± 0.15, Al+3 0.13 ± 0.13 cmolc dm-3, H++Al+3 4.43 ± 0.55 cmolc dm-3, Ca+2 3.07
± 0.79 cmolc dm-3, Mg+2 2.47 ± 0.37 cmolc dm-3, K+ 0.12 ± 0.03 cmolc dm-3, P 6.65 ± 2.17
mg dm-3, C 26.4 ± 1.3 g dm-3 and clay 447 ± 16 g kg-1.
The tree specie of ACS is Eucalyptus dunnii Maiden, which were implemented in 2007 in double line tracks. AGR was used to compare the predominant form of agriculture of the region and was located next to the arborized system (less than 200 m). Both systems were previously areas of native grassland, and had similar crop historic.
The tracks of trees were positioned in levels with guideline, where the track of trees located in the center of the slope of the area was set in level, and the other adjacent tracks were placed parallel to up and down on the slope. The spacing between two adjacent tree tracks
(intercropped track) along the guideline level direction is 20 m, the distance between two adjacent rows in a track is 4 m, and the distance of two trees in a row is 3 m.
The average tree height and diameter on April 2010 were 11.9 m and 13.9 cm, respectively. The eucalyptus trees were thinned out and the remaining trees had their branches pruned to half of trees height. Intercropped annual crops are planted one m from the tree stems because of physical limitation to approximation of agricultural implements, making oat track with 18 m long.
Before sowing (six days) the oat, glyphosate (0.9 kg ae ha-1) was applied to eliminate remaining weeds from the corn (Zea mays L.), the preceding crop. Using a no tillage implement, the oat (Avena sativa L. cv. IPR 126) was sown at the rate of 40 kg seeds ha-1 and fertilized at 300 kg ha-1 of 04-30-10 (N-P2O5-K2O), on June 16th 2011. Ten days after sowing,
the emergence occurred and this date was used as reference. During the oat cycle, for weed control metsulfuron-methyl (2.4 g ai ha-1) was applied before the tillering stage and to diseases control pyraclostrobin + epoxiconazole (183 g ai ha-1) was applied at the booting stage.
Experimental design
The experiment was carried out in a split-block, where each set of treatments were in a randomized complete block design arrangement, with four replicates, that included two levels of nitrogen (12.0 and 80.0 kg N ha-1) and blocks as main plots and six positions (five positions between two eucalyptus tracks and one outside the system) as split-blocks. At the tillering stage, 28 days after emergence (DAE), additional nitrogen in urea form (46 % N) was uniformly hand-applied (68.0 kg N ha-1) or non-applied (0.0 kg N ha-1). The split-blocks were 14 rows 5 m long with 18 cm between rows. A border of 0.4 m was left on each side of the split-block. The five positions between the eucalyptus tracks and latter one outside of the intercropping system are denoted as A, B, C, D and E for ACS and F for AGR. The positions within the integrated system (A_E) are distances between tree tracks. The letter A represents the smallest elevation of the slope, and the letter E the highest elevation of the slope. This is always valid because the system was implemented in curve level. Therefore, the distances, denoted as positions, represents the oats growing at A: 2.8 m, B: 6.4 m, C: 10.0 m, D: 13.6 m and E: 17.2 m away from track positioned at the lowest elevation of the slope, between two adjacent eucalyptus double line tracks.
Growth analysis of oat
For growth analysis, the area (12.6 m-2) of split-blocks was subdivided in seven crescent portions (0.3 m for the first with increment of 0.1 m for subsequent, until 0.9 m for the last) for sampling in time during the oat cycle. The samplings were done in the central position of each portion (described below).
Plant measurements during oat growth
Oat growth was assessed by harvesting 1 m-1 in seven sampling dates during the oat cycle. The oat development stages at the sample time were: leafy at 21 DAE, tillering at 42 DAE, tillering peak at 63 DAE, elongation start at 84 DAE, booting/flowering at 105 DAE, grain filling at 126 DAE and maturation at 152 DAE.
The plants were uprooted to enable the identification of the tillers, and then the roots were cut for determination of dry matter. 1 m-1 was collected from a central position of the portion designated for each sample (described above), by placing a rectangle cast iron, of 1.8 m long (positioned perpendicular to the tracks of trees) by 10 cm wide, that always comprised 10 rows of crop with 10 cm length.
All plants of 1 m-1 collected, were counted and separated into main shoot and tillers and each one into leaves, shoots (stems) and senescent material in the vegetative stages, as well as panicles in the reproductive stages, dried at 65° C and weighed after reaching a constant weight. The dry weights of panicles were evaluated at 126 DAE and 152 DAE. The grains were threshed using a motorcycle tire chamber and separated from other materials (rachis, branches, and glumes) with a pressurized air blower. The grains were re-dried at 65° C and weighed after reaching a constant weight. The grain to panicle ratio was determined at 152 DAE.
Growth data analyses
The oat phytomass per plant was determined from the product of the phytomass per square meter and the total number of plants per square meter. The growth data analysis was performed according to purely classical approach (Hunt et al. 2002).
From the oat phytomass per plant RGR (mg mg-1 day-1) was calculated using the respective equation (Hunt et al. 2002):
RGR = (1 / W) (∆W / ∆t) = (ln W2 – ln W1) / (t2 - t1) (equation 1)
where W 1 and W 2 are total dry weights in milligrams of the whole plant at times t 1 and t 2.
Using a mass basis (Reich et al. 2003) ULR (mg mg-1 day-1) was calculated using the respective equation (Hunt et al. 2002):
ULR = [(W2 – W1) (ln L W2 – ln L W1)] / [(L W2 – L W1) (t2 - t1)] (equation 2)
where LW1 and LW2 are leaf dry weights in milligrams of the whole plant.
LWF (mg mg-1) was determined using the respective equation (Hunt et al. 2002): LWF = LW / W = (LW1 / W1 + LW2 / W2) / 2 (equation 3)
Substituting the total dry weigh per plant on the equation 1, by the panicle dry weight in milligrams, was determined the panicle relative filling rate (PRFR) (mg mg-1 d-1) from 126 DAE to 152 DAE.
Statistical analyses
The statistical analyses were performed using the framework split block design, in the General Linear Models procedure of Statistica 8.0 for Windows (StatSoft, Inc., Tulsa, OK, USA), with the following factors: levels of nitrogen (supply or non-supply of additional nitrogen on tillering) and positions (five positions between two eucalyptus tracks and AGR). Other analyses were performed same as described, only with the five positions between two eucalyptus tracks, in order to test the effects inside the integrated system. The block and its interactions were treated as random effects. For verification of the distribution of a set of data, was used the Shapiro-Wilk test at α = 0.01 significance. Differences between means considering nitrogen effect, were determined using the Duncan method at α = 0.05 significance. For compare means of AGR (control treatment) with positions inside ACS, the Dunnett two sided method was utilized, at α = 0.05 significance. For the significant positions effects inside ACS, simple regression analyses for linear, quadratic and cubic polynomial degrees were determined. The mathematical models were chosen according to the equations with the best fit, confirmed by the higher determination coefficients and the significance of the regression F test, until 5% probability, or the lowest value of significance when it was above 5%.
Relative growth rate
In the systems comparison, the interaction of nitrogen and positions occurred only at 105 DAE (P = 0.04), however the AGR did not differ to ACS in both two nitrogen levels. At 105 DAE was observed with 12 kg N ha-1 had higher RGR than 80 kg N ha-1, inside positions C and F. The nitrogen influence occurred from 42 DAE until 105 DAE (42 DAE P = 0.02; 63 DAE P = 0.0004; 84 DAE P = 0.089; 105 DAE P = 0.09), however only until 84 DAE, RGR increased with 80 kg N ha-1, because at 105 DAE, 12 kg N ha-1 promoted the higher RGR. The position effect were significant at 21 DAE (P = 0.006), 42 DAE (P = 0. 017) and 126 DAE (P = 0.01), however only at 42 DAE, AGR had a higher RGR than ACS, which occurred relative to positions A and B (Table 1).
Within ACS there was not any significant interaction for RGR, in all assessments during oat cycle. The nitrogen effect increased RGR both at 42 DAE (P = 0.04) and 63 DAE (P = 0.001) (Table 1). RGR was altered by the position effect at 21 DAE (P = 0.005) and 126 DAE (P = 0.007), which were fitted by the regression analysis, to the quadratic degree and cubic polynomial degree, respectively. At 21 DAE RGR increased to the extent that the oats were furthest from the trees. At 126 DAE, RGR had a peak of the concavity facing downwards, between positions C and E, on position D, and a peak of the concavity facing upwards, between positions A and C, on position B, and the two positions next to the trees (i.e. positions A and E) as well as the central position between two tree tracks, remained approximately equals (Fig. 1a).
Unit leaf rate
In the systems comparison, there was ULR (mass basis) interaction with nitrogen and positions at 105 DAE (P = 0.045) and 152 DAE (P = 0.009). Where was applied 80 kg N ha-1, AGR had a lower ULR than ACS, however differing only to the position A, where was obtained the higher ULR at 105 DAE. With 12 kg N ha-1 at 105 DAE, AGR had similar ULR than ACS, being lower than the position C inside ACS. At 152 DAE where was applied 80 kg N ha-1, AGR as well as the position C inside ACS, had total leaves senescence (i.e. null ULR), however did not occur any difference between the positions in the systems comparison. In contrast to 12 kg N ha-1, wherewith AGR had a higher ULR than ACS, however did not differing to positions E and A, inside ACS. All other positions inside ACS had a null ULR at 152 DAE. The nitrogen effect was significant at 42 DAE (P = 0.011), 63 DAE (P = 0.017), 84
DAE (P = 0.077) and 152 DAE (P = 0.039). Until 84 DAE, 80 kg N ha-1 promoted the higher ULR, in contrast to the end of oat cycle (152 DAE), when 12 kg N ha-1 began to promote the higher ULR. The position effect were significant at 42 DAE (P = 0.016), 126 DAE (P = 0.005) and 152 DAE (P = 0.032). At 42 DAE, AGR had a higher ULR than positions A and B inside ACS. ULR of AGR did not differ to ACS at 126 DAE and was superior to the positions C and D at 152 DAE (Table 2).
For ULR within ACS, the interaction of nitrogen and position occurs only at 152 DAE. The regression analysis denoted for the nitrogen levels 80 kg N ha-1 and 12 kg N ha-1 the cubic and quadratic polynomial degrees, respectively. With 80 kg N ha-1, ULR had higher values between positions A and C, and lower values between positions C and E, with the peaks of concavities facing downwards and upwards, occurred on positions B and D, respectively. With 12 kg N ha-1 ULR was most expressive next to the trees, being higher at the highest than the smallest slope elevation, between two adjacent tree tracks (Fig. 1b). The nitrogen effect was significant at 42 DAE (P = 0.029) and 63 DAE (P = 0.029). In both stages of oat cycle 80 kg N ha-1 increase ULR (Table 2). Significant position effect occur at 126 (P = 0.003) DAE and 152 DAE (P = 0.099). The regression analysis denoted cubic and quadratic polynomial degree effect at 126 DAE and 152 DAE, respectively. At 126 DAE, ULR had on position B, a peak of the concavity facing upwards, which occur between positions A and C, and the lower values of ULR occurred between positions C and E, described by the concavity facing downwards. And at 152 DAE the concavity facing upwards comprised the entire oat track, which higher values on position E than position A (Fig. 1c).
Leaf weight fraction
Did not any interaction of nitrogen and positions was significant for LWF, both in the system comparison and within ACS. In the systems comparison, during oats reproductive phase, from 105 DAE until 152 DAE, 12 kg N ha-1 compared to 80 kg N ha-1 past to be increased LWF (105 DAE P = 0.02; 126 DAE P = 0.02; 152 DAE P = 0.08). The significant position effect occurred at 63 DAE as well as from 105 DAE to harvest (63 DAE P = 0.069; 105 DAE P = 0.06; 126 DAE P = 0.069; 152 DAE P = 0.03). The oat LWF cultivated in AGR did not differ to ACS, in exception at 105 DAE, from position A inside ACS (Table 3).
Within ACS, LWF at 63 DAE increased with 80 kg N ha-1 (P = 0.09), and from 105 DAE (P = 0.007) to 126 DAE (P = 0.02) with 12 kg N ha-1 (Table 3). The regression analysis denoted
