ABSTRACT - The replacement of natural vegetation by crop systems directly impacts the soil organic matter fractions. The objective of this study was to evaluate the total organic carbon (TOC) and nitrogen (TN) contents in different fractions of the soil organic matter (SOM) of an Oxisol of the Brazilian semiarid region under different irrigated crops and different soil management systems. Seven treatments were evaluated, which consisted of two soil management systems (no-tillandconventionaltillage) and three crops (maize, sunflower and sorghum), using as reference the soil under a native forest (NF). The summer crops preceded common bean crops in the autumn-winter. The total organic carbon content, total nitrogen, carbon content in humic substances and their constituents (fulvic acids, humic acids and humin) and labile, non-labile and water-soluble carbon contents were evaluated two years and three months after the experiment implementation to determine the carbon lability (L) lability index (LI), partitioning index (CPI) and management index (CMI). The greatest carbon, nitrogen and organic matter contents in the soil surface layer (0.00-0.05 m) were found in crops under no-till system (NTS), especially maize. The crops under NTS presented greater carbon content in humic substances than the conventionaltillage system (CTS) ones in the layer 0.05-0.10 m. The crops under NTS presented greater sustainability in the Brazilian semiarid region compared with those under CTS, as shown by their higher CMI in the soil surface layer.
The greatest spatial variability is observed in the plots subject to traditional tillage. As can be depicted from Figure 2, the plots under a no-till system show a lower average value than those obtained in the plots using tillage. Similarly, we can appreciate how the deviations from the average value represented by the standard error are higher in the plots using tillage than those under NT farming. These differences can be observed in all three locations studied. It is generally possible to state that soils subject to conventionaltillage have a less structured profile with large pores that store a great deal of gas and which differ to a great extent from one point to another in the plot. The soils subject to conservation agriculture techniques generally have a better structure with smaller pores and which is above all more uniform. As a result, there are less differences between points in terms of CO 2 emissions.
levels in the monitored soil layer was very similar to the one obtained in the crop and residue management trial (figure 2). Straw removal and the maintenance of stubble slightly increased the SOM content in the 20 cm top layer, whereas straw return and additional amounts of straw, which could occur under improved soil fertility conditions or irrigation, increased SOM up to 0.2% in the topsoil layer within a period of 3 years. Both trials reveal the potential of the combination of no-till as non soil disruptive form of crop establishment and the return or maintenance of slowly degradable crop residues such as wheat straw for the increase of SOM on the highly organic carbon depleted Mediterranean soils. These findings are in accordance with results published by other authors (Dick et al., 1998; Clapp et al., 2000; Layese et al., 2002; West and Post, 2002) that report an increase of carbon incorporated into SOM when changing from intensive tillage to no-till, but only if harvestable carbon residues like straw or cornstalks were left in the field. However, contradictory results can be found in the review performed by Wilhelm et al. (2004), indicating that residue return may lead or not to an accumulation of SOM. Sanchéz et al. (2002), measuring the CO 2 flux from conventionaland reduced tilled fields, found a reduction of 6660 kg CO 2 ha -1 year -1 under reduced tillage. This amount of carbon dioxide corresponds to around 3000 kg SOM ha -1 , which is approximately the yearly SOM increase found in the most favourable treatments in the trials, assuming a bulk density of 1.5.
Information on temporal variation of SPQ indicators is scarce in the literature (Alletto et al., 2015). Several authors emphasized that soil physical properties show temporal variation (Angulo-Jaramillo et al., 1997; Strudley et al., 2008; Alletto and Coquet, 2009; Hu et al., 2009; Afzalinia and Zabihi, 2014) during the crop season (Angulo-Jaramillo et al., 1997; Bodner et al., 2013) and during the crop rotation sequence (Lozano et al., 2014). Total porosity (TP) and K increase with tillageand decrease during the crop season under CT (Angulo-Jaramillo et al., 1997; Bormann and Klaassen, 2008). Under NT, stabilization of soil properties after some years was reported (Wander and Bollero, 1999; Álvarez et al., 2009a). However, other authors found that soil physical properties vary temporally under NT. Lozano et al. (2014) found that after a long period under NT, the porous system configuration and K of a Argiudoll from the pampas region did not reach steady values, regardless of the specific time in the crop sequence. Moreira et al. (2016) concluded that soil physical properties under NT vary during the crop growing season. Afzalinia and Zabihi (2014) concluded that measuring BD and cone index during the crop growing season gave more accurate data than measuring these parameters at the end of growth season.
in the soil. Similar results were observed in the South of Brazil (Hungria et al., 1997) and other parts of the world (Sij et al., 1979; Koutroubras et al., 1998). In 1998, three million hectares were cultivated under no-tillage (NT) in the Cerrados region (Freitas, 1999). With the expansion of NT cropping systems, there has been a revival of the idea that it is necessary to use small N rates at sowing to overcome problems related to N immobilization, mainly when soybean is cultivated after a non-legume crop. In this study we examined the response of inoculated soybean to starter N rates under no-till (NT) andconventionaltillage (CT) systems.
the ant species diversity in the tropical regions (Benson and Harada, 1988). The no-till system drive to an increase in the ant richness, population density and foraging activities over time, which can guide to a more efficient biological control of the insects considered pests. Some authors found that the higher densities of these arthropods for controlling the crop pests reduced the number of the insecticide applications (Brust and House, 1990; Brust, 1991; Clark et al., 1994). Barbosa and Fernandes (2003) also observed greater richness, diversity, and equitability of the ant fauna in the understory areas with more complex E. urophylla. In an experiment with the baits, however, they found a higher proportion of the bait removal in the areas under the management and explained that the areas with the higher plant complexity made available larger quantities of the food resources, thus avoiding the competition for baits offered. Many studies also have shown that not only the ant, but also the carabid (Coleoptera) and spider (Araneae) densities increased with the crop management techniques that reduced the soil tillage (Stinner and House, 1990; Clark et al., 1997). The tillage system also affects the physiochemical-biological soil complex, causing several kinds of the responses among the population and in the diversity levels of the organisms living in this environment (Kladivko, 2001).
ABSTRACT - The aim of the present study was to verify changes in the levels of photosynthetic pigments as well as gas exchange in the Fuyutoyo and Red Cabbage cultivars, grown under no-tillage (NT) andconventional (CT) systems. A randomised block design with four replications was used, in a 2 x 2 factorial scheme, where the Fuyutoyo and Red Cabbage cultivars were evaluated under two tillage systems. The levels of chlorophyll a, chlorophyll b, total chlorophyll and anthocyanins in the leaves were evaluated in triplicate. Localised gas exchange was measured at different times of the day, together with different photosynthetic photon flux density curves (PPFD). The Fuyutoyo cultivar showed a higher mean value for chlorophyll a (34.58%), chlorophyll b (35.09%) and total chlorophyll (34.76%), however, no difference was seen between cultivars for the levels of anthocyanin. Greater mean values for chlorophyll a (76.07%), chlorophyll b (77.87%), total chlorophyll (76.74%) and anthocyanin (72.24%) were found under CT compared to the cultivars grown under NT. The relative chlorophyll content of the Red Cabbage plants was influenced by adoption of the no-till system, showing a higher value for the SPAD index. The Fuyutoyo cabbage cultivar showed greater photosynthetic capacity during the day, promoting greater instantaneous carboxylation efficiency. All the cultivars andtillage systems gave a linear reduction in water use efficiency during this period. Under the conventional system, despite presenting higher rates of stomatal conductance, the Red Cabbage cultivar achieved lower values for net photosynthesis when submitted to light-curve analysis.
seasons (1997/98, 1998/99, 1999/00 and 2000/01). Planting dates were: 11/14/1997, 11/11/1998, 11/06/1999 and 11/14/ 2000. Plots were 7 m wide and 10 m long with seven rows spaced by 0.6 m. Five plants from each plot were dug at random from each of the four replicate plots in each conventionaland no-till systems at different periods during the season. Twenty roots from each treatment (conventionaltillageand no-till) were washed with a brush in running water to remove adhering soil, and the roots were subsequently dried with paper towels. From each root, four fragments (5 mm long) were randomly cut, disinfected in 50% alcohol for 30 s, transferred to sodium hypochloride (0.5%) for 1 min and rinsed in sterile water. Fragments from each plant were placed in one Petri plates that contained potato-dextrose-agar plus streptomycin sulfate (0.1 g/l). Plates were incubated in darkness at 26 ºC for seven days. The percentage of infection for each root was determined through identification of those 5 mm fragments with M. phaseolina. The incidences of infected fragments were used to get the area under disease progress curve (Shaner & Finney, 1977) for the percentage of infected roots.
Regardless of the tillage system used, herbicide application reduced MBC in both periods evaluated. At 12 DAA, fomesafen and the commercial mixture elicited the greatest reductions in MBC in CTS soil. Under NTS, MB decrease was higher under application of the herbicide alone than with the mixture. At 51 DAA, a greater MBC reduction was provided by the commercial herbicide mixture (Table 2). Aon et al. (2001) veriﬁed that fungal and bacterial biomass treated with the herbicides atrazine, glyphosate, 2,4-D, 2,4-DB, EPTC and ﬂumetsulan were less aﬀected and more expressive under NTS than CTS.
When tillage is applied, the protected organic matter becomes unprotected, in practice increasing the labile organic matter available to microbial activity (SIX et al., 1999). In addition, changes in soil carbon decay rate are expected with decreases in soil bulk density and increases in soil pore volume. Recently, based on these assumptions, conceptual models have been proposed to describe the tillage induced emission. LA SCALA et al. (2008) used no-till emission as a reference in order to model emission after tillage. REICOSKY & ARCHER (2007) suggested that the process is described by an initially rapid decline in CO 2 flux followed by a slower flux, requiring the use of
sion control as compared to the conventionaltillage system leads to smaller losses of organic carbon and nutrients, mainly Ca and Mg (Bertol et al., 2005). Con- sequently, the area under NT in Brazil has grown in the last few years. Regarding soil fertility management, there has been an increase in studies about liming in NT, focusing on forms and rates of application and correction of soil acidity (Alleoni et al., 2003, 2005; Amaral & Anghinoni, 2001; Caires et al., 1998, 1999, 2000, 2004; Kaminski et al., 2005). Assessments on the effects of liming on soil chemical attributes should be made in a long term basis in order to obtain the residual effects of liming (Caires et al., 2005, 2006b). Nevertheless, studies that also focus on the soil solu- tion under NT, especially through chemical speciation, are scarce. In a recent study with samples of an Oxisol collected in areas of distinct acidity conditions, and later placed in columns with several rates of phosphorus, Nolla & Anghinoni (2006) pointed out the importance of chemical speciation in the evaluation of the phyto- toxic potential of aluminum in soils cultivated under the NT system.
from March through September of 1998 and 1999. served that M. phaseolina recovery increased on buried fragments of stems and roots, suggesting that this fungus continues to grow on debris. This may be an important role in the epidemiology of this fungus and is in agreement with the report of Short et al. (1980) who observed that populations of viable scle- rotia in pieces of soybean residues were as great or greater than the initial infestation levels showing an ability to survive and grow on crop residues. Simi- larly, Adee et al. (1997) observed that brown stem rot caused by Phialophora gregata was more severe in no-till cropping systems due to the longer survival of P. gregata on residue positioned on the soil sur- face (no till) than in buried residue (simulated con- ventional tillage).
occurred because of the solubilization and migration of phosphates caused by rain water infiltration, as well as due to the mineralization of P-organic following de- composition of cover crops and soybean residues (Bayer and Mielniczuk, 1999; Guppy et al., 2005). A bet- ter distribution of soluble P may occur due to an in- crease in organic P forms resulting from the decompo- sition of the root systems from preceding crops (Rheinheimer et al., 2000). Besides, plant residues on the soil surface can increase soil inorganic P when mineralized by the microbial population (Beck and Sanches, 1994). An increase in labile P in the upper- most soil layer (0.05 m) coincided with a significant increase in organic carbon (C), in a soil under temper- ate climate, which supports the theory that competi- tion between organic anions and phosphate for the same sorption sites on oxide surfaces may enhance the lability of soil P (Muukkonen et al., 2007).
Where the room’s ceiling meets the back of the megalithic structure, there are crushed human bones. Similarly, under The Altar’s slab and all over the adjacent platform there are more crushed and, at least apparently, burnt human bones along with schist discoid beads and tiny fragments of charcoal. All these remains are embedded in a thin humic layer that covers the limestone bedrock (Fig. 2B – D). These pieces of evidence strongly suggest the existence of a cremation area at Bom Santo, which is an extremely rare find in Neolithic cemeteries in Portugal. At this point in the research, 3D laser-scanning and modelling with LIDAR technologies are still in progress and further work in Bracelets Room will be unavoidable in the future for thorough recording and sound interpretation of these structures and associated funerary and cult contexts. The only rooms that have been excavated so far — Rooms A and B — are located immediately below the steep slope that connects them to the entrance, in the cave’s upper level. Sediments form a ca. 40 cm-thick homogeneous deposit. Together with a very coherent material culture, this stratigraphy suggested a single period of use, a deduction confirmed by 19 radiocarbon results that point to a timespan of ca. 400 years (3800–3400 cal BC). As will be discussed below, these rooms were most probably intended for distinct funerary practices, with Room B being used for both primary and secondary depositions, and Room A mostly, if not exclusively, used for secondary depositions (Gonçalves et al. 2016).
This study aimed at an evaluation of the tolerance of the FABRIKA cultivar to trifloxysulfuron-sodium in three phenological stages. The experiment was realized in a green house, in 12 l-pots filled with loamy soil. A 3 x 4 factorial scheme was used where the first factor were the growth stages (two, four and six true leaves) and the second the trilfloxysulfuron-sodium doses (0.0; 5.0; 10.0; and 15 g ha -1 of the commercial product) in a completely randomized design with four replications. At the stage of two leaves, values above 60% of plant poisoning were observed 20 DAA under the doses 10 and 15 g ha -1 . When the dose of 5 g ha -1 p.c. was used, the maximum plant poisoning was 20% 20 DAA and lower than 10% 30 DAA. 30 DAA, plant poisoning in the herbicide-treated plants with two or four leaves was reduced to values close to 20% and to negligible levels in the plants with six leaves. The height was reduced with the increase of the trifloxysulfuron-sodium doses in the plants that erceived herbicide when they had grown four or six true leaves. At the cotton harvest the herbicide-treated plants with two true leaves presented a similar height to the non- treated. These plants were however less vigorous, with a thinner stem diameter and lower dry biomass production of the shoot part. Results indicate that cotton was more sensitive to the herbicide when it was applied to the plant at earlier stages (two true leaves). The use of 5 g ha -
The occasional soil tillage under consolidated NTS can neither have effect on soil organic carbon content (Crawford et al., 2015; Liu et al., 2016) nor substantially decrease it in the superficial layers (VandenBygaart & Kay, 2004), or even increase it in the subsuperficial layers (Kettler et al., 2000; Gál et al., 2007). Moreover, disk plows on soil under consolidated NTS can eliminate the stratification of the chemical and physical attributes of the soil, and invert soil layers (Quincke et al., 2007; Fidalski et al., 2015). This practice, therefore, can increase the potential of the system to sequester atmospheric C by favoring the humification of organic C in the subsurface layer, exposing soil with less C to the surface (Quincke et al., 2007). However, more than two-thirds of the organic C of the subsurface layer of sandy soil accumulated over years of NTS can be lost with a single mechanical intervention (VandenBygaart & Kay, 2004).