SUGARCANE NUTRITION AND FERTILIZATION - JAN MEYER Table of Contents Table of Contents

5. SUGARCANE NUTRITION AND FERTILIZATION ... 173 5.1 Introduction ... 173 5.1.1 Nutrients required by sugarcane ... 173 5.1.2 Principles of nutrient management ... 174 5.1.3 Amounts of nutrients taken up by sugarcane ... 175 5.1.4 Impact of climate on nutrient uptake ... 176 5.1.5 Soil factors affecting nutrient supply ... 176 5.1.6 Clay minerals ... 178 5.1.7 Cation exchange capacity ... 178 5.1.8 Soil organic matter... 179 5.1.9 Soil pH, acidity and alkalinity ... 180 5.1.10 Movement of nutrients in the soil ... 181 5.2 Nitrogen (N) ... 182 5.2.1 Importance of nitrogen... 182 5.2.2 Physiological role of nitrogen ... 182 5.2.3 The Nitrogen cycle ... 183 5.2.4 Nitrogen losses ... 184 5.2.5 Factors affecting the nitrogen requirement of sugarcane ... 186 5.2.6 How to adopt soil specific nitrogen recommendations ... 190 5.2.7 Nitrogen fertilizers ... 194 5.2.8 Managing N fertilizer ... 195 5.3 Phosphorus (P) ... 200 5.3.1 The importance of phosphorus ... 200 5.3.2 Physiological role of phosphorus ... 200 5.3.3 Phosphorus cycle in the soil ... 201 5.3.4 Factors affecting phosphorus availability ... 202 5.3.5 Phosphate carriers ... 203 5.4 Potassium (K) ... 206 5.4.1 Importance of potassium ... 206 5.4.2 Physiological role of potassium ... 207 5.4.3 Potassium cycle in the soil ... 207 5.4.4 Factors affecting potassium availability ... 208 5.4.5 Potassium sources ... 210 5.4.6 Managing the K requirement of sugarcane ... 210 5.5 Calcium (Ca) ... 213 5.6 Magnesium (Mg) ... 215 5.7 Sulfur (S) ... 216 5.8 Silicon (Si) ... 218 5.8.1 Reported benefits from silicon treatment ... 218 5.8.2 Soil Si source/sink pools ... 219

5.8.3 Managing silicon nutrition ... 219 5.8.4 Silicon fertilizer sources for sugarcane ... 220 5.9 Micronutrients ... 221 5.10 Good management practices for minimizing environmental impact ... 223 5.11 General conclusions ... 225 5.12 References ... 226

5. SUGARCANE NUTRITION AND FERTILIZATION

5.1 Introduction

In terms of crop production, an adequate supply of nutrients has the next greatest impact on sugarcane yields after the water requirements of the crop have been met. In an era of ever increasing economic constraints and community pressure to maintain the integrity of the environment, there is the need to fertilize efficiently. Over-application of fertilizers will not only affect the profitability of cane operations, but also the loss of applied nutrients such as nitrogen through surface runoff and leaching will impact adversely on aquatic environments and groundwater quality. Gaseous losses of nitrogen through volatilization and denitrification will also contribute significantly to greenhouse gas emissions.

A basic understanding of sugarcane nutrition will be of paramount importance to estate field managers and agronomists to ensure that a correct balance is maintained between the nutrient requirement of the crop, the capacity of the soil to supply nutrients and fertilizer management in terms of the amount, placement and timing of fertilizer, without compromising soil fertility and the other components of the environment. Information on general cane nutrition is available from texts such as Humbert ( 1968), Samuels (1969), Husz (1972), Blackburn (1984), Anderson and Bowen (1990), Calcino (1994), Bruce (1999), and a series of Information Sheets published by the South African Sugarcane Research Institute (SASRI) (1993-2008). More specialized information dealing with the relationship of plant nutrients to biochemical behavior and physiological functions may be obtained from Mengel and Kirby (1982) and the relationship between plant nutrition and diseases from Datnoff et al. (2007).

In this chapter some principles and concepts in crop nutrition for improved nutrient management are considered along with roles of mineral nutrients, the amounts of nutrients removed by sugarcane in relation to the stage of growth, symptoms of deficiency, how fertilizer

recommendations are made and good management practices for minimizing adverse environmental impacts.

5.1.1 Nutrients required by sugarcane

Sugarcane essentially consists of water, organic material and minerals made up from a wide range of elements as listed in the periodic table. However, only 16 elements are required for good growth.

The three structural elements carbon, hydrogen and oxygen, comprise about 95 % of the fresh mass of the plant and comes mainly from water and the air. The remaining 5 % is the mineral component, of which at least 13 elements are considered to be essential for good growth and for maintaining the reproductive cycle of sugarcane.

Box 5.1 Definition of essentiality

The definition of essentiality as originally proposed by Arnon and Stout (1939), made provision for the following three conditions:

 The plant cannot complete its full life cycle, from germination to production of viable seed, if the element is absent.

 The function of the element in question is specific and cannot be substituted by another element.

 The essential element must be directly involved in the nutrition of the plant through a metabolic pathway.

The macronutrients include nitrogen (N), phosphorus (P) and potassium (K), known as the primary nutrients, and calcium (Ca), magnesium (Mg) and sulfur (S), which are considered to be the secondary nutrients (Fig. 5.1).

Figure 5.1. Essential plant nutrients.

The remaining seven elements termed trace elements or micro nutrients that form part of the tertiary group, include zinc, copper, iron, manganese, boron, chlorine and molybdenum. These elements are essential for plant growth in small quantities, usually taken up in tens of grams compared to the macronutrients that are taken up by the sugarcane crop in tens of kilograms per hectare.

Silicon is the 14th element that has received widespread attention in recent years and, although it is not essential to plant growth, sugarcane is a large accumulator of this element. Because of its functional importance, Si is termed a beneficial nutrient for sugarcane (Berthelsen et al. 2001;

Kingston 1999; Savant et al. 1999; Meyer et al. 1999).

5.1.2 Principles of nutrient management

The relationship between growth rate or yield and nutrient supply is described by the well known

‘Law of Diminishing Returns’ (Mitscherlich 1909) which indicates that, as the supply or availability of nutrients increases, the growth rate and yield increase but with diminishing returns. An important characteristic separating micronutrients from macronutrients is the high efficiency value of micronutrients, since very small amounts are sufficient to produce optimum effects, while slight deficiencies or excesses can result in severe yield declines. This effect is illustrated by the

comparative response curves in Fig. 5.2, which show that when nutrients are expressed in the same mass units, the yield response curve to micronutrient treatment, when deficient, tends to have the steepest slope compared to the response curves for macronutrient treatment that tend to show shallower slopes.

Figure 5.2. Yield response curves for nitrogen n (), phosphorus () and micro nutrients () (Marschner 1986).

5.1.3 Amounts of nutrients taken up by sugarcane

Cane is capable of rapidly depleting the soil of mineral elements, particularly N and K. This is demonstrated in Table 5.1 which compares the elemental uptake of selected nutrients for average cane crops reported from a number of cane producing countries. The wide variations in nutrient removal are due to differences in prevailing climatic conditions, differences in nutrient use efficiency between cultivars, and differences in soil fertility and fertilizer practices. In general, sugarcane growing under irrigation in high temperature environments will remove more nutrients than sugarcane produced under rainfed conditions in cooler climates.

Table 5.1 Examples of comparative rates of nutrient removal by sugarcane for a range of countries (adapted from data given by Kingston 2000)

Country Source Macronutrients (kg/t)

N P K Mg Ca S

Australia Kingston 2000 1.3 0.18 2.23 0.22 0.29 0.36

India Zende 1983 1.2 0.20 1.19 − − −

Brazil Malavolta 1961 0.8 0.132 1.10 0.30 0.3 0.25

South Africa Thompson 1988* 1.35 0.16 3.26 0.39 0.42 −

Hawaii Humbert 1968 1.13 0.29 2.22 0.35 0.43 −

Average 1.16 0.19 2.00 0.31 0.36 0.31

*Pooled plant crop data from three different growth analysis trials

Country Source* Micronutrients (g/t)

Fe Mn Zn Cu B Mo

Australia Kingston 2001 78 42 4.95 0.75 − −

Brazil Malavolta 1982 31 11 4.5 2.0 2.0 0.01

South Africa Thompson 1988 − 11 2.5 0.5 1.2 −

*Pooled data

0 20 40 60 80 100 120

Relative yield (%)

Nutrient supply (eg kg/ha)

5.1.4 Impact of climate on nutrient uptake

In South Africa in the Pongola valley, a high yielding irrigated crop of cultivar N14, producing 165 tc/ha can remove up to 250 kg N, 30 kg P and 650 kg K, depending on crop stage and cycle (summer or winter). The high rate of K uptake is exceptional and can largely be attributed to luxury uptake of K in a plant crop of sugarcane growing in a deep, fertile sandy clay loam soil on relatively