Fertilizer

Fertiliser application is one of the more expensive aspects of establishing and maintaining a sugarcane crop. It is therefore in a grower’s best interest to manage this investment through improved nutrient use efficiency. This can prove to be a complex subject as there are numerous interacting factors affecting how effectively the crop uses the nutrients.

All our advice and information on Crop Nutrition can be found in the various publications, videos and smartphone apps described below.

Senior Soil Scientist

   
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Information Sheets

7.1 Developing a nutrient management programme

Sugarcane is considered a high nutrient use crop and a sound nutrition programme is necessary for optimal and sustainable production. However, crop nutrient and fertiliser management is a complex subject with numerous interacting factors affecting how effectively the crop uses the nutrients. Fertiliser application is also one of the more expensive aspects of establishing and maintaining a sugarcane crop. Thus, to ensure growers are getting the best from their fertiliser investment through improved nutrient use efficiency, it is essential that a robust nutrient management programme be developed.

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7.2 Nitrogen management

Nitrogen (N) is one the most commonly applied nutrients in sugarcane and is required in relatively large amounts by the crop. Typically, sugarcane requires between 1.2 and 1.8 kg of N/ton of cane. Nitrogen is required for photosynthesis and sugar production. Adequate supply is associated with vigorous growth. Careful management of N is necessary to prevent both sugar yield and nutrient losses.

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7.3 Nitrogen management: N-Monitor plots

Nitrogen (N) is one of the most important nutrients to ensure vigorous growth and production potential. However, it is also one of the most difficult nutrients to manage in a cropping system. Nitrogen is subject to several transformations, with unfavourable conditions leading to major N losses (gaseous losses, leaching, run-off), while it can be subject to lock-up and release depending on how organic matter cycles in the soil (see Info Sheet 7.1: Nitrogen Management Guidelines). Crop demand also varies due to the size and health of the crop. While many practices can strongly influence the efficiency of N, many of the site-specific factors that can influence N behavior are not known at the start of the growing season, making it difficult to get the precise N requirements. One of the simplest on-farm practices a grower can take to help guide their N management and align this best N fertiliser management practices is to establish N-strips or N-monitor plots.

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7.4 Phosphorus Management

Phosphorus (P) is taken up in much lower concentrations than either nitrogen (N) or potassium (K), but is critical for a successful crop. Typically, a 100 tc/ha sugarcane crop removes about 20 to 25 kg P/ha (about 2 – 2.5 kg P/kg cane). In general, the sugarcane growing soils in South Africa are considered P deficient and fertiliser is required to ensure optimal crop productivity. Phosphorus is required for root formation and is thus essential for the development of strong, vigorous root systems as well as for proper tillering and for crop maturation. It is used in cell division and protein formation and has several biochemical functions in photosynthesis, respiration and energy transfer. Phosphorus is prone to lock-up (immobilisation) in the soil and thus careful management to optimise crop uptake is necessary.

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7.5 Potassium management

Potassium (K) is an essential nutrient for sugarcane production with uptake typically ranging from about 1.5 – 2 kg K per ton of cane produced (a typical 100 tc/ha crop will remove between 150 – 200 kg K/ha). Potassium plays a role in several metabolic functions in the crop and is important for sugar production, photosynthesis and respiration in the plant. It is necessary for regulating uptake of other nutrients and provides protection against several stress conditions, such as drought. Sugarcane is also a luxury consumer of K so will take up amounts well in excess of crop requirement (luxury consumption). This can lead to poor sugar recovery and high ash content. Excessive K application represents an unnecessary cost to the grower with no benefit, thus it is important to understand the many factors that affect K availability and use in the crop, and to follow the recommended application rates.

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7.6 Sulphur management

Sulphur (S) is an essential nutrient, with sugarcane uptake ranging from 2 to 3 kg S/tc (or 20 to 30 kg S/ha for a 100tc/ha crop). Sulphur is required for chlorophyll formation, photosynthesis and plant growth and plays a key role in cell chemistry. Several enzymes and proteins contain S. It is similar to nitrogen in that it has a strong association with soil organic matter and microbial turnover, and thus is subject to similar processes that affect its availability. It is only taken up by plants in the sulphate (SO42-) form, which is the predominant mineral form of the element in the soil. This element has low binding capacity to soil minerals and is thus prone to leaching losses, particularly on sandy soils.

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7.7 Calcium and magnesium management

A typical 100 t/ha sugarcane crop removes between 40 – 50 kg calcium (Ca) /ha and 30 – 50kg magnesium (Mg) /ha. Deficiency is often associated with acidic soils, where crop removal and excessive leaching can lead to inadequate soil supply. Calcium is important for growth and development of the spindle, leaves and roots. It forms part of cell walls and is involved in nitrogen (N) chemistry in the plant. Calcium also protects roots against aluminium toxicity and promotes a vigorous root system. Magnesium is needed in photosynthesis, respiration and sugar production. Mg is used to move P through the plant and is essential for N chemistry in the leaves. While deficiencies are not commonly reported, these can occur on acidic soils, sandy soils, and sometimes where excessive potassium (K) is applied. Calcium deficiency often occurs in association with Mg deficiency due to the close association of these elements in the soil. In soils that have excessive Mg, relative to Ca, soils may become heavy and sticky with poor workability (known as a magnesic soil).

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7.8 Boron management

Sugarcane requirements for Boron (B) range between 20 and 40 grams per ton of cane harvested (a typical 100 t/ha sugarcane crop removes about 0.2 to 0.4 kg B/ha). Boron is essential for new cell growth and elongation through involvement with cell wall development. New roots and shoot development is strongly influenced by adequate B supply. It is also involved in translocating sugars in the plant and production of proteins. Boron is mainly available in solution as the borate ion (BO33-). It is highly mobile in most soils and easily leached, though this is worse in acid and sandy soils. Alkaline soil can also reduce plant availability. Plant requirements are in a very narrow range thus over supply can easily lead to toxicity.

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7.9 Iron management

Iron (Fe) is required in the highest amount of all the micronutrients. Sugarcane requires about 0.5 kg Fe per ton of sugarcane harvested (a typical 100 t/ha sugarcane crop removes about 5 kg Fe/ha). Iron is mainly used in the production of chlorophyll and is thus important for photosynthesis. Iron is one of the most common elements in the soil, with very few soils having low amounts. Iron availability is largely controlled by soil chemistry (aeration status and pH).

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7.10 Manganese management

Sugarcane requires about 30 grams manganese (Mn) per ton of cane harvested (a typical 100 t/ha sugarcane crop removes about 3 kg Mn/ha). Manganese is involved in chlorophyll production, thus playing a role in photosynthesis. It also has functions in nitrogen chemistry and respiration and is required for efficient germination and plant maturity. It has close associations with other micronutrients in several enzymatic processes in the plant. Deficiency is not common, though more likely on the irrigated, alkaline soils of the Lowveld. Toxicity is mainly associated with acidic soils and may also occur in waterlogged soils. The aeration status and pH of the soil are key drivers of availability, but in most soils Mn will exist as insoluble oxide forms. Soil microorganisms have been suggested to have a strong effect on Mn availability for crop uptake. Plant uptake is typically in Mn2+ form.

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7.11 Copper management

Sugarcane requirements for copper (Cu) are very low with the crop removing only about 1 to 2 grams per ton of cane harvested (a typical 100 t/ha sugarcane crop removes about 0.1 to 0.2 kg Cu/ha). Copper is important for the production of chlorophyll and for photosynthesis. It is also involved in protein and carbohydrate processes in the plant. Copper is taken up by the plant as the Cu2+ cation or as organic chelates. Due to the very low crop requirement, deficiencies are rarely reported as most soils have sufficient supply.

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7.12 Zinc management

Sugarcane requirements for zinc (Zn) are low with the crop removing only about 4 to 5 grams per ton of cane harvested (a typical 100 t/ha sugarcane crop removes about 0.4 to 0.5 kg Zn/ha). Zinc is important for the production of chlorophyll and is necessary in the regulation of the plant’s growth rate and development. It is essential for phosphorus chemistry in the plant and is also implicated in the efficient use of water.

Deficiencies are often linked to the well-weathered acidic clay and loam soils with high organic matter, as well very sandy soil types. Alkaline soils are also prone to deficiencies. 7.15 Sugarcane leaf sampling

Leaf sampling is an essential part of crop nutrient management. Application of fertiliser does not always result in better uptake of nutrients due to other constraining factors in the soil. The leaf nutrient status thus provides a good indicator of the ability of a crop to access nutrients in the soil under the conditions in which it was grown. Where nutrient imbalances are found, further investigation of causes can be undertaken.

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7.15 Sugarcane leaf sampling

Leaf sampling is an essential part of crop nutrient management. Application of fertiliser does not always result in better uptake of nutrients due to other constraining factors in the soil. The leaf nutrient status thus provides a good indicator of the ability of a crop to access nutrients in the soil under the conditions in which it was grown. Where nutrient imbalances are found, further investigation of causes can be undertaken.

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7.16 Soil sampling procedures

Soil sampling and testing are essential management practices that a grower can use to improve the value of their investment in nutrients, as well as identify certain crop limiting conditions. Soil sampling and analysis allows us to:

  • Determine the capacity of the soil to support plant growth.
  • Determine the nutritional status of the soil and identify deficiencies or toxicities.
  • Guide nutrient or remedial amendment requirements to ensure good plant growth.
  • Monitor changes in the soil due to management activities.

For soil testing to provide accurate assessment of the soil fertility status, the sample being analysed must be truly representative of the area under consideration. Consider that a few grams of sample used in the laboratory represents many thousands of tons of soil in the field. The following factors and guidelines should be considered for optimal benefit of the soil sample.

Note: No single, simple set of guidelines will apply to every sampling situation. The general principles will need to be adapted for each field and situation to get the best from the effort.

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FAS Report Guides

Understanding the FAS Leaf Analysis Report

The SASRI Fertiliser Advisory Service (FAS) conducts routine leaf analysis of sugarcane samples with guidance given on whether the test values are within a predetermined sufficiency range. This guide highlights key features when reading and interpreting this report.

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Understanding the FAS Soil salinity and sodicity Analysis Report

Soil salinity and sodicity are crop limiting conditions associated with the excess build-up of free salts (salinity) or excess sodium (sodicity). The FAS Agricultural Laboratory at SASRI undertakes routine soil salinity and sodicity analysis to identify the extent of the salinity or sodicity problem, while providing gypsum recommendations in the case of sodicity problems. This guide provides assistance on interpreting the salinity and sodicity report.

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Understanding the FAS top and subsoil fertility Analysis Report

The top and subsoil fertility reports produced by the FAS Agricultural Laboratory contain a considerable amount of information. For those not familiar with these reports, this can be overwhelming and confusing. This guide aims to highlight pertinent aspects in the reports and provides guidance on how to use the information to improve nutrient management and soil health.

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Understanding the FAS water quality Analysis Report

Irrigation water quality must be monitored to ensure suitability of the water for irrigation for different soil properties. Excess salt can lead to serious soil and crop health problems and is costly to remedy. The FAS Agricultural Laboratory undertakes routine irrigation water quality analysis focusing on determination of excess salt and the suitability of the water source for irrigation. In addition, some growers may use this water for agrochemical mixing. Using good quality water is important to optimise the efficacy of chemicals. This booklet provides guidance on interpreting the water quality report for irrigation purposes and interpreting the results for use in agrochemical mixing applications.

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Books

Understanding and managing soils in the SA sugar industry

Sugarcane production imposes unique stresses on the soil. Monocropping and the removal of large amounts of crop material from the land at harvest, often after burning away crop residues, impact on soil health in various ways. Fortunately, there are several practices that farmers can implement to optimise both soil health and productivity. 

This book has been written to serve as a reference guide for students and farmers. It starts by providing a basic understanding of the physical, chemical and biological properties of soils, and then goes on to describe some of the important practices which serve to conserve soil health and thereby promote sustainable agriculture.

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Identification and management of the soils of the SA sugar industry

Knowing the soils that occur on a sugarcane farm and understanding how and why they differ will assist growers in deciding how to manage the crop more effectively under different soil bioclimatic conditions and help to increase farm productivity and profitability in harmony with environmental issues. Cane grows well on good soils with relatively little management, but greater knowledge is required of the many poor soils in the sugar industry if they are to be conserved and managed in the best way possible. 

This book is designed to provide a practical guide on how to identify, name and manage the more common soils that occur in the industry. Several new soil forms have been identified and where appropriate soil families have been introduced into the system in line withthe publication, Soil Classification – A Taxonomic System for South Africa (published by the Institute for Soil, Climate and Water (formerly Soils and Irrigation Research Institute), 1991).

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Smartphone Apps

Helping you calculate fertiliser distances at the touch of a button!

A ‘Fertiliser distance’ is the distance that a given amount of fertiliser must cover in order to achieve the recommended rate per hectare. Whether you use the tin-and-string method, or wish to calibrate the flow-rate of a knapsack fertiliser applicator or some other application equipment, FertiCalc will simplify the process.

The app is available for free download from the Google Play and iPhone App stores.

GPlay

MS Excel version also available.

AppStore

Services

Analytical packages offered for soil, leaf, fertiliser, compost and irrigation water. Recommendations provided for sugarcane and selected crops for local and SADC clients.

SASRI Extension Specialists located throughout the South African sugar industry are available to offer advice and support on crop nutrition and all other aspects of sugarcane farming.

Service to investigate new products on behalf of commercial companies to facilitate registration. Investigations can include testing of herbicides, fungicides, ripeners, fertilisers and pesticides.

Research

Research in Crop Nutrition focuses on the development of knowledge, technologies, and resources to further enhance the accuracy of fertiliser recommendations to the grower community. Visit CROP PERFORMANCE & MANAGEMENT for more info.