Soil health and nutrient management

Excess potassium (K) fertiliser use can have a significant effect on sugar quality and refining costs but offers no benefit to sugarcane crop yield. Potassium fertiliser guidelines are based on soil texture and two measures of soil potassium: readily available or exchangeable K and reserve K. The maximum recommended K rate for the Herbert is 120 kg/ha. A long-term K trial was established on a sandy loam soil at Macknade. High K application rates increased soil exchangeable K levels and resulted in luxury K consumption by the sugarcane plant. This significantly increased juice conductivity and third-leaf K levels. It also resulted in significant reductions in third-leaf values for Ca and Mg.

This collaborative project involved the University of Southern Queensland (USQ) and the Sugar Research Australia (SRA) Technology Unit. It aimed to evaluate methods of matching nitrogen (N) supply (from soils and fertilisers) with crop N uptake and crop needs. It was conducted with cognizance of the industry’s production goal of 36 million tonnes of sugar per annum, and water quality targets for the Great Barrier Reef lagoon set by government and environmental groups. The project methodology comprised several discrete yet linked activities. The basic tenets of various N management strategies were reviewed. Several long-term N management trials that had previously been established in various districts were continued to provide essential background information. Additional field trials and pot experiments were established to assess N fertiliser formulations, uptake of N fertiliser and/or temporal aspects of N management. Adjustments to the N guidelines were considered in terms of existing evidence. A mechanism for incorporating future research outcomes and outputs into the SIX EASY STEPS nutrient management program was developed. An overarching objective was to subject trial and experimental results to multi-facetted evaluations by means of agronomic, economic and/or environmental assessments. The SIX EASY STEPS program continues to be recognised as the basis for best practice nutrient management in the Australian sugar industry. Trial results have indicated that the SIX EASY SYEPS guidelines are generally appropriate. However, scope exists for fine-tuning of N application rates for specific circumstances. This will be best achieved via STEPS 5 and 6 of the SIX EASY STEPS program. Nitrogen use efficiency (NUE) indicators are useful for alerting growers and/or advisors to inefficiencies or circumstance where alternative on-farm management are worth considering, but that are not appropriate for determining N application rates per se. Enhanced efficiency fertilisers, such as DMPP-coated urea and poly-coated urea, offer promise to improve NUE. However, their use will probably be limited to situations where N losses (by leaching and/or denitrification) are more likely. The flexibility of the SIX EASY STEPS program allows the component N guidelines to be amended and/or revised as new information becomes available. This also relates to the delivery channels, especially via the SIX EASY STEPS short course program and decision support tools such as NutriCalcTM. In particular, the formation of the SIX EASY STEPS Advisory Committee will provide a mechanism for additional nutrient management strategies to be incorporated in the program in future.

Soil health and nutrient management

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