This project will assist the cotton industry to reduce its impact upon the environment and improve the health of its soil resource and achieve its aims to use fertiliser inputs more efficiently.

Soil health benefits will be measured within the cropping systems experiment. A greater emphasis will be placed on biological aspects than in the past, especially in regard to remediating the subsoil. Soil physical and chemical fertility will continue to be monitored.

Changes in Soil C will be measured regularly in the cropping systems experiment to identify best management practices. This will include identifying better stubble management practices. The project aims to demonstrate that simple changes in management can improve soil C status that can balance eCO2 emissions from cotton production.

N use-efficiency will be further calibrated in N fertiliser rate experiments annually. With assistance from CRC adoption program, this project will extend the use cottonseed N analysis to assess NUE industry-wide that will provide feedback to growers about their use of N fertiliser in a field basis. This will help minimise fertiliser-derived nitrous oxide emissions from cotton crops. Better management practices will be developed to ensure GHG emissions are reduced by using data derived in the associated GHG project that will measure emissions of N2O and CO2.

Other nutrients: The NutriLOGIC program will be upgraded with more definitive guidelines for all nutrients including N. This will provide more effective guidelines to restore / maintain soil chemical fertility and avoid crop nutrient deficiencies. The use-efficiency of other nutrients (especially P and K) will also be assessed.

Soil Carbon status and stubble management:

Soil organic C (SOC) is reportedly declining in most cropping soils. Within the cotton cropping systems experiment at Narrabri, SOC has increased substantially, especially in the legume-based systems, and particularly in the subsoil. SOC increases of this magnitude are sufficient to offset the C emissions associated with cotton production. Soil C content is strongly related to how crop stubble is managed; incorporating stubble enables stubble-C to be assimilated within the soil microbial biomass compared with retaining stubble at the surface as most stubble-C is lost to the atmosphere. Increasing soil C is highly beneficial to crop production, soil health and the environment and is essential for consistently producing high-yielding cotton.

Efficient use of Nitrogen fertilisers:

Cotton NUE has declined across the industry in recent years due to excessive N fertiliser use. Several measures of NUE have been defined and correlated with the economic optimum rates of N fertiliser application derived from N fertiliser rate experiments at ACRI. One new measure of NUE analyses fuzzy seed for its N content at the gin, another assesses NUE using lint yield and N fertiliser application rate. All are capable of identifying where excessive amounts of N fertiliser have been used. Adopting these tools will help the industry use N fertiliser more effectively and reduce GHG emissions.

Greenhouse gas emissions (GHG):

Previous studies have shown substantial emissions of GHG’s, especially where high rates of N fertilisers are used and in irrigated systems which exacerbate the problem. Nitrous oxide (N2O) and carbon dioxide (CO2) are being measured in the cotton-based cropping systems experiment. This is providing insight into better management practices (i.e. optimising N fertiliser inputs and managing stubble better) to minimise GHG emissions.

Benefits of legume cropping on soil health:

Apart from improved soil N status, legume cropping improves soil structure, increases soil organic C status and promotes a more active and dynamic soil microbial biomass and enhances nutrient availability. Importantly, the amounts of water extracted from the legume-based systems has increased, which is closely correlated with higher-yielding systems. The cropping systems experiments at ACRI have shown changes in soil health parameters, particularly in the subsoil. Including legume crops in the systems benefits soil health in several ways, not just with N inputs, but by also improving soil water storage and extraction, soil structural improvement, and builds resilience into the soil system to provide for better crops.

Nutrient Management:

The NutriLOGIC DSS helps managers determine appropriate fertiliser management strategies based on soil and crop tissue analyses. It provides information on all nutrients and links to NUTRIpak. NutriLOGIC is regularly updated to ensure that the critical nutrient levels embedded in NutriLOGIC are appropriate for high-yielding cotton. The soil N section of NutriLOGIC is currently being revised in a way that will facilitate future revisions. This ensures the most recent high-yielding crops are included in the nutrient recommendation calibrations. It is important that cotton growers and consultants have access to a facility that interprets soil and crop tissue nutrient analyses and recommends fertiliser applications independently of fertiliser resellers and manufacturers.

This research project has identified cotton cropping systems that use inputs of fertiliser resources and energy efficiently, conserve soil carbon, produce low GHG emissions, and yet are highly productive and profitable. The health of these soils will continue to improve with the management systems employed and this will enable cotton productivity to increase in the future.