The objectives of this project were to (i) identify the causal factors for yield variability and (ii) develop strategic soil and crop management options to address yield variability and improve soil health and sustainability in cotton farming systems. The project conducted a paired field comparison during the 2018-19 season to identify the causes of yield variability between cotton fields in close proximity and of the same soil type. As drought impacted the number of cotton fields under cotton in that year, the investigation focused on soil property-induced yield differences at paired fields within five farms. The paired fields at each farm recorded an average yield difference of >284 kg/ha (1.25 bales/ha). Despite being the same soil type, several soil properties differed between the paired fields at each farm comparison. The soil organic carbon stocks were higher in the higher-yielding fields (five-year average yield) at all the farm comparisons and the normalised lint yield percentage was positively correlated with soil organic carbon stocks. Soil sodicity was higher in the lower-yielding fields at 3 of the 5 farms. Soil compaction was a potential causal factor for lower yield at one paired-field comparison in the Macquarie region. Results for most soil nutrient tests were above the critical concentrations recommended for Australian cotton production. Visual soil assessment (VSA) using the FAO method was carried out across paired sites, multiple CSD ambassador sites and within ACRI across multiple cropping systems. No earthworms were detected at any site during visual soil assessment or soil sampling across all the sites. The visual soil quality index using FAO method was not a sensitive predictor of cotton crop performance. However, future investigation into individual components such as scoring for soil structure, surface crusting etc. will improve the understanding of soil conditions and subsequent management decisions.
Comparing soil properties using a paired-field approach identified compaction, sodicity and soil organic carbon levels among casual factors of yield differences. To assess the relative contributions of selected soil constraints and strategic management to address the yield differences, further investigations were carried out at Australian Cotton Research Institute.