Changes in soil properties and crop performance on stubble-burned and cultivated water-repellent soils can take many years following reversion to no-till and stubble retention

Abstract

No-tillage and stubble retention have been widely adopted in south-western Australia to protect agricultural soils from erosion, but potentially exacerbate repellency. In a 10-year (2008–2017) field experiment, 4 combinations of tillage (no-till vs cultivation) and stubble management (retention or burning) were applied annually from 2008 to 2011. In 2012, all plots were returned to no-till and stubble retention to determine the recovery of crop performance and soil properties from stubble burning and/or cultivation, and this recovery phase is reported here. Changes to ground cover, soil water repellency, soil water content, soil carbon and crop performance during a 6-year period (2012–2017) were compared with plots where no-tillage and stubble retention had been practised for several decades. At the conclusion of monitoring in 2017, ground cover (average 55%) and soil carbon (average 1.2%) in the previously burned treatments remained significantly (P < 0.05) less than in treatments where stubble had always been retained (average ground cover 68% and soil carbon 1.7%). Soil water repellency (Molarity of Ethanol Drop (MED)) varied with seasonal conditions but was always highest (P < 0.001) in the treatment which had been continuously no-till, stubble retained (MED 1.7 in 2017) compared with the treatment that was previously burned and cultivated (MED 1.0 in 2017), but this did not influence soil water contents which were generally higher (P < 0.05) in the more repellent soils. The effect of previous tillage treatment on soil water contents resolved quickly after the reversion to no-tillage, likely due to the rapid establishment and preservation of root pathways to aid water infiltration. However, the effect of stubble burning on soil water contents remained significant (P < 0.001) with 2% v/v less water in 2017 in previously burned treatments compared with those where stubble had always been retained. Average grain yields where stubble had always been retained were significantly (P < 0.001) greater by 22–33% than where stubbles had previously been burned in 4 of the 6 seasons. The poor recovery in crop performance in the previously stubble-burned treatments was attributed to the slow build-up of soil carbon to support water- and nutrient-holding capacity, and crop residue ground cover to protect soils from water loss and erosion.