Changes in soil water storage with no-tillage and crop residue retention on a Vertisol: Impact on productivity and profitability over a 50 year period

Abstract

No-tillage (NT) has been widely adopted to assist in reducing soil erosion, lowering fuel costs, conserving soil water and promoting soil health. However, NT may also have a negative effect on yield depending on season and conditions due to inadequate weed/disease control, nutrient stratification and/or decreased soil temperatures. Therefore, to fully assess its impact, long-term studies are required to monitor changes over time. This study reports on the long-term effect of NT on crop yield and profitability (primarily for wheat, Triticum aestivum L.) using results from an experiment that has been running for 50 years in a semiarid subtropical region of Australia. In this experiment, the effect of tillage (conventional till (CT) v no-till (NT)), residue management (stubble burning (SB) v stubble retention (SR)), and three rates of nitrogen (N) fertiliser (0, 30 and 90 kg N/ha) were measured in a balanced factorial experiment on a Vertisol (Ustic Pellusert). Over the period of the trial (1969–2018), NT with SR resulted in greater average soil water storage in the top 1.5 m of the profile than CT with SB (390 v 346 mm). However, nitrate (NO3-N) accumulation during the fallow period was generally lower with SR and this prevented wheat from fully capitalising of on the increased soil water storage. Consequently, while crop yield was greater under NT v CT and more so under NT + SR v CT + SR (particularly in years where in-crop rainfall was <˜300 mm), N fertiliser was required to maximise yields. Within the NT treatments, SR also resulted in greater yield in the presence of applied N. Prior to 1992, nematodes prevented wheat crops from capitalising on the increased soil water and reduced yields, however, the introduction of nematode-tolerant cultivars helped maximise crop production. In line with yield effects, gross margins were greater under NT than CT and for SR when N was applied. However, despite greater yield advantages for the 90 N treatments, gross margins were lower at 90 N compared to 30 N. Nitrogen use efficiency with 90 N was approximately half that with 30 N, likely due to greater losses of N at the higher rates of application. To maximise profitability techniques to reduce losses of N are thus desirable. Good disease control, or the use of tolerant/resistant cultivars, is also essential to allow the crop to capitalise on gains in soil water in NT systems.