Impacts of conservation tillage on soil quality, including soil-borne crop diseases, with a focus on semi-arid grain cropping systems

Conservation tillage is a system of management that leaves at least 30 % of the soil surface covered by residue between crop harvests and planting, and may be combined with appropriate crop rotations to improve soil fertility and disease/weed management. This review examines the effect of conservation tillage on soil biological, chemical, and physical properties and how these interact to affect crop production. Improvements in physical attributes are widely observed under conservation tillage, and these improvements often lead to increased rates of water infiltration and storage. Increases in bulk density in the absence of cultivation, however, may lead to decreases in soil aeration. Conservation tillage may also lead to many soil chemical changes. Decreases in soil pH, changes to cation exchange capacity, and alterations to nutrient availability have all been observed. Changes to biological processes are generally characterised by increases in soil organic carbon (SOC) at or near the surface of the soil profile, along with subsequent increases in soil microbial biomass and diversity. However, the presence of plant diseases and weeds may also increase under conservation tillage management. In semi-arid environments, the increases in soil water storage afforded by conservation tillage often lead to increased yield, especially in dry years. However, where crop disease and weed growth, a lack of plant available nutrients, and/or adverse soil structure limit plant development, lower yields may also be observed. Holistic systems that incorporate appropriate crop rotations, fertiliser and weed management are required to help control the negative aspects of conservation tillage, and ensure that improvements in soil quality lead to increases in crop production