Quantifying the effectiveness of cover crops as a means of increased water infiltration and reduced evaporation in the northern region

Abstract

Effective capture and storage of rain are major challenges for grain and cotton growers in the northern region where only 20-40% of rainfall is typically transpired by dryland crops, with 60% of rainfall lost to evaporation, and 5-20% lost in runoff and deep drainage. Recent research showed cover crops and increased stubble loads could reduce evaporation, increase infiltration and provide net gains in stored soil water over traditional fallow periods.

This project ran 13 experiments on low-cover fallows around Yanco, Parkes/Canowindra and Goondiwindi. The best cover crop treatments recovered the 40-60 mm water deficit taken to grow them by the end of the fallow in most experiments, which modelling suggests may happen ~70% of years at Goondiwindi. While some cover crops stored up to 38mm extra plant available water, others lost water in some very dry seasons. It seems that cover crops can protect the soil from erosion in low cover fallows and maintain stored water in a majority of years.

The amount of stubble required to achieve major reductions in erosion is relatively low and easily achieved. Cover crops that produced 1 t/ha dry matter were predicted to reduce long-term erosion by up to 82%, 2 t/ha by 96% and 3 t/ha by 99%. In dry years, the feed value of cover crops that were grazed easily exceeded the loss of grain yield from the water lost from the fallow. Interestingly, cotton and wheat yield increases were larger than expected from this stored water alone and deserve further investigation to understand the underlying causes and potential across the northern region.