- Renick Peries (DEPI Geelong), LaTrobe University and Southern Farming Systems have been investigating the value of placing organic matter into the soil to improve water use efficiencies in grain crops
- Subsoil manuring is a new practice that involves the incorporation of high rates of organic amendments into the top of the B horizon of problematic duplex soils, where dense clay subsoils limit crop yields, particularly in seasons with dry springs
- The practice resulted in increased grain yields across sites and seasons in the high rainfall zone of Victoria. At nine site by season combinations from 2005 to 2011, grain yields were increased on average by 60 %, from 5.7 in the control to 9.1 t/ha with subsoil manuring
- The yield increases are attributed to the improvement in the physical properties of the clay subsoil. Measurements taken after one crop had been grown on the subsoil-manured plots showed that macroporosity in the clay subsoil between the rip-lines increased 2.7 times, from 8 to 19% v/v, while the saturated hydraulic conductivity increased almost 50-fold
- These improvements enabled the crop roots to extract more subsoil water during the crop cycle. The net effect was to increase the plant available water capacity of these soils, enabling the crop to use more the rain that fell during the year
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