Farm Table says:
What is the problem?
Plant available water in the soil is a key driver for crop production in water-limited environments. This is particularly apparent for large grain-growing areas of southern Australia where rainfall-use efficiency is restricted by subsoil constraints. Many of these soils have texture-contrast profiles, where lighter-textured topsoil, from sandy-loam to loamy clays, overlies dense clay subsoil. These are the duplex soils that are classified in the Australian soil classification system as Sodosols, Chromosols or Kurosols.
What did the research involve?
This paper reports on a field experiment on a Sodosol soil in the high rainfall zone of south-west Victoria in Australia, that set out to improve the physical properties of the dense, clay subsoil at the site. It was postulated that an improvement in the physical properties of the clay subsoil would enable roots to penetrate and extract water and nutrients from the subsoil, and this would then enable more rainfall to infiltrate and be stored in the clay subsoil.
What were the key findings?
There were marked improvements in grain yields with the subsoil manuring treatment (lucerne pellets), in comparison to the control for the first 2 crops following the subsoil intervention.An additional 5.3 t/ha of wheat grain was produced in 2005, representing a 70% yield increase, while an extra 1.9 t/ha yield increase represented a 53% gain in the 2006 drought year. In both years the lucerne amendment resulted in grain protein concentrations in excess of 13%, and these are attributed to the high N status of the subsoil manured plots due to the added N in the amendment. There was no benefit from deep ripping or added gypsum on grain yield or grain protein concentration compared to the control plants.
The increased grain productivity with subsoil manuring can be explained by the improved water supply to the wheat crops, and to improved supply of nutrients from the organic amendment. More water was extracted from the 40-60 and 60-80 cm subsoil layers in 2005 and 2006 by wheat plants in the subsoil manured treatments, compared to the controls (Table 2). The increases amounted to 2-3 fold increase in the 40-60 cm layer, and a 3-4 fold increase in the deeper 60-80 cm layer. Deep ripping resulted in close to a 60% increase in crop extraction in 2005 compared to the control, but this difference had disappeared in 2006. It is likely that additional water was extracted below 80 cm but this was not measured.