Combating Subsoil Constraints: R&D for the Australian grains industry

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Author: Phil Price
Date: Mar. 2010
From: Australian Journal of Soil Research(Vol. 48, Issue 2)
Publisher: CSIRO Publishing
Document Type: Article
Length: 2,171 words
Lexile Measure: 1630L

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The contributions to this special edition of the Australian Journal of Soil Research report recent research undertaken as part of a national R&D initiative on Combating Subsoil Constraints established by the Grains Research and Development Corporation (GRDC). The Corporation is a statutory authority established to plan and invest in R&D for the Australian grains industry. Its primary objective is to support effective competition by Australian grain growers in global grain markets, through enhanced profitability and sustainability. The 'Combating Subsoil Constraints Initiative' (code: SIP08) operated as a national R&D program over the period 2002-03 to 2007-08, with projects in each of the 3 major grains regions (west, south, and north).

Much of the Australian continent is geologically very old and highly weathered. Soils in many parts of our cropping regions reflect these characteristics, without the influence of renewal processes such as volcanism, glaciation, or alluvial deposition that have formed the younger soils found elsewhere. A long period of relative aridity has also influenced the physical structure and chemical composition of many soils. As a result, many of the soils used to grow grain in Australia contain in their subsoil layers (defined here as deeper than 0.20 m) a range of factors that limit or constrain crop growth and yield.

Growers, agronomists, and researchers report that these 'hostile subsoils' are a major limiting factor to crop returns, affecting at least half of all grain farms. Abundant moisture in the subsoil at harvest after a dry finish, large yield differences between soil and crop types in the same paddock, and root growth obviously restricted to the surface soil layer are all indications of subsoil barriers to crop growth. These effects are seen in particular soil types in all cropping regions, and overall the impact on the grains industries nationally is substantial in terms of potential yield and profit foregone. Subsoil constraints act to prevent the crop from making full use of potential water and nutrients in the profile, resulting in restricted crop growth, and yield falling short of its water-limited potential. The impact can vary depending on soil type, farming system and agronomic practices, the growing season, and the farmer's response based on knowing which constraints are occurring and where.

The main subsoil constraints found in Australia's cropping regions are:

* Acidity (pH <4.8), which leads to concentrations of aluminium and other elements that are toxic to, and slow or prevent growth of, crop roots;

* Sodicity, where an excess of sodium ions allows soils to slake or 'dissolve' so that pore structure is lost and crop roots cannot penetrate the soil to reach water or nutrients--often associated with toxicity due to boron;

* Transient or root-zone salinity (not due to rising groundwater) where high salt concentrations (and osmotic potential) mean that the crop plants have to expend more energy to take up water from the saline soil solution, and in extreme cases may will even when the subsoil appears wet;

* High soil strength and physical impermeability (not related to sodicity) where plant roots cannot penetrate...

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Gale Document Number: GALE|A225247431