Key Points

  • When evaluating a biological input for grain production, it may be useful to consider whether the input will alleviate yield constraints.

  • The major yield constraints in the southern grain-growing region are high soil density, sodicity and acidity.

  • The biological inputs with the most potential to help alleviate these yield constraints are manure, compost, vermicompost, biochar and some biostimulants.


Figure 1: The southern grain-growing region encompasses south-eastern Australia, including central and southern New South Wales, Victoria, Tasmania, and south-eastern South Australia. Image: GRDC.


Evaluating biological inputs

There are a wide range of biological inputs on the market including inocula, various biostimulants, composts, manures and biochar. It can be difficult to evaluate their potential effectiveness and return on investment for broadacre grain production for a number of reasons.

First, the properties of biological inputs are highly variable, even within a single type of input. This makes it difficult to evaluate whether one particular product is likely to be effective. Second, few previous scientific studies have been field experiments in broadacre grain cropping. Instead many were laboratory or glasshouse experiments with horticultural crops and farming systems. Finally, many of the mechanisms claimed by manufacturers have not been assessed by scientific investigations yet.

When considering using a biological input in broadacre grain production, it may be helpful to first consider what constrains yield on your property. A biological input is unlikely to improve crop growth or yield unless it alleviates a yield constraint. Previous scientific investigations can help determine which biological inputs have the most potential to alleviate particular yield constraints (table 1).


Table 1: The potential of different types of biological inputs to overcome particular yield constraints based on the findings of previous scientific investigations. (Black ticks indicate one or more studies observed the effect. Grey ticks indicate that the effect is widely claimed.)


Yield constraints in the southern grain-growing region

The southern region (figure 1) has soils with generally low fertility and many have subsoil constraints, such as salinity, sodicity and toxic levels of some elements. However, soils in this region are diverse and some areas have very productive soils. Crop production systems in the region are varied and include many mixed farming enterprises that have significant livestock and cropping activities.

Yield potential in the southern region depends on seasonal rainfall, especially in autumn and spring, and there is less dependence on stored soil moisture than in the northern region.

In the southern grain-growing region, the most significant yield constraints are high soil density, sodicity and acidity.


Alleviating yield constraints using biological inputs

When the high density of a soil constrains yield, applying manure, compost, vermicompost or biochar may increase crop growth and yield. Because these biological inputs are largely composed of organic matter they can increase soil aggregation and pore space in soil, both of which can decrease soil compaction and the bulk density of soil. However, if yield is being constrained by subsoil compaction, manure, compost or biochar are unlikely to alleviate this constraint unless they are applied below the soil surface or incorporated into soil.

When yield is constrained by soil sodicity, crop growth and yield may be increased by applying manure, compost, vermicompost or biochar. These biological inputs do not actually decrease the sodicity of soil. Instead, the highorganic matter content of these inputs means that they may help alleviate the poor structural properties associated with sodic soils. However, when sodicity constrains yield the simplest and most economic way of alleviating this constraint is applying gypsum to soil.

When soil acidity constrains yield, applying compost or biochar may increase crop growth and yield. Compost and biochar both have the potential to increase the pH of acidic soils. Compost can also have a strong pH buffering capacity, which can help minimise future changes in soil pH. Although compost and biochar can increase soil pH, when soil acidity constrains yield the simplest and most economic way of alleviating this constraint is applying lime to soil.


Author: Jennifer Carson (Ghost Media)

The National Soil Quality Monitoring Program is being funded by the Grains Research and Development Corporation, as part of the second Soil Biology Initiative.

The participating organisations accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.

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