Turning unproductive soil into profits

Preeti Roychand

La Trobe University
AgriBio Centre for AgriBioscience
Melbourne, VIC, Australia

Sandy soils in Western Australia are bad soils for growing plants due to their poor nutrients and water holding capacity (see an example in Figure 1). In general, these soils are water repellent, which leads to land degradation by increasing soil erosion risk and run-off rates. Nevertheless, these soils may be improved by clay addition, which leads to increase soil organic carbon content (Franzluebbers et al. 1996). Several ways have been used to increase soil organic carbon content in soils: i) no-tillage systems, ii) addition of bio char , iii) organic amendments or fertilizer addition and iv) switch to perennial plants. But there is another potential method for enhancing soil organic carbon storage in soils which has received little attention: mixing of isolated clay with sandy soils.

Figure 1. Sandy soils in Western Australia (http://www.florabank.org.au).

Clay has potential to protect soil organic carbon from decomposition by soil microbes. But different types of clay differ in their capacity to bind organic carbon. The surface area and cation exchange capacity of clay determines its capacity to bind soil organic carbon.

We can use different types of clay for sequestering organic carbon in sandy soils. Smectite is a type of clay which has a large surface area, able to bind organic matter. In my studies, I used isolated clay from Vertisol subsoil, where smectite is the dominant type of clay (Figure 2).

Figure 2. Black clay soil (black vertosol) of Victoria, Australia (http://www.depi.vic.gov.au).

In texture contrast soils, subsoil clay can be mixed into the sandy top soils. In Western and South Australia, subsoil clay is added to sandy topsoils to overcome non-wetting issue of natural sandy soils (Cann, 2000). However, the effect of clays isolated from subsoil clay can be different as it will be associated with more percentage of clay. Clay addition will reduce the accessibility of soil organic carbon to soil microorganisms. Little is known about this management practice.

This management practice may help the farmers to convert unproductive land into productive land.

References

Cann MA. 2000. Clay spreading on water repellent sands in the south east of South Australia – promoting sustainable agriculture. Journal of Hydrology 231-232: 331-341. DOI: 10.1016/S0022-1694(00)00205-5.

Franzluebbers A, Haney R, Hons F, Zuberer D. 1996. Active fractions of organic matter in soils with different texture. Soil Biology and Biochemistry 28: 1367-1372. DOI: 10.1016/S0038-0717(96)00143-5.