Responses of soil properties and grain yields to deep ripping and gypsum application in a compacted loamy sand soil contrasted with a sandy clay loam soil in Western Australia
Authors: Hamza M. A. , Anderson W. K. 
Published: August 2003

In the low rainfall, cropping area of Western Australia, massive soil structure due to machinery traffic is common on a range of soil types and is a major obstacle to crop yield improvement. Yield increases on compacted soils have been poor in the last decade compared with those on other soils. An experiment was conducted over 4 years (1997–2000) on a loamy sand soil with massive subsoil structure using a factorial combination of soil ripping to 0.4 m (DR), and application of commercial grade gypsum at 2.5 t/ha (G) to address the soil compaction problem. Complete nutrients, based on soil test each year, were applied to all treatments and regarded as the control treatment. All crop residues were retained after harvest and returned to the soil. The experiment was conducted in a wheat–grain legume (chickpea in 1998, field pea in 2000) rotation at Tammin in Western Australia. The purpose of the experiment was to assess possible improvements in soil properties and grain yields that may result from deep soil disturbance and application of an aggregating agent such as gypsum on a loamy sand soil in a low rainfall cropping system. Soil water infiltration rate, soil strength, porosity, water-stable aggregates, exchangeable Ca and Mg, cation exchange capacity, and grain yields were measured.
The results of this experiment on a loamy sand soil are compared and contrasted with those from a similar experiment on another common soil type in the low rainfall zone, a sandy clay loam soil (reported earlier by MA Hamza and WK Anderson). Grain yields were increased slightly more on the loamy sand soil at Tammin than on the sandy clay loam soil at Merredin due to deep ripping and gypsum application, even though the corresponding improvements in soil parameters were not as great on the loamy sand soil. The yield increases of wheat and legumes due to gypsum treatment were significantly lower on both soil types than those due to the combination of gypsum and ripping, whereas ripping alone without gypsum produced a yield decrease in the third and subsequent years after treatment. The main treatment effects on yield were additive, as significant interactions between the treatments on yield were seldom found.
Deep ripping and gypsum application (DRG) resulted in the greatest improvement in the soil physical properties as indicated by crop growth on both soil types. The DRG treatment increased soil water infiltration rate by about 90% on the loamy sand soil but by more than 130% on the sandy clay loam soil 4 years after the application of the treatments. Strength and porosity of the topsoil were decreased much more on the sandy clay loam soil. Summer rain stored in the soil prior to seeding was increased almost 3 times in both soils. The increase in water-stable aggregates was only 8% in the loamy sand soil but 46% on the sandy clay loam soil. Cation exchange capacity and exchangeable calcium were also increased more on the clayey than on the sandy soil by the use of DRG.
Economic analysis of the yield improvements showed that the DRG treatment produced significantly higher profit than the G or DR treatments alone on both soil types, but was slightly greater on the loamy sand soil type.
The combination of soil ripping and gypsum application in the presence of complete nutrients and annual return of crop residues to the soil had somewhat different effects on the soil physical properties and grain yields at a loamy sand soil site compared with the sandy clay loam soil site. However, the effect in both cases was favourable and is suggested to improve crop grain yield and soil physical fertility on both commonly occurring soil types in the low rainfall, cropping zone of Western Australia.