Manure use as soil organic amendments in broadacre agriculture

Summary

The use of feedlot and other manures in broadacre farming has traditionally been based on their potential to provide an alternative and cost-effective source of nutrients to conventional fertilisers. Recently, there has been growing interest in these products for their potential to provide long term increases in soil organic matter.

The choice of both product and application rate is generally based on cost of product ($/tonne) or cost of nutrient ($/kg), without any real consideration of the physical, microbial and chemical benefits the product can provide. However, it is important that choice of product and application rate take into account economic, agronomic and environmental benefits, as these products are highly variable and can cause unforeseen consequences with long term applications.

This project utilised field trials to examine the effect of long term applications of feedlot manure and other manure/soil amendment products on a range of soil parameters, including nutrient and organic matter levels, microbial activity and physical structure. The economic value of these attributes was also evaluated, so feedlot manure could be valued for the physical, microbial and chemical benefits it provides, not just $/kg of nutrient, when applied as a soil amendment in broadacre farming systems.

Unfortunately, due to drought conditions during the last two years of the trial, while manure applications continued to be applied, there were no crops grown. As a consequence, the nutrient effects and the impact of the manure applications on soil organic matter levels, microbial activity and physical structure were not able to be meaningfully measured, and the project was terminated.