Trenching and compost sustain grain yield increases over nine years on deep sands but at a cost.

David Hall; Tom Edwards

Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

Trenching and compost sustain grain yield increases over nine years on deep sands but at a cost.

David Hall , Tom Edwards

Abstract

Abstract Aims Crops grown on deep sands on the south coast of WA are limited by soil physical and chemical properties including compaction and poor nutrition. Our aim was to determine what effects deep placed organic amendments have on soil properties and crop production in a deep sand and whether such amendments are profitable. Methods A long-term field trial was conducted over nine years (2015 – 2023) to investigate soil amendments including lime (0 and 2 t ha-1) and composted chicken litter (0, 10 and 20 t ha-1) with and without incorporation in trenches (0.1 m wide, 0.5 m deep spaced at 0.9 m) in an incomplete factorial design on crop yields, soil chemistry, soil physical properties, root growth and economics. Key results Grain yields were increased by more than 1 t ha-1 yr-1 where compost and lime were incorporated to 0.5 m. Grain yields for the highest yielding treatments were at or near their rainfall limited yield potential. The yields for surface applied compost did not differ to those that were trenched. The yield increases were attributed to higher nutrient (N, P, K, S) supply, higher pH and organic carbon, reduced bulk density and soil strength within the trench lines, along with increased root activity. The time taken for the compost applied treatments to exceed the cumulative profits of the Control treatment ranged from 19 to 29 years assuming current prices, costs and yield trends. Conclusion. Reduced bulk density and soil strength associated with trenching was found to persist within the trench lines for at least six years resulting in increased root growth at depth. The addition of composted chicken litter, either surface spread or incorporated in trenches increased grain yields more so than trenching alone. The trenched treatments had higher cumulative yields than those treatments that were not trenched. In the absence of compost, the trenched treatments were the most profitable with discounted returns $282 to $931 ha-1 higher than the Control over nine years. The compost treatments, at the rates applied, were not commercially viable.

SR24221 Accepted 25 March 2025