Peter W Sale
La Trobe University, Australia
Title: Harvesting rainfall in dense clay subsoils to increase yields of rain-fed crops
Biography
Biography: Peter W Sale
Abstract
Yields of managed agricultural crops relate directly to the soil water taken up by their roots and transpired through their leaves. The availability of this water for rain-fed crops depends on the rainfall and the soil’s ability to capture and store the rain for use by the crop. Unfortunately, there are many soils with dense impermeable clay subsoils that have limited capacity to capture and store rainfall. Past attempts to ameliorate these subsoils have failed. Field experiments were therefore carried out across the high rainfall zone (>500 mm annual rainfall) of Victoria, Australia with the aim of ameliorating the constraints posed by these subsoils. The key finding was that deep-banding of high rates of nutrient-rich organic amendment, into the dense, dispersive clay subsoil, a practice known as subsoil manuring, transformed the subsoil into a friable, aggregated soil. Pore-space and permeability increased after one crop and large, consistent and profitable increases in the yield of wheat and canola crops, were measured over four consecutive crops. The improved yields were associated with enhanced nutrient uptake and the increased use of subsoil water by the crops. Crop responses resulted when preceding rainfall was sufficient to replenish subsoil water and when one or more rainfall events occurred during the spring months, as crops filled their grain. The improvement in crop productivity is attributed to the increased capture and storage of rainfall in the subsoil, and its use by crops during their critical pre-flowering, flowering and grain-fill periods. Increased nutrient supply from the mineralizing organic amendment during these periods also contributed to the crop response. Soils with dense clay subsoils occur in many countries. They may well respond to this practice and grow more resilient and productive rain-fed crops, as rainfall becomes more variable.
Figure 1. Transformation of the physical structure of a dense, dispersive clay subsoil, four years after deep-banding 20 t/ha of nutrient-rich organic amendment, at a depth of 30-40 cm. Photos show untreated subsoil (left) and treated subsoil (right).