New insights into high soil strength and crop plants; implications for grain crop production in the Australian environment

Abstract

High soil strength is a problem in grain production systems worldwide. It is most severe in deep sands where the high strength occurs at greater depth, and is therefore more difficult to remedy. High strength is not an intrinsic soil physical property but the outcome of abiotic, biotic, climatic and management factors. Consequently, soil strength needs to be measured in situ with a penetrometer which, despite imperfections, provides approximate benchmarks. Following examination of laboratory, glasshouse and field literature, we hypothesise that the primary effect of high soil strength on crops is a reduction in tillering or branching, resulting in reduced radiation interception, crop transpiration and grain density (grains m− 2). This effect appears to be manifest via strigolactone hormones. While deep tillage allows deeper root growth and access to more water in deep soil layers, we contend that it is the direct effects of hormones on shoot development which has the largest effect on yield. The development of high soil strength cropping environments is not simply a function of soil properties and increased machinery mass and traffic frequency, it arises from a confluence of these with the farming system, the climate and perhaps plant breeding activities. An improved understanding of the relative importance of the unintended consequences of breeding, the effects of changes in fallowing practices, crop rotation, soil fertility, climate and traffic, along with a better understanding of the possible importance of bio- and macropores types provide avenues for improved management of high soil strength in grain crop production systems.