Estimating soil strength in the rooting zone of wheat

Abstract

When roots abstract water thus drying the soil, crop growth may be reduced by increasing strength of soil as well as the lack of water. Strong soil impedes root growth, restricting access to deeper water. As a result, there is a need to estimate soil strength in order to model crop response to dry soil correctly. The strength of soil can be routinely assessed with a penetrometer but measurements are time consuming and hard work to acquire at the frequency required to understand soil-water-plant relations. To make progress, a published relationship that derives penetrometer pressure from both water relations in soil and density was improved to take account of the effects of depth including the friction that results from the increasing hydrostatic pressure. These relationships were then incorporated into an agroecosystem model so that the dynamics of strong soil and its effect on wheat could be simulated. The combined model requires the moisture release curve (but this can be derived from other commonlymeasured soil properties), daily rainfall, temperature, and potential evaporation and the agronomy of the crop. Modelled values of penetrometer pressure were simulated well compared with measured values in artificially strengthened (compacted) and weakened (irrigated) soils. Simulations of the strength of soil and the matric potential before anthesis are compared with measured total dry-matter yields of winter wheat in experimental fields. The results lend weight to the hypothesis that wheat yield is limited by the strength of soil in the field and that soil strength, rather than soil matric potential, better explains differences between soils.

Nutrient Management in Support of Environmental and Agricultural Sustainability

“…Waines and Ehdaie [25] conclude that the root systems of modern wheat cultivars are small, having perhaps two thirds of the root mass of the landraces from which they derive. Whitmore et al [26] argue that the physical impediment to root growth is a more significant stress than the lack of accessibility of water. There thus seems scope for breeding to improve nutrient acquisition and to reduce other constraints to maximum yield and nutrient uptake such as water stress.…”

The velocity of shear waves in unsaturated soil

“…Although, S is widely used to estimate x (e.g. Whitmore et al, 2011) an alternative has been suggested by Khallili and Khabbaz (1998) who proposed that…”

Effect of soil depth and increasing fertilization rate on yield and its components of two durum wheat varieties

“…This beneficial effect is due to several factors including the higher volume explored by the roots (Zhang et al, 2004) and the higher soil volume with no mechanical restrictions (Whitmore et al, 2011). The increase in the fertilization rate also had an effect on grain yield; there were differences in production associated with effective soil depth ( Figures 2a and 2b) when taking into consideration the greater root exploratory capacity and its relationship with the recovery of applied nutrients (Richards, 2008).…”

“…Busscher et al (2001) mention that corn (Zea mays L.) yield is limited by deep compacted strata because these reduce root exploration within the soil profile. Similarly, Whitmore et al (2011) point out that wheat production is limited by soil mechanical resistance, a factor that is part of the root environment. Various studies of soil profile reserve indicate that determining nutrient availability in the superficial stratum (0-20 cm) is an inadequate indicator of the soil chemical properties or the effect of residual fertilization from the previous crop (Eghball et al, 2003;Hirzel et al, 2007;Li et al, 2011); this suggests the need to monitor these properties within the root-explorable soil profile.…”