Deep blade loosening increases root growth, organic carbon, aeration, drainage, lateral infiltration and productivity

Abstract

All cultivated soils are prone to rapid reconsolidation when wet, particularly structurally unstable soils. This predisposes them to waterlogging, slow and limited infiltration, rapid drying, and poor establishment, growth and production of crops. Field-scale research was undertaken to develop soil management and/or engineering practices that will maintain a stable, loose tilth with aeration, drainage and infiltration properties that prevent waterlogging, enhance infiltration and increase crop production.The effects of deep ripping plus gypsum, permanent raised beds (PRB), deep blade loosening at 250 mm depth (DBL) and no-tillage crop establishment (NT) were studied in controlled traffic regimes on rainfed and irrigated crops. The DBL treatment severs roots at about 250 mm depth and loosens without inverting the overburden. Experiments were undertaken from 1997 to 2011 on winter waterlog-prone unstable sandy loam over clay soils in Western Australia, on an unstable fine sandy clay loam in Pakistan and on a self-mulching clay in Queensland. All sites were operated on a field scale as part of the commercial operations of collaborating farmers. Root zone soil conditions were monitored with measurements (0–400 mm) of bulk density, tilth porosity, hydraulic conductivity, perched water table depth, root mass, organic carbon, total nitrogen and moisture profiles. Irrigation applications and crop yield were also recorded.Bulk density data on all experimental sites showed reconsolidation of the tilth created by deep ripping with or without gypsum in the NT treatment occurred substantially within one growing season. The reconsolidated NT treatment in Western Australia also had low hydraulic conductivity, air-filled porosity values of only two to 4% at a soil moisture potential of −250 mm (PRB height) and suffered long duration waterlogging events. The DBL-PRB treatment on these soils remained largely unconsolidated, had larger hydraulic conductivity, an air-filled porosity at −250 mm moisture potential of ≥10%, and did not suffer waterlogging. Modelling using drainage theory showed that DBL-PRB could be as wide as three metres and easily drain saturated beds within two days, thus precluding waterlogging.Root mass in the 0–400 mm in DBL-PRB treatment was, on average, seasonally 31% greater than the NT treatment. This increase in root mass is shown to have produced increases of 48% in soil organic carbon and 34% in total soil nitrogen content, and, over 19 cropping seasons with six different types of crop, the DBL-PRB treatment produced an annual average increase in grain yield of 23% over that of the NT treatment.The DBL-PRB treatment also substantially increased the amount and rate of lateral infiltration. Irrigation wetting fronts were both measured and predicted by infiltration theory to reach the centre of 2 m wide DBL-PRB in one third to one half of the time taken in NT-PRB.DBL practice has the potential to stabilise a deepened tilth in all soil types through the conservation of the structure and mass of enhanced root growth, which increases soil organic carbon, total soil nitrogen and crop productivity, as well as preventing waterlogging and improving irrigation efficiency.