Extension of crop sowing time during dry weather by means of stubble mulching and water injection

Abstract

The practices of stubble mulching and water injection were tested to determine what extension of crop sowing time they provided during dry weather at four sites on the Darling Downs, Queensland (Acland, Toowoomba, Moola and Dalby). Crops tested were wheat, sunflower, sorghum and maize. Crop residues (wheat, barley and sorghum) retained on the soil surface as mulches reduced soil water loss from the seedbed after prolonged soil drying. This resulted in a lower rainfall requirement to refill a mulched seedbed, despite some absorption of rainfall by the mulch itself. A lower rainfall requirement could make sowing possible on a mulched but not an unmulched seedbed, given a suitably marginal sowing rain. Higher soil water contents under mulch increased seedling emergence of wheat, sunflower, sorghum and maize after prolonged soil drying. This effectively extended sowing time. On the assumption that sowing time was the period that resulted in crop emergence > 50%, extensions of sowing time were determined from graphs of emergence vs time. For example, about 2000 kg/ha of wheat stubble at Acland extended the sowing time of sunflower (6 cm deep) by 4.0 d. Water injection at 60 ml/m extended sorghum, sunflower and maize sowing time by up to 2.5 d in dry soil but reduced sowing time of these three crops at high soil water levels (under mulch). It was concluded that the additional periods of sowing time obtained during dry weather from stubble mulching or water injection could help distribute the peak demand for labour during sowing operations more evenly.