Fallow management in dryland agriculture: Explaining soil water accumulation using a pulse paradigm

The use of a fallow period to conserve rainfall as stored soil water is a long-established component of many dryland agricultural systems and there is general understanding that fallow management can play an important role in whole system water-use efficiency. Nevertheless there remain questions about the amount of residue required to make a difference and whether residue type or configuration matters. The magnitude of the observed effects on soil water accumulation has been variable, especially in short fallow systems. We present the results of field and lysimeter experiments of fallow management effects and extend these using simulation analyses to capture the impacts of climatic variability. The results allow identification of levels of evaporative demand and rainfall patterns that influence the effects of residue management and weed control. To move beyond whole-of-fallow, retrospective explanations of fallow management effects, we explain the results using a simple and easy to understand pulse paradigm approach adopted from the field of arid land ecology. Rainfall variability is viewed in terms of different possible sequences of rainfall events, which create pulses of soil water. By considering pulse size, frequency, duration and depth we explain the observed and simulated fallow management effects and provide a qualitative approach towards understanding and assessing soil water accumulation within the fallow period.

► We examine the impacts of fallow management practices on soil water accumulation.
► We view rainfall variability as causing different sequences of soil water pulses.
► This pulse paradigm successfully explains variable fallow management effects.
► Management effects depend on soil water pulse size, frequency, duration and depth.
► The conceptual framework captures the essence of complex interactions.