Effects of hardpan disruption on irrigated dry-season maize and on subsequent wet-season lowland rice in Lao PDR

Abstract

The hardpan in a lowland rice soil, produced by the puddling process, can both restrict percolation to preserve wet-season rice yield and restrict the root growth and yield of subsequent non-rice crops. Disrupting the hardpan could benefit a post-rice crop grown in the dry season, but may increase wet-season percolation and hence can decrease wet-season rice yield.The effect of hardpan disruption on dry-season maize was assessed in three experiments under different irrigation water input conditions (high input under furrow irrigation, low input by increasing irrigation interval, and, in one experiment, with drip irrigation as well); two on a sandy-loam soil and one on a loamy-clay soil. The effect of disruption on subsequent wet-season percolation was measured in two of these experiments.On a loamy-clay soil, the hardpan had a soil mechanical resistance (SMR) of 3.1MPa and hardpan disruption had no effect on maize grain yield. On a sandy-loam soil with a hardpan of average peak SMR of 4.5MPa, in one year, disruption increased yield by 14% and there was no interaction between hardpan disruption and water input. In the previous year with an average peak hardpan SMR of 5.2MPa, however, there was interaction between hardpan disruption and water input: hardpan disruption increased grain yield and water productivity (grain yield per unit water input) by 29% with drip irrigation and by 24% with high water input, but had no significant effect with low water input.Hardpan disruption had no effect on percolation in the following wet season, although it increased percolation by 56–70% in two of the four fields in the first 30 days after transplanting. Consequently, hardpan disruption gave gross benefits 2.7–9.8 times the costs of disruption, with a maize price of US$ 180t−1, in those situations where it increased maize grain yield.