The objective of this experiment was to estimate drainage beyond maize rooting depth of 80 cm in relation to tillage and mulch by using Darcy Buckingham’s equation for unsaturated, one-dimensional, vertical flow. Three land management systems were investigated, namely; untilled-mulched, tilled-mulched and tilled-unmulched. The three treatments were replicated three times in a randomized complete block design (RCBD). Individual plots had dimensions of 10 m × 10 m and were planted to maize. The mulch material was rice straw and the application rate was 5 t ha-1. Triplicate tensiometers were installed at 70 and 90 cm depth in the three plots that made up the middle replication for the determination of hydraulic gradient across that depth interval on a daily basis for a 97-day evaluation period. The unsaturated hydraulic conductivity of the same depth interval was determined near the experimental site by the instantaneous profile method. The application of 5 t ha-1 of rice straw mulch increased drainage approximately five times and altered the drainage fraction of rainfall from 4 to 22% compared with unmulched soil. Mulch effect on drainage overshadowed tillage effect.
Key words: Drainage, unsaturated hydraulic conductivity, tillage, mulch.
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