Land preparation requirements for rainfed rice as affected by climatic water balance and tillage properties of lowland soils

Abstract

Tillage effects on four lowland soils were evaluated and the relationship between climatic water balance ( W = difference between cumulative rainfall and evaporation) and rice ( Oryza sativa L. var. IR20) response to land preparation was determined under rainfed conditions. Tillage treatments included zero tillage, rototilling, conventional plowing, shallow puddling and thorough puddling. The soils were Maahas clay (Andaqueptic Haplaquoll), San Miguel sandy loam (Aeric Tropaquept), Maligaya clay loam (Vertic Tropaquept) and Maligaya clay (Vertic Tropaquept) Conventional plowing increased hydraulic conductivity ( K s) in all four soils. Wet tillage had the contrary effect, which was more apparent in sandy loam and clay loam soils than in clay soils. Soil penetration resistance decreased with increase n tillage intensity under favorable climatic water balance ( W > 100 cm). Under inadequate moisture conditions ( W < 100 cm), however, conventional plowing was more favorable for soil tilth than was wet tillage. IR20 suffered a significant yield loss at K s > 1.31 cm day −1 when the root length density was <1.24 cm cm −3. Root activity was severely reduced at moisture stress > 0.005 MPa and soil penetration resistance > 0.57 MPa. Decreasing K s improved the profile moisture retention in sandy loam soil, but had no effect on moisture regime in clay soils with a shallow water table (0–30 cm deep) or in clay loam under high climatic water balance ( W > 100 cm). As a result, tillage had no effect on grain yield in clay soils with a shallow water table or in clay loam soil under high climatic water balance. In sandy loam, however, thorough puddling significantly increased grain production. It was concluded that tillage is not required to alleviate soil physical limitations in rainfed lowland rice production in low permeable soils under an adequate climatic water balance. Wet tillage is a prerequisite for rice productivity in medium- to coarse-textured soils in drought-prone environments, although thorough puddling showed no advantage over shallow puddling.