Studies on the cultural management of soybeans (Glycine max (L.) Merrill) in lowland rice-based cropping systems [Philippines].

Irrigation was found to affect the height of the plant at harvest, seed yield, and yield components of soybeans. Irrigation at 30 days after emergence produced higher seed yield than either irrigation at 14 DAE or the control. Tillage and mulch did not significantly affect seed yield. Under conventional and no-tillage system, differences in soybean cultivars were observed. SJ-2 variety was found to be more productive than UPL Sy-2 under no-tillage condition in CLSU. Yield, plant height, LAI [leaf area index], and biomass increased as population density increased. Pod number decreased as the population density increased. Row spacing was not significantly affected at both location; however, variety and row spacing interaction effect was found to be significant at IRRI [International Rice Research Inst., Los Banos, Laguna, Philippines]. Use of rice straw mulch one handweeding at three weeks after emergence under zero-tillage planting was the most effective in controlling weeds and in relatively increasing the yield. Tillage and one handweeding, or one interrow cultivation or burning of rice straw before planting had similar effect on controlling weeds. The most predominant weed species are Rottboellia exaltata L., Echinochloa colona (L.) Link and Trianthema portulacastrum L. The number and weight of weeds were inversely proportional to the control methods employed, indicating that addition of handweeding and/or interrow cultivation at 3-4 week after emergence will increase the yield of soybeans. Although zero-tillage did not give higher yield, use of this method of growing soybeans will conserve soil moisture and reduce the cost of production.