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- Deficit Irrigation during the Reproductive Stages of Soybean
Deficit Irrigation during the Reproductive Stages of Soybean
Abstract:
In recent years, surface and even subsurface water resources supply has become insufficient for the irrigation of farmlands, leaving a lot of them uncultivated especially during the dry season. In the other regions of the world, this problem was successfully addressed by the practice of deficit irrigation, which conserved water, increased the opportunity cost of water and most importantly, enhanced the sustainability of crop production. Deficit irrigation is the practice of reducing the volume of irrigation water applied to plants in order to increase the area of land under irrigation.
A field experiment was conducted to quantify the effect of the level and timing of deficit irrigation on the increase of plant height, dry matter production, yield and yield components, and water-use efficiency of soybean plants; to know how the length of the growing season of soybean plants was affected by the deficit irrigation; to determine which of the yield components was responsible for the for the increase/ decrease in grain yield; and to determine the economic feasibility of practicing deficit irrigation for soybean production in Northern Samar.
Two croppings were conducted starting 1 April 1997 (first cropping) and 15 April 1997 (second cropping) in the experimental area of the University of Eastern Philippines (UEP), Catarman, Northern Samar. The soybean plants were sowed on split plots laid out in a randomized complete block design with three replications. The factors considered were the level (D) and timing (T) of deficit irrigation. The level treatments (DO or FI, D20, D40) were assigned as the subplots while the timing treatments (T1, T2, T3) were the main plots.
The results of this study showed that as the level of deficit irrigation increased from 20 to 40 percent, significant reductions were observed in the average incremental increase in plant height (24.2-32.6%), total vegetative dry matter production (25.7- 34.8%), pod dry matter production (25.8-37.4%), total reproductive dry mater production (18.8-27.6%), number of pods per square meter (14.9-27.1%), and grain yield (18.7-30.3%). However, reductions were generally higher when water deficits were imposed during seed enlargement stage (17.4-36.7%) than when they were imposed during the flowering stage (10.2-23.6%) or pod formation (7.7-15.2%).
The number of seeds per pod and the 100 seed weight were reduced by deficit irrigation, but such reductions were insignificant.
The length of growing period of soybean plants under deficit irrigation was shorter by almost two days than that of the fully irrigated plants. However, no significant differences were observed between the length of growing period of the 20 and 40 percent water deficient plants. Plants under deficit irrigation during the flowering and pod formation stages also matured in about two days earlier than the fully irrigated plants. Deficit irrigation carried out during seed enlargement stage failed to shorten the growing period of soybean plants.
Deficit irrigation significantly improved the average water-use efficiency of soybean plants when this was accomplished during the flowering (127-132%) and pod formation (130-133%) stages compared with the fully irrigated plants. Plants under 20 percent deficit irrigation had the highest average WUE, while the fully irrigated plants had the lowest average WUE. The practice of deficit irrigation during the seed enlargement stage did not improve the WUE over that of full irrigation.
The economic feasibility of deficit irrigation was determined through the potential net returns from soybean cropping. The average potential net returns of soybean cropping under 20 and 40 percent deficit irrigation were higher and lower than that of the full irrigation practice, respectively. Deficit irrigation reduced the potential net returns of soybean cropping when it was imposed during the seed enlargement stage. The highest potential net return of P61,093.65 was obtained when a 20 percent deficit irrigation was imposed during pod formation stage.
Of the different yield components, only the number of pods affected the grain yield of soybean plants and consequently, the potential net returns.
The study confirmed that 20 percent deficit irrigation could be beneficially practiced during pod formation stage and to a lesser extent during the flowering stage.