Abstract
Soybean is the world’s major oilseed crop. Field experiments were conducted for 2 years on soybeans in order to study the effects of deficit irrigation (DI) during reproductive stages on radiation interception, radiation use efficiency (RUE), seed yields, harvest index (HI) and crop water productivity (WP). The water regimes were full irrigation (FI), DI every other week during flowering, pod initiation, seed filling and commencement of maturity. Average seasonal extinction coefficient (λ) ranged from 0.45 for DI during commencement of maturity to 0.47 for the other deficit methods. Pooled over the seasons and across water regimes, the fraction of incident photosynthetically active radiation was strongly correlated with the leaf area index (LAI). The aerial dry matter was strongly correlated with daily photosynthetically active radiation (PAR) for all water regimes. Across the water regimes, average seasonal RUE ranged from 1.07 g MJ−1 incident photosynthetically active radiation (IPAR) for FI to 1.19 g MJ−1 IPAR for DI during pod initiation. Reduction in the seasonal RUE ranged from 3.8 to 19.7 % for DI, while for the yield it ranged from 15.6 to 45.8 %. Seed yield was positively and significantly correlated (p < 0.0001) with RUE, cumulative intercepted PAR and HI across water regimes. WP is positively related with seed yield (r2 = 0.98; p < 0.0001), total intercepted PAR (r2 = 0.99; p < 0.0001) and RUE (r2 = 0.54; p = 0.02). DI reduced LAI, cumulative incident photosynthetically active radiation (TIPAR) and seed yield. DI during pod initiation and seed filling reduced substantially the seasonal RUE and seed yield than other reproductive stages. In conclusion water stress did not have significant impacts on λ and RUE during every reproductive stage for soybeans (TGX 1448 2E).
Highlights
Under field conditions, the development of crops depends on capacity of the canopy to intercept incident radiation and convert it into new biomass (Gifford et al 1984)
Seed yield in soybeans and some other crops depends on soil fertility and water, but significant correlation between seed yield and radiation use efficiency (RUE) and TIPAR in the current study clearly indicates that RUE and TIPAR are key factors for yield formation in soybeans
In this study, it is hereby concluded that the fraction of incident photosynthetically active radiation (fIPAR) is strongly and significantly correlated with green leaf area index (LAI) under full and deficit irrigation (DI) conditions
Summary
The development of crops depends on capacity of the canopy to intercept incident radiation and convert it into new biomass (Gifford et al 1984). This research was carried out in order to study the effects of water stress using drip irrigation during the reproductive stages on the development of canopy in terms of LAI and fIPAR, total incident photosynthetically active radiation (IPAR) and model the relationship between intercepted PAR and RUE, LAI and seed yield of soybeans in Ile-Ife, Nigeria. Volume of water required per plant per day at the initial stage was determined from the ratio of the product of peak evapotranspiration (1.13 mm day−1) and wetted area of each plant to the emission uniformity. Dry above ground biomass (DAB) At intervals of 7 days from 14 DAP in both irrigation seasons, the above ground biomass was taken from an area of 0.179 m2 at random from the plot and replicates of each treatment and edge effects were avoided. In situations where the F-test showed significant differences among treatment means, the differences among treatments were compared using Duncan’s Multiple Range Test at 5 % significance level
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