Soil moisture is one of the major factors that determines volatilization of urea. In this study, we investigated the effect of soil moisture on urea volatilization from an Alfisol (Reddish Brown Earth soil). A bulk soil sample was collected from the research field of the Faculty of Agriculture, Rajarata University of Sri Lanka. A pot experiment was arranged under completely randomized design with four replicates per treatment. Soil moisture levels were maintained at 0 kPa (volumetric water content (VWC): 33%), 33 kPa (VWC: 16%), 44 kPa (VWC: 8%), and 54 kPa (VWC: 2%) as the treatments. A 50% overhead shade net was hung at 1.8 m aboveground covering the treatment pots. Urea was applied to each pot at a rate of 1,276.5 mg kg -1 and emitted NH3 was collected using the enclosure method. Soil NO 3 − -N, NH 4 + -N, pH, and EC were determined at six times at two-day intervals. The effect of soil moisture, time, and their interaction effect on NH3 volatilization was analyzed using repeated measure ANOVA with post-hoc Tukey HSD test for mean comparison. The NH3 volatilization significantly decreased with time (p < 0.05). Time and treatment interactions effect were significant for volatilized NH3 and other soil parameters measured except for soil NO 3 − -N (p < 0.05). A decreasing trend was observed for NH3 volatilization at 0 kPa, 33 kPa, 44 kPa & 54 kPa metric suctions as 6.3 g m -2 day -1 , 4.9 g m -2 day -1 , 4.7 g m -2 day -1, and 0.065 g m -2 day -1 respectively. Soil NH 4 + -N and EC fluctuated significantly among the treatments. Maintaining the soil moisture at 33 kPa during urea application is recommended for achieving high fertilizer use efficiency.
The future of food crop production is uncertain due to the negative effects of global warming. Cowpea is grown in warm environments including in Sri Lanka, where less is known about the potential acclimation of ecophysiological and agronomic traits to increasing temperatures. We evaluated the acclimation potential of yield components and ecophysiological traits of three recommended cowpea genotypes to the seasonal variation in growth temperature in Anuradhapura, Sri Lanka. This study was conducted at the Faculty of Agriculture, Rajarata University of Sri Lanka, in two consecutive seasons with average daytime temperatures of 30.4°C and 33.2°C. Three genotypes, Dhawala, Waruni, and MI-35, were tested in this study, and their rates of leaf photosynthesis and respiration at the 50% flowering stage and final yield parameters were measured at their respective average growth temperatures in both seasons. The total yield per hectare showed an average decrease of 16%, 17%, and 22% in the Dhawala, Waruni, and MI-35 genotypes at high average growth temperature, respectively. These reductions were associated with the reduction in the number of seeds per pod, hundred seed weight, and number of pods per plant, suggesting that there could be an among-genotype variation in flower abscission, fertilization, and biomass partitioning during the season in which the average growth temperature was high. In the season with high average growth temperature, genotype Dhawala showed an increased carbon gain per unit carbon loss and increased water use efficiency compared to MI-35 and Waruni genotypes. Therefore, genotype Dhawala is a better candidate than MI-35 and Waruni genotypes in the face of global warming, which may be considered in further breeding programs and market preferences. More work is proposed to examine the patterns of biomass partitioning and radiation use efficiency in three cowpea genotypes at elevated temperatures.
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