Evapotranspiration and seed yield of field grown soybean under deficit irrigation conditions |
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| Institution: | 1. Department of Irrigation and Agro-Meteorology, Lebanese Agricultural Research Institute, Tal Amara, P.O. Box 287, Zahlé, Lebanon;2. Faculty of Agricultural Sciences, Lebanese University, P.O. Box 12500, Beirut, Lebanon;3. Department of Crop Production, University of Murcia, Apartado de Correos, 4195, 30100 Murcia, Spain;4. Department of Crop Production, Faculty of Agriculture, University of Tuscia, Via Camillo de Lellis, I-01100 Viterbo, Italy;1. Department of Agricultural Economics and Agribusiness, University of Arkansas, 217 Agriculture Building, Fayetteville, AR 72701, USA;2. Bayer Crop Science, Greensboro/Winston-Salem, NC, USA;3. Department of Crop, Soil and Environmental Sciences, University of Arkansas, Fayetteville, AR, USA;1. Cátedra de Cultivos Industriales, Departamento de Producción Vegetal, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, C1417DSE Buenos Aires, Argentina;2. Cátedra de Cerealicultura, Departamento de Producción Vegetal, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, C1417DSE Buenos Aires, Argentina;3. CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), Av. Rivadavia 1917, C1033AAJ Buenos Aires, Argentina;4. IFEVA (Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura), Av. San Martín 4453, C1417DSE Buenos Aires, Argentina;1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina;2. INTA Balcarce – Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata CC 276, 7620 Balcarce, Argentina;1. Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of the Ministry of Education, Northwest A&F University, Yangling 712100, Shaanxi, China;2. College of Agronomy, Northwest A&F University, Yangling 712100, Shaanxi, China |
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| Abstract: | Evapotranspiration was measured for a reference crop, rye grass (Lolium prerenne) and soybean (Glycine max L. Merril) grown over two seasons in 2000 and 2001 at Tal Amara Research Station, Lebanon, using drainage and weighing lysimeters. Climatic data from the field weather station were recorded daily. Within the experimental plots, irrigation was withheld at full bloom, R2 stage (S1 treatment), at seed enlargement, R5 stage (S2 treatment) and at mature seeds, R7 stage (S3 treatment). Further, a control (C) was fully-irrigated throughout the growing period.Average crop evapotranspiration (ETc) as measured by the drainage lysimeters in 2000 totaled 800 mm for a total growing period of 140 days. However, when ETc was measured by the weighing lysimeter in 2001, it was 725 mm during a growing period of 138 days. Average crop coefficients (Kc) were computed for different growth stages for the two growing periods by dividing the measured crop evapotranspiration (ETc) by the corresponding measured reference evapotranspiration (ETo-rye grass). Kc values ranged from 0.62 at V10 stage (10th node on the main stem beginning with the unifoliolate node) to 1.0 at pod initiation, then to 0.81 at mature pods.Growth parameters, leaf area index (LAI) and dry matter accumulation, have been shown to be sensitive to water stress caused by the deficit irrigations. However, growth parameters were found to compensate for water stress at early stages, while at seed maturity the compensation ability was decreased.Plants of the lysimeters produced average aboveground biomass and seed yield of 8.1 and 3.5 t ha?1, respectively. However, in the well-irrigated field treatment, aboveground biomass and seed yield averaged 7.3 and 3.2 t ha?1, respectively. Deficit irrigation at R2 stage reduced aboveground biomass and seed yield by 16 and 4%, respectively, while deficit irrigation at R5 stage reduced these two parameters by 6 and 28%, respectively, with comparison to the control. The significant decrease in biomass at R2 stage due to water deficit may be attributed to a pronounced reduction in the number of vegetative nodes. However, limited irrigation at this stage did not reduce significantly (P < 0.01) neither seed number nor seed weight, while at R5 stage these two parameters were reduced by 20 and 10%, respectively, with comparison to the control. Results showed also that deficit irrigation at R7 stage (S3) was more profitable than irrigation deficit at any other crop phenology and did not cause significant reductions either in seed number or seed weight. |
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