Effect of Water Stress on Crop Coefficient of Irrigated Soybeans (Glycine max L merr.) under sub-humid Conditions

Abstract

In order to manage irrigation systems effectively and sustainably for food production, it is important to estimate crop evapotranspiration with high precision and understand the relationship between functional parameters in the soil-water-plant-atmosphere system. Soybean was drip irrigated for two seasons in Ile-Ife, Nigeria. The experimental factor was the timing of irrigation. The treatments consisted of full irrigation (T1111); skipping of irrigation every other week during flowering (T0111); pod initiation (T1011); seed filling (T1101) and maturity (T1110). The treatments were arranged in a randomized complete block design with three replicates. Leaf area index (LAI), canopy cover (CC) and crop coefficient (kc) were measured and the single crop coefficient approach was used to determine evapotranspiration (ETc). The crop coefficient (kc) during flowering and maturity ranged from 1.14-1.29 and 0.49-1.19 respectively, while during pod initiation and seed filling, it was 1.29 in the seasons. The actual crop coefficient (kci) when irrigation was skipped during flowering, pod initiation, seed filling and maturity ranged from 1.04-1.46; 1.30-1.48; 0.82-1.48 and 0.77-1.17 respectively in the seasons. The kci when irrigation was skipped during flowering, pod initiation, seed filling and maturity reduced by 13.4, 11; 26 and 17% respectively compared with the fully irrigated soybeans. Exponential equations described excellently the relationship between kci and green leaf area index (LAI) (0.87 ≤ r2 ≤ 0.97; p < 0.0001). There was strong linear correlation between kci and daily actual evapotranspiration (ETc) (0.73 ≤ r2 ≤ 0.84; p < 0.0001) in the seasons. The kci and canopy cover (CC) are highly and significantly linearly related (0.89 ≤ r2 ≤ 0.97; p < 0.0001) and intercept very close to zero. Skipping of irrigation during the reproductive stages of soybeans reduced the crop coefficient and evapotranspiration.

Keywords

• Drip irrigation
• soybeans
• crop coefficient
• full and deficit irrigation

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