Evapotranspiration of Common Beans (Phaseolus Vulgaris) Depending on the Irrigation Regime

Abstract

The experiment was carried out in Agricultural University - Plovdiv in the period 2014-2016 to study the evapotranspiration of common beans crop under different irrigation levels. The used variety was Dobrudzhanski 7. The experiment was set up by the block method in four repetitions. Data from the following variants are used: 1) without irrigation; 2) 25% of the optimum irrigation rate (25%m); 3) 50%m; 4) 75%m; 5) with full irrigation rate (100%m). An optimum irrigated bean spends 385 mm (total) water on average in the layer 0-60 cm. The reduction of irrigation rates decreases the total evapotranspiration from 7% to 23% on average. For the variants with maximum irrigation and irrigation with 25% reduction of irrigation rate, the maximum values of evapotranspiration are registered at the beginning of grain filling phase, reaching 5-6 mm/day. The high values of evapotranspiration (over 4 mm/day) were observed from the first to the third decade of July. The increase of water stress induced by reduction of irrigation rates is a reason for reaching evapotranspiration maximum values earlier with 1-2 decades. In the same time, it has a negative effect on evapotranspiration values. Evapotranspiration is formed between 85-96% in layer 0-60 cm of the whole one-meter soil layer. From 50 to 60% of evapotranspiration are consumed by the soil layer 0-20 cm, depending on the year conditions. The annual irrigation rate forms over ⅓ (37%) of evapotranspiration for the optimum irrigated beans, as with the reduction of the irrigation norms its contribution decreases in favor of the precipitation and the initial water supply.