A field experiment was conducted at "La Tola" University Experimental Station, Tumbaco, Pichincha, Ecuador, on a sandy loam soil (Typic Haplustoll) to identify specific growth stages of the common bean crop at which the plant is less sensitive to water stress, in which irrigation could be omitted without significant decrease in final yield. The climate of the area is temperate and dry (mean air temperature 16°C and mean relative humidity 74%) during the cropping season, and 123 mm of rainfall were recorded from July to November, 1994. To achieve the proposed goal seven irrigation regimes were used, including normal watering, full stress, traditional irrigation practice, single stress at vegetation, at flowering, at yield formation and at ripening and, two levels of applied N (20 and 80 kg/ha). Plot sizes were 33.6 m2 (8 rows, 7 m long) with a population of 120,000 plants/ha arranged in a split-plot design with four replicates. The irrigation treatments started after uniform germination and crop establishment. Soil moisture was monitored with neutron probe down to the 0.50 m depth, 24 hours before and after each irrigation. The actual evapotranspiration (ETa) of the crop was estimated by the water-balance technique. Field water efficiency and crop water use efficiency were calculated dividing the actual grain yield (10% seed water content) by irrigation and by ETa, respectively. Yield data show that treatments with irrigation deficit had lower yield than those with supplementary irrigation (1% prob.). The pod formation stage was the most sensitive to moisture stress, in wich crop water use efficiency (0.46 kg/m3) was the lowest and the yield response factor (Ky = 2.2) was the highest. Nitrogen fertilization significantly increased the number of pods and grain yield.
Phaseolus vulgaris; irrigation; water stress; water use efficiency; neutron probe; common bean; Phaseolus vulgaris
