Measurement of evapo-transpiration and crop coefficient of irrigated spring wheat in Naiman sandy cropland
奈曼地区灌溉麦田蒸散量及作物系数的确定

Lysimeter experiments were conducted with spring wheat during cropping seasons to measure the crop evapo-transpiration at Naiman region, and reference evapo-transpiration during these seasons was calculated with FAO Penman-Monteith and other four methods. The relationship between FAO Penman-Monteith and other reference evapo-transpiration methods was established, and the crop coefficients for spring wheat based on crop evapo-transpiration and reference evapo-transpiration were also developed. The results showed that the average weekly ETc of spring wheat was less than 3 mm.d-1 in the seedling phase. With the LAI increased, the average weekly ETc reached the peak of 6.49 mm.d-1 (at heading phase), and declined to 1.94 mm.d-1 during maturity phase. The local precipitation in the year of experiment did not satisfy the water demand for wheat production, and seedling, jointing, heading phases of spring wheat were the key phases in the course of water management. The differences in ETr estimates between FAO Penman-Monteith and Penman and FAO Blaney-Criddle methods were obviously lower than those between FAO Penman-Monteith and Makkink and Priestley-Taylor methods. The calculated values of crop coefficient for spring wheat at the four crop growth phases (initial, crop development, reproductive and maturity) were 0.45, 0.90, 1.11 and 0.52, respectively. The coefficient at maturity stage differed considerably from those suggested by FAO-24.