Analysis of irrigation water requirement and irrigation requirement index for cotton of Hebei province

Abstract: The analysis of water requirement and irrigation water requirement for crop in different hydrological years can provide a basis for determining the irrigation quota and for optimal water management in crop growing season. Based on some meteorological data in Hebei Province, water requirement and irrigation demand index of cotton were analyzed to provide detailed and targeted data for agricultural water resources planning of Hebei Province and for cotton optimal water management. Cotton water requirement (ETc) was estimated by using FAO Penman-Monteith equation and crop coefficient method. The average annual value of effective precipitation (Pe), cotton water requirement (ETc) and cotton irrigation demand (IR) in different cotton growth stages were statistically analyzed. And the effective precipitation (Pe), cotton water requirement (ETc) and cotton irrigation demand (IR) in different hydrological years were analyzed by P-Ⅲ distribution frequency calculation with frequency analysis. According to the above calculations, cotton irrigation demand index (IDI), the ratio of cotton irrigation demand (IR) to cotton water requirement (ETc), was analyzed. Cotton water requirement and cotton irrigation demand index of Eastern Hebei Plain, Heilonggang region and Piedmont Plain of Taihangshan in the study area were also analyzed respectively to provide detailed data for regional water resources planning. The results of cotton effective precipitation (Pe) analysis showed that the average annual effective precipitation in cotton growth period was 436.3 mm, and the effective precipitation in wet year (P=75%), in median year (P=50%) and in dry year (P=25%) was 525.9, 421.4 and 330.5 mm respectively for the study area. The results of cotton water requirement (ETc) analysis showed that the average annual cotton water requirement for the study area was 648.9 mm, and the cotton water requirementwas 629.9, 646.0 and 665.3 mm in wet year (P=25%), median year (P=50%) and dry year (P=75%) respectively. The results of cotton irrigation demand (IR) analysis showed that the average annual cotton irrigation demand was 190.6 mm, and the cotton irrigation demand was 299.1, 182.8 and 84.7 mm in dry year (P=75%), median year (P=50%) and wet year (P=25%) respectively for the study area. According to the above analysis, the average annual cotton irrigation demand index (IDI) for the study area was 0.29, and the cotton irrigation demand index was 0.45, 0.28 and 0.13 in dry year (P=25%), median year (P=50%) and wet year (P=25%) respectively for the study area. Based on the regional analysis of the study area, the average annual effective precipitation for Eastern Hebei Plain, Heilonggang region and Piedmont Plain of Taihangshan was 502.0, 452.6 and 416.6 mm respectively, the average annual cotton water requirement for the three regions was 619.1, 673.6 and 651.4 mm respectively, the average annual cotton irrigation demand for the three regions was 117.1, 200.3 and 222.5 mm respectively, and the average annual cotton irrigation demand index for the three regions was 0.19, 0.30 and 0.34 respectively. Cotton irrigation demand and cotton irrigation demand index for Piedmont Plain of Taihangshan in the study area were in an upward tendency from north district to south district.