The single crop coefficient and basal crop coefficient at initial stage corrected was 0.93 and 0.23 at 2003 at Xiangcheng county by the method of FAO-56, 1.13 and 1.09 at middle stage, 0.54 and 0.45 at end stage;
which correlation coefficient is above 0.90.(4) In 2001, the average daily ET of cotton in the whole growth season is 1.75mm/d, the total ET is 307.48mm,and the average crop coefficient (kc) is 0.39 under deficient irrigation .
（4）Under the climate conditions of Yangling in Shaanxi, if variety is no changes, basalcrop coefficients of winter wheat: Kcbini=0.25, Kcbmid=1.20, Kcbend=0.20, water stress摘要 3conditions in the mid-season stage and late season stage may influence basal crop coefficients;
Crop coefficients were analyzed later and compared with values recommended by FAO56.Results show that: groundwater and rainfall contributed was 40%~50% of water requirement respectively and irrigation was small when groundwater depth was 0.6~0.9 m.
The concepts of crops water requirements、reference crops evapotraspiration quantity、crops coefficient and Pengman formula are explained and the method of calculating with reference crops evapotranspiration quantity according to Pengman formula is introduced.
The estimated crop factors (K_c) were 1.62, 1.77, and 1.79 and the water requirement coefficients based on Chinese Evaporation Pan were 0.62, 0.68, and 0.69 for Poa pratensis, Festuca arundinacea, Lolium perenne respectively.
The absolute warp of Xiangcheng county at initial stage, development stage, middle stage and end stage was respectively -3mm, 5mm, -19mm, 2mm and -14mm at 2003, the relative warp was respectively 12.70%, 4.87%, -8.36% 3.08% and-3.08%;
This paper calculated the crops evapo-transpiration in 94 counties and cities of Shanxi using the peaman (H.L.Peaman)method and calculated the wheat water requirement ETm according to crop transpiration coefficient Kc.
Screened Class A pan evaporation, adjusted by monthly crop coefficients, proved a dependable guide for irrigation.
Crop coefficients and water requirements of irrigated wheat (Triticum aestivum L.) in the Nigerian savannah zone
Crop coefficients were determined for various time intervals during each growing season using the lysimeter data and a grass-based reference crop evapotranspiration estimated with Class A pan evaporation data.
Mean crop coefficients for each ten-day period of crop growth were then determined.
Wheat crop water requirements (CWR) were then estimated for major irrigation projects in the Nigerian Sudan and Sahel savannah zones, between latitudes 10°N and 14°N, using the crop coefficients obtained and long term mean climatic data.