Effect of pjant density on evapotranspiration estimation and crop coefficients of maize in greenhouse

摘要

Maize (Zea mays, Pioneer 31G98) was planted in an unheated and naturally ventilated greenhouse during the summer of 2004 at the Arid Land Research Center, Tottori University, Japan. The objectives were to examine the effect of plant density (4 and 8 plants/m~2) on the performance of estimating evapotranspiration components and crop coefficients. Cumulative transpiration and soil evaporation were estimated better for 8 plants/m~2 than those for 4 plants/m~2, except for an early growth period. Cumulative transpiration was overestimated from 25 to 58 days after emergence for 4 plants/m~2. Cumulative soil evaporation was overestimated from 22 to 32 days after emergence and then the differences between measured and estimated values were constant. The ratios of daily transpiration to evapotranspiration of two plant densities were related to leaf area indexes and a logarithmic relationship was obtained. When the leaf area index was between 4 and 5, the ratio of soil evaporation to evapotranspiration was less than 0.15 but not zero. Daily crop coefficients were related to days after emergence and different crop coefficient curves were obtained for two plant densities. Then, daily crop coefficients of two plant densities were related to leaf area indexes and an exponential relationship was obtained.