| With the increasingly understanding of the water circulation process and the development of computer sciences,the research on the construction of agro-hydrological models for the soil-crop system has greatly been advanced,resulting in a series of influential models.These models are helpful for quantitative analysis of water in the Soil-Plant-Atmosphere Continuum(SPAC),and provide theoretical basis and guidance for precise irrigation,optimum use of agricultural water resources and increasing crop yield.In this study,the agro-hydrological model named CROP-WATER,devised from the water module of the EU-ROTATE_N decision support system for agricultural water and nutrients use,together with the meteorological data measured at the Wellesbourne weather station in the United Kingdom from 1989 to 2009,were used to investigate the effects of the key model parameters(crop rooting depth and root length density distribution,groundwater level,soil texture,rainfall distribution,etc.)on the transpiration of winter wheat.Further,an attempt was made to develop an agro-hydrological model for water dynamics in the soil-crop system using the compensation mechanism of root water uptake.Based on the simulated results from the CROP-WATER model,it was found that when the groundwater table was deep,the ratio of the cumulative simulated transpiration to the potential transpiration for the maximum rooting depth of winter wheat of 100 cm was 0.639 and 0.657 in a fine soil and a medium soil,respectively.Both figures would further increase by about 10%for a 50 cm increase in the rooting depth.For a root system with root length density distribution according to a normalized exponential function,the cumulative transpiration of winter wheat was by 5.6%greater with the shape parameter az=1 than that for az=3,indicating that a more even distribution of roots was beneficial for crop transpiration.When the groundwater table approached the root zone,the cumulative transpiration of winter wheat in a medium soil increased by 16.0%,much greater than that in a fine soil.It followed that groundwater could make a great contribution to crop transpiration in a medium soil.Furthermore,it was found that crop transpiration was related to not only the cumulative rainfall during the growing season,but also the rainfall distribution.When there was a shortage of rainfall,the reduced crop transpiration could be compensated by irrigating during the middle and late growth stages.For the case of roots distributing extensively in the top soil,it was essential to maintain sufficient water in the top soil during the middle of crop development stage to ensure crop grew properly.In this study,an agro-hydrological model for the soil-crop system based on the compensation mechanism of root water uptake was also developed and validated by extending the water module in the SMCR N model.The testing data was from a field experiment on cabbage conducted at the Horticulture Research International in the United Kingdom.The simulations for soil water potential at various depths were carried out with the soil,crop and meteorological data collected during the cabbage experiment.The results showed that the simulated values of soil water potential at different soil depths agreed well with the measurements.The calculated Nash-Sutcliffe efficiency coefficient and Willmott's index of agreement were 0.633 and 0.916,respectively.This suggested that the proposed model performed well overall,and thus had the potential to be applied for water management in crop production. |
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