小麦/玉米套作田棵间土壤蒸发的数学模拟

Mathematical simulation of soil evaporation from wheat/maize intercropping field

为了探明小麦/玉米套作条件下棵间土壤蒸发规律及内在机制,该文将Ritchie模型和间套作群体光能传输模型结合起来模拟了小麦/玉米套作田的棵间土壤蒸发,并用2012年和2013年微型蒸渗仪的实测值对该方法进行了验证。结果表明,2 a模拟值和实测值的变化趋势都非常一致。与实测蒸发相比,该文所建模型2012年模拟结果的均方根误差为0.447 mm/d,平均绝对误差为0.331 mm/d,分别比原Ritchie模型降低16.8%和20.8%。在实测数据的88 d,累计实测蒸发量为107.2 mm,而模型的模拟值为100.5 mm,仅低估实测值6.7%。在2013年实测数据的68 d,累计实测蒸发量为83.1 mm,而模型的模拟值为73.7 mm,低估11.3%。模拟值与实测值的均方根误差和平均绝对误差分别为0.465和0.333 mm/d,略大于2012年。套作群体根系层水量平衡分析结果表明,小麦/玉米套作系统整个生育期土壤蒸发占总蒸发蒸腾的比例高达41.1%,故有必要在该套作农田实施秸秆覆盖等农艺措施,以减少棵间土壤蒸发,提高土壤水分的利用效率。该研究成果可为小麦套作种植模式下田间水分管理提供依据。

Soil evaporation is one of the most important components of crop field water balances, especially in arid and semiarid environments where soil evaporation can be prominent due to incomplete cover. Understanding and reducing this part of water consumption is important, since it can not be used by a crop. The effects of a crop and of crop management on this water loss from the soil have been estimated in the past using combinations of field measurement and simple models, but few works have been done for the wheat/maize intercropping system,which is a commonly practiced planting pattern in arid and semiarid areas of China due to its high productivity.The primary objects of this were to develop a mathematic model that was suitable for the intercropping system and then use this model for analyzing the soil evaporation from a wheat/maize intercropping field. The Ritchie model has been successfully applied to simulate soil evaporation from different kinds of sole crop fields. In this study, the Ritchie model and specific light transmission models were combined together to simulate the soil evaporation from an intercropping system. The performance of the models was evaluated with micro-lysimeter measured values. Soil evaporation data from two dry circles of bare soil after rain and irrigation were used to calculate the parameter αof the Ritchie model and a value of 4.62 was derived. The parameter U was set as 9mm according to the soil hydraulic properties. Results showed that during the 2012 growing season, the estimated soil evaporation with the new model showed almost the same trend as the measured values, and they had a correlation coefficient of 0.705 with the measured ones. During the 88 days that had measured soil evaporation,the total measured value was 107.2 mm, while the total simulated value was 100.5 mm, which revealed that the models only underestimated the measured values by 6.7%. The root mean square error and mean absolute error of the modeled values from the measured ones were 0.447 mm/d and 0.331 mm/d respectively. If the original Richie model was used, the root mean square error and mean absolute error of the modeled values from the measured ones would be 0.537 mm/d and 0.418 mm/d, which were 16.8% and 20.8% higher than the refined model. During the 2013 growing season, the total measured value was 83.1 mm, while the total simulated value was 73.7 mm,which revealed that the models underestimated the measured values by 11.3%. The root mean square error and mean absolute error of the modeled values from the measured ones were 0.465 mm/d and 0.333 mm/d, which are slightly higher than that of 2012. These results demonstrated the superiority of the model developed here. Analysis of the soil root zone water balance showed that total actual evapotranspiration of the intercropping system was 485.9 mm. The soil evaporation calculated from the new model throughout the growing season was 199.7 mm,which accounted for as much as 41.1% of the actual evapotranspiration across the whole intercropping season.This value was very significant and could cause a large waste of water. The results of this study implied that some evaporation reducing actions should be applied to improve water use efficiency of this intercropping system. The results of this paper will provide some theoretical basis for the water management of a wheat/maize intercropping field and the methods provided here can also be applied to other intercropping systems.