Mathematical simulation of soil evaporation from wheat/maize intercropping field

Abstract: 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 9 mm 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.