Managing Crop Production and Water Quality

A common application of cropping system models is to simulate various management options in different agro-ecosystems to predict effects on crop production. Crop growth models are also used in yield-gap analyses to quantify potential yield compared with actual yield; that is, the models are used to estimate potential yields at multiple locations to determine how genotype x environment x management interactions can be optimized. Simulating differences in yield among varieties is typically by using the appropriate genetic/phenotypic coefficients to characterize each crop variety. The cropping system models (CSM) within the DSSAT framework and the APSIM model have been extensively used for this purpose; for example, the DSSAT framework has been used to derive optimum combinations of management and planting dates for various crops. Another common application of crop models is simulating interactions between crop yield and levels of agricultural inputs such as irrigation water or nitrogen (N) fertilizer. Because agricultural models keep track of the water balance and

N amounts in the system as well as the estimated uptake by crops, the models can help estimate the proper amounts and timing of irrigation or N fertilization.

Other major applications in crop production modeling are assessing the sustainability of existing cropping systems and potential for yield improvement through introduction of alternative crops in a rotation, especially in a dryland agriculture context. For example, models have been used in conjunction with experimental field data to show that cropping intensification more effectively utilized available soil moisture and increased overall system productivity compared to the prevalent rotation. In addition, an important requirement for the sustainability of current agricultural systems is the mitigation of adverse environmental effects. Intensive crop production has been recognized as a significant nonpoint source of water contaminants. A major concern is the movement of nitrate (NO3-N), phosphorus, and agricultural chemicals (e.g., pesticides and herbicides) from agricultural fields into surface and groundwater bodies. Agricultural system models that have the capability to simulate transformations and movement of agricultural chemicals (e.g., GLEAMS, SWAT, and RZWQM) have been extensively used to assess the interactions between water quality and crop production management.

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