Evaluation of urea–ammonium–nitrate fertigation with drip irrigation using numerical modeling

Microirrigation with fertigation provides an effective and cost-efficient way to supply water and nutrients to crops. However, less-than-optimum management of microirrigation systems may cause inefficient water and nutrient use, thereby diminishing expected yield benefits and contributing to ground water pollution if water and nitrogen applications are excessive. The quality of soils, ground, and surface waters is specifically vulnerable in climatic regions where agricultural production occurs mostly by irrigation such as in California. Robust guidelines for managing microirrigation systems are needed so that the principles of sustainable agriculture are satisfied. The main objective of this research was to use an adapted version of the HYDRUS-2D computer model to develop irrigation and fertigation management tools that maximize production, yet minimize adverse environmental effects. This software package can simulate the transient two-dimensional or axi-symmetrical three-dimensional movement of water and nutrients in soils. In addition, the model allows for specification of root water and nitrate uptake, affecting the spatial distribution of water and nitrate availability between irrigation cycles. Recently, we analyzed four different microirrigation systems in combination with five different fertigation strategies for various soil types using a nitrate-only fertilizer, clearly demonstrating the effect of fertigation strategy on the nitrate distribution in the soil profile and on nitrate leaching. In the present study, the HYDRUS-2D model was used to model the distribution of soil nitrogen and nitrate leaching using a urea–ammonium–nitrate fertilizer, commonly used for fertigation under drip irrigation. In addition, the distribution of phosphorus and potassium was modeled. Model simulations are presented for surface drip and subsurface drip tape, each associated with a typical crop in California.