|PEREA-ESTRADA, HUGO - UNIV OF AZ, TUCSON, AZ
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2006
Publication Date: 11/1/2006
Citation: Strelkoff, T., Clemmens, A.J., Perea-Estrada, H. 2006. Calculation of non-reactive chemical distribution in surface fertigation. Agricultural Water Management. 86:93-101
Interpretive Summary: To ensure that all the plants in a field receive sufficient fertilizer without excesses that can lead to ground water pollution, the amount applied and its distribution over the cropped area need to be controlled. The convenience and control of fertilizer applied with irrigation water has made fertigation a common technique with pressurized irrigation systems. The method is also used by growers with surface irrigation systems. In this context, it is still easy to control the injection schedule of fertilizer, but difficult to relate the injection timing to the resultant post-irrigation distribution of fertilizer in the field. Thus it is difficult to make recommendations on whether to apply fertilizer during the entire irrigation period, or during selected fractions of it -- e.g., the first half, middle third, in pulses, etc. Subject to some significant assumptions, a simple addition to existing surface irrigation simulation software allows viewing the ultimate longitudinal distribution of chemical consequent to any trial injection schedule. This allows playing a number of what-if scenarios in the search for an optimum. This tool, used by action agencies like the NRCS, University Extension personnel, and consultants, can assist in developing recommendations to growers and irrigators that will limit fertilizer use and help prevent environmental contamination.
Technical Abstract: A simplified Lagrangian-based theory and practical computation of the longitudinal distribution of fertilizer injected into the inflow to a border strip, basin, or furrow is presented as an adjunct to an existing surface-irrigation simulation model. The simplification consists primarily in the assumption that the chemicals are non-reactive, move by advection of the flowing water and that no mixing, dispersion, or diffusion of the chemical takes place. In a corollary calculation, the composition of runoff, in terms of water fractions selected for fertilizer injection, is also simulated. Comparisons of calculated post-irrigation longitudinal distribution of infiltrated chemical are made with the results of a complete advection-diffusion model that had already been validated in the field for injection of fertilizer pulses into the furrow inflow.