|Hunsaker, Douglas - Doug|
Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2005
Publication Date: 6/15/2005
Citation: Adamsen, F.J., Hunsaker, D.J., Perea, H. 2005. Border strip fertigation: distribution of water and bromide. Transactions of the ASAE. 48(2):529-540 Interpretive Summary: Many agricultural producers in the western United States who use surface irrigation apply fertilizer by dissolving it in the irrigation water in a process commonly referred to as fertigation. Fertigation has become popular with growers because it is an inexpensive method of fertilizer application and fertilizer can be applied regardless of the size of the crop. For many vegetable crops, being able to apply fertilizer until it is almost harvest time is very beneficial for yield and quality. However, few guidelines have been developed for fertigation using surface irrigation systems. A fertigation experiment was conducted on narrow sloping closed-end border strips planted to date palms which employed different strategies for the timing of the injection of a bromide tracer. It was found for the conditions of the experiment that injection during the entire irrigation produced the most uniform distribution of fertilizer across the field. However, the presence of ditches which formed when the border dikes were created transmitted water to the end of the field more quickly than one dimensional (1-D) models predict. As a result, the 1-D model did not predict the fate of the bromide accurately. The results of this field study indicate that more complete 2-D models may be necessary to predict the fate of fertilizer injected into surface irrigation systems. These result will be of value in the development of guidelines for fertigation using surface irrigation systems and other researchers for model development.
Technical Abstract: Surface irrigation is and for the foreseeable future will continue to be the most commonly used method of applying water to agricultural crops. Producers are currently applying fertilizer to their crops by injecting fertilizer into the irrigation water (fertigation) because it is cost effective and allows small applications to be made throughout the entire growing season. However, there are few guidelines available for fertigation using surface irrigation. The primary objective of this study was to compare different strategies for timing injection of bromide on its fate when injected into the irrigation water, as a surrogate for nitrate, during the irrigation of narrow sloping border strips. A fertigation experiment was conducted on sloping borders strips in the Coachella Valley Irrigation District, California on a Coachella fine sand, (sandy, mixed hyperthermic Typic Torrifluvents) and the crop was date palms (Phoenix dactylifera L.). Four treatments, bromide injection during the first half, the last half, the middle half of the irrigation, and during the entire irrigation (100%) were used. The average Christiansen's Uniformity coefficient (UC) for water application was 0.81 and ranged from 0.63 to 0.92 for individual plots. For bromide, UC values ranged from 0.36 for the last half and middle half injection strategies to 0.63 for the 100% treatment. The results of this study support the general finding that injection during the entire irrigation produced the best distribution uniformity of added bromide. However, the one dimensional analysis methods used in this and previous studies do not account for the effect of the furrow created when the border dike is formed, resulting in significant yet explainable differences between field and model results. Additional field studies are needed with a variety of soil types and operational conditions to develop more complete guidelines for fertigation using surface irrigation.