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Irrigation and nitrate movement evaluation in conventional and alternate-furrow irrigated cotton

Rice, R.C., Hunsaker, D.J., Adamsen, F.J., Clemmens, A.J.
Transactions of the ASAE 2001 v.44 no.3 pp. 555
furrow irrigation, nitrate nitrogen, leaching, evapotranspiration, Gossypium hirsutum, irrigated conditions, Arizona
One of the important criteria in determining best management practices for irrigated agriculture is understanding the interaction between irrigation system performance and the movement of water and solutes through the soil. The objective of this four-year study was to evaluate the irrigation efficiency (IE) and the potential movement of applied nitrogen for a commercial cotton field in Arizona. In the first two cotton seasons, the grower used a conventional furrow irrigation practice consisting of 1.0-m row spacing and irrigation in every furrow. To reduce the amount of surface water runoff (RO) observed during the first two seasons, the grower changed to alternate-furrow irrigation and narrowed the row spacing to 0.8 m in the third and fourth seasons. Measurements of irrigation inflow and outflow and estimates of daily crop evapotranspiration were used to calculate the amount of RO, deep percolation (DP), and soil water storage during each irrigation event, which in turn were used to estimate the IE attained in each cotton season. Potassium bromide (KBr) was applied to 15 sample sites at the start of the growing season in each year to monitor the movement of bromide (Br(-)). Prior to the application of KBr and after harvest for each year, soil samples were taken from the sample plots to a depth of 2.7 m and analyzed for bromide and nitrate. Runoff of applied irrigation water decreased from an average of 21% under the conventional practice to 13% after changing to alternate furrows. However, since the average fraction of irrigation water lost to DP was increased from 18% to 22% under the alternate-furrow practice, the overall gains in IE (3% to 4%) were small. Furthermore, bromide and nitrate leaching below the cotton root zone appeared to be somewhat increased with the alternate-furrow practice. Implementing a tailwater recovery system and improving irrigation scheduling would potentially increase IE and reduce the over-irrigation and nitrate leaching observed for the commercial cotton production system.