Project Summaries

11-921  Project Manager: E. M. Barnes


Kevin F. Bronson, USDA-ARS

Land and canal infrastructure means that level-basin surface irrigation in raised beds is the predominant irrigation system for cotton production in central Arizona. High yields (i.e., statewide averages 1500 lb. lint/acre) are achieved with typical 40 inches of in-season surface irrigation. Nitrogen requirements of the plant are assumed to be high for these high yields. Nitrogen (N) fertilizer is usually managed with early season ground applications followed by "fertigations," i.e., dribbling 32-0-0 UAN into the canal. With typical surface irrigations in the range of 4-5 inches, there is potential for deep leaching N fertilizer when it is fertigated. Additionally, there is concern about the uniformity of N fertigations in surface irrigation systems. There is little research, however, that compares ground applications of N fertilizer with fertigations in these systems. The pre-plant soil profile NO3 test has been shown to be valuable to cotton N management in West Texas, but this has not been tested in Arizona. Similarly, canopy reflectance has been tested in West Texas as a valuable aid to the soil test for in-season N management but this approach has not been tested in Arizona. The objectives of this study are to:

Compare urea ammonium nitrate (UAN) fertigation to: a) knife applications of UAN; and to b) ammonium sulfate fertigation.
Compare soil test-based N fertilizer management to canopy reflectance-based N management in surface-irrigated cotton.
Construct N balances for surface-irrigated cotton, i.e., quantify total N uptake, recovery N use efficiency, NO3 leaching, and denitrification losses.

In the 2012 year of study, we compared applying nitrogen fertilizer with the irrigation water (fertigation) to application by direct injection to the soil with a coulter equipped applicator (knifing) to cotton grown in central Arizona. We also compared soil-test based N management with reflectance-based and ammonium sulfate was compared to urea ammonium nitrate. Nitrogen fertilizer response was observed, but was not different among the N treatments. Nitrogen recovery efficiency was relatively low (maximum of 30%), but similar to the previously published surface irrigation studies in Texas. The internal N use efficiency was greater than expected (40 lb. N/bale), compared to previous Arizona data, and surprisingly similar to other recent nitrogen rate studies across the Cotton Belt. Emissions of N2O were very low economically (maximum 0.2% loss of N fertilizer), but were still elevated (2 - 4X) compared to the zero-N plots. Inorganic soil N transects indicated that fertigation was as uniform as knifing N fertilizer. Amber NDVI showed N deficiency in zero-N plots before red NDVI. Ultimately these results will be used to update nitrogen management recommendations for cotton grown in arid environments.


Project Year: 2012

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