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The use of nitrification inhibitors delays the conversion of ammonium fertilizers to the nitrate form and has the potential to increase nitrogen use efficiency in irrigated agriculture. Two field experiments were conducted at the Maricopa Agricultural Center in 1986 to evaluate the effect of two nitrification inhibitors (N-Serve and an experimental compound, ACP) on the growth, yield, nitrogen uptake, and fertilizer use efficiency obtained by growing cotton using buried-drip and furrow irrigation. ¹⁵N labeled ammonium sulfate was applied with and without nitrification inhibitors at the beginning of the season. Whole plant samples were taken at the end of the season to determine N uptake efficiency. No significant differences in growth, lint yield or N uptake efficiency were detected due to the application of either inhibitor. The conditions where nitrification inhibitors might improve nitrogen use efficiency in furrow irrigated cotton production are discussed.

In 1987, seed samples from three cotton fields in Avra Valley, Arizona, grown with liquid sewage sludge and inorganic nitrogen fertilizer, were analyzed for five heavy metals. Concentrations of cadmium, copper, lead, nickel, and zinc were similar in cotton seeds fertilized with either sewage sludge or inorganic nitrogen fertilizer. The levels of all five metals were well below the allowable EPA limits.

Plant growth products manufactured by BioHumaNetics, Inc. (BHN) were evaluated at the Maricopa Agricultural Center for the third consecutive year in the same field. Treatments included: 1) no fertilizers added; 2) standard fertilization used on cotton at the farm; and 3) a treatment schedule prescribed by BHN. Yields in 1987 were significantly different; the BHN treatment produced the highest yield, and the unfertilized treatment produced the lowest yield. Yields from all three treatments were substantially lower than corresponding 1986 yields.

Three field experiments were conducted in Avra Valley, Arizona, in 1986, to compare the lint quality of upland cotton fertilized with liquid sewage sludge with the lint quality of cotton fertilized with commercial inorganic fertilizer. Most lint quality components were similar for cotton fertilized with sewage sludge or inorganic nitrogen. Fertilization of cotton with sewage sludge tended to increase lint yield and decrease lint quality. Fertilization of cotton with sewage sludge increased vegetative growth and delayed lint maturity.

A field experiment was conducted in 1987 in Avra Valley, Arizona, to compare the plant growth and cotton lint yield from upland cotton fertilized with liquid sewage sludge with the plant growth and cotton lint yield from cotton fertilized with commercial inorganic fertilizer. Plant growth and cotton lint yields were similar when cotton was fertilized with liquid sewage sludge or inorganic fertilizers.

A preplant application of zinc was made to a short staple cotton field where the soil analysis had shown a zinc concentration of 0.64 ppm. No significant yield response was measured.

In 1981, the University of Arizona's Department of Plant Pathology and Office of Arid Lands Studies (Arizona Remote Sensing Center) began a joint research project to map and estimate concomitant reductions in yield caused by Phymatotrichum root rot (PRR) using simulated orbital and airborne imagery. With support from the U.S. Department of Agriculture, Cooperative States Research Service and NASA-Ames Research Center, substantial progress has been made in improving estimates of yield. While work to date has been limited to cotton, future studies will include additional crops and other diseases.

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