ABSTRACT

Nitrogen is the nutrient most required by cotton, however less than 50% of soil applied N is recovered by cotton plants (Morrow and Krieg, 1990). Due to the rising cost of fossil fuels, N fertilizer cost is increasing rapidly. Optimizing N fertilizer rates are important, because a lower rate will limit yields, while excessively high rates promote vegetative growth (Hutchinson et al., 1995). Another reason for maximizing N fertilizer use is the environmental concerns from nitrates in runoff and ground water. Improving N fertilizer use efficiency could involve replacing a portion of soil applied N with a slow release foliar source. There are advantages to foliar feeding including rapid and efficient plant response to nutrient needs, and treatment implementation under adverse field conditions. However, there are some disadvantages. Those would include inconsistencies in plant responses, and difficulties in suppling adequate quantities of fertilizer (Oosterhuis et al., 2000). Past research with N foliar feeding to plants has largely involved KNO₃ or feed grade urea. The problem with feed grade urea is that it is difficult to dissolve in water, and once applied it is easily washed off the leaf by rainfall (Kenty et al., 2002). A slow release foliar N fertilizer, that is readily available for uptake as needed, could eliminate some of the inconsistencies and improve production cost. Earlier research conducted by Howard in 1988, showed that cotton responded to foliar N when 80 lb of N was applied at planting. However, later research by Howard et al., (2001) showed soil applied N at higher than recommended rates failed to boost yields. A response to foliar N may be more likely when applications are made close to flowering, because the N demand is greater at this time. The use of soluble and slow release N fertilizer source for foliar feeding for timely availability may have an impact on lint yields and fertilizer use efficiency. This research evaluated CoRoN as a potential product satisfying such a need. CoRoN is composed of 25% control release N(long chain of polyethylene urea) coupled with 75% foliar urea(fast release low biuret urea) (Helena Chemical Co.). It is a non-drying foliar fertilizer in nature, that retains moisture therefore reducing crystallization on the leaf. Also, the slow release CoRoN reduces the chance of NH3 volatilization and is believed to adhere tighter to the plant leaf. With this in mind, our objectives in this study were to determine if (1) reducing the N soil test recommended rate of 60-20-0 by 1/3 to 40-20-0 followed by foliar feeding can sustain cotton yields and (2) can lint yields be increased above those from soil test recommended N rate due to foliar nutrition. Also, an additional purpose of this study was to evaluate the addition of HM9754 to N fertilizer at both the recommended and the 2/3 recommended rates for their influence on lint yields and fiber properties.