Sintim: Side-Dress Nitrogen Considerations in Cotton

Henry Sintim, Glendon Harris
Department of Crop and Soil Sciences, University of Georgia

Nitrogen (N) constitutes 78% of the earth’s atmosphere, and it is present as N₂, an inert gas. By conversion, there is 117,000 tons/ac N in the atmosphere [1]. However, plants can not assimilate N in the N₂ form, and hence, the need to supply inorganic forms of N for crop production. Ammonium (NH₄⁺) and nitrate (NO₃^–) are the inorganic forms of N readily utilized by crops. In moist, warm, and well-aerated soil conditions, as commonly found in Georgia soils, NO₃^– is more prevalent than NH₄⁺. Also, the rate of NO₃^– uptake by crops is greater, but crops need to metabolize the NO₃^– to NH₄⁺, followed by the conversion of NH₄⁺ to amino acids, and the conversion of amino acids to proteins. The reduction of NO₃^– to NH₄⁺ is an energy-requiring process. Two NO₃^– reductase enzyme molecules are needed for each NO₃^– reduced. Plants supplied with more NH₄⁺ are reported to accumulate higher carbohydrates and protein than those supplied with more NO₃^–, especially at the early growth stage [1,2]. Overall, however, crops perform better under the combined application of NO₃^– and NH₄⁺ sources of N [3]. This is because plants can regulate intracellular pH more easily and store some of the N at low energy costs.

As N is susceptible to losses, especially under the prevailing conditions in the state, the University of Georgia Extension recommendation is to split-apply N in cotton. The total N rate for cotton is based on soil type, previous crop, growth history, and yield potential. The base N rate for 750; 1,000; 1,250; and 1,500 lb/ac lint yield is 60, 75, 90, and 105 lb/ac N, respectively, with the recommendation for 1,250 and 1,500 lb/ac lint yield assuming irrigated conditions. Recommended adjustment to the base rate is as follows:

The current recommendation is to apply between 25% to 33% of the total N rate at planting, and the remainder as side-dress between the square and 1^st week of bloom stages. Make side-dress application closer to the square stage if the plant is showing stunted growth and the leaves are chlorotic (pale, yellow, or yellow-white). Side-dress application closer to the 1^st week of bloom is suggested if the crops show good vigor with dark green foliage. If possible, a two-way side-dress application (half at the square stage and the remaining half between the 1^st and 2^nd week of bloom) would work fine. This would actually be beneficial in seasons of intensive rainfall conditions at critical stages, as has been the case this year. Several cotton fields were past the square stage before the current surge of thunderstorms, which will inevitably lead to the loss of some N, especially the NO₃^– forms of N. Recent studies conducted across six production conditions in Midville and Camilla showed cotton can tolerate early-season nutrient stress. Skipping initial fertilizer application until the square stage did not significantly affect cotton yield at all production conditions [4]. The previous crop was peanut under four production conditions and corn under two production conditions. However, we do not recommend skipping at-planting N if the previous crop was not a well-established legume crop or the initial soil inorganic N (sum of NO₃-N and NH₄-N) level within one week of planting is not above 10 ppm. The figure below shows the seasonal N uptake of cotton in Texas (A) and California (B). As can be seen, N uptake is very marginal at the early growth stages and increases rapidly after the square stage. The ability to tailor N availability with crop demand will enhance N use efficiency.

Figure: Seasonal N uptake in cotton reported (A) Texas [5] and (B) California [6].

As previously noted, crops under the combined application of NO₃^– and NH₄⁺ sources of N tend to perform better than the application of either source. Urea ammonium nitrate (UAN), ammonium nitrate, and urea are common sources of N for side-dress application. Due to potential hazards, ammonium nitrate is sometimes blended with other compounds, such as sulfur (S). Thus, there are various formulations of ammonium nitrate, which all tend to work fine. The choice of side-dress fertilizer should be based on accessibility, cost, efficacy, and ability to safely handle the product. As S application is routinely recommended, the value of S should be accounted for in determining the cost of side-dressed N sources.

Plant nutrient uptake is regulated by several abiotic and biotic factors. While not often, N deficiency could occur regardless of applying the recommendation rate. It is important to therefore monitor the nutritional health of the crop, especially between the square stage and 3^rd week of bloom with tissue test analysis. The recommended tissue N level is between 3 to 4.5%. Low N rates can reduce yield and quality while excessive N rates can cause rank growth, boll rot, delayed maturity, difficult defoliation, and poor quality and yield. Thus, ensuring an optimum supply of N is critical. Nitrogen deficiency in cotton occurs as chlorosis of the leaves and red leaf blades when deficiency becomes severe. Deficiency appears first on older (lower) leaves, and plants show reduced growth, height, boll size, and an increase in boll drop.

Figure: Photos of N deficiency symptoms in cotton. Photo credits: Yara US (A and B)¹, and North Carolina State University (C)².

¹ https://www.yara.us/crop-nutrition/cotton/nutrient-deficiencies/nitrogen-deficiency-cotton/

² http://deficiencies.soil.ncsu.edu/cotton%20N%20def%20pbrs%202006%20c.jpg

Contact Information

Henry Sintim at hsintim@uga.edu

Glendon Harris at gharris@uga.edu

Article HSL-N230626

References:

1. Havlin, J.; Tisdale, S.L.; Nelson, W.L.; Beaton, J.D. Soil Fertility and Fertilizers: An Introduction to Nutrient Management; 8th ed.; Prentice Hall, Pearson: Upper Saddle River, NJ, United States, 2014;
2. Sintim, H.; Amissah, S.; Ankomah, G.; Rogers, S.; Roth, R.; Lee, R. DAP and TSP for Phosphorus Nutrition: The Tradeoffs between Efficacy and Cost; University of Georgia, Athens, GA, USA, 2022;
3. Marschner, P. Marschner’s Mineral Nutrition of Higher Plants; Marschner, P., Ed.; 3rd ed.; Academic Press, Waltham, MA, 2012; ISBN 9780123849052.
4. Sintim, H.Y.; Amissah, S.; Agyei, B.K.; Hollifield, S.; Dowdy, M.; Sapp, P.; Harris, G. Nutrient Stress Effects on Cotton Productivity. In Proceedings of the 2022 Beltwide Cotton Conferences; The National Cotton Council: San Antonio, TX, January 4-6, 2022, 2022; pp. 27–30.
5. Pabuayon, I.L.B.; Lewis, K.L.; Ritchie, G.L. Dry Matter and Nutrient Partitioning Changes for the Past 30 Years of Cotton Production. Agron. J. 2020, 112, 4373–4385, doi:10.1002/AGJ2.20386.
6. Geisseler, D. Cotton Nitrogen Uptake and Partitioning; University of California, Davis, CA, USA, 2020;