Considerations for Efficient Side-dress Nitrogen Application
By Dr. Henry Sintim
Although nitrogen (N) is a primary essential nutrient, it is not included in routine soil test analyses in Georgia. The sandy soil nature and high rainfall conditions in the state cause the available forms of N, especially nitrate, to readily leach and not accumulate in the soil.It needs to be mentioned though that soil nitrate levels above 50 lbs/ac have been observed in fields with a prolonged history of organic amendment, coupled with other integrated soil health management systems.
Keep Reading →
As N is susceptible to losses, 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:
Factors to increase base N rate by 25%
Factors to decrease base N rate by 25%
Farming in deep sandy soils
Cotton following a leguminous crop such as peanuts or soybeans
The previous crop was cotton
Cotton following a good establishment of winter legumes, such as clover or vetch
There is a history of inadequate stalk growth.
There is a history of rank or excessive vegetative growth
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 first week of bloom stages. A side-dress application should be made 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 first 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 first and second week of bloom) would work fine. This would be beneficial in seasons of intensive rainfall conditions at critical stages. Studies conducted across six production conditions in Midville, Georgia, and Camilla, Georgia, 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.
The previous crop was peanut under four production conditions and corn under two production conditions.
However, skipping at-planting N is not recommended if the previous crop was not a well-established legume crop or the initial soil inorganic N (sum of nitrate-N and ammonium-N) level within one week of planting is not above 20 lbs/ac.
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].
Crops under the combined application of nitrate and ammonium 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, all of which 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 third 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.
Dr. Henry Sintim is Associate Professor, Crop & Soil Sciences, and Soil Fertility and Plant Nutrition Specialist at the University of Georgia, Tifton. This information was published originally by the UGA Cotton Team Newsletter.
