How much fertilizer nitrogen does sugarcane need?

Authors: VIATOR, HOWARD - LSU Agcenter; Johnson, Richard; TUBANA, BRENDA - LSU Agcenter

Submitted to: Sugar Journal
Publication Type: Trade Journal
Publication Acceptance Date: 10/21/2013
Publication Date: 10/21/2013
Citation: Viator, H.P., Johnson, R.M., Tubana, B.S. 2013. How much fertilizer nitrogen does sugarcane need? Sugar Journal. 76(5):24-26.

Interpretive Summary:

Technical Abstract: Nitrogen rate recommendations for sugarcane in Louisiana take into account crop age (plant cane or stubble) and soil texture (light or heavy). Recommended rates in the 1950s ranged from 40 pounds N/A for plant cane on light-textured soil to 100 pounds of N/A for stubble cane on heavy-textured soil and increased over the next three decades to a range of 80 pounds N/A for plant cane on light-textured soil to 160 pounds of N/A for stubble cane on heavy-textured soil. The predominant N source also changed over the years from ammonium nitrate to anhydrous ammonia to urea-ammonium nitrate (UAN). These changes in source were driven by availability, cost and efficiency. In 2007, researchers at the USDA-ARS Sugarcane Research Unit in Houma, LA and LSU AgCenter embarked on an ambitious program to re-evaluate the N requirements for both the leading and newly released sugarcane varieties. Over 75 individual N fertilizer rate tests have been performed to produce information to re-formulate recommended N application rates to sugarcane growers. Separate application trials were conducted for plant-cane and first- and second-stubble crops of the production cycle. Nitrogen rates compared to the non-fertilized control were 40, 80, 120, and 160 pounds of N per acre with UAN as the N source. In keeping with previous observations, mean sugar yields among the fertilizer rates were not statistically different for over a fourth of the trials. Even more remarkable, over half of the plant-cane tests showed indifference to N inputs. This insensitivity to applied N fertilizer certainly tends to undermine the formulation of application protocols to serve as recommendations to growers. Nevertheless, several consistencies were observed over the years. Sugar yields were generally greater on light textured soil, and higher rates of N were required on heavy-textured soil to achieve equivalent yield. Older stubble crops required the greatest amount of N to achieve optimum yields, whereas plant-cane and first-stubble crop yields optimized at similar N rates, particularly on light-textured soils. Sugar content was often depressed at the greatest application rate of 160 pounds N per acre, which not only confirms the need to reduce rates but also allays fears that N deficiencies might occur at the lower rates. Though yield of varieties optimized at different rates in different tests, these differential varietal responses were minor and did not result in unique N recommendations for individual varieties. Results from the trials allowed for reductions of 20 pounds of N per acre for plant cane and 40 pounds of N per acre for stubble crops, as shown in the table. Revised recommendations provide both economic and environmental benefits. Full adoption of the revised rates could save the sugar industry over $5 million annually in fertilizer costs. Additional economic value from enhanced sucrose recovery should also be realized. By increasing sugar yield per ton of sugarcane, it is likely that transportation costs should decrease because fewer tons of cane would produce the same sugar yield per acre.