|VIATOR, H - LSU Agcenter|
|TUBANA, BRENDA - LSU Agcenter|
Submitted to: Louisiana Agriculture
Publication Type: Trade Journal
Publication Acceptance Date: 5/15/2013
Publication Date: 6/15/2013
Citation: Viator, H.P., Johnson, R.M., Tubana, B. 2013. Nitrogen fertilizer trials with sugarcane in Louisiana (Re-evaluation leads to lower recommended nitrogen fertilizer rates for sugarcane). Louisiana Agriculture. 56(2):14-15.
Technical Abstract: Nitrogen (N) is considered the nutrient, which most often limits crop production, yet its optimal management remains a somewhat elusive goal. Sugarcane, a high biomass crop that demands high N inputs, is particularly difficult to manage for efficient N utilization. Excessive N can delay maturity, increase lodging, and suppress sucrose content, while the primary effect of insufficient N is lower potential biomass yield. Louisiana sugarcane N fertilizer recommendations have been based on N response trials conducted across varieties, soil types, and years. Currently, recommendations for N application for sugarcane take into account crop age (plant cane or ratoon) and soil texture (light or heavy). Researchers in the LSU AgCenter and the USDA-ARS Sugarcane Research Unit in Houma, LA conducted research 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. The evaluations included all of the major commercial varieties, LCP 84-384, L 99-233, Ho 95-988, L 97-128, CP 89-2143, HoCP 96-540, L 99-226, HoCP 00-950, L 01-283, L01-299, and the newly released cultivars, L 03-371, and HoCP 04-838. Trials were placed on most of the major soil series in the sugar belt. These soil series of widely disparate attributes are broadly classified as either light- or heavy-textured soil for the purpose of recommending N fertilizer rates. Separate application trials were conducted for plant-cane and first- and second-ratoon crops of the production cycle. Nitrogen rates compared to the non-fertilized control were 45, 90, 134, and 179 kilograms of N per hectare with 32% urea ammonium nitrated (UAN) as the N source. 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. Nevertheless, several consistencies were observed over the years. Sugar yields were generally greater on light-textured soil with higher rates of N required on heavy-textured soil to achieve equivalent yield. Older ratoon crops required the greatest amount of N to achieve optimal yields, whereas plant-cane and first-ratoon crop yields optimized at similar N rates, particularly on light-textured soils. Sugar content was often depressed at the greatest application rate of 179 kilograms N per hectare, which not only confirms the need to reduce rates but also allays fears that N deficiencies might occur at the lowered rates. Though yield of varieties optimized at different rates in different tests, these differential varietal responses were minor and did not result in unique varietal recommendations for N application practices. The net result of the re-examination of N rates was that N rates could be reduced using 32% UAN without compromising yield. Results from the trials allowed for reductions of 22 kilograms of N per hectare for plant-cane and 44 kilograms of N per hectare for ratoon crops. Revised recommendations provide both economic and environmental benefits. Full adoption of the revised rates could save the sugar industry over $10 million annually in fertilizer input costs. Additional economic value from enhanced sucrose recovery should also be realized. By increasing sugar yield per ton of sugarcane, it is probable that transportation costs would decrease because it would take fewer tons of cane to achieve the same sugar yield per acre.