|Viator, Howard - LSU AG CTR JEANERETTE, LA|
|Legendre, Benjamin - LSU AG CTR, B.R., LA|
Submitted to: Sugar Bulletin
Publication Type: Trade Journal
Publication Acceptance Date: February 19, 2008
Publication Date: March 1, 2008
Citation: Johnson, R.M., Viator, H.P., Legendre, B.L. 2008. Sugarcane Fertilizer Recommendations for the 2008 Crop Year. Sugar Bulletin. 86:11-13. Technical Abstract: Louisiana sugarcane producers continue to face challenges as they attempt to maximize profits and increase production efficiency. This year yet another challenge has been added through the significant increase in the cost of nitrogen (N), phosphorus (P) and potassium (K) fertilizers. Due to these increases, many growers are looking for ways to reduce fertilizer costs, while maintaining yields. In this article we would like to discuss the important components of a balanced sugarcane fertility management program, while highlighting potential areas in which cost savings may be achieved. The single, most important component of a soil fertility program involves the proper management of soil acidity. This is because the soil acidity level, as estimated by the soil pH, determines the availability of nutrients to growing crops and thus the efficiency with which crops makes use of fertilizers. As the soil pH drops to below 5.5 the availability of soil N, P and K drops dramatically, while levels of aluminum and manganese may increase to toxic levels. Excess soil acidity is neutralized by applying lime (CaCO¬3) at a rate determined by a soil test to raise the soil pH, ideally to 6.5. In addition to correcting soil acidity problems, lime also supplies calcium, an essential plant nutrient, and can also be used to correct magnesium deficiencies through the use of a dolomitic lime, (i.e. MgCO3 vs. CaCO3). Finally, maintaining the proper soil pH enhances the activity of soil microorganisms and may improve the availability and ultimately the residual activity of soil applied herbicides. Recent studies by USDA-ARS personnel indicate that lime application improved the overall cane and sugar yields for a 3-year crop cycle by 14 tons and 2,990 lbs, respectively. They also showed that variable rate lime application reduced the total lime applied as compared to uniform application. Lime should be applied when the soil pH is less than 5.8 on the lighter textured sandy loam and silt loam soils and when the soil pH is less than 5.2 on the heavier textured clay loam and clay soils. Ideally, lime should be broadcast to fallow fields, but can also be applied in the fall or winter. Nitrogen fertilizer is another critical component of a sugarcane fertility management program. Several factors come into play when determining N rates. Sufficient N must be applied to insure that cane yields are maximized. However, application of excess N can delay maturity and may increase the risk of lodging. The timing of N application is also very important. In Louisiana, optimal N use efficiency occurs if fertilizer is applied to cane that is actively growing. The target application date should be between April 1 and April 30; however, N can be applied in May with equally good results. Application of N too early can result in increased loss of N due to denitrification, leaching and volatilization, depending on the form of N applied. Over the past several years researchers from the USDA-ARS, Sugarcane Research Laboratory and the LSU AgCenter have conducted tests with our newly released varieties to determine if N rates could be modified from previous levels. In 2007, replicated studies were conducted on commercial farms with HoCP 96-540, L97-128, Ho 95-988, LCP 85-384, L 99-226, L 99-233, and CP 89-2143 in plant-cane, first- and second-stubble fields. Results from these experiments combined with those conducted over the last several years have allowed us to revise our recommendations. Overall, the new recommendations call for a 15-20% reduction in N rates for all soil types and crop ages. These new recommendations are based on the use of 32% UAN, which is a much more efficient N source than anhydrous ammonia, the N source used to formulate the old recommendations. The inherent volatility of anhydrous ammonia necessitated the use of higher N rates to account for the fertilizer lost during the application process. It appears that there is little difference in N requirements for plant-cane and first-stubble crops; however, slightly more N is recommended for the first-stubble crop. Additional N fertilizer is indicated for second- and older stubble crops. There was some confusion as to the N rates recommended for plant-cane, with some producers apparently hearing that we were not recommending N for HoCP 96-540 plant-cane crops. This is simply not the case. In our results from 2007, several tests did not show a statistical advantage to N fertilizer. However, when previous year’s results are taken into account, the recommended rates for plant-cane were determined to be 60-80 lbs N/A in a light soil and 80-100 lbs N/A in a heavy soil, for all varieties. Phosphorus and potassium are also important components of a balanced fertility program. Approximately one pound of P and three pounds of K are removed from the soil for every ton of cane harvested. As previously mentioned, the availability of both nutrients, particularly P, is closely related to soil pH levels. Rates of both P and K are determined through soil testing. The optimum application time for P and K is between April 1 and April 30; however, earlier application will also give good results. Recent test results from cooperative studies conducted by the USDA-ARS, Sugarcane Research Laboratory and the LSU AgCenter have shown limited benefits from P fertilizer with stubble crops of LCP 85-384. In addition, high levels of P and sulfur (S) have been associated with an increased incidence of brown rust. For these combined reasons, P fertilizer should only be considered for soils testing low or very low for P. Sulfur fertilizer should only be considered if recommended by soil test. If indicated by soil tests, the recommended rate of S for both plant an stubble cane, irrespective of soil type is 24 lb S/A. Sulfur should optimally be applied with P and K in April. Also note that stubble cane is more likely to respond to S than plant cane and the greatest response is more likely to occur on medium-heavy to heavy textured soils. There are currently no recommendations for applying micronutrients to sugarcane in Louisiana, and application should only be considered if soil or plant tissue tests indicate deficiencies are present. In conclusion, a properly managed sugarcane fertility program will lead to increased production efficiency and more importantly improved profitability. The first and most important consideration in this fertility program should be the management of soil acidity due to the significant effects that soil pH can have on fertilizer availability. Significant cost savings can be realized by the adoption of new N rates, provided that N fertilizer is applied to actively growing cane (April 1-30) and not too early in the season. Finally, application of P, K and S fertilizer should be in accordance with soil tests and recommended rates, as over-application may result in increased incidence of brown rust.