Variable-Rate Application Of Nitrogen And Potassium Fertilizers In Louisiana Sugarcane Production Systems.
1B. J. Viator, 2R. M. Johnson
1. Calvin Viator, Ph.D. & Associates, LLC
2. USDA-ARS, Sugarcane Research Unit
If sugar and cane yields are to be optimized and profitability improved, it is critical that a sugarcane crop receive the proper levels of plant nutrients. Under-fertilization can result in reduced cane yields, while over-fertilization can reduce sugar recovery. In addition, improper fertilization may increase crop susceptibility to environmental stresses and disease and insect pests. Nitrogen (N) continues to be one of the most important and costly components of a sugarcane fertility program, directly affecting both cane and sugar yields. Potassium (K) has been associated with plant water use and may aid in drought tolerance and potassium deficient plants are also more prone to certain diseases and are more likely to lodge. It is therefore critical that the proper rates of both N and K be applied to achieve a balance between cane and sugar yields. The objective of these studies was to determine if variable-rate application of N and K could help optimize sugarcane yields, while increasing production efficiency. Two commercial fields were selected in 2012 for these studies: a 3.0-ha field of plant cane 'Ho-CP 96-540' for the N trial and a 7.0-ha field of plant cane 'Ho-CP 96-540' for the K trial. Two different approaches were used to develop management zones for variable-rate fertilizer application. For the N trials, a Veris soil electrical conductivity (EC) mapper was used to identify areas in the field with a similar soil texture or soil type. Three zones were developed with corresponding nitrogen rates of 90, 100, 112 kg N ha-1. The lowest N rate was applied to the lighter (silt loam) soil and the higher rates were applied to the heavier (clay) soil. The VR N treatment was compared to a uniform application of 100 kg N ha-1. For the K trials, management zones were determined by grid soil sampling, using a 0.75-ha grid. Three zones were developed with corresponding rates of 110, 147, 184 kg K2O ha-1. It was not possible to determine yields from a uniform application in the K trials, but yield variability was evaluated. To estimate yields, selected rows from each field were harvested in 30.5-m increments in the K trial and 36.5-m in the N-trial, using a John Deere, single-row chopper harvester. Cane yields were determined using a field transport wagon equipped with electronic load sensors, and theoretically recoverable sucrose (TRS) levels were estimated by the core-press method. Results from the N trial in 2012 showed that both cane and sugar yields exhibited significant variability with yields ranging from 37 to 127 t cane ha-1, 93 to 129 kg sugar t-1, and 4,480 to 15,190 kg sugar ha-1, respectively. No significant differences between the VR and uniform application procedures were observed. Significant variability was also observed in the K trials, with yields ranging from 84-161 t cane ha-1, 116-147 kg sugar t-1, and 11,160 to 21,000 kg sugar ha-1, respectively. Spatial maps of cane and sugar yields from both the N and K trials exhibit significant spatial correlation, with variability in the K trial more closely correlated with the developed management zones than in the N trial. Cane and sugar yields will be determine in the 1st-ratoon fields of both trials in December, 2013. Results suggest that VR application of both N and K may offer Louisiana sugarcane producers a viable method to decrease costs, while increasing production efficiency.
