Utilization of Yield Mapping and Variable-Rate Lime Application in Louisiana Sugarcane

Authors: Johnson, Richard; Richard Jr, Edward

Submitted to: International Society of Sugar Cane Technologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2004
Publication Date: 1/30/2005
Citation: Johnson, R.M., Richard Jr, E.P. 2005. Utilization of Yield Mapping and Variable-Rate Lime Application in Louisiana Sugarcane. Proc. International Society of Sugar Cane Technologists. 25:351-356.

Interpretive Summary: Louisiana sugarcane producers, like most U.S. agricultural producers, have faced increased economic pressure in recent years. Growers must find ways to decrease costs and maximize profits. Precision Agriculture, specifically, variable rate lime and fertilizer application, may offer an important tool to accomplish this task. The first step in this study was to evaluate the variation in sugarcane yield and quality. Experiments were conducted in two locations in South Louisiana for three growing seasons. This was done to determine if sufficient natural variability existed in Louisiana sugarcane to justify a precision agricultural approach. In all years and at both locations sugarcane yield and quality were found to vary significantly with 2-5 fold changes in yield occurring within the same field. These properties were also found to vary across the field. The observed variation was not random, but was instead found to be spatially correlated. Samples that were spaced at a distance less than the range of spatial correlation were more similar than those at distances greater than this range. This data combined with the variability data indicated that there was sufficient variability present to try a precision agricultural approach. An experiment was conducted for two years in a 48-acre sugarcane field to determine if variable rate lime application could benefit the sugarcane industry. In the variable rate method, soil samples are taken in a grid pattern in the field and are used to predict how much lime is need in different areas of the field. In the traditional method, only one rate of lime (based on an average of several soil samples) is applied to all parts of the field. In both years there was a significant yield benefit to applying lime by either the variable rate or traditional method compared to no lime additions. The traditional method resulted in yields that were slightly higher the variable rate method; however, in the second year the difference between the two methods was much lower. These combined results are promising, because if similar yields can be obtained with the variable rate system, which is actually applying less inputs, then an overall increase in profitability will be observed. The results also indicate that further research on the VR application method is required to achieve maximize yields. Sugarcane growers that adopt these methods may benefit from decreased fertilizer and lime costs, while minimizing the environmental impact of their application.

Technical Abstract: Precision agriculture may offer sugarcane growers a management system that decreases costs and maximizes profits, while minimizing any potential negative environmental impact. In the first phase of this study we evaluated the spatial variability of sugarcane yield and quality in two locations in Southern Louisiana. Each field was planted to sugarcane cv 'LCP 85-384' and harvested in a grid cell pattern (10.6 x 15.2 m) using a single row, chopper sugarcane harvester with weights determined using a field transport wagon equipped with electronic load sensors. At the first site in 2001, 2002, and 2003, all sugar yield and quality parameters were spatially correlated with the exception of TRS and Fiber in 2003. The ranges of spatial correlation varied from 27 to 187-m. At the second site in 2001, 2002, and 2003, all sugar properties were spatially correlated with ranges of spatial correlation varying from 27 to 106-m. In the second phase of the study, we investigated the utility of variable-rate (VR) lime application. In this study a conventional (uniform rate) lime application method was compared to a VR application method and a no-lime control. Prior to lime application, soil samples (0-20 cm) were taken on a 0.4-ha grid to determine VR application maps. Results from 2002 show an advantage to both the conventional and VR treatments in terms of sugar yield as compared to the no-lime check with yields of 7653 and 6548 kg/ha compared to 6108 kg/ha. In 2003 sugar yields were 8995, 8564 and 8085 kg/ha for the conventional, VR and no-lime treatments, respectively. Although the VR treatment decreased total lime applied by targeting application to only areas where lime was required, yields were not equal to the uniform application. Additional research is needed to refine the VR lime application method.