|Richard Jr, Edward|
Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2009
Publication Date: 10/8/2010
Citation: Johnson, R.M., Richard Jr., E.P. 2010. Variable rate lime application in Louisiana sugarcane production systems. Precision Agriculture. 11:464-474. DOI: 10.1007/s11119-009-9140-2.
Interpretive Summary: Soil pH has a direct influence on the amount of various soil nutrients that is available to plants. More specifically, as soil pH decreases or increases over a target level of 6.5 the availability of soil nutrients, and applied fertilizers, will decrease. Variable-rate (VR) application systems were developed to help growers target their applications lime and fertilizer to maximize nutrient use efficiency, while minimizing any potential negative environmental impacts from the overuse of fertilizer. In this study, we conducted three variable-rate lime tests in newly planted commercial sugarcane fields over a three year period to determine if this method could help growers increase profitability. The traditional, uniform rate (UR) 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 in a grid pattern to map the variability present in soil pH. Lime prescription VR application maps were developed from the soil pH maps. Soil samples were also taken after each crop was harvested to determine the residual effects of lime application on soil properties. Neither the UR nor VR lime application method consistently improved cane or sugar yields over the no lime control. Location differences in the soil fertility at the time of lime application in the plant-cane crop and the rates of supplemental nitrogen applied each year of the production cycle may have obscured any positive yield effects of liming to increase soil pH; hence improve nutrient availability during the growing season. It is also possible that, because of the high degree of variability present in soil pH, VR lime applications of lime over several crop cycles will be required before the soil pH levels are stabilized to the point that even fertilizer rates can be reduced. This possibility will be investigated in future studies.
Technical Abstract: Precision agriculture may offer sugarcane growers a management system that decreases costs and maximizes profits, while minimizing any potential negative environmental impact. The utility of variable-rate (VR) lime application in the initial production year (plant cane) of a 3-yr sugarcane crop cycle was investigated at three locations planted to the cultivar LCP 85-384 for a total of nine site-years. A conventional, uniform rate (UR) 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 produce VR application maps. Soil samples were also taken after each crop of the 3-year production cycle was harvested to determine possible effects of lime application on soil properties. The combined results showed that neither the UR nor VR lime application method consistently improved cane or sugar yields over the no lime control. Cane and sugar yields at Naquin Farms (NF) were increased with both the UR and VR methods, with the UR method having a slight advantage. At St. Louis Plantation (SLP), only the VR method in the first-ratoon crop increased cane and sugar yields in response to lime application and there were no yield differences due to lime application at Ellendale Plantation (EP). At NF and SLP application of lime in the plant-cane crop increased soil pH and phosphorus over the entire three-year production cycle. At EP, lime application did not influence any of the soil properties measured. The failure to get a yield response from lime application at SLP and EP may have been due to the fact that fertility levels at both SLP and EP at planting were already greater than those at NF and the nitrogen fertilizer rates used by the grower at EP were higher than those at either SLP or NF. This may have obscured any positive yield effects that would be realized from increased nutrient availability. It is also possible that multiple VR lime applications will be required over a number of crop cycles to stabilize soil pH levels before a consistent positive affect on cane and sugar yields is observed with VR application. This possibility will be investigated in future studies.