Soil Chemical and Biological Fertility, Microbial Community Structure and Dynamics Under Different Sugarcane Planting Systems on Florida Histosols.

Sugarcane is typically planted in either “fallow” or “successive” planting system on Histosols of Florida. In the fallow planting, the field is either rotated with a different crop, or kept flooded or under chemical fallow after the final ratoon harvest. In the successive planting system (synonymous to sugarcane monoculture), sugarcane is replanted soon after harvest of the final ratoon. Continuous cane harvests are possible with successive plantings, such that the acreage devoted to successive sugarcane planting is increasing. Sugarcane yields in successive plantings are lower than with either fallow or rotation plantings; however, the reasons for this yield decline are not known. The objective of this study was to compare the soil properties in successive plantings with flooded fallow and crop rotation (rice, sweet corn) plantings with green or burnt cane harvest methods. Successive planting with green cane harvest exhibited greater soil organic matter concentrations, total microbial biomass, mycorrhizal associations and slow growing bacterial groups than were similar to the fallow planting with sweet corn rotation. The CLPP of Biolog assay and PLFA profiles of fallow planting indicated greater diversity than the conventional successive planting under burnt cane harvest system. The flooded fallow and rice rotation systems exhibited different properties related to soil health, such as soil chemical, microbial and biological properties, compared to successive planting. Overall, our results indicated significantly lower organic matter and available micro nutrients (Zn and Mn) concentration, higher proteases activity, low N mineralisation rates, lower PLFA microbial biomass, lower fungi to bacteria ratios, lower functional and metabolic diversities of microbial communities in the successive planting with preharvest burnt cane compared to other planting systems which may be the cause for yield decline.