Changes in soil carbon and nitrogen associated with switchgrass production

Greater knowledge of the short- and long-term effects of biomass production practices on soil biological and chemical properties is needed to determine influences on sustainable land management. Soil samples under switchgrass (Panicum virgatum L.), other forage grasses, cultivated crops, and forest were collected seasonally at six locations. Soil organic C (SOC), total N, soil microbial biomass C (SMBC) and N (SMBN), soil mineralizable C and N, and basal soil respiration (BSR) were in general greatest under long-term coastal bermudagrass [Cynodon dactylon (L.) Pers.] pasture (>40 years), second highest under Alamo switchgrass and kleingrass (Panicum coloratum L.) planted in 1992 and forest, followed by Alamo switchgrass planted in 1997, and was lowest under the cultivated soils. Soil organic C at 0-5 cm was 42-220% greater in soils under Alamo switchgrass planted in 1992 than cultivated soils, except at College Station where SOC values under Alamo planted in 1992 and the cultivated rotation were not significantly different. Although the rotation treatment is cultivated at this location, two high residue crops are used, wheat (Triticum aestivum L.) and sorghum [Sorghum bicolor (L.) Moench.]. Similar trends were noted for total N, SMBC, SMBN, mineralizable C and N, BSR, and the ratio of SMBC/SOC. Insufficient information was collected in this study to determine whether the parameters evaluated for forest and switchgrass were different. In addition to its high yield potential, adaptation to marginal sites and tolerance to water and nutrient limitations, switchgrass appeared to be a competitive crop in terms of land sustainability, resulting in enhanced soil quality characteristics compared to long-term cultivated soils