Bioenergy Crops Effect on Aggregate Stability after Long-Term Land Conversion.

Bioenergy Crops Effect on Aggregate Stability after Long-Term Land Conversion

T.Stephenson, J.L. Heitman, A.M. Howard

Land use changes in agricultural systems alter soil properties. In the North Carolina piedmont there is currently interest in converting marginal farmland from traditional (fescue) to potential bioenergy cropping systems. There is limited long-term information available about how these candidate bioenergy crops and their associated rooting systems affect soil aggregation. Soil aggregation is an important factor for soil sustainability. The objective of this project is to compare macro and micro aggregation under five cropping systems: giant miscanthus, switchgrass, fiber sorghum, corn, and fescue hay after five years of management. Aggregate stability of the surface (0-7.6 cm) and subsurface (7.6-15.24 cm) soil was measured using wet sieving for macro aggregates and the dispersion ratio for micro aggregates. Crop residue cover and soil physical properties were assessed to determine their relationship to soil aggregation. Surface macroaggregation was more variable than in the subsurface layer and was most stable in corn, miscanthus, and fescue systems (p<.05). Surface microaggregate stability was similar throughout the systems except for switchgrass, which was significantly less stable (p<.05). Surface macro aggregate stability was positively correlated to the amount of crop residue cover left on the surface following the harvest operations (r²=.60). There was a negative inverse relationship between macroaggregate stability and bulk density (r²=.73). While soil aggregation did not significantly improve under these new cropping systems, corn and giant miscanthus maintained the same amount of soil aggregation as fescue.