Nitrogen and harvest effects on soil properties under rainfed switchgrass and no-till corn over 9 years: implications for soil quality

Authors

Catherine E. Stewart, USDA-ARSFollow
Ronald F. Follett, USDA-ARSFollow
Elizabeth G. Pruessner, USDA-ARSFollow
Gary E. Varvel, USDA-ARSFollow
Kenneth P. Vogel, USDA-ARS, University of Nebraska-LincolnFollow
Robert B. Mitchell, USDA-ARS, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2014

Citation

GCB Bioenergy (2014), doi: 10.1111/gcbb.12142

Comments

This article is a US Government work and is in the public domain in the USA

Abstract

Nitrogen fertilizer and harvest management will alter soils under bioenergy crop production and the long-term effects of harvest timing and residue removal remain relatively unknown. Compared to no-tilled corn (NT-C, Zea mays L.), switchgrass (Panicum virgatum L.) is predicted to improve soil properties [i.e. soil organic C (SOC), soil microbial biomass (SMB-C), and soil aggregation] due to its perennial nature and deep-rooted growth form, but few explicit field comparisons exist. We assessed soil properties over 9 years for a rainfed study of N fertilizer rate (0, 60, 120, and 180 kg N ha 1) and harvest management on switchgrass (harvested in August and postfrost) and NT-C (with and without 50% stover removal) in eastern NE. We measured SOC, aggregate stability, SMB-C, bulk density (BD), pH, P and K in the top 0–30 cm. Both NT-C and switchgrass increased SMB-C, SOC content, and aggregate stability over the 9 years, reflecting improvement from previous conventional management. However, the soils under switchgrass had double the percent aggregate stability, 1.3 times more microbial biomass, and a 5–8% decrease in bulk density in the 0–5 and 5–10 cm depths compared to NT-C. After 9 years, cumulative decrease in available P was significantly greater beneath NT-C (24.0 kg P ha1) compared to switchgrass (5.4 kg P ha 1). When all measured soil parameters were included in the Soil Management Assessment Framework (SMAF), switchgrass improved soil quality index over time (DSQI) in all depths. NT-C without residue removal did not affect DSQI, but 50% residue removal decreased DSQI (0–30 cm) due to reduced aggregate stability and SMB-C. Even with best-management practices such as NT, corn stover removal will have to be carefully managed to prevent soil degradation. Long-term N and harvest management studies that include biological, chemical, and physical soil measurements are necessary to accurately assess bioenergy impacts on soils.