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

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 À1 ) 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 (À24.0 kg P ha À1) compared to switchgrass (À5.4 kg P ha À1). 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.Keywords: harvest timing, no-till corn, P, K, N fertilizer, residue removal, soil C sequestration, soil organic C, switchgrass IntroductionBioenergy production has increased exponentially over the past 30 years (U.S. Department of Energy, 2013) in part leading to a dramatic increase in US acreage planted to corn (Zea mays) USDA-NAAS, 2013 and consuming over 30% of the US corn production in 2009 (Robertson et al., 2011). The primary feedstock for producing cellulosic bioethanol, corn stover, is attractive due to the large quantity of biomass available (Karlen et al., 2011a, b). However, concerns have been raised about the long-term annual removal of 50% or more of the crop residue and its potential to decrease both plant and soil productivity while also increasing the potential for soil erosion-ultimately reducing future yields and decreasing soil organic carbon (SOC) content (Johnson et al., 2011; Karlen et al., 2011a, b).Switchgrass (Panicum virgatum L.) is a perennial, native, C4 grass capable of growing on a broad range of soil types and under non-irrigated conditions (Sander...

Corn Stover Harvest, Tillage, and Cover Crop Effects on Soil Health Indicators

“…The index values from this study (Table 3) fit within existing ranges found in agricultural soils in this region (Hammac et al, 2016;Jokela et al, 2011;Karlen et al, 2014bKarlen et al, , 2017Stewart et al, 2015). Generally, higher index values suggest improved soil functioning.…”

“…Though these four studies were not focused on stover removal in continuous corn, the results offer a useful comparison with other agricultural soils. Stewart et al (2015) included corn stover removal at a marginally productive site in Nebraska. The no-till 50% residue removal rate lowered soil quality index scores for SOC, aggregate stability, and MBC compared with no residue removal.…”

Dedicated Energy Crops and Crop Residues for Bioenergy Feedstocks in the Central and Eastern USA

“…Use of perennial grasses on landscapes, especially where soils are marginally productive and/or erosion prone, has been shown to enhance SOC storage and nutrient retention (i.e., P), improve soil bulk density, and reduce erosion risk [45,89,99]. Although direct plant measurements of switchgrass grown under higher atmospheric CO 2 concentrations indicate that switchgrass may be limited in its potential to boost productivity as atmospheric CO 2 concentrations increase [100], model simulations of drought-tolerant cultivars predict switchgrass could withdraw between 3 and 19 % less water than conventional crops under future climate change scenarios [101].…”

Inhibition of microbial biofuel production in drought-stressed switchgrass hydrolysate

“…Corn stover is currently the feedstock of choice due to its current widespread availability and economic potential [2, 10]. Switchgrass is a promising perennial bioenergy crop that can be grown on marginal lands [11] and provides superior environmental benefits compared to corn, including support for biological diversity [12], lower nitrous oxide emissions [13], and improved soil properties [14, 15]. In order to investigate how interannual variation in precipitation influences the processing characteristics and microbial fermentation of these two important biofuel feedstocks, we compared switchgrass and corn stover that were harvested following the 2012 Midwestern US drought to those harvested during two non-drought years with different precipitation patterns (2010 and 2013).…”