Soil Greenhouse Gas Emissions and Carbon Dynamics of a No-Till, Corn-Based Cellulosic Ethanol Production System

Abstract

Crop residues like corn (Zea mays L.) stover perform important functions that promote soil health and provide ecosystem services that influence agricultural sustainability and global biogeochemical cycles. We evaluated the effect of corn stover removal from a no-till, corn-soybean (Glycine max (L.) Merr) rotation on soil greenhouse gas (GHG; CO 2 , N 2 O, CH 4 ) fluxes, crop yields, and soil organic carbon (SOC) dynamics. We conducted a 4-year study using replicated field plots managed with two levels of corn stover removal (none; 55 % stover removal) for four complete crop cycles prior to initiation of ground surface gas flux measurements. Corn and soybean yields were not affected by stover removal with yields averaging 7.28 Mg ha −1 for corn and 2.64 Mg ha −1 for soybean. Corn stover removal treatment did not affect soil GHG fluxes from the corn phase; however, the treatment did significantly increase (107 %, P = 0.037) N 2 O fluxes during the soybean phase. The plots were a net source of CH 4 (∼0.5 kg CH 4 -C ha −1 year −1 average of all treatments and crops) during the generally wet study duration. Soil organic carbon stocks increased in both treatments during the 4-year study (initiated following 8 years of stover removal), with significantly higher SOC accumulation in the control plots compared to plots with corn stover removal (0-15 cm, P = 0.048). Non-CO 2 greenhouse gas emissions (945 kg CO 2 -eq ha −1 year −1 ) were roughly half of SOC (0-30 cm) gains with corn stover removal (1.841 Mg CO 2 -eq ha −1 year −1 ) indicating that no-till practices greatly improve the viability of biennial corn stover harvesting under local soil-climatic conditions. Our results also show that repeated corn stover harvesting may increase N loss (as N 2 O) from fields and thereby contribute to GHG production and loss of potential plant nutrients.

Long‐term no‐till and stover retention each decrease the global warming potential of irrigated continuous corn

“…Other rainfed studies in warmer climates have also noted lower soil N 2 O emissions when crop residue is removed (Jin et al ., ; Guzman et al ., ). In contrast, rainfed studies from colder climates have shown that stover removal can increase soil N 2 O emissions (Congreaves et al ., ; Lehman & Osborne, ), possibly due to warmer soil temperatures or changes in moisture/aeration conditions that stimulate denitrifier activity. In a meta‐analysis of 28 crop residue removal studies of mostly nonirrigated systems, Chen et al .…”

“…Although increasing crop rotation complexity generally enhances SOC storage, limited SOC changes occur when continuous corn is converted to a corn-soybean rotation (West & Post, 2002). Thus, similar to SOC losses observed under continuous corn, residue removal in a rainfed corn-soybean system also resulted in SOC losses (Lehman & Osborne, 2016). Other corn rotational systems (e.g., corn-wheat Triticum aestivum L.) have shown numerical but not statistically significant SOC losses after crop residue removal (Lemke et al, 2010;Huang et al, 2013).…”

“…Some researchers suggest that soil N 2 O emissions are expected to be greater in NT compared to conventional tillage (CT) due to greater expected soil water-filled pore space (WFPS) and less aeration due to greater soil bulk densities (Linn & Doran, 1984;Baggs et al, 2003;Rochette, 2008), but others predict smaller emissions under NT because of improved soil structure and cooler soil temperatures (Snyder et al, 2009;Venterea et al, 2011;Sainju et al, 2012;Guzman et al, 2015). Similarly, crop residue management can result in contrasting responses, with residue removal decreasing (Jin et al, 2014;Guzman et al, 2015) or increasing (Congreaves et al, 2016;Lehman & Osborne, 2016) direct GHG emissions from soils.…”

Soil N2O emissions as affected by long‐term residue removal and no‐till practices in continuous corn

“…The lack of an effect in the present study challenges the assumption that crop residue removal will reduce N 2 O emissions based on IPCC methodology (IPCC, ). A wide variety of responses to residue removal have been observed and the fact that field results do not always support top‐down GHG accounting protocols has been argued in previous studies (Congreves et al, ; Hao et al, ; Lehman & Osborne, ; Yao et al, ). Together these findings suggest the impacts of residue removal cannot easily be predicted for maize production in this region, which presents a challenge for accurately estimating the net GHG impacts of cellulosic biofuel production.…”

“…Consistent with IPCC emission factors, a number of previous studies have found that residue removal decreases N 2 O emissions (Abalos, Sanz‐Cobena, Garcia‐Torres, Groenigen, & Vallejo, ; Jin et al, ; Mutegi, Munkholm, Petersen, Hansen, & Petersen, ; Yao et al, ). However, studies have also shown N 2 O emissions can either increase or remain unchanged with crop residue removal (Congreves, Brown, Németh, Dunfield, & Wagner‐Riddle, ; Hao, Chang, Carefoot, Janzen, & Ellert, ; Lehman & Osborne, ; Yao et al, ). Increased N 2 O emissions may be due to larger soil temperature fluctuations or changes in moisture/aeration conditions compared to the practice of incorporating crop residues.…”