Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2016
Publication Date: 2/28/2017
Publication URL: https://handle.nal.usda.gov/10113/5763073
Citation: Jin, V.L., Schmer, M.R., Stewart, C.E., Sindelar, A.J., Varvel, G.E., Wienhold, B.J. 2017. Long-term no-till and stover retention each decrease the global warming potential of irrigated continuous corn. Global Change Biology. 23:2848-2862.

Interpretive Summary: Row-crop production systems can help reduce global warming by storing carbon in agricultural soils. Management practices, however, can add greenhouse gases into the atmosphere and counteract the benefit of soil carbon storage. Limited information is available for irrigated row-crop systems. Crop residue removal in high-level production systems such as those under irrigation can supply feedstocks for both livestock and bioenergy. The use of no-till is often recommended as a companion practice for removing crop residues. We found that in a long-term irrigated continuous corn system in eastern Nebraska, all management systems were net greenhouse gas producers and so had limited potential to decrease global warming. We also found that there was no global warming benefit to using both no-till and residue retention practices together. Instead using either conservation practice reduced the amount of greenhouse gases released to the atmosphere compared to more conventional practices (disk tillage, residue removal). Although this irrigated corn system did not store carbon, conservation management practices could provide other benefits to producers, such as decreased soil erosion and increased soil health.

Technical Abstract: Over the last 50 years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long-term agronomic management impacts on soil organic carbon (SOC) stocks, soil greenhouse gas (GHG) emis-sions, and global warming potential (GWP) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quanti'ed by measuring soil nitrous oxide (N2O) and methane (CH4) 'uxes and SOC changes (DSOC) at a long-term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska, United States. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8 Mg DM ha''1 yr''1, respectively) under no-till (NT) or conventional disk tillage (CT) with full irrigation (n = 4). Soil N2O and CH4 'uxes were measured for 've crop-years (2011–2015), and DSOC was determined on an equivalent mass basis to ~30 cm soil depth. Both area- and yield-scaled soil N2O emissions were greater with stover retention compared to removal and for CT compared to NT, with no interaction between stover and tillage practices. Methane comprised <1% of total emissions, with NT being CH4 neutral and CT a CH4 source. Surface SOC decreased with stover removal and with CT after 14 years of management. When DSOC, soil GHG emissions, and agronomic energy usage were used to calculate system GWP, all management systems were net GHG sources. Conservation practices (NT, stover retention) each decreased system GWP compared to conventional practices (CT, stover removal), but pairing conservation practices conferred no additional mitigation bene't. Although cropping system, management equipment/timing/history, soil type, location, weather, and the depth to which DSOC is measured affect the GWP outcomes of irrigated systems at large, this long-term irrigated study provides valuable empirical evidence of how management decisions can impact soil GHG emissions and surface SOC stocks.