Initial nitrous oxide, carbon dioxide, and methane costs of converting conservation reserve program grassland to row crops under no‐till vs. conventional tillage

Abstract

Around 4.4 million ha of land in USDA Conservation Reserve Program (CRP) contracts will expire between 2013 and 2018 and some will likely return to crop production. No-till (NT) management offers the potential to reduce the global warming costs of CO2, CH4, and N2O emissions during CRP conversion, but to date there have been no CRP conversion tillage comparisons. In 2009, we converted portions of three 9–21 ha CRP fields in Michigan to conventional tillage (CT) or NT soybean production and reserved a fourth field for reference. Both CO2 and N2O fluxes increased following herbicide application in all converted fields, but in the CT treatment substantial and immediate N2O and CO2 fluxes occurred after tillage. For the initial 201-day conversion period, average daily N2O fluxes (g N2O-N ha−1 d−1) were significantly different in the order: CT (47.5 ± 6.31, n = 6) ≫ NT (16.7 ± 2.45, n = 6) ≫ reference (2.51 ± 0.73, n = 4). Similarly, soil CO2 fluxes in CT were 1.2 times those in NT and 3.1 times those in the unconverted CRP reference field. All treatments were minor sinks for CH4 (−0.69 ± 0.42 to −1.86 ± 0.37 g CH4–C ha−1 d−1) with no significant differences among treatments. The positive global warming impact (GWI) of converted soybean fields under both CT (11.5 Mg CO2e ha−1) and NT (2.87 Mg CO2e ha−1) was in contrast to the negative GWI of the unconverted reference field (−3.5 Mg CO2e ha−1) with on-going greenhouse gas (GHG) mitigation. N2O contributed 39.3% and 55.0% of the GWI under CT and NT systems with the remainder contributed by CO2 (60.7% and 45.0%, respectively). Including foregone mitigation, we conclude that NT management can reduce GHG costs by ∼60% compared to CT during initial CRP conversion.

Methane uptake by four land-use types in the agro-pastoral region of northern China

“…We found that the highest CH 4 uptake occurred in CL that had been cropped for more than 30 years, which was inconsistent with the findings of Mosier and Delgado (1997) who found that soil CH 4 oxidation in the shortgrass steppe had not recovered even after plowing for 79 years. Ruan and Robertson (2013) observed no significant difference in CH 4 uptake between a Conservation Reservation Program (CRP) pasture (Bromus inermis) and a converted soybean (Glycine max) cropland in the Great Plains of Northern America. Ussiri et al (2009) reported higher CH 4 uptake in no-till fields compared to conventionally tilled fields.…”

Agricultural Management Impact on Greenhouse Gas Emissions

“…Various studies have shown that both net GWP and GHGI were lower with no-tillage than conventional tillage, regardless of soil and climatic conditions, cropping systems, and methods Agricultural Management Impact on Greenhouse Gas Emissions http://dx.doi.org/10.5772/intechopen.72368 91 of calculations [3,7,44,47,49,55]; Sainju [56] observed that reductions in net GWP and GHGI due to no-tillage vs. conventional tillage vary among regions with various soil and climatic conditions, but largest difference occurred in sandy soil under moderate annual precipitation (900 mm). Net GWP values, however, increased in regions with higher air temperature.…”

“…Some have used the sum of CO 2 equivalents of N 2 O and CH 4 emissions [21,41,42], while others [43,44] have included CO 2 equivalents of all three GHGs. Still others have used CO 2 equivalents of N 2 O and CH 4 emissions and soil carbon sequestration rate [45][46][47].…”

“…Using partial accounting of CO 2 sources and sinks, Liebig et al [63], however, did not found significant difference in net GWP between alternate-year fallow and continuous cropping in North Dakota. Perennial crops can reduce net GWP and GHGI compared with annual crops [7,44,50] due to higher root biomass production [64,65] and increased soil carbon sequestration [55]. Because land under perennial crops is not tilled and perennial crops are not applied with fertilizers, herbicides, and pesticides, GHG emissions are usually lower with perennial than annual crops [4].…”

Reduced Snow Cover Increases Wintertime Nitrous Oxide (N2O) Emissions from an Agricultural Soil in the Upper U.S. Midwest

“…Total available N including ammonium (NH þ 4 ) and nitrate (NO À 3 ) availability was estimated using in situ ion exchange resin strips to minimize sampling disturbance (Ruan and Robertson 2013). Three pairs of anion and cation resin strips (2.5 cm 9 10 cm 9 0.62 mm thick; GE Power & Water, Trevose, PA, USA) were buried directly to a soil depth of 12 cm in each treatment plot one day before the experiment commenced each winter and left in place for the season.…”