| Popis: |
Although the Midwestern United States is one of the world's major agricultural production areas, few studies have assessed the effects of the region's predominant tillage and rotation practices on greenhouse gas emissions from the soil surface. Our objectives were to (a) assess short-term chisel (CP) and moldboard plow (MP) effects on soil CO 2 and CH 4 fluxes relative to no-till (NT) and, (b) determine how tillage and rotation interactions affect seasonal gas emissions in continuous corn and corn–soybean rotations on a poorly drained Chalmers silty clay loam (Typic Endoaquoll) in Indiana. The field experiment itself began in 1975. Short-term gas emissions were measured immediately before, and at increasing hourly intervals following primary tillage in the fall of 2004, and after secondary tillage in the spring of 2005, for up to 168 h. To quantify treatment effects on seasonal emissions, gas fluxes were measured at weekly or biweekly intervals for up to 14 sampling dates in the growing season for corn. Both CO 2 and CH 4 emissions were significantly affected by tillage but not by rotation in the short-term following tillage, and by rotation during the growing season. Soil temperature and moisture conditions in the surface 10 cm were significantly related to CO 2 emissions, although the proportion of variation explained by temperature and moisture was generally very low (never exceeded 27%) and varied with the tillage system being measured. In the short-term, CO 2 emissions were significantly higher for CP than MP and NT. Similarly, mean seasonal CO 2 emissions during the 2-year period were higher for CP (6.2 Mg CO 2 -C ha −1 year −1 ) than for MP (5.9 Mg CO 2 -C ha −1 year −1 ) and NT (5.7 Mg CO 2 -C ha −1 year −1 ). Both CP and MP resulted in low net CH 4 uptake (7.6 and 2.4 kg CH 4 -C ha −1 year −1 , respectively) while NT resulted in net emissions of 7.7 kg CH 4 -C ha −1 year −1 . Mean emissions of CO 2 were 16% higher from continuous corn than from rotation corn during the two growing seasons. After 3 decades of consistent tillage and crop rotation management for corn and soybean producing grain yields well above average in the Midwest, continuous NT production in the corn–soybean rotation was identified as the system with the least soil-derived C emissions to the atmosphere from among those evaluated prior to and during corn production. |
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