Tillage, Nitrogen, and Cropping System Effects on Soil Carbon Sequestration

With increased cropping intensity, one would expect that more crop residue and C would be added to the Soil C sequestration can improve soil quality and reduce agriculsoil than with a crop-fallow system (Campbell et al., ture’s contribution to CO2 emissions. The long-term (12 yr) effects of tillage system and N fertilization on crop residue production and 1995, 2000b; Janzen et al., 1998a; Peterson et al., 1998). soil organic C (SOC) sequestration in two dryland cropping systems As the amount of crop residue returned to the soil is in North Dakota on a loam soil were evaluated. An annual cropping increased, SOC sequestration is expected to increase if (AC) rotation [spring wheat (SW) (Triticum aestivum L.)–winter the residue C is not lost as CO2 to the atmosphere wheat (WW)–sunflower (SF) (Helianthus annuus L.)] and a spring because of tillage induced decomposition (Larney et al., wheat-fallow (SW-F) rotation were studied. Tillage systems included 1997; Reicosky, 1997a,b). Research in the Great Plains conventional-till (CT), minimum-till (MT), and no-till (NT). Nitrogen has shown that SOC sequestration is enhanced by N rates were 34, 67, and 101 kg N ha 1 for the AC system and 0, 22, fertilization (Campbell and Zentner, 1993; Campbell et and 45 kg N ha 1 for the SW-F system. Total crop residue returned al., 2000a; Halvorson et al., 1999c, 2000c; Nyborg et to the soil was greater with AC than with SW-F. As tillage intensity al., 1995). Campbell et al. (1996, 1997, 1998) reported decreased, SOC sequestration increased (NT MT CT) in the AC system but not in the SW-F system. Fertilizer N increased crop increased SOC levels as fallow frequency and tillage residue quantity returned to the soil, but generally did not increase intensity decreased within Canadian Prairie Province SOC sequestration in either cropping system. Soil bulk density decropping systems in the northern Great Plains. Bauer creased with increasing tillage intensity in both systems. The results and Black (1994) demonstrated the value of SOC in suggest that continued use of a crop-fallow farming system, even with enhancing soil water–soil fertility–crop productivity reNT, may result in loss of SOC. With NT, an estimated 233 kg C ha 1 lationships. The benefit of increasing SOC is not only was sequestered each year in AC system, compared with 25 kg C ha 1 improved soil structure and water-nutrient relationwith MT and a loss of 141 kg C ha 1 with CT. Conversion from cropships, but includes the ability to store C in the soil to fallow to more intensive cropping systems utilizing NT will be needed reduce atmospheric CO2, a greenhouse gas (Janzen et to have a positive impact on reducing CO2 loss from croplands in the al., 1999; Lal et al., 1998, 1999). northern Great Plains. Bauer and Black (1981) pointed out the lack of longterm cropping systems data evaluating SOC sequestration in the northern Great Plains. In 1983, A.L. Black, N and MT systems have allowed producers in USDA-ARS, at Mandan, ND initiated a long-term cropthe semi-arid Great Plains to intensify the freping system study to evaluate the influence of tillage quency of cropping when compared with the traditional and N fertility level on crop yields and soil C and N crop-fallow system (Aase and Schaefer, 1996; Farahani changes within SW-F and annual cropping (SW-WWet al., 1998; Halvorson, 1990; Halvorson and Reule, SF) rotations (Black and Tanaka, 1997). Grain yields 1994; Halvorson et al., 1999a,b, 2000a). Deibert et al. for this study have been reported by Halvorson et al. (1986) and Peterson et al. (1996) point out that more (1999a,b, 2000a,b). Since initiation of this study, numercontinuous cropping and less crop-fallow is needed in ous Canadian Prairie Province studies have reported on the Great Plains to attain more efficient use of limited the effects of tillage system, fertility, and crop rotation water supplies. Cihacek and Ulmer (1995) point out that on SOC sequestration as summarized by Janzen et al. more intensive cropping systems than crop-fallow along (1998b). Peterson et al. (1998) summarized the positive with reduced tillage is needed to prevent the loss of SOC influences of reduced tillage and intensified cropping from Great Plains soils. The fallow period represents a systems on soil C in the U.S. Great Plains. No dryland time of high microbial activity and decomposition of studies on SOC sequestration were found in the northsoil organic matter with no input of crop residue. Annual ern Great Plains that included sunflower in the intensive cropping reduces the amount of time decomposition crop rotation. This paper reports on the long-term efis occurring without crop residue inputs. Fallow also fects of tillage system (CT, MT, and NT) and N fertilizer represents a time when the soil is susceptible to wind rate on crop residue production and SOC sequestration erosion which is another major loss mechanism for soil within two dryland cropping systems (SW-WW-SF and organic matter in the northern Great Plains (Haas et SW-F) located in the U.S. northern Great Plains. al., 1974). MATERIALS AND METHODS A.D. Halvorson, USDA-ARS, P.O. Box E, Fort Collins, CO 80522; B.J. Wienhold, USDA-ARS, 119 Keim Hall, East Campus, Univ. of The study was initiated in 1984 on a Temvik-Wilton silt loam Nebraska, Lincoln, NE 68583; A.L. Black, USDA-ARS, retired, 226 soil (fine-silty, mixed, superactive, frigid Typic and Pachic E. Circle Dr., Canon City, CO 81212. Contribution from USDA-ARS. Haplustolls) with a 2 to 4% southeasterly slope located about The USDA offers its programs to all eligible persons regardless of race, color, age, sex, or national origin, and is an equal opportunity Abbreviations: AC, annual crop; CT, conventional-till; F, fallow; LSD, employer. Received 9 Apr. 2001. *Corresponding author (adhalvor@ least significant difference; MT, minimum-till; NT, no-till; Db, soil lamar.colostate.edu). bulk density; SF, sunflower; SOC, soil organic C; SW, spring wheat; WW, winter wheat. Published in Soil Sci. Soc. Am. J. 66:906–912 (2002).