Tillage and Crop Rotation Effects on Dryland Soil and Residue Carbon and Nitrogen

Sustainable management practices are needed to enhance soil productivity in degraded dryland soils in the northern Great Plains. We examined the effects of two tillage practices [conventional till (CT) and no-till (NT)], five crop rotations [continuous spring wheat (Triticum aestivum L.) (CW), spring wheat-fallow (W-F), spring wheat-lentil (Lens culinaris Medic.) (W-L), spring wheat-spring wheat-fallow (W-W-F), and spring wheat-pea (Pisum sativum L.)fallow (W-P-F)], and a Conservation Reserve Program (CRP) on plant biomass returned to the soil, residue C and N, and soil organic C (SOC), soil total N (STN), and particulate organic C and N (POC and PON) at the 0to 20-cm depth. A field experiment was conducted in a mixture of Scobey clay loam (fine, smectitic, frigid Aridic Argiustolls) and Kevin clay loam (fine-loamy, mixed, superactive, frigid Aridic Argiustolls) from 1998 to 2003 near Havre, MT. Mean annualized plant biomass returned to the soil from 1998 to 2003 was greater in W-F (2.02 Mg ha) than in W-L and W-W-F, regardless of tillage. In 2004, residue cover was greater in CW (60%) than in other rotations, except in W-W-F. Residue amount and C and N contents were greater in NT with CW (2.47 Mg ha and 963 and 22 kg ha, respectively) than in NT with W-L and CT with other crop rotations. The POC at 0 to 5 cm was greater in W-W-F and W-P-F (2.1–2.2 Mg ha) than in W-L. Similarly, STN at 5 to 20 cm was greater in CT with W-L (2.21 Mg ha) than in other treatments, except in NT with W-W-F. Reduced tillage and increased cropping intensity, such as NTwith CW and W-L, conserved C and N in dryland soils and crop residue better than the traditional practice, CT with W-F, and their contents were similar to or better than in CRP planting. CONVENTIONALTILLAGE andwheat-fallow systems have been traditional farming practices in northern Great Plains for a long time (Haas et al., 1957). Studies have shown that during the last 50 to 100 yr of cultivation in this semiarid region, SOC and STN have declined by 30 to 50% of their original levels (Haas et al., 1957; Campbell and Souster, 1982; Mann, 1985; Peterson et al., 1998). Intensive tillage increases the oxidation of soil organic matter (Follett and Schimel, 1989; Bowman et al., 1999; Schomberg and Jones, 1999) and fallowing increases its loss by reducing the amount of plant residue returned to the soil (Black and Tanaka, 1997; Campbell et al., 2000; West and Post, 2002). Although expanding fallow increases soil water storage and crop yields (Eck and Jones, 1992; Jones and Popham, 1997), increased soil water and temperature during fallowing can also accelerate mineralization of SOC and STN (Haas et al., 1974). As a result, the traditional system of farming has become unsustainable partly due to increased dependence of producers on federal aids (Aase and Schaefer, 1996; Dhuyvetter et al., 1996; Krall and Schuman, 1996). Improved soil and crop management practices that reduce tillage intensity, increase the amount of plant residue returned to the soil, and adapt to the harsh environmental conditions of northern Great Plains are needed to increase soil organic matter and the sustainability of the farming system. Studies have shown that NTwith increased cropping intensity can increase SOC and STN compared to CT with W-F system in the drylands of central Great Plains (Halvorson et al., 2002a; Sherrod et al., 2003; Allmaras et al., 2004). Halvorson et al. (2002b) observed that NT with continuous cropping increased C sequestration in the drylands of northern Great Plains by 233 kg ha yr compared with a loss of 141 kg ha yr in CT. They pointed out that continued use of crop-fallow system even in NT increased SOC loss. Similarly, Sherrod et al. (2003) reported that increased cropping intensity in NT increased SOC and STN in drylands of central Great Plains after 12 yr. After analyzing data from long-term experiments in various locations, West and Post (2002) concluded that conversion from CT to NT can sequester an average of 570 6 140 kg C ha yr, reaching equilibrium in 15 to 20 yr and enhanced crop rotation can sequester 2006 120 kg C ha yr, reaching equilibrium in 40 to 60 yr. The benefits of increasing SOC and STN lie not only in enhancing soil structure and soil water-nutrient-crop productivity relationships (Bauer and Black, 1994), but also includes the ability of the soil to store atmospheric C and N, thereby reducing the concentration of greenhouse gases, such as CO2 and N2O (Paustian et al., 1997; Janzen et al., 1999; Lal et al., 1998, 1999). Limited volume of soil water content is a major factor for dryland crop production in the Great Plains. The use of NT has allowed producers to increase cropping intensity (Aase and Schaefer, 1996; Halvorson et al., 1999, 2000; Peterson et al., 2001), because NT conserves surface residues and retains water in the soil profile more than CT does (Farhani et al., 1998). As a result, soil water can be used more efficiently by crops in NT (Deibert et al., 1986; Peterson et al., 1996), which can reduce or eliminate summer fallow by growing continuous crops (Peterson et al., 1993, 2001; Farhani et al., 1998). In NT, winter wheat yield in wheat-corn (Zea mays L.)-fallow rotation is greater or similar to that in wheat-fallow rotation, thereby making the NT system more profitable (Halvorson et al., 1994, 2002a; Dhuyvetter et al., 1996). As a result, the NT system provides better opportunities to sustain crop yields by growing USDA-ARS, 1500North Central Avenue, Sidney,MT 59270. Received 25 Mar. 2005. *Corresponding author ([email protected]). Published in Soil Sci. Soc. Am. J. 70:668–678 (2006). Soil&WaterManagement&Conservation, SoilBiology&Biochemistry doi:10.2136/sssaj2005.0089 a Soil Science Society ofAmerica 677 S. SegoeRd.,Madison,WI 53711USA Abbreviations: CRP, Conservation Reserve Program; CT, conventional till; CW, continuous spring wheat; NT, no-till; POC, particulate organic C; PON, particulate organic N; SOC, soil organic C; STN, soil total N; W-F, spring wheat-fallow; W-L, spring wheat-lentil; W-P-F, spring wheat-pea-fallow; W-W-F, spring wheat-spring wheat-fallow. R e p ro d u c e d fr o m S o il S c ie n c e S o c ie ty o f A m e ri c a J o u rn a l. P u b lis h e d b y S o il S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 668 Published online February 27, 2006