Do Productivity and Environmental Trade-offs Justify Periodically Cultivating No-till Cropping Systems?

No-till management has been shown to increase soil aggregation, reduce erosion rates, and increase soil organic matter across a range of soil types, cropping systems, and climates. Few agricultural practices provide similar opportunities to deliver positive benefits for farmers, society, and the environment. The potential benefits of no-till are not being fully realized, however, in large part because no-till is rarely practiced continuously and many fields suitable for no-till are still conventionally tilled. We present here three arguments, based on recent research, in support of the agronomic and environmental benefits of continuous no-till: (i) although there exist agronomic challenges with no-till, long-term yields in these systems can equal or exceed those in tilled soils; (ii) cultivating no-till systems can decrease soil aggregation and accelerate C and N losses so rapidly that years of soil restoration can be undone within weeks to months; and (iii) over time, changes in soil structure and organic matter, coupled with producer adaptation to the need for spatially and temporally explicit chemical applications, increase plant N availability and reduce environmental N losses. At least in theory, then, continuous no-till can be widely practiced to improve the environment and maintain yields with little or no economic sacrifice by producers. In practice, however, many diverse challenges still limit no-till adoption in different regions. These challenges are surmountable, but potential solutions need to be interdisciplinary and address the ecological and especially the social and economic constraints to deploying continuous no-till. N CROPPING has been used for decades to reduce soil erosion, improve soil physical structure, conserve soil water, and restore organicmatter (Franzluebbers andArshad, 1997;Wright andHons, 2004; Lal et al., 2004). More recently, soil organic matter gains under no-till have been promoted as an immediate, high-impact method for partially offsetting increases in atmospheric CO2 (Kauppi and Sedjo, 2001; Caldeira et al., 2004). Current rising energy costs combined with an expected fuel savings ranging from33 to 53Lha (Kern and Johnson, 1993) provide further incentive to growers to adopt no-till. With increasing recognition by producers, researchers, and policymakers of the substantive benefits of no-till, its use has steadily increased in the U.S., and between 1994 and 2004 the percentage of total U.S. cropland in no-till rose from 13.7 to 22.6%, or 9.5 million ha (CTIC, 2004). The deployment of no-till, however, continues to be far below its potential. Many fields suitable for no-till are still managed using conventional plowing methods. Moreover, only a fraction of no-till cropping systems are permanent no-till. In the U.S. Midwest, for example, many farmers rotate conventionally cultivated corn (Zea mays L.) with no-till soybean [Glycine max (L.) Merr.]. In the western U.S., periodic plowing is used to control downy brome (Bromus tectorum L.) and other winter annual grasses (Wicks, 1997; Kettler et al., 2000). Soils that are restored through set-aside programs such as the Conservation Reserve Program (CRP) gain no-till attributes even faster than no-till cropping (CAST, 2004) but are routinely converted back to conventional tillage (Zheng et al., 2004). Reasons for periodically cultivating no-till soils are both agronomic—e.g., tomineralize stored soil N, interrupt pest cycles, incorporate manure, and alleviate compaction and associated problems, particularly in soilswith high clay contents—andeconomic—e.g., to reduce production costs associated with increased herbicide use (Rice et al., 1986; Yiridoe et al., 2000; Martens, 2001). At the W.K. Kellogg Biological Station (KBS) LongTerm Ecological Research (LTER) site in southwest Michigan, we examined the effects of 14 yr of no-till corn–soybean–wheat (Triticum aestivum L.) cropping on yields and N cycling. Our objectives are to determine whether soil N concentrations, N2O fluxes, and yields are similar in long-term till and no-till cropping systems. Producers, researchers, and policymakers need to weigh potential changes in yields and N cycling in long-term no-till soils against the immediate and short-term consequences of cultivating soils in long-term no-till. We therefore also performed a series of experiments in a previously uncultivated grassland soil to determine the potential for tillage to immediately alter soil aggregation, organic matter dynamics, N cycling, and CO2 and N2O fluxes. The results from these and other experiments, in addition to recent advances in evaluating ecosystem services, demonstrate the importance—and feasibility—of deploying continuous no-till. CROP YIELDS AND SOIL PROPERTIES IN LONG-TERM NO-TILL The KBS is located in the northern portion of the midwestern Corn Belt in southwest Michigan. Soils at the KBS LTER are co-occurring Kalamazoo fine loam and Oshtemo coarse loam (Crum and Collins, 1995). Although the clay content in these soils is typically between 15 and 20%, the silt content is high (» 40%). Because of its location and soil type, field-crop systems at theKBSLTERare potentially susceptible tomany of the A.S. Grandy and G.P. Robertson, W.K. Kellogg Biol. Stn. and Dep. of Crop and Soil Sci., Michigan State Univ., Hickory Corners, MI 49060; and K.D. Thelen, Dep. of Crop and Soil Sci., Michigan State Univ., East Lansing, MI 48824-1325. A.S. Grandy, current address: Dep. of Geol. Sci., Univ. of Colorado, Boulder, CO 80309-0399. Received 1 May 2006. *Corresponding author ([email protected]). Published in Agron. J. 98:1377–1383 (2006). Forum doi:10.2134/agronj2006.0137 a American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: CRP,ConservationReserveProgram;KBS,W.K.Kellogg Biological Station; LF, light fraction organic matter; LTER, Long-Term Ecological Research Project; MWD, aggregate mean weight diameter. R e p ro d u c e d fr o m A g ro n o m y J o u rn a l. P u b lis h e d b y A m e ri c a n S o c ie ty o f A g ro n o m y . A ll c o p y ri g h ts re s e rv e d .