Long-Term Effects of Tillage on Soil Chemical Properties and Grain Yields of a Dryland Winter Wheatâ•fiSorghum/Cornâ•fiFallow Rotation in the Great Plains

Tillage systems and nutrient management influence soil chemical properties that can impact the long-term sustainability of dryland production systems. This study was conducted to compare the effects of no-till (NT) and conventional till (CT) on the soil chemical properties and grain yield of a dryland winter wheat (Triticum aestivum L.)– grain sorghum [Sorghum bicolor (L.) Moench]/corn (Zea mays L.)– fallow rotation. The effects of tillage practice over a 27-yr period (1962– 1989) and the effect of the conversion of CT to NTover a 14-yr period (1989–2003) on selected soil chemical properties [pH, cation exchange capacity (CEC), base saturation (BS), soil organic C (SOC), K, Ca, Mg, and Bray-P] at different soil depths was determined. The acidification rate of the NT treatment from 1962 to 2003 was also determined. The study was conducted at North Platte, NE on a Holdrege silt loam (fine-silty, mixed, mesic Typic Argiustolls). In 1989, there were differences in soil chemical properties between CT and NT at some depths after 27 yr. However, in 2003, 14 yr after converting from CT to NT, there were no differences in the soil chemical properties compared with continuous NT. In 1989 and 2003, the soil chemical properties varied with soil depth. The acidification rate from 1962 to 2003 for the NT treatment in the 0to 15-cm depth was 1.3 kmol H ha yr. This rate of acidification represents 38% of the total potential acidity from N fertilizer applications over 41 yr. Acidification was attributed to nitrification of ammonium-based fertilizers and leaching of NO3. Long-term winter wheat (1966–1983) and grain sorghum (1964–1988) grain yields were higher for NT (2718 and 4125 kg ha) than CT (2421 and 3062 kg ha). Retention of soil moisture as a result of increased residue cover under NT likely contributed to higher NT yields. Soil chemical properties in the wheat–sorghum/corn–fallow rotation will likely continue to change as a result of current management practices. Lime additions may become necessary in the future to ensure the sustainability of crop production in this system. THE 2-YR winter wheat–fallow (WF) rotation was the traditional dryland cropping system in the semiarid, central Great Plains in the USA from the time this area was converted to agriculture until the early 1970s. Since then, a 3-yr rotation of winter wheat (Year 1), grain sorghum or corn (Year 2), and fallow (Year 3) (WS/CF) has become a common dryland cropping system (Wicks et al., 1995). Research data showing increased crop yields and profitability of the WS/CF rotation over the WF rotation have facilitated the conversion to the WS/CF rotation (Wicks and Fenster, 1981). This rotation is often called the ecofarming system when it utilizes NTor minimal tillage to conserve soil moisture, which allows more intensive cropping and more stable and higher yields than in the traditional WF rotation (Wicks et al., 1988). Herbicides are applied to winter wheat stubble after grain harvest to keep the field weed free and to conserve soil moisture for grain sorghum or corn that is planted the following spring (Wicks et al., 1995). Some producers still utilize varying degrees of tillage during the fallow period following the row crop to control weeds and facilitate winter wheat planting with conventional drills. The long-term impact of this dryland system, which receives minimal agricultural inputs, on soil properties needs to be assessed. Therefore, it is necessary to assess the differences and changes in soil chemical properties with NTand CT in this rotation. Studies conducted in semiarid dryland production systems have compared the effects of NT and CT on soil chemical properties. Tillage has been found to decrease SOC compared with NT (Follett and Peterson, 1988). Converting from the traditional WF rotation to more intense cropping systems such as a wheat–corn–fallow (WCF) rotation with NT in the Great Plains can increase SOC in surface soils (Sherrod et al., 2003; Bowman et al., 1999; Wood et al., 1991). The higher SOC under NT was attributed to reducing the amount of tillage and increasing soil water storage, which increases the amount of plant biomass returned to the soil surface. However, in an established WCF rotation in Nebraska, Wicks et al. (1988) found that there were no differences in surface SOC between NTand CT treatments over a 15-yr period (1964–1979). They also concluded that exchangeable K and Ca were found to decrease in both CT and NTover time, mostly due to removal in harvested grain. These nutrients were not replenished with fertilizer or lime applications over the life of the study. Research has shown that exchangeable bases decrease in soil not receiving lime as a result of acidification (Bouman et al., 1995). This is often due to removal of exchangeable bases from the exchange sites on clay and organic matter by H and Al (Singer and Munns, 1999). Differences in acidification between NT and CT can also result in differences in exchangeable bases. There is a need for data on the changes in exchangeable bases due to CT and NT on WS/CF production systems in the Great Plains, which rarely receive lime applications. The time it takes to detect changes in soil properties D.D. Tarkalson, Dep. of Agron. and Hortic., Univ. of Nebraska– Lincoln, West Central Res. and Ext. Cent., 461 West University Dr., North Platte, NE 69101; G.W. Hergert, Dep. of Agron. and Hortic., Univ. of Nebraska–Lincoln, Panhandle Res. and Ext. Cent., 4502 Ave. I, Scottsbluff, NE 69361; and K.G. Cassman, Dep. of Agron. and Hortic., Univ. of Nebraska–Lincoln, 387 Plant Science, Lincoln, NE 68583. A contribution of the University of Nebraska Agricultural Research Division, Lincoln, NE 68583. Journal Series no. 14720 Received 10 Sept. 2004. *Corresponding author ([email protected]). Published in Agron. J. 98:26–33 (2006). Soil Quality and Fertility doi:10.2134/agronj2004.0240 a American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: BS, base saturation; CEC, cation exchange capacity; CT, conventional till; NT, no-till; SOC, soil organic carbon; UAN, urea ammonium nitrate; WCF, wheat–corn–fallow; WF, wheat–fallow; WS/CF, wheat–sorghum/corn–fallow; WSF, wheat–sorghum–fallow. 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 . 26 Published online January 3, 2006