Tillage Intensity in a Long-Term Wheat-Sorghum-Fallow Rotation Tillage Intensity in a Long-Term Wheat-Sorghum-Fallow Rotation

This study was initiated in 1991 at the Kansas State University Southwest Research-Ex-tension Center near Tribune, KS. The purpose of the study was to identify the effects of tillage intensity on precipitation capture, soil water storage, and grain yield in a wheat-sorghum-fallow rotation. Grain yields of wheat and grain sorghum increased with decreased tillage intensity in a wheat-sorghum-fallow (WSF) rotation. In 2017, available soil water at sorghum planting was greater for reduced tillage (RT) than no-tillage (NT) or conventional tillage (CT). For wheat there were no differences in available soil water at planting. Averaged across the 17-yr study, available soil water at wheat planting was similar for RT and NT and about 1 inch greater than CT. For sorghum, average available soil water at planting was greater in the order RT>NT>CT. Averaged across the past 17 years, NT wheat yields were 4 bu/a greater than RT and 6 bu/a greater than CT. Grain sorghum yields in 2017 were similar for long-term NT and short-term NT while greater than CT. Averaged across the past 17 years, sorghum yields with long-term NT have been 57% greater than with short-term NT (74 vs. 47 bu/a).


Tillage Intensity in a Long-Term Wheat-Sorghum-Fallow Rotation Tillage Intensity in a Long-Term Wheat-Sorghum-Fallow Rotation
Cover Page Footnote Cover Page Footnote The U.S. Department of Agriculture, Agricultural Research Service Ogallala Aquifer Program partially supported this research project.

Summary
This study was initiated in 1991 at the Kansas State University Southwest Research-Extension Center near Tribune, KS. The purpose of the study was to identify the effects of tillage intensity on precipitation capture, soil water storage, and grain yield in a wheatsorghum-fallow rotation. Grain yields of wheat and grain sorghum increased with decreased tillage intensity in a wheat-sorghum-fallow (WSF) rotation. In 2017, available soil water at sorghum planting was greater for reduced tillage (RT) than no-tillage (NT) or conventional tillage (CT). For wheat there were no differences in available soil water at planting. Averaged across the 17-yr study, available soil water at wheat planting was similar for RT and NT and about 1 inch greater than CT. For sorghum, average available soil water at planting was greater in the order RT>NT>CT. Averaged across the past 17 years, NT wheat yields were 4 bu/a greater than RT and 6 bu/a greater than CT. Grain sorghum yields in 2017 were similar for long-term NT and short-term NT while greater than CT. Averaged across the past 17 years, sorghum yields with longterm NT have been 57% greater than with short-term NT (74 vs. 47 bu/a).

Experimental Procedures
Research on different tillage intensities in a WSF rotation at the Tribune, KS, unit of the Southwest Research-Extension Center was initiated in 1991. The three tillage intensities in this study are conventional (CT), reduced (RT), and no-tillage (NT). The CT system was tilled as needed to control weed growth during the fallow period. On average, this resulted in 4 to 5 tillage operations per year, usually with a blade plow or field cultivator. The RT system originally used a combination of herbicides (1 to 2 spray operations) and tillage (2 to 3 tillage operations) to control weed growth during the fallow period; however, in 2001, the RT system was changed to using NT from wheat harvest through sorghum planting (short-term NT) and CT from sorghum harvest through wheat planting. The NT system exclusively used herbicides to control weed growth during the fallow period. All tillage systems used herbicides for in-crop weed control.

Soil Water
The amount of available water in the soil profile (0 to 8 ft) at wheat planting varied greatly from year to year (Figure 1). In 2017, available soil water at wheat planting was greater with RT than NT and least with CT. Averaged across the 16-yr study, available soil water at wheat planting was similar for RT and NT (about 7 inches) and about 1 inch greater than CT.
Similar to wheat, the amount of available water in the soil profile at sorghum planting varied greatly from year to year (Figure 2). In 2017, available soil water at sorghum planting was greater with RT than NT and least with CT. On average, available soil water at sorghum planting was greater with RT than NT and NT was greater than CT.

Grain Yields
Wheat yields in 2017 were low because of severe infestation of wheat streak mosaic (Table 1). Since 2001, wheat yields have been depressed in 11 of 17 years, primarily because of lack of precipitation, while winterkill reduced yields in 2015 and disease in 2017. Reduced tillage and NT increased wheat yields. On average, wheat yields were 6 bu/a higher for NT (23 bu/a) than CT (17 bu/a). Wheat yields for RT were 2 bu/a greater than CT even though both systems had tillage prior to wheat. Yields of NT were significantly less than CT or RT in only 1 of the 17 years.
Grain sorghum yields in 2017 were more than twice as high as the long-term average (Table 2). Sorghum yields were similar for NT and RT with both being greater than CT. The yield benefit from reducing tillage is greater for grain sorghum than wheat. Grain sorghum yields for RT averaged 17 bu/a more than CT, whereas NT averaged 27 bu/a more than RT. For sorghum, both RT and NT used herbicides for weed control during fallow, so the difference in yield could be attributed to short-term compared with long-term NT. This yield benefit with long-term vs. short-term NT has been observed in most years since the RT system was changed in 2001. Averaged across the past 17 years, sorghum yields with long-term NT have been 57% greater than with short-term NT (74 vs. 47 bu/a).

Acknowledgment
The U.S. Department of Agriculture, Agricultural Research Service Ogallala Aquifer Program partially supported this research project.   Tillage