Tillage practices and their effects on crop yield, soil health, and weed abundance in semi-arid dryland cropping systems

Abstract

Implementing tillage in long-term no tillage (NT) fields in the semi-arid Central Great Plains is a concern for producers because soil improvements gained from NT could be lost. However, producers are dealing with herbicide resistant weeds and nutrient stratification, which is forcing them to consider tillage to mitigate these issues. Two experiments were conducted in western Kansas to assess the influence of strategic tillage (ST) and occasional tillage (OT) on crop yields and soil properties. In the current studies, ST is defined as a one-time tillage operation prior to winter wheat (Triticum aestivum L.) or grain sorghum (Sorghum bicolor L.) planting then the field returns to NT, and OT is defined as a single tillage operation in the fallow phase of a 3-yr winter wheat-grain sorghum-fallow rotation. The objectives of these studies were to investigate the influence of ST and OT on soil physical and chemical properties, crop yields, and weed diversity. A long-term study initiated in 1976 at the KSU Agricultural Research Center – Hays was used to investigate the influence of NT, ST, and reduced tillage (RT) on weeds, crops yields and soil properties. Reduced tillage is defined as two to three tillage operations in the fallow period prior to winter wheat planting and an additional pass before sorghum planting. The experimental design was a randomized complete block with three replications in a split-plot treatment structure with crop rotation as main plots and tillage as sub-plots. The cropping systems compared included continuous wheat (WW), wheat-fallow (WF) and wheat-grain sorghum-fallow (WSF). Subplots were continuous NT, ST, and RT. Results of soil samples collected in 2022 showed soil organic carbon concentration was highest in the soil surface, and RT had 8% less soil organic carbon than ST and NT. There were no differences across tillage treatments in soil bulk density, penetration resistance, or wind erodible fraction. However, mean weight diameter of water stable aggregates in NT was 31% greater than RT, and ST was not significantly different from NT or RT. Reduced tillage and ST increased wheat yields in WW compared to NT. Grain sorghum yields were greater in NT and ST compared to RT. Shannon’s Diversity Index values were greatest in NT and least in RT, so there is greater weed diversity in NT compared to RT. For weed density, the WSF (137 plants m²) and WF (167 plants m²) rotations had 50% and 59% greater density than the WW (68 plants m²) rotation. However, there were no differences across tillage treatments. Overall, this study indicated ST had no negative influence of soil properties or crop yield and could aid in minimizing weed diversity. A second study was initiated in 2013 at Garden City and Tribune, KS and 2014 in Hays, KS, and the tillage treatments were NT, single tillage pass before wheat (STBW), two tillage passes before wheat (2TBW), single tillage after wheat (STAW), and two tillage passes after wheat (2TAW) in a winter wheat-grain sorghum-fallow rotation. Soil sampling occurred pre-tillage in 2022 and post-tillage in 2022 and in 2023. Tillage treatments did not influence soil organic carbon, pH, Mehlich-3 phosphorus, bulk density, mean weight diameter, or wind erodible fraction. However, soil nitrate-N (NO₃-N) concentrations were increased with increased tillage intensity, and the gravimetric water content often depended on the tillage treatment and depth. Tillage tended to increase cumulative water infiltration compared to NT. Winter wheat yields in Garden City increased with tillage in 4 out of 5 years of the study, but tillage had no significant effect on wheat yields in Hays or Tribune. Grain sorghum yields were decreased with tillage in 2019 and 2020 at Hays, but the other locations observed no significant differences. The Shannon’s Diversity Index values were greatest in NT, which was 17% and 33% greater than STBW and 2TBW. However, weed density was not different across tillage treatments, but there was a significant effect of location. Overall, the implementation of OT had minimal negative effects on soil physical and chemical properties. However, there are some soil chemical properties that can be increased with the use of OT, such as NO₃-N, but some soil physical properties, specifically gravimetric water content, could be influenced with OT. Occasional tillage can increase grain yield but often has no influence. Weed diversity can be lowered with the use of OT. The findings of these studies suggest ST and OT can mitigate the influence of nutrient stratification and herbicide resistant weeds.