No-tillage (NT) systems provide several benefits to dryland crop production in the semiarid central Great Plains (CGP). These include improvements to soil health, reduced wind erosion, fewer energy inputs, increased retention of soil moisture, and improved crop yields. Despite these benefits, maintaining continuous NT and the associated soil conservation benefits are at risk due to a lack of effective control of herbicide-resistant (HR) weeds, as well as issues of compaction and stratification (abrupt changes by soil depth) of soil pH and nutrients (Figure 1). Stratification of soil nutrients and soil acidity could reduce nutrient availability and uptake by crops and increase the chances of nitrogen and phosphorus losses in surface runoff.
Figure 1. Grasses in the long-term no-tillage plots. Photos by Augustine Obour, K-State Research and Extension.
What is strategic tillage?
Strategic tillage (ST) with a sweep plow, timed when soil erosion risk is low in an otherwise NT cropping system, could help manage HR weed populations and reduce stratification of soil properties. After the one-time tillage operation, the field goes back to NT production.
This ST approach could increase productivity and profitability of dryland cropping systems in the region. However, the soil health impacts of ST are unclear, particularly in water-limited environments of the CGP where susceptibility to wind erosion can be high. Few studies have investigated the effects of ST on soils that have been in continuous NT (> 40 years) in dryland conditions in the CGP.
The objectives of this study were to determine the effects of strategic tillage in long-term NT systems on:
This strategic tillage study was conducted using long-term tillage and crop rotation experiment plots established in 1976 at the K-State Agricultural Research Center near Hays. Since their creation, these plots had five crop rotation treatments with two tillage treatments. The five crop rotations were continuous winter wheat (WW), wheat-fallow (WF), wheat-sorghum-fallow (WSF), continuous sorghum (SS), and sorghum-fallow (SF). The tillage treatments were reduced tillage (RT) and NT.
This long-term study was modified in 2016 to include a strategic tillage component. The three tillage treatments were: RT, continuous NT, and strategic tillage (ST) of the long-term NT plots. To create the ST plots, the long-term NT plots were split into two equal plots of 20-ft wide by 80-ft long. One half was left in continuous NT and the other half was tilled. The ST plots were tilled twice with a sweep plow at depths between 3 and 6”. All tillage operations in the wheat rotations were performed in July prior to wheat planting in October. For crop rotations involving sorghum, tillage operations were done in May before sorghum planting in June. Tillage in the RT treatments were accomplished with the same tillage implement to 6- to 8-in. depth. Two to three tillage operations were usually done in the RT plots over the fallow period.
Soil water content at wheat planting was measured down to 4 ft, in 6-in. depth increments in 2016 and 2017. Wheat and sorghum grain yields were determined using a small plot combine. Soil samples were collected in increments down to 1 foot after tillage operations in 2017. The soil was analyzed for changes in bulk density, soil organic carbon (converted to a soil organic matter value), dry aggregate size distribution, and soil nutrients.
Summary of strategic tillage study
Weed control. In general, broadleaf and grass weeds were significantly less with RT and ST compared to the NT treatments (Figure 2).
Figure 2. Comparison of the continuous wheat (WW) plots with strategic tillage (ST) and the continuous no-tillage (NT) wheat plots containing abundant cheatgrass. Photos by Augustine Obour, K-State Research and Extension.
Soil water content. Irrespective of crop rotation, soil water content at wheat planting was significantly less with RT treatments compared to NT or ST (Figure 3). Soil water content with NT was not different from that of ST under cropping systems with fallow (WF or WSF). Tillage (ST or RT) reduced soil water content at wheat planting in WW system.
Figure 3. Soil water content at winter wheat planting as affected by tillage in each crop rotation system. Data averaged across two years and three replications (n=6). Graph from KAESRR: Vol. 5: Iss. 4. https://doi.org/10.4148/2378-5977.7756
Wheat yield. Winter wheat grain yields decreased with increasing cropping intensity, WF (26-48 bu/a) > WSF (22-33 bu/a) > WW (15-19 bu/a) (Figure 4). Averaged across years and crop rotations, wheat yield with ST was 30 bu/a, which was greater than the NT (23 bu/a) or RT (28 bu/a) systems, mostly due to better weed control and increased nutrient availability.
Figure 4. Winter wheat grain yield as affected by crop rotation system in 2017 and 2018 growing seasons at Hays, KS. Data are averaged across three tillage systems and three replications (n=9). Graph from KAESRR: Vol. 5: Iss. 4. https://doi.org/10.4148/2378-5977.7756
Sorghum yield. Sorghum grain yield over the 2 years with ST (63 bu/a) was not different from that of NT (61 bu/a), but were both greater than RT (54 bu/a). Increasing cropping intensity reduced sorghum grain yield, average grain yield with SF was 73 bu/a, similar to WSF (68 bu/a), but greater than SS (38 bu/a).
Soil properties. Tillage had no effect on soil bulk density. However, increasing cropping intensity lowered the bulk density measured in the upper 0 to 2 in. of the soil. Tillage and crop rotation effects on soil organic matter (SOM), pH, and nutrient concentrations occurred only in the top 0- to 2-in. depth. The SOM, iron (Fe), and manganese (MN) concentrations were greater in soils under WW compared to WF or WSF. Soil pH and potassium (K) were least in soils under WW. The SOM concentration in the top 0 to 2 in. with NT was 3.34%, which was similar to that of soil under ST (3.02%) but both were greater than RT (2.65%). Nitrate-N concentration increased with ST but ammonium-N concentration was greatest in soils under NT.
These results suggest strategic tillage could provide a mitigation option for herbicide-resistant weeds in no-till crop production with little impact on crop yields and soil chemical properties. Currently, research studies at Garden City, Hays, and Tribune are evaluating occasional tillage (one or two tillage operations every three years in a wheat-sorghum-fallow rotation compared to NT) to determine the effect of low-frequency tillage in the cropping system.
For more detailed information on this study, please refer to: “Strategic Tillage in Dryland No-tillage Crop Production Systems,” Kansas Agricultural Experiment Station Research Reports: Vol. 5: Iss. 4. https://doi.org/10.4148/2378-5977.7756
Augustine Obour, Soil Scientist, Agricultural Research Center - Hays
John Holman, Cropping Systems Agronomist, Southwest Research-Extension Center – Garden City
Alan Schlegel, Agronomist-in-Charge, Southwest Research-Extension Center - Tribune