Using strip-till and no-till drastically reduced sediment loss compared to disc-till, chisel-till and conventional till in onfarm research simulations in the fragile soils of Iowa’s Loess Hills, according to Iowa State University Extension scientists.

In the research, strip-till and no-till sediment losses were 1.73 and 1.14 tons per acre per year, respectively, far less than those of more aggressive tillage. Disc-till and chisel-till losses were 5.83 and 7.45 tons of sediment per acre per year, while conventional tillage losses were 12.15 tons per acre per year.

Iowa’s Loess Hills, which are along the Missouri River, are extremely susceptible to gully erosion in the absence of good farming systems. The area has one of the highest erosion rates in the U.S. In this study, the Water Erosion Prediction Project (WEPP) model was used to simulate the impact of conservation practices on soil erosion for a farm in the Loess Hills.

Materials and Methods

The study site was located within the West High Creek Watershed in Fremont County. The total size of the site was approximately 108 acres. The mean slope was about 2.9 %, ranging between 1.5 % and 10.9 %. The slope range of the study area may not be truly representative of more steeply sloping areas, the scientists note.

Soil erosion was simulated for four reduced tillage systems (no-till, strip-till, disc-till, and chisel-till) and conventional-till with a corn-soybean rotation. No-till had no soil or crop residue disturbance except for that occurring during planting.

Strip-tillage prepared narrow rows for seedbed after soybean harvest in the fall, while no-till was used after corn harvest. Disc-till included a discing after corn harvest in the fall and field cultivating for both corn and soybean in the spring.

Chisel-till consisted of stalk shredding and chisel operation after corn harvest in the fall and field cultivating for both corn and soybean in the spring before planting. Conventional-till consisted of shredding stalks and subsoiling after corn harvest, and discing and cultivating for corn and soybean in the spring.

Soil erosion was simulated by the WEPP model for a 30-year period to obtain the mean annual surface runoff and sediment yield for the entire study area.

Results

Simulation results showed that reduced tillage systems could greatly reduce soil loss caused by erosion. For more intense tillage practices such as conventional-till, chisel-till and disc-till, the mean annual soil loss all exceeded the tolerable soil loss rate (5 tons per acre per year), while sediment yield was only 1.14 and 1.73 tons/acre/year for no-till and strip-till, respectively (Table 1).

Most of the areas with an annual soil loss rate greater than the target value under conventional-till would meet the target under a no-till system. However, simulation results showed that tillage had little impact on surface runoff amount in this study site. In field conditions, tillage operations often destroy soil structure and macropore connectivity of the near-surface soil layers, and, therefore, decrease infiltration and increase surface runoff.

The total amount of phosphorus loss with sediment was lowest in no-till, and increased as more field operations occurred. The phosphorus loss was 1.31 pounds per acre per year in no-till, about one-tenth of the amount in conventional-till (13.88 pounds/acre/year).

Soil erosion showed a quick and significant response to the amount of biomass remaining on soil. Higher biomass removal rates dramatically increased sediment yield regardless of tillage types. All tillage systems showed a big increase of soil erosion when the biomass removal rate exceeded 70%, especially for no-till and strip-tillage. However, even a 100% biomass removal in no-till and strip-till had a lower sediment yield than the other three more intense tillage types (disc-till, chisel-till and conventional-till) without any biomass removal.

Grassed waterways greatly reduced sediment yield in each tillage system compared with the tilled waterways, which had the same field operations as other row-crop areas. With the implementation of grass waterways, the simulated annual sediment yield was below the commonly used tolerable soil loss rate even under conventional-tillage at the study site.

Soil erosion is a severe problem in the Loess Hills region. More no-till or strip-till and good residue management would greatly help reduce sediment yield and nutrient loadings in this region.

Table 1.

Simulation results of surface runoff, sediment yield, and phosphorus bound to sediment for different tillage systems in corn-soybean system.