Michael J. Lindstrom

Quantifying tillage erosion rates due to moldboard plowing

Abstract Tillage erosion, the movement of soil downslope by mechanical implements, has been recognized as a problem, but primarily in a qualitative manner. This study was initiated to quantify soil movement by tillage on a hillslope landscape by computer simulation of long-term moldboard plowing. Regression equations describing soil movement as affected by slope gradient were developed from a hillslope at the University of Minnesota Southwest Experiment Station where individual plots could be located on the frontslope, apex, and backslope. Based on these equations, yearly soil movement calculations were made for a moldboard plowing operation over two hillslope landscapes. The first landscape was generated to give concave, linear, and convex slope gradients. The second landscape was a measured line segment from the experimental site. From a starting elevation and slope, one-dimensional calculations were based on forward moment of soil blocks, 0.24 m (plow depth)× 0.46 m (plow share width) × 1.5 m (increment length), over the hillslope to simulate 1 years moldboard plowing. Elevation and slope of each soil block position was recalculated, and forward movement was then calculated in the opposite direction to simulate the next years plowing. This process was continued to simulate 100 years of moldboard plowing at opposing direction during alternate years. Results from this analysis showed that a net loss in soil will occur on convex slope positions (tillage erosion), soil accumulation will occur in concave slope positions, and little change occurs in linear slope positions regardless of slope gradient. Calculated average annual net soil movement rates away from convex slope position were up to 30 t ha −1 year −1 and could easily account for the presence of observed lighter colored soil in convex slope positions on many landscapes. The magnitude of net soil movement calculated strongly suggests that soil movement by tillage is a serious problem.

Modeling spatial variation in productivity due to tillage and water erosion

The advent of precision farming practices has heightened interest in managing field variability to optimize profitability. The large variation in yields across many producer fields demonstrated by yield‐monitor‐equipped combines has generated concern about management-induced causes of spatial variation in soil productivity. Soil translocation from erosion processes may result in variation in soil properties across field landscape positions that produce long-term changes in soil productivity. The objective of this study was to examine the relationships between soil redistribution caused by tillage and water erosion and the resulting spatial variability of soil productivity in a soil catena in eastern South Dakota. An empirical model developed to estimate tillage erosion was used to evaluate changes expected in the soil profile over a 50-year period on a typical toposequence found in eastern South Dakota and western Minnesota. Changes in the soil profile due to water erosion over a 50-year period were evaluated using the WEPP hillslope model. The tillage erosion model and the WEPP hillslope model were run concurrently for a 50-year period to evaluate the combined effect of the two processes. The resulting changes in soil properties of the root zone were evaluated for changes in productivity using a productivity index model. Tillage erosion resulted in soil loss in the shoulder position, while soil loss from water erosion occurred primarily in the mid to lower backslope position. The decline in soil productivity was greater when both processes were combined compared to either process acting alone. Water erosion contributed to nearly all the decline in soil productivity in the backslope position when both tillage and water erosion processes were combined. The net effect of soil translocation from the combined effects of tillage and water erosion is an increase in spatial variability of crop yields and a likely decline in overall soil productivity. # 1999 Elsevier Science B.V. All rights reserved.

Effect of subsoiling and subsequent tillage on soil bulk density, soil moisture, and corn yield☆

Abstract Many producers use subsoilers periodically to alleviate suspected compaction caused by traffic from tillage, planting, and harvesting equipment. In the fall of 1988 a study was initiated in the upper Midwest region of the USA near Morris, Minnesota to study the effects of a one-time subsoiling and its interaction with four subsequent primary tillage systems (fall moldboard plowing, fall chisel plowing, spring disking, and no-tilling) on soil compaction, soil moisture, penetrometer resistance, and corn ( Zea mays L.) growth and grain yield. The experiment was established on a Hamerly clay loam (Aeric Calciaquoll)-Aastad clay loam (Pachic Udic Haploboroll) complex. Subsoiling was performed in the fall of 1988 and the study was cropped to continuous corn from 1989 to 1991 on a site that had been farmed many years by normal 6-row, 76-cm row width equipment. Results show that subsoiling had very little effect on plant growth and no effect on grain yield over three cropping seasons following the subsoiling operation. Subsoiling had significant effects on soil bulk density and volumetric soil moisture content in 1989, but by 1990–1991 these effects were not significant. Volumetric soil moisture content generally increased in relation to soil bulk density increases. Tillage impacted surface residue accumulation, but did not affect soil bulk density, volumetric soil moisture, or grain yield. Results from this study indicate that subsoiling soils does not necessarily result in better yields or better soil moisture availability, particularly if compaction problem are not evident.

Wettability of soil aggregates from cultivated and uncultivated Ustolls and Usterts

Soil organic matter can modify the interaction of clay minerals with water, limiting the rate of water intake of swelling clays and stabilising soil aggregates. Soil structural stability and organic C content usually decrease with cultivation. Faster wetting increases stresses on aggregates and decreases stability. Aggregate wettabilities of prairie soils under 3 different management systems (grassland, no-till, and conventional-till) were compared in the Northern Great Plains of the USA. Six Ustolls and 2 Usterts were selected as replications along the Missouri River. Wettability was measured as water drop penetration time (WDPT) and as rate of water intake under 30 and 300 mm tension. At low tension, aggregates from both cultivated fields and uncultivated grasslands showed similar wettability. Water intake in grass aggregates was attributed to a greater amount of stable pores relative to cultivated aggregates. In cultivated aggregates, slaking created planes of failure that allowed rapid water entry. Differences of wettability between management systems at 300 mm tension (in Ustolls, grasslands had greater wettability than cultivated soils, 0.24 v. 0.17 g water/h.g dry soil) and between soil orders (Usterts had longer WDPT than Ustolls, 2.9 v. 1.7 s) were explained by both clay and organic C contents. Simple measurements of aggregate wettability may be effectively used for soil quality characterisation. Aggregate wettability is a desirable property for agricultural soils when it is related to stable porosity, as may be found in high organic matter soils (e.g. grasslands). Wettability is excessive when fast aggregate wetting results in aggregate destruction as observed in low organic matter cultivated soils.

Patterns of water and tillage erosion on topographically complex landscapes in the North American Great Plains

Two field sites located in the northern region of the North American Great Plains were examined to investigate the contributions of water and tillage erosion towards total soil erosion in topographically complex landscapes (hummocky and undulating landscapes). Results indicated that both water and tillage erosion contributed substantially to total erosion in the undulating landscape while tillage erosion dominated in the hummocky landscape. The patterns of water, tillage and total soil erosion can be predicted using landscape segmentation in such landscapes. Soil properties and crop yield are also related to soil erosion. Landscape segmentation can be used as a simple tool to more easily represent the spatial variability of soil erosion and affected biophysical processes such as crop production, nutrient cycling, greenhouse gas emission and pesticide fate, and to target soil conservation practices toward the most intensive erosion processes on given landform elements.