Joseph F. Giles, Allan Cattanach, Norman R. Cattanach, and John G. Lamb
Associate Professor, Soil Science Department, North Dakota State University, Fargo, North
Dakota, Extension Sugarbeet Specialist, North Dakota State University and University of
Minnesota, Fargo, North Dakota.; Research Assistant Soil Science Department, North Dakota
State University, Fargo, North Dakota and Associate Professor, Soil Science, University of
Minnesota, St. Paul, Minnesota
Erosion damages hundreds of thousands of acres of arable land producing low residue crops in Minnesota and North Dakota each year, according to Soil Conservation Service data. An annual sugarbeet grower survey showed the most common tillage tools used after the 1991 sugarbeet harvest were chisel plows, disks, field cultivators, and deep tillage tools; 48, 24, 14, and 7 percent respectively. Field experiments were conducted from 1989 to 1994, to determine the effect of tillage after sugarbeet harvest on subsequent crop yields, percent ground cover, surface roughness, and soil aggregate size.
Use of a field cultivator after beet harvest increased residue cover by 72 percent versus untilled checks. Residue cover was increased by 22 percent with a disk and 10 percent with a chisel plow, but reduced 85 percent with a moldboard plow.
Field surface random roughness was greatly increased by moldboard plowing and significantly increased by the chisel plow and disk operations.
Soil aggregate geometric mean diameter in the fall was greatly increased by moldboard plowing and small increases occurred after fall tillage with a disk and chisel plow. Tillage with a field cultivator after beet harvest had almost no effect on soil aggregate geometric mean diameter. Overwinter weathering processes reduced geometric mean diameter of soil aggregates from 20-50 percent for the no-till, chisel, disk, and field cultivator treatments, depending on soil type. Aggregate geometric mean diameter decreased about 80 percent over winter on all soils following fall moldboard plowing. Geometric mean diameter aggregate size remained above the 0.84 mm minimum particle size erosion threshold for all soil types and tillage operations in all years.
Small grain yields the year following fall tillage were not affected by tillage treatment at any location.
Wind erosion threatens millions of acres of vulnerable land across the Great Plains each year. Production of low residue crops like sugarbeets, potatoes and dry edible beans, leaves thousands of acres of Minnesota and North Dakota farmland exposed to erosion. Loss of valuable topsoil is potentially high in years with dry falls and open winters with little snowfall.
After sugarbeet harvest the soil is exposed to possible wind erosion. Much of the field will have fine pulverized soil particles left on the soil surface from the harvesting operation. The harvesting operation leaves only about 20 percent residue cover on the land and buries the remaining crop residue 1-3 inches deep.
There are two strategies that can reduce susceptibility to erosion; residue and soil roughness management. Tillage affects both of these management strategies. Use of the correct tillage tool can increase the amount of residue left on the soil surface, (sugarbeet tops) by "unburying" the tops and at the same time leaving the surface in a rougher condition. In the fall of 1989, a study was started with the objective to determine if there is an optimal primary tillage operation after sugarbeet production that will minimize soil erosion and maintain crop production the following year.
Studies have been conducted since 1989 on varying soil types at seven locations in Minnesota and North Dakota to determine tillage effects on soil susceptibility to erosion. The soil series and classification and location of research sites is given in Table 1.
Five primary tillage treatments were completed after sugarbeet harvest. They were selected based on a survey of sugarbeet grower practices commonly used in Minnesota and North Dakota (4). The tillage treatments were implemented between October 15th and October 25th each year. Each treatment was replicated four times. Individual plots were 35 feet wide and 100 feet long. Implements used were: a moldboard plow; chisel plow; a field cultivator with harrow; a tandem disk; and a no-tillage treatment. The tools were operated at a depth of 8-9", 7-8", 2-3", and 3-4" deep, respectively. Speed of operation was 5-6 mph for the moldboard plow and 7-8 mph for the other implements. All equipment was standard sized, commonly used farm implements.
Percent ground cover was measured immediately after fall tillage, immediately prior to spring tillage before planting, and immediately after spring planting with a press drill. The line-transect method was used to estimate percent residue cover (6).
Immediately after fall tillage and again prior to spring tillage, five quart samples of soil were taken from the top 2" of soil. Dry aggregate size distribution determinations were made on each of these samples (2,3). The geometric mean diameter of soil aggregates was calculated for each treatment from these determinations.
Random roughness values for the surface of each tillage treatment were made using a micro-relief drop-pin apparatus. The determinations were made on a 4 foot square area of each treatment. Random roughness measurements were made immediately after tillage in late October and again after overwinter weathering prior to spring tillage (1,5).
Nitrogen, phosphorus, and potassium fertilizer was applied according to North Dakota State University soil testing laboratory recommendations for a 60 bushel per acre yield goal. Fertilizer was applied in early April and incorporated to a depth of 2-3" with a field cultivator with harrow attachment. Hard red spring wheat was seeded at a rate of 100 lbs/A between April 5th and April 20th. A conventional double disk press drill with 7" row spacing was used for seeding. Two 4 foot by 100 foot long strips of grain were harvested with a Hegge plot combine to determine wheat yields. Grain yields were determined on a 12.5 percent kernel water content basis.
The experiment was conducted as a randomized complete block design. Analysis of variance was completed and a LSD calculated to determine effects of each treatment.
Results over the three years show the use of a field cultivator maintained 41 percent residue cover which was a 72 percent increase over the untilled checks (Table 2). Residue cover was increased by 22 percent and 10 percent with a disk and a chisel plow, respectively, but reduced 78 percent using a moldboard plow. The amounts measured in early spring before tillage had similar differences with small ground cover reductions over the winter. After planting, the soil tilled with a field cultivator, disk, and no tillage maintained 19, 17 and 23 percent cover. The chisel plow maintained 18 percent cover and the plow 3 percent. This suggest a shallow tillage operation such as with a field cultivator, disk and chisel will provide as much wind erosion protection as no tillage at all in the fall.
Field surface random roughness was greatly increased by moldboard plowing and significantly increased by the chisel plow and disk operations (Table 3). Random roughness values for the field cultivation treatment were not significantly different than the untilled check treatment. An 18 to 33 percent reduction in random roughness occurred over the winter, with the shallow tillage treatments decreasing the most.
The geometric mean diameter (GMD) is a measure of soil clodiness. Aggregate (clods) with a size of 0.84 mm and greater are considered to be nonerodible. The greater the GMD, the less erodible a soil is. GMD in the fall was greatly increased by moldboard plowing (table 4). Small increases in GMD occurred after fall tillage with a disk and chisel plow. Tillage with a field cultivator had a negative effect on soil aggregate GMD. Overwinter weathering processes reduced GMD of soil aggregates an average of64 percent for the no-till, chisel, disk, and field cultivator treatments on the Fargo silty clay soil. GMD was reduced only about 20 percent after over winter on the Bearden-Lindass silt loam soil. Aggregate GMD decreased about 64 percent over winter on both soils following fall moldboard plowing. Shallow incorporation of residue with a field cultivator increased GMD over the winter by an average of 29 percent on all soil types. This compares to an increase of 31 percent in the no-till treatment. Aggregate GMD remained above the 0.84 mm minimum particle size erosion threshold for all soil types and tillage operations.
Small grain yields the year following fall tillage were not affected by tillage treatment at any location (table 5).
Random roughness and geometric mean diameter data analysis has not yet been completed on sites six and seven.
Thanks is extended to farmer cooperators G. Johansen, M. Kreps, L. Brakke, M. Hendrickson, and D. Johnson for use of land and equipment. A special thanks is extended to the Sugarbeet Research and Education Board of Minnesota and North Dakota for partial financial support of this research. Use of equipment from the USDA-ARS research station at Morris, Minnesota and the advise of Dr. M. Lindstrom is greatly appreciated.
1994 Sugarbeet Research and Extension Reports. Volume 25, pages 191-198.
