Donald C. Erbach

Crop residue effects on soil quality following 10-years of no-till corn☆

Numerous biological, chemical, and physical indicators of soil quality have been suggested, but few have been evaluated using data from long-term field studies. Our objective was to evaluate several proposed soil quality indicators to determine effects of removing, doubling, or maintaining crop residues for 10 years in a no-till, continuous corn (Zea mays L.) production study. Soil aggregate characteristics, penetration resistance, bulk density, volumetric water content, earthworm populations, respiration, microbial biomass, ergosterol concentrations, and several soil-test parameters (pH, P, K, Ca, Mg, Total-N, Total-C, NH4-N, and NO3-N) were measured on samples collected from Rozetta and Palsgrove silt loam (fine-silty, mixed, mesic Typic Hapludalfs) soils. Soil aggregates from double residue treatments were more stable in water than those from normal and removal treatments. The double and normal residue treatments had higher total carbon concentrations and higher levels of microbial activity as measured by CO2 evolution. Ergosterol concentrations where crop residues were removed were 8 to 10 times lower suggesting this biochemical measurement of fungal biomass may be a sensitive soil quality indicator. Earthworm populations where crop residues had been removed for 10 years were significantly lower than in either normal or double residue treatments. Measures of force and energy required to crush soil aggregates were extremely variable and showed significant differences only for aggregate size. Several parameters were used to develop a soil quality index that gave ratings of 0.45, 0.68, or 0.86 for removal, normal, or double residue treatments, respectively. This study demonstrates a framework for soil quality evaluation and shows how crop residue management can affect this rating.

Long-term tillage effects on soil quality

Public interest in soil quality is increasing, but assessment is difficult because soil quality evaluations are often purpose- and site-specific. Our objective was to use a systems engineering methodology to evaluate soil quality with data collected following a long-term tillage study on continuous corn (Zea mays L.). Aggregate characteristics, penetration resistance, bulk density, volumetric water content, earthworm populations, respiration, microbial biomass, ergosterol concentrations, and several soil-test parameters (pH, P, K, Ca, Mg, Total-N, Total-C, NH4-N, and NO3-N) were measured on Orthic Luvisol soil samples collected from Rozetta and Palsgrove silt loam (fine-silty, mixed, mesic Typic Hapludalfs) soils. Plots managed using no-till practices for 12 years before samples were collected for this study had surface soil aggregates that were more stable in water and had higher total carbon, microbial activity, ergosterol concentrations, and earthworm populations than either the chisel or plow treatments. Selected parameters were combined in the proposed soil quality index and gave ratings of 0.48, 0.49, or 0.68 for plow, chisel, or no-till treatments, respectively. This indicated that long-term no-till management had improved soil quality. The prediction was supported by using a sprinkler infiltration study to measure the amount of soil loss from plots that had been managed using no-till or mold-board plow tillage. We conclude that no-till practices on these soils can improve soil quality and that the systems engineering methodology may be useful for developing a more comprehensive soil quality index that includes factors such as pesticide and leaching potentials.

Effect of wetting and drying on soil physical properties

Abstract Agricultural soils are subject to seasonal wetting and drying cycles. Effect of drying stress, as influenced by one cycle of wetting and drying, on physical properties of a clay–loam soil was investigated in the laboratory. The physical properties studied were soil bulk density, cone penetration resistance, shear strength, adhesion and aggregate size and stability. Three drying stress treatments were made by wetting air-dried soil of initial moisture content of 12% (on dry weight basis) to three different higher moisture contents, namely 27, 33 and 40%, and then drying each of them back to their original moisture content of 12%. Thus, the soil was subjected to three different degrees of drying stress. The results showed that the soil strength indicated by cone penetration resistance and cohesion, and soil aggregate size, increased with the degree of drying stress. However, the soil bulk density did not change significantly with the drying stress.

Seed-row residue management for corn establishment in the northern US Corn Belt

In the northern US Corn Belt, plant residue retained on the soil surface increases risk of poor stand establishment and growth of corn (Zea mays, L.). This limits adoption of no-tillage and other conservation tillage systems which are effective in reducing soil erosion. Field and laboratory research has shown that surface residue reduces soil heat unit accumulation by reducing soil heat flux, and conserves soil water by reducing evaporation rate. Surface residue also hinders planter operation and uniformity of seed placement. Removing excessive or non-uniform plant residue from the seed row increases germination and emergence rate by improving seed depth uniformity and by increasing soil heat unit accumulation. Appropriate use of planter attachments to manage surface plant residue has been shown to improve conditions in the seed zone for reliable corn establishment in the northern US Corn Belt.

Drying stress effect on mechanical behaviour of a clay-loam soil

The mechanical behaviour of agricultural soils has a large role in determining the performance of agricultural implements and the resulting soil tilth. Seasonal wetting and drying of these soils induces drying stresses that alter the soil physical state and its properties. The performance of a simple vertical tine was investigated in a clay-loam soil subjected to three different levels of drying stress in a soil bin. Results showed that changes in most soil properties caused by tillage depended on drying stress. Soil bulk density decreased after tillage, although it was not significantly affected by drying stress. Soil shear strength, tine draft and aggregate size increased significantly with drying stress. Dried soils subjected to high drying stress broke in a less periodic manner and into larger masses than unwetted soil.

Hysteresis in soil mechanical behavior

Abstract The performance of a vertical tine was investigated at various water contents during wetting and drying cycles in a clay-loam soil. Results showed that at a given water content the soil during the wetting cycle failed by fracture mode and offered relatively more draft. Soil during the drying cycle cracked, and when a tine was pushed through the soil, it failed along the cracks. This failure mode was referred to as preferential fracture. For a given water content, tine forces and soil shear strength properties were found to be greater during the wetting cycle than the drying cycle, which leads to the conclusion that there is a hysteresis effect in soil caused by drying stress induced by seasonal wetting and drying.

CULTIVATOR DESIGN FOR INTERROW WEED CONTROL IN NO-TILL CORN

More than 95% of Iowa row crop acres are treated with herbicides. Such extensive use is an environmental concern. Banding of herbicides over the crop row, along with mechanical cultivation to control interrow weeds, has been proposed as a way to reduce herbicide use. Though cultivation is used on 74% of Iowa corn (Zea mays L.) land, herbicides are applied in a band on only 17% of the corn acres. This indicates that cultivation is not relied upon for interrow weed control. The risk that weather conditions will hinder completion of mechanical cultivation seems to discourage the use of herbicide banding. Higher speed cultivation could improve the odds of timely completion of needed cultivation. An experiment was conducted on a Clarion loam soil near Boone, Iowa in 1993 through 1996 to determine the effect of cultivator design and speed, when combined with the banding of chemicals, to control weeds. Three cultivator styles, two bands [19 cm (7.5 in.) and 38 cm (15 in.)], and two speeds were tested. A single cultivation management strategy was used. Data were taken in a no-till continuous corn rotation on 76-cm (30-in.) row spacings. Faster speed did not impede weed control or yield. In two years, the corn yield was greater and weed cover was reduced in plots cultivated at 11.2 km/h (7.0 mph) than in plots cultivated at 6.4 km/h (4.0 mph). Weed populations were greater in the 19-cm (7.5-in.) band than in the 38-cm (15-in.) band three of four years. In three of four years, leaf heights and yields were also significantly less for herbicide applied in a 19-cm (7.5-in.) band than in a 38-cm (15-in.) band. There was no difference between yield in a broadcast treatment and treatments which used a wide band of herbicide and a cultivator with disc hillers. In two years, the sweep and smith fin (a vee-shaped flat sweep with low rake angle) cultivator treatments resulted in less weed cover than the point-and-share treatment. In one year, the sweep and smith fin cultivator treatments had greater yield than the point-and-share treatment. Groundcover among cultivators showed few differences.

Methods for measuring soil velocities caused by a sweep

Abstract A field experiment was conducted to measure surface soil velocity and to determine the relation between soil aggregate velocities at the tool surface and at the soil surface. A technique incorporating use of both a video camcorder and wood blocks was developed to measure surface soil velocity. Soil velocity direction at the tool surface was measured from scratch marks on the tool. Velocity measurements were made for three sweeps with different rake angles operated at three speeds and two depths. Surface soil moved in either of two modes: V-flow (upward and laterally in the shape of one leg of the letter V) or snowplow (initially moving upward and subsequently being buried in a wave of soil). Surface soil velocities were uncorrelated with velocities on the tool surface, indicating that soil flow paths over the sweep were not parallel. The ratio of vertical to lateral soil flow at the tool surface increased with larger rake angle and was greater than the ratio at the soil surface. At the soil surface, vertical velocity was greater near the nose than near the wing tip and velocity parallel to the travel direction increased with increased speed and rake angle.