A critical objective of belowground research is to collect and process representative soil samples. Mechanical devices have been developed to quickly take soil cores in the field; however, techniques to rapidly process large-diameter soil cores are lacking. Our objective was to design and construct a soil extraction-cutting system that could effectively reduce processing time. Soil cores were extracted from large diameter steel core tubes using a custom hydraulic cylinder device that vertically pushes the soil core to a desired depth increment before cutting in a horizontal direction with another hydraulically driven device. As many as eight large cores per hour could be processed with this system. This system has been effectively used in processing soil samples from both agricultural and forestry sites to meet desired experimental goals.

Reliable sampling of belowground components in the field is essential to agroecosystem research. Factors such as hardpans and dry soil conditions often increase sampling time and impede adequate sampling. The objective was to design and construct a soil coring system for rapid field sampling that minimized such limitations. Cores were extracted using a custom-made telescoping hydraulic cylinder device assisted by a hydraulic post driver mounted to the front of a small tractor. The telescoping device inserted the core tube into the ground, and the post driver was activated only when insertion had been slowed or stopped. The tractor's hydraulics powered the telescoping device and the post driver; both were controlled by the tractor operator. Custom driving heads were constructed to fit the upper end of core tubes to collect large-diameter soil samples (25 cm diam. by 0.6 m deep) or small samples (3.8 cm diam. by 1.0 m deep). As many as 14 large cores or 24 small cores per hour could be collected with this system. The coring system has been successfully used on various soil types and to sample both agricultural and forest sites for a number of experimental objectives.

Land application of manure may produce unacceptable odors. Field experiments in undisturbed (no-till) soybean and corn residue were conducted to evaluate six liquid swine manure application/incorporation methods. The methods were injection with a commercial(1) chisel or (2) sweep, (3) incorporation with tandem disk harrow after broadcast application, (4) broadcast application with no incorporation, (5) injection with a narrow-profile knife, and (6) surface application behind row cleaners. The row cleaner and all injection treatments used spoke-covering wheels. Air samples over the soil surface were obtained immediately following and one day after manure application, and odor level was measured by olfactometry (i.e., the amount of air dilutions to reach odor threshold). Residue cover and yield were also measured. Incorporation techniques typically reduced odor level by a factor of three to ten as compared with a broadcast application. One day after application, odor was greatly reduced and often indistinguishable from that of untreated soil (no manure application). Residue cover differences among application methods were more pronounced in soybean residue. Application by the narrow-profile knife, row cleaner and chisel maintained soybean residue cover better than other incorporation methods yet limited odor similar To these methods. Although cover was reduced over winter, greater soybean residue cover remained after planting with fall than with spring manure applications. Differences in odor level and residue cover among methods were less in corn than soybean residue. All incorporation techniques reduced odor levels, and chisel incorporation maintained corn residue cover after planting similar to broadcast application. For both crops, broadcast application maintained the greatest residue cover but had the highest odor level. Incorporation of manure generally reduced odor reduced residue cover increased corn yield, and did not affect soybean yield.

Soil structure is an important measure of soil quality that significantly affects crop production, water-useefficiency, and soil erosion. More effective techniques to measure soil structure are needed to determine if a tillageoperation achieves the desired result and whether soil management practices are improving or degrading soil structure. Afiber-optic displacement sensor was used to scan the surface of bulk samples of soil aggregates. The soil was air driedand sieved to aggregate size fractions of < 0.18, 0.18-0.25, 0.25-0.5, 0.5-1, 1-2, 2-4, and 4-8 mm. The sensor, following ablade to level the surface at a constant distance beneath the sensor tip, was moved at 5.08 mm/s by a universal testingmachine. Voltage output of the sensor was recorded with data acquisition software at sampling rates of 10, 100, and200 Hz. Mean sensor output voltage decreased significantly (P = 0.05) as aggregate size increased. Values measured forthe aggregate size fractions, in the order listed above, were 4.6, 3.1, 2.5, 1.5, 0.8, and 0.2 V, respectively. Data samplingrate had negligible effect on mean output voltage. The number of peaks in the sensor output signal was affected byaggregate size, but was comparatively independent of the gap between sensor and soil surface. Data sampling rate shouldbe greater than 20 readings/mm in order to use the number of peaks in the sensor output signal for discriminating amongaggregates of the sizes evaluated in this research. The results indicated that the fiber-optic soil structure sensor may havepotential for use in evaluating soil structure.

Replacing herbicides with mechanical cultivation can reduce pesticide use in row crop production. Although amajority of Iowas corn land is cultivated, most is cultivated only once and herbicide is broadcast applied. To increasegrower confidence in reducing herbicide use and in using cultivation for interrow weed control, a three-year fieldexperiment compared various single-cultivation plus band-herbicide application strategies with broadcast applicationstrategy and no-control strategy. To cover larger acreages in a narrow window of time, cultivation speed was increasedeach year from 11.3 to 14.1 to 16.9 km/h (7.0, 8.8, and 10.5 mph). A 38-cm (15-in.) herbicide band treatment had lessweed growth, and generally greater yield, extended leaf height, and corn population than did a 19-cm (7.5-in.) bandtreatment. Few differences were noted among cultivator styles. Weed management and grain yield were as good or betterwith the traditional low-crown sweep as with other styles. Its wider cutting width (56-cm or 22 in.) in 76-cm (30-in.) rowsresulted in a lower corn population, however, when operated at 16.9 km/h (10.5 mph) with a crosswind. Differences inweed population and visual weed cover rankings when comparing single-cultivation with broadcast-only strategies variedwith years. Grain yield from a treatment using a single cultivation with a low-crown sweep and a 38-cm (15-in.) wideherbicide band was statistically equivalent to that from a broadcast-only treatment in all three years. Results of this studyindicate that herbicide use can be halved and weed control and corn yield can be maintained by use of a 38 cm (15 in.)herbicide band and a single sweep cultivation.

Excessive rainfall inundated many midwestern agricultural fields in 1993 and resulted in numerous questions regarding the depth and number of tillage operations needed to prepare fields for crop production in 1994. Five on-farm locations were selected to compare effects of shallow, moderate, and deep tillage on soil compaction and crop yield. Bulk density, soil water content (theta(v)), penetration resistance, and yield of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were measured, and net return was computed for the three tillage treatments. Preplant bulk density within the upper 12 in. averaged 1.27, 1.26, and 1.22 g/cu cm for no-till, chisel, and subsoiled treatments, respectively. Penetration resistance averaged 130, 120, and 97 psi for the no-till, chisel, and subsoil treatments, respectively (LSB(0.05) = 7), and showed highly significant differences at depths from 0.5 to 12 in. Post-harvest bulk density was not significantly different, but penetration resistance averaged 378, 341, and 283 psi (LSD(0.05) = 19) for no-till, chisel, and subsoiled areas, respectively. Increased preplant tillage intensity significantly affected some soil physical properties, but corn and soybean yields were not affected. With regard to return on investment and time, we conclude it would be more profitable to limit tillage in fields subjected to excessive rainfall and inundation events like those occurring throughout the Midwest in 1993.

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.

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. (C) 1998 Elsevier Science B.V. All rights reserved.

Seed furrow sidewall smearing describes compaction of soil in the seed zone that is caused, in some soil conditions, by the planter furrow opener and that may interfere with crop stand establishment. Soil smearing caused by planting with double disk furrow openers was investigated by measuring physical properties of soil in the seed furrow and by evaluating corn (Zea mays, L.) emergence and growth. Planter attachments for row preparation (no-coulter; single offset bubble coulter; and triple offset fluted coulter planter attachments) were evaluated for their influence on seed furrow sidewall smearing over a range of soil moisture contents. Planting tended to reduce soil bulk density in the 0 to 100 mm layer in the seed zone. In general, the soil was least dense when the triple-coulter attachment was used Air permeability of soil samples taken from the seed furrow sidewall, before the furrow was closed tended to decrease with increasing soil moisture. The triple-coulter treatment resulted in greater air permeability than did other coulter treatments. Soil penetration resistance below the seed and in the seed furrow sidewall was greatest for the single coulter and least for the triple coulter. We observed that more roots grew parallel to the soil surface with no-coulter and single-coulter treatments than with the triple-coulter treatment especially when soil property measurements indicated that more sidewall smearing had occurred. This research showed that row preparation by coulter planter attachments placed ahead of double-disk openers can reduce seed furrow sidewall smearing and may improve stand establishment of corn.

Surface plant residues increase the risk of poor stand establishment for corn (Zea mays. L.) and soybean [Glycine max (L.) Merr.] in no-till. This may result in reduced crop yield and may limit adoption of no-till by farmers. A three-year field study int an established no-till system with three rotation sequences was conducted to compare the effect of three planter attachments on surface and subsurface residue, and on stand establishment, emergence rate, and yield of corn and soybean. The study was conducted near Ames, Iowa, on dark-colored soils with corn-following-corn, corn-following-soybean, and soybean-following-com rotation sequences. Both corn and soybean were planted with three different attachments placed in front of the planter double-disc openers: an offset-bubble coulter,; a staggered-discs row cleaner, and a powered horizontal-disc row cleaner The continuous-corn rotation increased subsurface residue only in 1992 and had no effect on surface residue. The continuous-corn rotation, however did reduce final emerged population, emergence rate, and corn grain yield in some years. In general, there were no significant interactions between rotation sequence and planter attachments. Both row cleaner planter attachments reduced the amount of surface and subsurface residue in the seed raw compared with the offset-bubble coulter attachment. Row cleaner planter attachments also increased final populations of corn in 1990 and soybean in 1991, increased emergence rate indexes of soybean in 1991 and of corn in all three years, and had no effects on grain yield. The two row cleaner attachments, however had fewer barren corn plants in two years. Because row cleaner planter attachments reduce the risk of poor stand establishment in no till, they should improve corn and soybean yield potential and stability in years when stand establishment limits yields.

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.

The mechanical behavior of agricultural soils has to be understood to quantify and manage soil tilth. The development of theoretical soil mechanics has been limited to the failure of soil by shear, as applied to foundation structures in civil engineering. Recent soil failure studies in agricultural soils have shown that there are at least five different ways the soil will react depending upon soil type and applied stress conditions. Tine force prediction models, which are based upon passive earth pressure theory, have been reported to be inappropriate for agricultural soils. A survey of theoretical developments in agricultural soil mechanics suggests the need to develop new concepts to describe the response of agricultural soils to applied stresses.

Ridge height, ridge surface index (ratio of row width to ridge surface width), ridge cross-sectional area, and ridge form were measured to evaluate ridges formed during cultivation. Ridges were constructed with three tool types (disk, shovel, and sweep), operated at three speeds [5, 7, and 9 km/h (3, 5, and 7 mph)] and at three depths [5, 10, and 15 cm (2, 4, and 6 in.)]. Ridge forms were classified as convex, triangular, and concave-convex. Tool operating depth was the most important factor affecting ridge characteristics. Tool type affected cross-sectional area and ridge form, but had no effect on ridge height or ridge surface index.

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.

The distribution of granular pesticides, used to control insects in turfgrass, may influence the pesticide hazard to birds foraging for food; however, there is little information on the exposure of birds to granules applied to turfgrass. Granules were spread onto golf course greens [creeping bentgrass (Agrostis palustris 'Penncross')], fairways [perennial ryegrass (Lolium perenne) and annual bluegrass (Pea annual], and roughs [Kentucky bluegrass (Pea pratensis)]. Granule height in the grass profile was measured and granules visible from above were counted. Within one hour after application, granules in the rough were less visible (15%) than those in the fairway (38%) or on the green (67%). Irrigation (4 mm) decreased the percentage of granules visible from above to 7% for the rough, 20% for the fairway, and 46% for the green. After irrigation, granules in the rough were higher (mean height 9 mm) above the soil surface than were granules applied to fairways (6 mm) and greens (4 mm). The most likely place for waterfowl to be exposed to granular insecticides is on the fairway, where the birds' habit of grazing to a height of 10 to 20 mm would expose them to I to 15% of the applied granules if they feed soon after an irrigation following granule application.

A method of designing tillage tool shapes based on mathematical expressions is needed A mathematical equation for the macroshape of passive tillage tools is developed The equation includes the main geometrical parameters and can be used for designing many different tillage tools. The mathematical description of tool geometry may determine how the design parameters influence the energy requirement and quality of operation. This description has the potential of achieving a quantitative analysis of the tillage process. A computer program has been developed to design and display selected passive fool shapes. The tool surface is represented by a multiplicity of quadrilateral faces limited by user-selected bounding curves. The (x,y,z) face coordinates are generated by a FORTRAN program and read into AutoCAD using an AutoLISP program. The method permits a complete study of the influence of the geometrical parameters upon the final soil condition and energy requirements, thus optimization of the tillage process may be possible.

A relationship between tire sinkage depth and depth at which traffic increased bulk density by 0.05 Mg/m(3) was developed from data in published literature. Laboratory and field experiments were also conducted to verify the relationship. In the laboratory, a universal testing machine was used with the aid of dimensional analysis and modeling theory to physically simulate compaction by a tractor tire. An oval metal plate 100 mm wide and 122 mm long was used to apply stresses of 25, 50, 100, and 150 kPa to soil in containers. Three soil water contents were used. For field verification, a tractor was used to traffic soil. Different tire inflation pressures and loads were used to create different tire sinkage depths. Differences in bulk density were used to determine depth at which applied stress caused significant soil compaction. Based on previous research and on laboratory and field experiments, compaction depth, Y, was found to be related to sinkage depth, X, by the empirical equation, Y = bX(m) where b and m are regression constants.