Abstract Agricultural systems produce both detrimental and beneficial effects on soil quality (SQ). We compared soil physical properties of long-term conventional (CON) and alternative (ALT) cropping systems near Akron, Colorado (CO); Brookings, South Dakota (SD); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan (ND); Mead, Nebraska (NE); Sidney, Montana (MT); and Swift Current, Saskatchewan (SK), Canada. Objectives were to quantify the changes in soil physical attributes in cropping systems and assess the potential of individual soil attributes as sensitive indicators of change in SQ. Soil samples were collected three times per year from each treatment at each site for one rotation cycle (4 years at Brookings and Mead). Water infiltration rates were measured. Soil bulk density (BD) and gravimetric water were measured at 0–7.5, 7.5–15, and 15–30 cm depth increments and water-filled pore space ratio (WFPS) was calculated. At six locations, a rotary sieve was used to separate soil (top 5 cm) into six aggregate size groups and calculate mean weight diameter (MWD) of dry aggregates. Under the CON system at Brookings, dry aggregates (>19 mm) abraded into the smallest size class (<0.4 mm) on sieving. In contrast, the large aggregates from the ALT system abraded into size classes between 2 and 6 mm. Dry aggregate size distribution (DASD) shows promise as an indicator of SQ related to susceptibility of soil to wind erosion. Aggregates from CON were least stable in water. Soil C was greater under ALT than CON for both Brookings and Mead. At other locations, MWD of aggregates under continuous crop or no tillage (ALT systems) was greater than MWD under CON. There was no crop system effect on water infiltration rates for locations having the same tillage within cropping system. Tillage resulted in increased, decreased, or unchanged near-surface BD. Because there was significant temporal variation in water infiltration, MWD, and BD, conclusions based on a single point-in-time observation should be avoided. Elevated WFPS at Fargo, Brookings, and Mead may have resulted in anaerobic soil conditions during a portion of the year. Repeated measurements of WFPS or DASD revealed important temporal characteristics of SQ that could be used to judge soil condition as affected by management.

The processes for the formation of porosity are thought to differ between tilled and non-tilled cropping systems. The pores are created primarily by the tillage tool in the tilled systems and by biological processes in non-tilled systems. Because of the different methods of pore formation, the pore size distribution, pore continuity and hydraulic conductivity functions would be expected to differ among tillage systems. The objective of this study was to determine effects of three tillage systems — mold-board plow (MP), chisel plow (CP), and no-till (NT) — on hydraulic properties of soils from eight long-term tillage and rotation experiments. Tillage effects on saturated and unsaturated hydraulic conductivity, pore size distribution, and moisture retention characteristics were more apparent for soils with a continuous corn (CC) rotation than for either a corn-soybean (CS) rotation or a corn-oats-alfalfa (COA) rotation. Pore size distributions were similar among tillage systems for each soil except for three soils with a CC rotation. The MP system increased volume of pores >150 μm radius by 23% to 91% compared with the NT system on two of the soils, but the NT system increased the volume of the same radius pore by 50% on one other soil. The NT system had 30 to 180% greater saturated hydraulic conductivity than either the CP or MP systems. The NT system with a CC rotation showed a greater slope of the log unsaturated hydraulic conductivity; log volumetric water content relationship on two of the soils indicating greater water movement through a few relatively large pores for this system than for either the CP or MP systems.

Corn (Zea mays L.) grown following corn, on poorly drained, fine-textured soils, with no-till tends to yield less than with other tillage systems. Surface residues conserved with no-till reduce erosion, thus, techniques must be found to avoid yield reductions. Field experiments were conducted to evaluate use of the Paraplow (Howard Rotovator Co., Inc.), a tillage tool that loosens soil without inversion, for continuous corn production. No-till, chisel plow, moldboard plow, and Paraplow systems were evaluated on three poorly drained, medium- and fine-textured soils in Iowa. All tillage tools reduced bulk density and penetration resistance to the depth of tillage. However, after planting only the soil tilled with the Paraplow remained less dense. Plant residue cover had more effect on corn growth than did soil loosening. Emergence and yield of corn were inversely related to amount of residue on soil surface after planting.

Ridged soil surface configurations are often used as a management tool to improve the plant root environment. Possible benefits for ridge tillage systems include warmer and dryer seed-zone soil conditions in the spring, better control of wheel-traffic patterns, and better crop residue management for erosion control. This study compared soil physical properties in the plant row, the untracked interrow, and the wheel-tracked interrow positions for a ridge tillage system on three soils. Soil property information was used to model the effects of soil variability and ridge height on subsurface water and heat transport. Simulated water and heat flow in a ridge seemed to be different from that of a flat surface. Taller ridges had a greater influence on water and heat movement than shorter ridges. There seems to be an optimum ridge height for fastest warming and drying. Variable soil properties affected predicted soil temperature distributions less than predicted matric potential distributions. The compacted zone had a lower matric potential deep in the profile and a higher matric potential near the surface than the uncompacted zone.

AbstractStudy of ridge‐tillage effects on the soil environment has been impeded by the lack of models to adequately describe water and heat movement in the ridge system. The ridge system introduces many nonuniform characteristics into the field problem, such as variable solar radiation across the soil surface, unevenly distributed surface mulches, and variable water and heat transport properties caused by ridge construction or wheel traffic. A finite‐element model was developed to simulate coupled water and heat flow in ridge systems. The finite‐element solution scheme was chosen because of the ease by which nonuniform soil transport properties and nonuniform boundary conditions can be included in the problem specifications. Model predictions of soil water and temperature were compared with field measurements for two ridge configurations. Predicted and measured average daily temperatures over a 10‐d period were within 1 °C and water contents were within 0.02 m3 m−3 for 80% of the measurements.

AbstractOne‐ and three‐row corn (Zea mays L.) microplots were compared for determining 15N‐depleted fertilizer recovery from in‐row N applications. Studies were conducted with Iowa ridge‐tillage systems on Monona silt loam (fine‐silty, mixed, mesic Typic Hapludoll), Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll), and Marna silty clay loam (fine, montmorillonitic, mesic Typic Haplaquoll). Corn rows were injected with 15N‐depleted NH4NO3 (99.99% 14N) at 56 and 112 kg N ha−1 on Monona silt loam and at 67 and 157 kg N ha−1 on Webster and Marna silty clay loams. Percentage N from fertilizer in the mature‐plant samples ranged from 19.8 for grain fertilized at 56 kg N ha−1 to 50.0 for stover at 157 kg N ha−1. One‐ and three‐row microplots were not significantly different for determining corn N recovery in the application year from in‐row N placements.

AbstractPoint injection of liquid fertilizer has shown promise as an alternative to standard surface or subsurface fertilizer application, particularly with no‐till and ridge‐till planting systems. Field‐scale point injector applicators are difficult to use in small plots, especially with labeled fertilizer materials such as 15N. This paper describes the construction and use of a small, inexpensive fertilizer application system, which simulates fertilizer injection by a large point injection applicator. Use of the applicator for 3 yr has shown the unit to be relatively accurate, durable and compatible with a variety of fertilizer materials.

An experiment was conducted to determine the effect of four tillage systems (moldboard plow, chisel plow, Paraplow and no-till) on soil aggregate shear strength and bulk density. Two soils, a Canisteo clay loam (fine-loamy, mixed (calcareous), mesic, Typic Haplaquoll) and a Haig silt loam (fine, montmorillonitic, mesic, Typic Argiaquoll) were used in this study. Soil samples were collected from the 0.075–0.15-m-depth increment in 1983 and the 0.075–0.15- and 0.225–0.30-m-depth increments in 1985. Shear strength of soil aggregates 0.02–0.03 m in diameter was measured by a fall-cone penetrometer and bulk density of the same aggregates was measured by gamma-ray attenuation. Aggregates were tested at soil water matric potentials (ψm) of −0.2, −1.1 and −4.0 kPa in 1983 and at ψm of −0.2, −1.1, −4.0 and −7.9 kPa in 1985. Tillage for the 1983 growing season was conducted under very wet conditions, whereas tillage for the 1985 growing season was conducted under much drier conditions. Samples collected in 1983 showed little tillage effect on shear strength or bulk density. In 1985, tillage had an effect on shear strength and bulk density for the Haig soil, but not for the Canisteo soil. Much of the tillage effect on soil aggregate shear strength could be explained by tillage-induced changes in the aggregate bulk density. As bulk density decreased, soil aggregate shear strength decreased.

AbstractA method was developed to measure soil aggregate shear strength and bulk density at soil water matric potentials <0. Strength measurements were made with the Swedish fall‐cone penetrometer, and bulk density measurements were made by gamma‐ray attenuation. The method allowed both density and strength measurement on the same aggregate. Tests were conducted at soil water matric potentials of −0.2, −1.1, and −4.0 kPa. As the matric potential decreased, the shear strength of the soil aggregates increased. The method described by this paper is an improvement on the standard wet‐sieve technique for determination of aggregate stability as follows: (i) it allows the measurement of aggregate strength at matric potentials <0, (ii) the strength measurement is in units of stress, and (iii) the aggregate density as well as aggregate strength can be measured on each sample. The disadvantage is that aggregates with diameters ≥ 2 cm are required for the measurement.