R. L. Raper

Effects of residue management and controlled traffic on carbon dioxide and water loss

Management of crop residues and soil organic matter is of primary importance in maintaining soil fertility and productivity and in minimizing agricultural impact on the environment. Our objective was to determine the effects of traffic and tillage on short-term carbon dioxide (CO2) and water (H2O) fluxes from a representative soil in the southeastern Coastal Plain (USA). The study was conducted on a Norfolk loamy sand (FAO classification, Luxic Ferralsols; USDA classification, fine-loamy siliceous, thermic Typic Kandiudults) cropped to a corn (Zea mays L.) — soybean (Glycine max (L.) Merr) rotation with a crimson clover (Trifolium incarnatum L.) winter cover crop for eight years. Experimental variables were with and without traffic under conventional tillage (CT) (disk harrow twice, chisel plow, field cultivator) and no tillage (NT) arranged in a splitplot design with four replicates. A wide-frame tractive vehicle enabled tillage without wheel traffic. Short-term CO2 and H2O fluxes were measured with a large portable chamber. Gas exchange measurements were made on both CT and NT at various times associated with tillage and irrigation events. Tillage-induced CO2 and H2O fluxes were larger than corresponding fluxes from untilled soil. Irrigation caused the CO2 fluxes to increase rapidly from both tillage systems, suggesting that soil gas fluxes were initially limited by lack of water. Tillage-induced CO2 and H2O fluxes were consistently higher than under NT. Cumulative CO2 flux from CT at the end of 80 h was nearly three times larger than from NT while the corresponding H2O loss was 1.6 times larger. Traffic had no significant effects on the magnitude of CO2 fluxes, possibly reflecting this soil’s natural tendency to reconsolidate. The immediate impact of intensive surface tillage of sandy soils on gaseous carbon loss was larger than traffic effects and suggests a need to develop new management practices for enhanced soil carbon and water management for these sensitive soils. # 1999 Elsevier Science B.V. All rights reserved.

Assessing Indices for Predicting Potential Nitrogen Mineralization in Soils under Different Management Systems

A reliable laboratory index ofN availability would be useful for making N recommendations, but no single approach has received broad acceptance across a wide range of soils. We compared several indices over a range of soil conditions to test the possibility of combining indices for predicting potentially mineralizable N (N 0 ). Soils (0-5 and 5-15 cm) from nine tillage studies across the southern USA were used in the evaluations. Long-term incubation data were fit to a first-order exponential equation to determine N 0 , k (mineralization rate), and N 0 * (N 0 estimated with a fixed k equal to 0.054 wk -1 ). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KCI (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to N 0 (r > 0.85) and had linear regressions with r 2 > 0.60. None of the indices were good predictors ofk. Correlations between indices and N 0 * improved compared with N 0 , ranging from r = 0.90 to 0.95. Total N and Hush of CO 2 determined after 3 d (Fl_CO2) produced the best multiple regression for predicting N 0 (R 2 = 0.85) while the best combination for predicting N 0 * (R 2 = 0.94) included TN, Fl_CO2 Cold_N, and NaOH_N. Combining indices appears promising for predicting potentially mineralizable N, and because TN and Fl_CO2 are rapid and simple, this approach could be easily adopted by soil testing laboratories.

Conservation Tillage and Traffic Effects on Soil Condition

The soil condition resulting from a five-year cotton-wheat double cropping experiment in a sandy loam Coastal Plain soil was investigated using intensive measurements of cone index and dry bulk density. Four tillage treatments including a strip-till (no surface tillage with in-row subsoiling) conservation tillage practice were analyzed. The traffic was controlled in the experimental plots with the USDA-ARS Wide-Frame Tractive Vehicle. Besides the environmental benefits of maintaining the surface residue, the strip-till treatment decreased cone index directly beneath the row, decreased surface bulk density, increased surface moisture content, decreased energy usage, and increased yields. Controlled traffic was beneficial only when in-row subsoiling was not used as an annual tillage treatment. Although differences in soil condition were seen beneath the row middles where traffic occurred, this did not affect the soil condition directly beneath the row.

SOIL CARBON RELATIONSHIPS WITH TERRAIN ATTRIBUTES, ELECTRICAL CONDUCTIVITY, AND A SOIL SURVEY IN A COASTAL PLAIN LANDSCAPE

Soil organic carbon (SOC) estimation at the landscape level is critical for assessing impacts of management practices on C sequestration and soil quality. We determined relationships between SOC, terrain attributes, field scale soil electrical conductivity (EC), soil texture and soil survey map units in a 9 ha coastal plain field (Aquic and Typic Paleudults) historically managed by conventional means. The site was composite sampled for SOC (0-30 cm) within 18.3 × 8.5-m grids (n = 496), and two data sets were created from the original data. Ordinary kriging, co-kriging, regression kriging and multiple regression were used to develop SOC surfaces that were validated with an independent data set (n = 24) using the mean square error (MSE). The SOC was relatively low (26.13 Mg ha−1) and only moderately variable (CV = 21%), and showed high spatial dependence. Interpolation techniques produced similar SOC maps but the best predictor was ordinary kriging (MSE = 9.11 Mg2 ha−2) while regression was the worst (MSE = 20.65 Mg2 ha−2). Factor analysis indicated that the first three factors explained 57% of field variability; compound topographic index (CTI), slope, EC and soil textural fractions dominated these components. Elevation, slope, CTI, silt content and EC explained up to 50% of the SOC variability (P ≤ 0.01) suggesting that topography and historical erosion played a significant role in SOC distribution. Field subdivision into soil map units or k-mean clusters similarly decreased SOC variance (about 30%). The study suggests that terrain attributes and EC surveys can be used to differentiate zones of variable SOC content, which may be used as bench marks to evaluate field-level impact of management practices on C sequestration.

New roller crimper concepts for mechanical termination of cover crops in conservation agriculture

Rollers crimpers have been used in conservation agriculture to terminate cover crops; however, excessive vibration generated by the original straight-bar roller design has delayed adoption of this technology in the United States. To avoid excessive vibration, producers generally reduce operating speeds that increase the time needed to perform the field operation. The objectives of this research were to identify roller crimper designs that terminated rye cover crops consistently, resulted in soil moisture conservation after use, and minimized vibrations when operated in the field. Six different roller types were developed and tested at 3.2 and 6.4 km h - 1 in Alabama field experiments during the 2006, 2007 and 2008 growing seasons. All roller types were used alone and one also in combination with glyphosate. Rye mortalities were evaluated 1, 2 and 3 weeks after rolling and compared with the check (non-rolled standing rye). Soil volumetric moisture content (VMC) was measured at the day of rolling, and then at 1, 2 and 3 weeks after rolling. Vibration was measured on the rollers’ and tractor’s frames during operation. Mortality for rolled rye 2 weeks after rolling was at least 98% compared with 96% for the check in 2006, 93% for rolling compared with 75% for the check in 2007, and 94% for rolling compared with 60% for the check in 2008 (P < 0.10). There were no consistent differences in rye mortality across roller types (without glyphosate) and speeds. VMC for soil in non-rolled rye plots was consistently lower than in rolled rye plots, averaging 3% compared with 7% 2 weeks after rolling in 2006, and 4% compared with 8% in 2008. During 2007, VMC was affected by severe drought conditions, and differences between roller treatments were detected but minor. The - 1 - 2 straight-bar roller generated the highest vibration on the tractor’s frame at 6.4 km h (0.71 m s , RMS), which exceeded International Standards (International Standard Office (ISO)). At 6.4 km h - 1 , new roller designs generated significantly lower acceleration levels from 0.12 to 0.32 m s - 2 on the tractor’s frame and were below detrimental effects on health ‘health limits’ classified by ISO. Overall, 2 weeks after rolling, all roller designs effectively terminated rye above 90%, which is the recommended termination level of rye to plant a cash crop into residue mat, while protecting soil surface from water loss. New roller designs generate less vibration than the original design and can be used safely at higher operating speeds.

SOIL STRESSES UNDER A TRACTOR TIRE AT VARIOUS LOADS AND INFLATION PRESSURES

Abstract Soil stresses were measured under a 18.4R38 R-1 radial-ply tractor tire, operated at two levels each of dynamic load and inflation pressure. Stress state transducers were placed at two depths beneath the centerline of the path of the tractor tire in two different compaction profiles in each of two soils. Peak soil stresses and soil bulk density increased with increases in both dynamic load and inflation pressure.

The effects of reduced inflation pressure on soil-tire interface stresses and soil strength

Abstract Inflation pressures as low as 41 kPa have been recommended by agricultural tire manufacturers for minimizing an oscillatory vibration problem, commonly called “power hop”. Other benefits of these lower inflation pressures might include decreased soil-tire interface pressures, increased tire performance, and decreased soil compaction. Measurements of soil-tire interface stresses were made at four positions on the lugs and a three positions between lugs on an 18.4-R38 R-1 radial factor tire operated at four combinations of dynamic load and inflation pressure. These measurements showed that as inflation pressure increased, the soil-tire interface stresses near the center of the tire increased, while the stresses near the edge of the tire did not change. The increased stresses near the center of the tire were also transferred to the soil as a compaction increase sensed with the cone penetrometer. “Correctly” inflated tires (i.e. lower inflation pressures) also improved net traction and tractive efficiency.

Inflation Pressure and Dynamic Load Effects on Soil Deformation and Soil-tire Interface Stresses

An 18.4 R38 R-1 radial tractor tire at inflation pressures of 41 and 124 kPa and at dynamic loads of 13.1 and 25.3 kN was evaluated to determine the effects of the new load-inflation pressure tables on soil deformation and contact stresses. Measurements of rut width and deformed rut area were conducted with a profile meter. Soil-tire interface stress measurements were also made to determine stresses occurring between the tire and the soil and to determine the tire footprint length. Inflation pressure and dynamic load effects were found on rut width, contact length, and contact area. Dynamic load effects were also found on deformed rut area. Increased levels of soil-tire interface stress was found near the center of the tire when inflation pressure or dynamic load was increased.

Interactive effects of wheel‐traffic and tillage system on soil carbon and nitrogen

Abstract Wheel‐traffic induced soil compaction has been shown to limit crop productivity, and its interaction with tillage method could affect soil nutrient transformations. A study was conducted during 1993–1994 to determine interactive effects of tillage method (conventional tillage and no‐tillage) and wheel‐traffic (traffic and no traffic) on soil carbon (C) and nitrogen (N) at a long‐term (initiated 1987) research site at Shorter, Alabama. The cropping system at this study site is a corn (Zea mays L.) ‐ soybean [Glycine max (L.) Merr] rotation with crimson clover (Trifolium incarnatum L.) as a winter cover crop. Soil organic C, total N, and microbial biomass carbon (MBC) were not significantly affected by six years of traffic and tillage treatments. However, conventional tillage compared to no‐tillage almost doubled the amount of CO2‐C respired over the entire observation period and during April 1994 field operations. Soil respiration was stimulated immediately after application of wheel‐ traffic, but...

Tire lug height effect on soil stresses and bulk density

Soil stresses and increases in soil bulk density were measured beneath the centerline of one new 18.4R38 radial-ply R-1 tractor tire and two similar tires with lug heights of 55% and 31% of the new tire lug height. Each tire was operated with an inflation pressure of 110 kPa, a dynamic load of 25.0 kN and 10% slip. Soil stress state transducers (SSTs) measured the stresses at three depths in both a hardpan soil profile and a uniform soil profile, each in a sandy loam and a clay loam soil. The initial depths of the SSTs ranged from 164 to 288 mm. Analysis of the original soil stress data showed that lug height did not significantly affect the peak octahedral normal stress or its corresponding octahedral shear stress. When outliers were removed from the peak stress data, however, lug height significantly affected the octahedral normal stress in the sandy loam soil. In the uniform profile of the sandy loam and in the hardpan profile of the clay loam, the new tire generated the greatest bulk density increase, which was significantly greater than the bulk density increase caused by the 55% tire. In the sandy loam with the hardpan profile, the 55% lug height tire generated a significantly greater bulk density increase than either the new or 31% tire.