Randy L. Raper

Tillage Depth, Tillage Timing, and Cover Crop Effects on Cotton Yield, Soil Strength, and Tillage Energy Requirements

During the early 1990s, declining cotton (Gossypium hirsutum L.) yields plagued farmers in the Tennessee nValley Region of North Alabama who tried to eliminate moldboard and/or chisel plowing from their conventional farming nsystems to meet conservation compliance programs. The severely reduced yields were possibly due to inadequate rooting nsystems caused by excessive soil compaction. A study was conducted from 1995-1998 to investigate conservation tillage nsystems which incorporated a rye (Secale cereale L.) cover crop to maintain surface cover and in-row tillage to disrupt nroot-impeding soil layers. Energy requirements for shallow tillage (0.18 m) and deep tillage (0.33 m) performed in the nautumn and spring were also assessed. Factors investigated included time of tillage, depth of tillage, and use of a cover ncrop. A rye cover crop was found to be the largest single factor in increasing seed cotton yield, with positive results seen nin three of four years. Of somewhat lesser importance, autumn tillage and shallow tillage increased seed cotton yield in nthose years containing more typical growing seasons. The conservation tillage practice of shallow, autumn, in-row nsubsoiling in conjunction with a cover crop may offer the best alternative for farmers trying to reduce the negative effects nof soil compaction, maintain adequate residue cover, and improve seed cotton yield.

PERFORMANCE OF DIFFERENT ROLLER DESIGNS IN TERMINATING RYE COVER CROP AND REDUCING VIBRATION

Rollers may provide a viable alternative to herbicides for terminating cover crops; however, excessive vibration ngenerated by rollers and transferred to tractors hinders the adoption of this technology in the United States. To avoid excessive nvibration, producers must limit their operational speed, which increases time and cost of rolling. The effect of speed on cover ncrop termination rate and vibration level was tested on several roller designs. Two field experiments were conducted with ndifferent roller designs to terminate a cover crop of rye (Secale cereale L.). In the first experiment, three single-section roller ndesigns (long straight bars, curved blunt bars, and a smooth roller with an oscillating crimping bar) were tested at 1.6, 4.8, nand 8 km/h operating speeds. In the second experiment, two triple-section commercial width rollers, one with long straight nbars and the other, a smooth roller with an oscillating crimping bar, were tested at speeds 3.2 and 6.4 km/h. Data from the nfirst experiment showed that all three roller designs terminated at levels greater than 90% with the highest termination rate nproduced by the smooth roller with crimping bar (93.4%). Three weeks after rolling, termination rates varied from 88.3% to n94.0% for all designs and speed ranges, all of which were sufficient mortality rates for rye before planting a cash crop without nneed to use herbicide. Reduced vibration levels measured on the tractor’s frame were generated by the smooth roller with noscillating crimping bar with the highest vibration levels being generated by the roller with the straight bars. In the second nexperiment, three weeks after rolling significantly higher rye termination rates resulted from the roller with long straight bars n(96%) in comparison with the smooth roller (94%). Despite these differences, both rollers effectively terminated rye prior nto planting without use of herbicides. The smooth roller with crimping bar transferred significantly lower vibration levels to nthe tractor’s frame than long straight bar roller at both speeds but vibration levels exceeded acceptable health and comfort nlevels.

Influence of compaction from wheel traffic and tillage on arbuscular mycorrhizae infection and nutrient uptake by Zea mays

Interactive effects of seven years of compaction due to wheel traffic and tillage on root density, formation of arbuscular mycorrhizae, above-ground biomass, nutrient uptake and yield of corn (Zea mays L.) were measured on a coastal plain soil in eastern Alabama, USA. Tillage and soil compaction treatments initiated in 1987 were: 1) soil compaction from tractor traffic with conventional tillage (C,CT), 2) no soil compaction from tractor traffic with conventional tillage (NC,CT), 3) soil compaction from tractor traffic with no-tillage (C,NT), and, 4) no soil compaction from tractor traffic with no-tillage (NC,NT). The study was arranged as a split plot design with compaction from wheel traffic as main plots and tillage as subplots. The experiment had four replications. In May (49 days after planting) and June, (79 days after planting), root biomass and root biomass infected with arbuscular mycorrhizae was higher in treatments that received the NC,NT treatment than the other three treatments. In June and July (109 days after planting), corn plants that received C,CT treatment had less above-ground biomass, root biomass and root biomass infected with mycorrhizae than the other three treatments. Within compacted treatments, plants that received no-tillage had greater root biomass and root biomass infected with mycorrhizae in May and June than plants that received conventional tillage. Corn plants in no-tillage treatments had higher root biomass and root biomass infected with mycorrhizae than those in conventional tillage. After 7 years of treatment on a sandy Southeastern soil, the interactive effects of tillage and compaction from wheel traffic reduced root biomass and root biomass infected with mycorrhizae but did not affect plant nutrient concentration and yield. ei]J H Graham

EFFECT OF ANNUAL, BIENNIAL, AND TRIENNIAL IN-ROW SUBSOILING ON SOIL COMPACTION AND COTTON YIELD IN SOUTHEASTERN U.S. SILT LOAM SOILS

For those soils that require deep tillage to alleviate soil compaction, subsoiling can be an expensive and ntime-consuming tillage event. Alternative tillage methods are needed which conserve natural resources without sacrificing ncotton yields. An experiment was conducted in the Tennessee Valley region of north Alabama to determine how frequently ndeep tillage is needed to alleviate soil compaction problems in these soils. Three different subsoilers (an in-row subsoiler and ntwo bentleg subsoilers) were tested against a no-till treatment to determine if differences in crop productivity or soil condition ncould be detected. Annual subsoiling resulted in reduced bulk density compared to biennial subsoiling, triennial subsoiling, nor no subsoiling. Reductions in draft force were also found for annual subsoiling. However, cotton yield results over a two-year nperiod from tillage three-years previous, two-years previous, and one year previous found no differences.

Reducing Vibration while Maintaining Efficacy of Rollers to Terminate Cover Crops

Rollers may provide a valuable alternative to chemicals for terminating a cover crop. Several producers are now nusing versions that they have made or have purchased. Most of these producers, however, complain about excessive vibration nthat is caused by the roller passing over the cover crop. To avoid this excessive vibration, they must limit their operational nspeed. Experiments were performed to determine if two alternative roller blade designs would decrease vibration while nmaintaining the ability to kill a cover crop. Results showed that a spiral blade system or a short-staggered straight blade nsystem significantly reduced vibration as compared to the standard long-straight blade system typically found on rollers. nThese two alternative blade systems were also found to kill the cover crop as effectively as the long-straight blade system.

The Economic Benefit of Improving the Proximity of Tillage and Planting Operations in Cotton Production with Automatic Steering

Producers in the Coastal Plain of the southeastern United States manage soil compaction in conservation tillage systems by in-row subsoiling prior to planting. However, planting directly over the loosened zone of soil can be difficult in high-residue conservation tillage systems where cover crop production is maximized. Tractors with automatic steering capability could assist with placement of deep tillage in close proximity to planting operations, but little is known about the accuracy necessary to maximize rooting development, reduce succeeding soil compaction, and optimize crop production. An experiment was conducted in south-central Alabama to evaluate the distance the cotton row can be from deep tillage and still affect cotton yield and economic performance. Results showed as distance between the planted row and tillage pass increased, seed cotton yields were reduced by as much as 24% to 52% and net revenues from cotton production by as much as 38% to 83%. An economic analysis of on-farm adoption showed that auto-guidance systems with accuracy of less than 2.5 cm may be the most profitable for larger farms, while systems with less than 10 cm accuracy may provide a better economic alternative for smaller farms.

ACOUSTIC COMPACTION LAYER DETECTION

The ASAE standardized tool to detect the depth and strength of compaction layers in the field is the cone penetrometer. Since this method is point-to-point, researchers have experimented with on-the-fly alternatives that can be used as, or in combination with, a standard tillage tool. On-the-fly compaction layer sensing also enables adaptive tillage, where the soil is only tilled as deep as necessary, which can lead to significant energy savings and erosion reduction. Wedged tips, strain gauges mounted on a deflecting tine, air bubbles pushed into the soil, as well as ground-penetrating radar have been tested for this purpose. In this research, passive acoustics was used to detect the compaction layer by recording the sound of a cone being drawn through the soil. The premise was that a more compacted layer should cause higher sound levels, which might reveal the depth and strength of the compaction layer. Two experiments were conducted in the soil bins of the USDA-ARS National Soil Dynamics Laboratory in Auburn, Alabama. First, constant-depth tests (15 and 30 cm) at three compaction levels (0.72, 2.8, and 3.6 MPa) revealed the relationship of sound amplitude with depth and compaction. Second, to test the detection capability, the cone was gradually inserted in the soil, passing through an artificial compaction layer. A windowed, short-time Fourier transform (STFT) analysis showed that the compaction layer is detectable since the sound amplitude was positively related to depth and compaction levels, but only in the highest frequency range of the spectrum. This led to the conjecture that the soil-cone interface acts as a low-pass filtering mechanism, where the cutoff frequency becomes higher in the compaction layer due to a more intimate contact between sensor and soil.

A PORTABLE TILLAGE PROFILER FOR MEASURING SUBSOILING DISRUPTION

A portable tillage profiler (PTP) was constructed using a laser distance sensor, a linear actuator, a portable PC, nand a lightweight aluminum frame that can quickly and accurately measure aboveground and belowground soil disruption ncaused by tillage. A laboratory experiment was conducted that determined that soil color did not detrimentally affect the PTP, nwith expected vertical errors of 2.3 mm and horizontal errors of 0.6 mm being found. However, when pure white and black nobjects were examined, the errors increased to 4.2 mm vertically and 11 mm horizontally. This maximum error was established nwhen attempting to measure the height and width of a wedge, which had a sharpened edge pointing vertically upward. The nPTP was used in the National Soil Dynamics Laboratory soil bins to measure both aboveground and belowground soil ndisruption caused by two subsoiler shanks. The PTP gave results that enabled differences between the aboveground ndisruptions caused by each subsoiler to be statistically established.

Finite Element Analysis of Cone Penetration in Soil for Prediction of Hardpan Location

An accurate determination of soil hardpan location is important for maximum precision tillage performance. Cone penetrometers are often used to locate hardpans in soils. This determination in layered soils is more complex due to the complexity of soil reaction to cone penetration. An axisymmetric finite element (FE) model was developed to simulate cone penetration for the prediction of the hardpan location in a layered Norfolk sandy loam soil. The soil was considered as a non-linear elastic-plastic material, and it was modeled using a Drucker-Prager model with the Hardening option in ABAQUS, a commercially available FE package. ABAQUS/Explicit was used to simulate soil-cone contact pair interaction. The results showed that the FE model captured the penetration resistance trend with two deflection points indicating the start of the hardpan and the peak cone penetration resistance. The FE-predicted results showed the hardpan at a depth of 7.29 cm compared to 11.08 cm from cone penetration tests. Soil moisture, bulk density, and cone surface conditions significantly affected the predicted and experimental results. The simulation also showed soil deformation zones about 3 times the diameter of the cone that developed around the advancing cone.

SOIL MOISTURE EFFECTS ON ENERGY REQUIREMENTS AND SOIL DISRUPTION OF SUBSOILING A COASTAL PLAIN SOIL

An experiment was conducted to determine the optimum moisture content to subsoil based on tillage forces and nsoil disruption. Two different shanks, a straight shank and a “minimum-tillage” shank, were tested in a Coastal Plain soil nin the soil bins of the National Soil Dynamics Laboratory in Auburn, Alabama. A three-dimensional dynamometer measured ntillage forces, and a laser profilometer measured soil disruption. Tillage forces and soil disruption measured in the driest soil ncondition were greatest. The “minimum-tillage” shank required more energy and disrupted less surface soil than the straight nshank. An index, the trench specific resistance (TSR), was developed to aid in determining the minimum amount of draft force nnecessary for maximally disrupting a deeper soil profile. Reduced values of TSR were found for the straight shank compared nto the “minimum-tillage” shank, as minimum draft produced maximum soil disturbance. Reduced values of TSR were also nfound for subsoiling operations conducted at all soil conditions other than the driest. Based on this research, subsoiling should nnot be conducted at the extreme driest soil condition due to increased draft forces and increased aboveground soil disruption.