Enhancement of subsoiling effect on soil strength by conservation tillage

The effects of deep tillage are believed to differ for conventional vs. conservation tillage in the sandy Ultisols of the southeastern Coastal Plains of the United States. To test this, cone indices were measured for a conventional tillage and a conservation tillage treatment before and after in-row subsoil-planting. In the first year of the study, the conservation tillage treatment had a significantly higher moisture content (15.1 vs 12.1% on a dry weight basis) and a mean soil strength that was 0.70 MPa less than the conventional treatment. In the second year, the conservation tillage treatment had a lower moisture content (13.2 vs. 14.9%) and a mean soil strength that was 0.29 MPa greater than the conventional treatment. However, after conventional treatment strengths were corrected for soil moisture content differences, the mean strengths were about the same. The differences in the distribution of the strengths favored the conservation tillage treatment which was evenly distributed while the conventional tillage treatment had areas of higher strength that could more easily inhibit root growth

Intensive cropping of maize in the Southeastern United States

The long growing season of the southeastern Coastal Plains allows planting of a second crop after spring-planted maize (Zea mays L.). Second crops have been shown to reduce erosion and prevent leaching of nutrients and pesticides. Maize grown with a second annual crop might also have a yield advantage over mono-cultured maize. Seven tillage/cropping systems were compared. They included disking for weed control, disking for seedbed preparation, or no disking. Double-cropped treatments included sunflower (Helianthus annuus L. ), soybean ( Glycine max. L.), a cover crop [crimson clover (Trifolium incarnatum L.) ] or no double crop. Double-cropped soybean yields did not respond to irrigation. They averaged 0.63 Mg/ha over 4 years. This is less than half of the local non-double-cropped yields. Sunflower yields averaged 0.89 Mg/ha, also less than non-double-cropped yields (1.0-2.5 Mg/ ha). The best continuous maize yields (7-8 Mg/ha) were from treatments with disking in some phase of the operation. Treatments with lower maize yields generally had higher plant nutrient contents. Double-cropped maize yields significantly (P < 0.10) outyielded mono-cropped maize yields in two of the three years. In 1984, a dry year, the minimum tillage treatment had lower tensiometer readings than the conventionally tilled treatment

Conservation tillage in soybean and corn in the South Carolina Coastal Plain

Numerous variations of conservation tillage (CT) systems have been adopted for soybean, corn and double-crop wheat grown on Coastal Plain Ultisols. A systematic investigation of the effect of these variations in cultural practices on yields was needed. A long term tillage study was established in Florence, SC to study these variations in conservation tillage systems. Soybean yields were favored by CT but were reduced by drilling. Burning of double-crop residues showed no yield advantage. Corn yields were slightly reduced by conservation tillage systems in which residues were left standing at planting. Double-crop yields were greatly increased by deep primary tillage. Double-cropped wheat and reduced operations with CT in soybean increased cash returns. However, caution is still in order when considering CT for corn in the Coastal Plain

Penetration resistance isopleths for assessment of soil strength under varying management regimes

Diagnostic techniques to evaluate cultural practice effectiveness for managing soil strengths are needed. A recording penetrometer used on a uniform grid of penetrations produced analog records (on 3 x 5 cards) of soil strength vs depth. These were used to develop profile contour plots of soil strength. Digitization was done using a flatbed plotter, programmed to aid in placement of the digitizing eyepiece. Contour depth, shape, and frequency of strength observations were used to compare tillage treatments. Methods of strength correction for soil water differences and other applications are discussed

Alternative intensive cropping with corn

Corn (Zea mays L.) was continuously cropped in seven systems, with or without irrigation. Baseline irrigated corn yields of 200- 210 bu/acre were reduced 65-75 bu/acre by not utilizing standard rotational practices. The best continuous corn yields were from systems with disking in some phase of the operation. The only follow-crop to consistently approach an economically attractive level was sunflower (Helianthus annuus L.), but continuous corn yields remained depressed in this system. Corn yields benefitted from soybean (Glycine max L.) as a follow-crop, but soybean itself yielded well only 1 of 4 years. In the absence of a follow-crop, delaying disking until immediately before spring corn planting yielded as well as any other treatment compared

Comparison of log transformed and scaled cone indices

Changes in soil properties with time and position make it difficult to analyze cone index data taken throughout a growing season. It was hypothesized that scaling would aid in interpretation. Cone indices were measured at 10 different dates over two growing seasons in conventional- and conservation-tillage plots in Florence, SC. They were measured at 0.05-m depth intervals to a depth of 0.55 m at spacings of 0.1 m across two 0.76-m wide rows of soybean or maize. Cone indices were scaled by subtracting each value by the mean and dividing by the range of cone indices for each date of measurement. This yielded an equal mean (zero) for each date with a unique distribution. Unscaled values were transformed by taking their logarithm to normalize the data. Log transformed data varied significantly with date of measurement but not between treatments. Scaled values did not vary with date of measurement but did vary between tillage treatments. Both unscaled and scaled cone indices varied significantly with water content. Scaling has the potential to improve the analysis of cone index data by reducing or eliminating some of the confounding treatment effects

Environmental Benefits of Biochar

Understanding and improving environmental quality by reducing soil nutrient leaching losses, reducing bioavailability of environmental contaminants, sequestering C, reducing greenhouse gas emissions, and enhancing crop productivity in highly weathered or degraded soils, has been the goal of agroecosystem researchers and producers for years. Biochar, produced by pyrolysis of biomass, may help attain these goals. The desire to advance understanding of the environmental and agronomic implication of biochar utilization led to the organization of the 2010 ASA-CSSA-SSSA Environmental Quality Division session entitled Biochar Effects on the Environment and Agricultural Productivity (Long Beach, CA; Oct. 31-Nov. 3). Twenty-five presentations from this session, and sessions at the 2010 U.S. Biochar Initiative Conference (Ames, IA; June 27-30) and Biochar Symposium 2010 (organized by Dr. Bruno Glaser; University of Bayreuth, Bayreuth, Germany, July 8-9), make up a special collection of review and technical research papers focused on biochar creation and utilization. Individual contributions deal with improvement of the biochar knowledge base, current information gaps, and future biochar research needs. The prospect of biochar utilization is promising, as biochars may be custom designed for specific environmental applications

In situ strength, bulk density, and water content relationships of a durinodic xeric haplocalcid soil

Compaction significantly reduces yield, quality, and profitability of irrigated crops in the US Pacific Northwest (PNW). Compaction assessment is usually done via bulk density measurement, even though crops respond negatively to excessive compaction largely because of root penetration (soil strength) limitations, not because of bulk density per se. For most soils, strength is thought to depend primarily on the interaction of water content and bulk density. We hypothesized that the soil strength (expressed as cone index) of an important PNW soil, Portneuf silt loam (Durinodic Xeric Haplocalcid), could be predicted for a given bulk density or water content and that it would increase with increasing bulk density and decreasing water content. To test this, the in situ cone index, the bulk density and water content profile of a 1.5-ha field was intensively sampled three times over a 2-year period, producing 688 data triplets. These data were used to produce soil water strength-bulk density response surface relationships using robust curve fitting. Cone index relationships were poor when derived from full-profile data sets but improved when data were segregated by depths. When grouped by depth intervals, cone indices of individual layers were always correlated strongly with soil water content, but not always with bulk density. The high calcium carbonate content of this soil was thought to have produced cementation effects on the cone index that varied with prolonged wetting versus prolonged drying. Variability among in situ strength penetrations and bulk density cores was also thought to reduce model accuracy. The difficulties inherent in developing the comprehensive relationships of soil strength to bulk density, and the overriding dependency of strength on the dynamic variable of water content, suggest great uncertainty when using bulk density sampling for realistic assessment of overall soil status affecting root restriction or crop performance unless sampling is extensive and the relationships between strength, bulk density, and water content have been intensively documented for an individual soil

A conservation tillage research update from the Coastal Plain Soil and Water Conservation Research Center of South Carolina: A review of previous research

In the U.S. Southeastern Coastal Plains conservation tillage (CT) became useful as a management system with the development of in-row subsoiling systems capable of planting into heavy residues. Research priorities associated with the development of CT included: reducing cover crop water loss, improving stand establishment, assessing nutrient and water management requirements, determining optimal subsoiling strategies, understanding long-term conservation tillage effects on soil properties, evaluating the interaction of crop residue removal with tillage systems, and documenting tillage impact on pests and beneficial organisms. Since the late 1970s the Coastal Plains Soil and Water Conservation Research Center in Florence, SC has made a concerted effort to study these interactions and alleviate them as obstructions to the use of CT management. These studies showed that for Coastal Plain soils such as Norfolk sandy loam ( fine-loamy, siliceous thermic, Typic Paleudults ) winter cover crops such as rye (Secale cereale L.) desiccated the soil profile by evapotranspiration in the spring. This delayed emergence and early season growth of corn (Zea mays L.) but not full-season soybean (Glycine max ( L. ) Merr. ). Conservation tillage helped manage soil strength by gradually increasing soil organic matter content, restricting traffic patterns and maintaining higher soil water contents. Laboratory studies demonstrated a negative correlation (R2=0.85 ) between proctor soil strength and organic matter content. Conservation tillage affected nematode, Bradyrhizobium japonicum and Heliothis species populations. Alternate cropping systems using rapeseed (Brassica napus L.) as a winter crop or sunflower (Helianthus annuus L.) either before soybean or after corn provided crop cover against potential soil loss from late autumn through early spring, when bare soil is exposed to intense rainfall. Water quality questions associated with CT have been raised but remain unanswered. Although CT can reduce runoff and erosion, the crop residues can support higher insect populations and pathogen inoculum levels, and thus prompt greater pesticide use. Quantifying relationships between soil strength, macropore formation and persistence, and water infiltration with surface and subsurface water quality is the focus of new long-term evaluations. The findings of these studies, published to date, are summarized in this paper

A decade of progress in conservation tillage in the South Carolina Coastal Plain

Stream discharge measurements with chemical dilution techniques have been proposed in several forms since the beginning of this century (Groat4). Early techniques consisted of introducing a chemical, usually brine, at a known rate into flowing water and determining the resulting concentration of the chemical in the stream at a section far enough downstream to assure adequate mixing of the chemical with the water. A variation of this method, and the technique used in the present study, was described by Barbagelata5 in 1928. In that method, a known quantity of tracer was added, as a slug, to the stream to be measured. At a sampling station sufficiently far downstream for adequate lateral mixing, the tracer concentration-time curve was determined. The stream discharge was then calculated from the amount of tracer added and the area measured under the curve