Warren J. Busscher

IMPACT OF BIOCHAR AMENDMENT ON FERTILITY OF A SOUTHEASTERN COASTAL PLAIN SOIL

Agricultural soils in the southeastern U.S. Coastal Plain region have meager soil fertility characteristics because of their sandy textures, acidic pH values, kaolinitic clays, low cation exchange capacities, and diminutive soil organic carbon contents. We hypothesized that biochar additions will help ameliorate some of these fertility problems. The study objectives were to determine the impact of pecan shell-based biochar additions on soil fertility characteristics and water leachate chemistry for a Norfolk loamy sand (fine-loamy, kaolinitic, thermic typic Kandiudults). Soil columns containing 0, 0.5, 1.0, and 2.0% (wt/wt) biochar were incubated at 10% (wt/wt) moisture for 67 days. On days 25 and 67, the columns were leached with 1.2 to 1.4 pore volumes of deionized H2O, and the leachate chemical composition determined. On days 0 and 67, soil samples were collected and analyzed for fertility. The biochar had a pH of 7.6, contained 834.2 and 3.41 g kg−1 of C and N, respectively, and was dominated by aromatic C (58%). After 67 days and two leaching events, biochar additions to the Norfolk soil increased soil pH, soil organic carbon, Ca, K, Mn, and P and decreased exchangeable acidity, S, and Zn. Biochar additions did not significantly increase soil cation exchange capacity. Leachates contained increasing electrical conductivity and K and Na concentrations, but decreasing levels of Ca, P, Mn, and Zn. These effects reflect the addition of elements and the higher sorption capacity of biochar for selective nutrients (especially Ca, P, Zn, and Mn). Biochar additions to the Norfolk soil caused significant fertility improvements.

Correction of cone index for soil water content differences in a coastal plain soil

Soil penetration resistance (cone index) varies with water content. The field variation of water content could mask treatment differences. The correction of cone index data to a single water content would help prevent this. We used equations from TableCurve™ software and from the literature to correct cone indices for differences in soil water contents. Data were taken from two field experiments where cotton (Gossypium hirsutum L.) was grown using conventional and conservation tillage without irrigation, and beans (Phaseolus vulgaris L.) were grown using conventional tillage with microirrigation. Boundary conditions based on hard, dry and soft, wet soils were imposed on the equations. Equations fit the data with coefficients of determination ranging from 0.55 to 0.92 and error mean squares from 1.37 to 6.35. After correction, cone index dependence on water content was reduced. A single-equation correction did not always fit the data across all treatments. Separate corrections, based on treatment, might be required. When corrections required multiple equations, differences may be real or may be a manifestation of the correction differences. In this case, the correction may not be feasible (unless some future work can coordinate different equations and assure a uniform correction).

Influence of Pecan Biochar on Physical Properties of a Norfolk Loamy Sand

Because the southeastern US Coastal Plain has high temperatures and abundant rainfall, its sandy soils have poor physical characteristics and low carbon (C) contents. To increase soil C, we added switchgrass (Panicum virgatum) and nonactivated recalcitrant pecan biochar. Biochar was developed by pyrolyzing ground pecan shells at 700 °C. Biochar had 88% C, 0.4% N (C:N ratio, 220:1); 58% of its C resided in polymerized aromatic ring structures. Biochar treatments were 0, 5, 10, or 20 g kg−1 of soil, which was the Ap horizon of a Norfolk loamy sand, a thermic Typic Kandiudult. Switchgrass was ground to a fine powder and added to the biochar treatments at rates of 0 or 10 g kg−1. Treatments were incubated in 750-g columns for 70 days at 10% (wt wt−1) water content. Biochar decreased soil penetration resistance; adding switchgrass also decreased it by the end of the experiment. Biochar and switchgrass affected aggregation, infiltration, and water-holding capacity; but results were mixed. Although the nonactivated biochar (and switchgrass) improved some soil physical characteristics, other biochar formulations may have more of an effect on soil properties.

Biochars impact on soil moisture storage in an Ultisol and two Aridisols

Abstract Biochar additions to soils can improve soil-water storage capability; however, there is sparse information identifying feedstocks and pyrolysis conditions that maximize this improvement. Nine biochars were pyrolyzed from five feedstocks at two temperatures, and their physical and chemical properties were characterized. Biochars were mixed at 2% wt wt−1 into a Norfolk loamy sand (Fine-loamy, kaolinitic, thermic Typic Kandiudult), a Declo silt loam (Coarse-loamy, mixed, superactive, mesic xeric Haplocalcid), or a Warden silt loam (Coarse-silty, mixed, superactive, mesic xeric Haplocambid). Untreated soils served as controls. Soils were laboratory incubated in pots for 127 days and were leached about every 30 days with deionized water. Soil bulk densities were measured before each leaching event. For 6 days thereafter, pot-holding capacities (PHC) for water were determined gravimetrically and were used as a surrogate for soil-moisture contents. Water tension curves were also measured on the biochar-treated and untreated Norfolk soil. Biochar surface area, surface tension, ash, C, and Si contents, in general, increased when produced under higher pyrolytic temperatures (≥500°C). Both switchgrass biochars caused the most significant water PHC improvements in the Norfolk, Declo, and Warden soils compared with the controls. Norfolk soil-water tension results at 5 and 60 kPa corroborated that biochar from switchgrass caused the most significant moisture storage improvements. Significant correlation occurred between the PHC for water with soil bulk densities. In general, biochar amendments enhanced the moisture storage capacity of Ultisols and Aridisols, but the effect varied with feedstock selection and pyrolysis temperature.

Recompaction of a coastal loamy sand after deep tillage as a function of subsequent cumulative rainfall

For many coastal plain soils in the southeastern USA, high soil strength within subsurface horizons requires that deep tillage be performed to provide a suitable rooting environment for row crops such as maize (Zea mays L.), wheat (Triticum aestivum L.), and soybean (Glycine max L. Merr.). We hypothesized that water filtering through the soil was recompacting it and that recompaction could be correlated with cumulative amount of rainfall since tillage. We measured cone indices in a structureless, fine loamy Acrisol near Florence, South Carolina, from 7 days to about 6 years after treatments were deep tilled. Measurements were made to a depth of 0.55 m at the point of maximum disruption of a bent-leg subsoiler (Paratill ® ) that tilled to a depth of 0.35–0.40 m. Regressions of cone indices with cumulative rainfall explained 67–91% of the recompaction and indicated that water filtering through the soil was causing the recompaction. Recompaction was slow, still taking place 6 years after tillage (the end of the experiment) probably because of controlled traffic or excessive disruption by the paratill. Recompaction was also temporarily greater for the 0.1–0.2 m depths when compared with that in the 0.25–0.35 m depths indicating that it was moving down the profile. Recompaction in other climates may be faster or slower depending on their cumulative rainfall relative to an annual amount of 900–1350 mm per year for this study and recompaction for structured soils may be faster or slower depending on whether the structure is stable or not. Though recompaction in this study was slow, tillage may still be necessary annually or seasonally because yield can be reduced even by incomplete recompaction that increases soil strength after a year or less. Published by Elsevier Science B.V.

Influence of biochar on nitrogen fractions in a coastal plain soil.

Interest in the use of biochar from pyrolysis of biomass to sequester C and improve soil productivity has increased; however, variability in physical and chemical characteristics raises concerns about effects on soil processes. Of particular concern is the effect of biochar on soil N dynamics. The effect of biochar on N dynamics was evaluated in a Norfolk loamy sand with and without NHNO. High-temperature (HT) (≥500°C) and low-temperature (LT) (≤400°C) biochars from peanut hull ( L.), pecan shell ( Wangenh. K. Koch), poultry litter (), and switchgrass ( L.) and a fast pyrolysis hardwood biochar (450-600°C) were evaluated. Changes in inorganic, mineralizable, resistant, and recalcitrant N fractions were determined after a 127-d incubation that included four leaching events. After 127 d, little evidence of increased inorganic N retention was found for any biochar treatments. The mineralizable N fraction did not increase, indicating that biochar addition did not stimulate microbial biomass. Decreases in the resistant N fraction were associated with the high pH and high ash biochars. Unidentified losses of N were observed with HT pecan shell, HT peanut hull, and HT and LT poultry litter biochars that had high pH and ash contents. Volatilization of N as NH in the presence of these biochars was confirmed in a separate short-term laboratory experiment. The observed responses to different biochars illustrate the need to characterize biochar quality and match it to soil type and land use.

Switchgrass Biochar Affects Two Aridisols

The use of biochar has received growing attention because of its ability to improve the physicochemical properties of highly weathered Ultisols and Oxisols, yet very little research has focused on its effects in Aridisols. We investigated the effect of low or high temperature (250 or 500°C) pyrolyzed switchgrass () biochar on two Aridisols. In a pot study, biochar was added at 2% w/w to a Declo loam (Xeric Haplocalcids) or to a Warden very fine sandy loam (Xeric Haplocambids) and incubated at 15% moisture content (by weight) for 127 d; a control (no biochar) was also included. Soils were leached with 1.2 to 1.3 pore volumes of deionized HO on Days 34, 62, 92, and 127, and cumulative leachate Ca, K, Mg, Na, P, Cu, Fe, Mn, Ni, Zn, NO-N, NO-N, and NH-N concentrations were quantified. On termination of the incubation, soils were destructively sampled for extractable Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Zn, NO-N, and NH-N, total C, inorganic C, organic C, and pH. Compared with 250°C, the 500°C pyrolysis temperature resulted in greater biochar surface area, elevated pH, higher ash content, and minimal total surface charge. For both soils, leachate Ca and Mg decreased with the 250°C switchgrass biochar, likely due to binding by biochars functional group sites. Both biochars caused an increase in leachate K, whereas the 500°C biochar increased leachate P. Both biochars reduced leachate NO-N concentrations compared with the control; however, the 250°C biochar reduced NO-N concentrations to the greatest extent. Easily degradable C, associated with the 250°C biochars structural make-up, likely stimulated microbial growth, which caused NO-N immobilization. Soil-extractable K, P, and NO-N followed a pattern similar to the leachate observations. Total soil C content increases were linked to an increase in organic C from the biochars. Cumulative results suggest that the use of switchgrass biochar prepared at 250°C could improve environmental quality in calcareous soil systems by reducing nutrient leaching potential.

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.

Site-specific modeling of corn yield in the SE coastal plain

Abstract When site-specific agriculture became technologically feasible, existing crop models made computer simulation a natural choice for predicting yield under various combinations of soil, weather, and management. However, modeling for site-specific farming may require both greater accuracy and sensitivity to more parameters than current models allow. The objective of this paper was to evaluate the DSSAT V3.5 corn model, CERES-Maize, for sensitivity to parameters important to site-specific farming. The model was unexpectedly insensitive to inputs for soil type, depth to clay, nitrogen, and plant population, suggesting areas for attention. Although it was appropriately sensitive to rainfall, indicating sensitivity to soil water content is generally correct, there are known problems with the curve number procedure that calculates runoff. The runoff routine needs improvement, and a separate routine may be needed to accommodate within-field redistribution of runoff. The model also responded to maximum air temperature, but since crop temperature varies more than air temperature, perhaps crop temperature should be calculated from air temperature and water stress. Model accuracy issues aside, accommodating spatial inputs and model runs requires enhanced interfaces. These and other suggested enhancements to the model would improve its applicability for site-specific agriculture.

Physical effects of organic matter amendment of a Southeastern US coastal loamy sand.

Abstract We tested 12 organic sources as amendments for E horizon and a mixture of E and Bt horizons of a southeastern coastal loamy sand. Amendments were intended to increase carbon and improve soil physical properties. Amendments included biochar, cellulose, corn (Zea mays L.) stalk, corn starch, cotton (Gossypium hirsutum L.) hull, cotton meal, manure residual, peanut (Arachis hypogaea L.) hull, poultry litter, soybean (Glycine max L. Merr.) plant, wheat (Triticum aestivum L.) straw, and wood shavings. Amendments were added at a rate of ∼1% (wt wt−1) or ∼22 Mg ha−1 organic carbon content to 450 g soil and incubated in a laboratory for 60 days. Cellulose, corn stalk, and corn starch amendments had the most dry-sieved aggregation at 35% versus the control, peanut hull, poultry litter, wood shavings, and biochar, which had the least at 21%. Biochar, wood shavings, and corn starch–amended treatments had the highest penetration resistances at 0.25 to 0.38 MPa above the mean; cellulose and cotton meal had the lowest at 0.24 to 0.32 MPa below the mean. Poultry litter and manure residual–amended treatments needed the least amount of water added to maintain 0.1 (wt wt−1); cellulose, biochar, and soybean plant needed the most. All needed less than the control. Mixing Bt horizon into the E improved most physical properties. All amendments improved some physical properties—more carbon, more aggregation, or reduced soil penetration resistance. Biochar retained 26% of its carbon, more than other amendments that retained 13% to 23%.