Thomas E. Schumacher

Effect of biochar on chemical properties of acidic soil

The effect of biochar addition on the chemical properties of acidic soil such as soil pH, electrical conductivity (EC), cation exchange capacity (CEC), and exchangeable acidity were investigated to determine the liming potential of biochars. This study was conducted by incubating acidic soil (clayey, smectitic, acid, mesic, shallow, Aridic Ustorthent) of pH < 4.80 with biochars for 165 days. The biochars were produced from two biomass feedstocks such as corn stover (Zea mays L.) and switchgrass (Panicum virgatum L.) using microwave pyrolysis (at 650°C). Corn stover biochar, switchgrass biochar, and lime (calcium carbonate) were applied at four rates (0, 52, 104, and 156 Mg ha−1) to acidic soil. Amendment type, application rate, and their interaction had significant effects (p < 0.05) on soil pH, EC, and CEC of acidic soil. Exchangeable acidity was significantly affected by amendment type. Application of corn stover biochar had shown a relatively larger increase in soil pH than switchgrass biochar at all application rates. The ameliorating effect of biochars on chemical properties of acidic soil was consistent with their chemical composition.

Phosphorus effects on root growth and development in two maize genotypes

Soil phosphorus (P) availability is critical for the early growth and development of maize (Zea mays L.). Soil P also affects root morphological and physiological characteristics that are important for P uptake. The objective of this study was to evaluate the effects of P on seedling root growth and development of two maize genotypes differing in root system plasticity. Two maize genotypes, CM37 (high plasticity) and W153R (low plasticity), were selected based on a preliminary study. Maize plants were evaluated at six vegetative stages of development for three soil P treatments (0, 45, and 300 mg kg-1). Seedlings were grown in a controlled environment using a soil with low native P, Maddock sandy loam (sandy, mixed Udorthentic Haploborolls). The addition of P decreased the time to reach a given growth stage and increased the relative growth rate of roots to a greater degree in CM37 than in W153R. The effects of P on shoot dry weight and root surface area during the V4–V6 growth period appeared to be related to the effects of P on development and relative growth rates during the V1–V3 growth period. Evaluation of the time course of phenotypic change is an important consideration when developing adapted genotypes for specific environments.

Molecular characterization of biochars and their influence on microbiological properties of soil.

The tentative connection between the biochar surface chemical properties and their influence on microbially mediated mineralization of C, N, and S with the help of enzymes is not well established. This study was designed to investigate the effect of different biomass conversion processes (microwave pyrolysis, carbon optimized gasification, and fast pyrolysis using electricity) on the composition and surface chemistry of biochar materials produced from corn stover (Zea mays L.), switchgrass (Panicum virgatum L.), and Ponderosa pine wood residue (Pinus ponderosa Lawson and C. Lawson) and determine the effect of biochars on mineralization of C, N, and S and associated soil enzymatic activities including esterase (fluorescein diacetate hydrolase, FDA), dehydrogenase (DHA), β-glucosidase (GLU), protease (PROT), and aryl sulfatase (ARSUL) in two different soils collected from footslope (Brookings) and crest (Maddock) positions of a landscape. Chemical properties of biochar materials produced from different batches of gasification process were fairly consistent. Biochar materials were found to be highly hydrophobic (low H/C values) with high aromaticity, irrespective of biomass feedstock and pyrolytic process. The short term incubation study showed that biochar had negative effects on microbial activity (FDA and DHA) and some enzymes including β-glucosidase and protease.

Combined use of colorimetric and microelectrode methods for evaluating rhizosphere pH

Plant control of rhizosphere pH is important for nutrient mobilization and uptake, and also affects microbial activity and pathogens in the vicinity of the root. Limited information is available on the ability of plant species and genotypes within a species to induce pH changes in the rhizosphere. A growth chamber study was conducted to characterize patterns of pH change within the rhizosphere of selected genotypes in an alkaline environment with a balanced nutrient supply. After germination in incubators, seedlings of 32 genotypes of maize (Zea mays L.), soybean (Glycine max. L.), sorghum (Sorghum bicolor L.), sordan [sorghum (Sorghum bicolor L.), sudangrass (Sorghum sudanese L.) hybrid], wheat (Triticum aestivum L.), oats (Avena sativa L.), and barley (Hordeum vulgare L.) were transferred into aseptic agar medium (pH 7.6) with bromocresol purple indicator. Ability of the embedded roots to induce rhizosphere pH change was followed by photographing the color change of the bromocresol purple indicator. The pH for selected genotypes at different root zones (maturation, elongation, meristematic) was also monitored by a microelectrode at 1-, 2-, 3- and 4-mm distances from the root surface. Rhizosphere acidification for selected genotypes within a species were in the order: soybean, Hawkeye>PI-54169; maize, Pioneer-3737>Pioneer-3732>CM-37; sordan, S-757>S-333; sorghum, SC-33-8-9EY≃SC-118-15E; barley, Bowman>Primus II; oats, Hytest>SD-84104. The pH patterns within the root system varied from species to species. The highest amount of acidification was found at the elongation and meristematic zones for soybean, while the highest amount of acidification was found at the maturation zone for barley under the same experimental conditions. The agar method allowed the determination of a genotypes capability to induce rhizosphere pH changes while the microelectrode method is necessary for quantifying the spatial variation of specific root developmental zones with high resolution.

Wettability of soil aggregates from cultivated and uncultivated Ustolls and Usterts

Soil organic matter can modify the interaction of clay minerals with water, limiting the rate of water intake of swelling clays and stabilising soil aggregates. Soil structural stability and organic C content usually decrease with cultivation. Faster wetting increases stresses on aggregates and decreases stability. Aggregate wettabilities of prairie soils under 3 different management systems (grassland, no-till, and conventional-till) were compared in the Northern Great Plains of the USA. Six Ustolls and 2 Usterts were selected as replications along the Missouri River. Wettability was measured as water drop penetration time (WDPT) and as rate of water intake under 30 and 300 mm tension. At low tension, aggregates from both cultivated fields and uncultivated grasslands showed similar wettability. Water intake in grass aggregates was attributed to a greater amount of stable pores relative to cultivated aggregates. In cultivated aggregates, slaking created planes of failure that allowed rapid water entry. Differences of wettability between management systems at 300 mm tension (in Ustolls, grasslands had greater wettability than cultivated soils, 0.24 v. 0.17 g water/h.g dry soil) and between soil orders (Usterts had longer WDPT than Ustolls, 2.9 v. 1.7 s) were explained by both clay and organic C contents. Simple measurements of aggregate wettability may be effectively used for soil quality characterisation. Aggregate wettability is a desirable property for agricultural soils when it is related to stable porosity, as may be found in high organic matter soils (e.g. grasslands). Wettability is excessive when fast aggregate wetting results in aggregate destruction as observed in low organic matter cultivated soils.

Nitrogen fertilizer and landscape position impacts on CO2 and CH4 fluxes from a landscape seeded to switchgrass

This study was conducted to evaluate the impacts of N fertilizer and landscape position on carbon dioxide (CO2) and methane (CH4) fluxes from a US Northern Great Plains landscape seeded to switchgrass (Panicum virgatum L.). The experimental design included three N levels (low, 0 kg N ha−1; medium, 56 kg N ha−1; and high, 112 kg N ha−1) replicated four times. The experiment was repeated at shoulder and footslope positions. Soil CO2 and CH4 fluxes were monitored once every 2 weeks from May 2010 to October 2012. The CO2 fluxes were 40% higher at the footslope than the shoulder landscape position, and CH4 fluxes were similar in both landscape positions. Soil CO2 and CH4 fluxes averaged over the sampling dates were not impacted by N rates. Seasonal variations showed highest CO2 release and CH4 uptake in summer and fall, likely due to warmer and moist soil conditions. Higher CH4 release was observed in winter possibly due to increased anaerobic conditions. However, year to year (2010–2012) variations in soil CO2 and CH4 fluxes were more pronounced than the variations due to the impact of landscape positions and N rates. Drought conditions reported in 2012, with higher annual temperature and lower soil moisture than long‐term average, resulted in higher summer and fall CO2 fluxes (between 1.3 and 3 times) than in 2011 and 2010. These conditions also promoted a net CH4 uptake in 2012 in comparison to 2010 when there was net CH4 release. Results from this study conclude that landscape positions, air temperature, and soil moisture content strongly influenced soil CO2 fluxes, whereas soil moisture impacted the direction of CH4 fluxes (uptake or release). However, a comprehensive life cycle analysis would be appropriate to evaluate environmental impacts associated with switchgrass production under local environmental conditions.

Optimization of Oxygen Parameters for Determination of Carbon and Nitrogen in Biochar Materials

Recently, there has been increased focus on biochar materials due to their ability to sequester carbon for long-term in soil. In the production of biochar or charcoal, plant biomass is heated in a low or no oxygen environment. This process results in a product with unique characteristics. But there is limited research on the standardization of methods for determining total carbon (C) and nitrogen (N) in the biochar materials whose properties vary by feedstock type and pyrolytic conditions. The objective of this study was to determine the oxygen dosing time (OT) and dose (OD) for total organic carbon (TC) and nitrogen (TN) analysis in biochar materials by dry combustion method (using Vario Max CNS analyzer). Central composite rotatable design was used to determine the effect of five levels of oxygen dosing time (OT) and dosing level (OD) on measurement of total carbon and total nitrogen in four types of plant originated biochars. OT and OD level interaction had significant impact on the measurement of TC and TN in all types of biochar materials. Optimum levels of OT and OD were determined as 103 to 110 sec and 180 to 232 ml/min, respectively.

Biomass estimation approach impacts on calculated soil organic carbon maintenance requirements and associated mineralization rate constants.

To reduce atmospheric CO(2) concentrations and provide food for a growing world population, sustainable management practices must be adopted. An important consideration in the development of sustainable practices is the maintenance of soil organic carbon (SOC). Critical assumptions, with unknown errors, are used to calculate SOC maintenance requirements. This study investigated the impact of three approaches for estimating belowground nonharvested carbon (NHC) on SOC maintenance requirements, SOC and nonharvested C mineralization rate constants, and the capacity of the soil to sequester carbon. Common protocols were used to develop databases from eight historical carbon studies. The SOC to CO(2) (k(SOC)) and NHC to SOC (k(NHC)) rate constants were calculated using the model NHC(a)/SOC(i) = k(SOC)/k(NHC) + dSOC/dt(1/k(NHC)SOC(i)), where NHC(a) is the amount of applied NHC, SOC(e) is SOC at the equilibrium point, t = time, and SOC(i) is the initial SOC value. Analysis showed that (i) despite the difficulty in measuring belowground biomass, it is needed to calculate the SOC and NHC mineralization rate constants when using nonisotopic approaches; (ii) decreasing NHC by reducing the relative contribution of roots to NHC reduced the calculated SOC maintenance requirements and the amount of corn stover that could be sustainably harvested; iii) changes in the belowground NHC calculation approach do not result in a consistent impact on calculated rate constants; iv) changes in the belowground NHC calculation approach had a minimal impact on the calculated carbon sequestration potential (k(NHC)NHC)/k(SOC); (v) SOC at the beginning of the experiments was negatively correlated with temperature, while k(SOC) was positively correlated with tillage intensity; and (vi) the k(SOC) and k(NHC) rate constants can be used to directly assess the impact of different management scenarios on carbon turnover.

Rhizosphere soil-water collection by immiscible displacement-centrifugation technique

Progress in determining nutrient availability in the rhizosphere is restricted by a lack of reliable and convenient methods for rhizosphere soil-water collection. A modified centrifugation method with a fluorocarbon (Fluorinert™,FC-70) as an immiscible displacement liquid was developed. Our objectives were to: i) obtain an adequate soil-water volume from a small rhizosphere sample within a reasonable time; ii) collect rhizosphere soil-water at container capacity (≈ 90% of field capacity) to determine soluble soil ions; and iii) evaluate FC-70 as an extractant. The soil used was a Beadle clay loam (fine, montmorillonitic mesic Typic Argiustoll) with low and high levels of CaCO3 (5 and 204g kg-1). Soil samples from the rhizosphere of 30-days-old sordan (sorghum (Sorghum bicolor L.), sudangrass (Sorghum sudanese L.) hybrid seedlings were thin-sectioned at 1-, 2- and 3-mm from the root surface. The extraction parameters (sample size, volume of extractant, relative centrifugal force and centrifugation time) were varied to determine optimal values. We obtained adequate amounts of aqueous solutions from moist soil (≈ 6 g) when mixed with 2 mL of FC-70, packed into a filter unit, and centrifuged for 1 hour at 14,500 × g. The displaced soil-water was analyzed by inductively coupled plasma spectrometry. The modified centrifugation technique with FC-70 offers a reliable, rapid, safe, and contamination-free method for obtaining unaltered soil-water from the rhizosphere, at a moisture content normally found in soil.

Nitrogen Use and Carbon Sequestered by Corn Rotations in the Northern Corn Belt, U.S.

Diversified crop rotation may improve production efficiency, reduce fertilizer nitrogen (N) requirements for corn (Zea mays L.), and increase soil carbon (C) storage. Objectives were to determine effect of rotation and fertilizer N on soil C sequestration and N use. An experiment was started in 1990 on a Barnes clay loam (U.S. soil taxonomy: fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, SD. Tillage systems for corn–soybean (Glycine max [L.] Merr.) rotations were conventional tillage (CS) and ridge tillage (CSr). Rotations under conventional tillage were continuous corn (CC), and a 4-year rotation of corn–soybean–wheat (Triticum aestivum L.) companion-seeded with alfalfa (Medicago sativa L.)–alfalfa hay (CSWA). Additional treatments included plots of perennial warm season, cool season, and mixtures of warm and cool season grasses. N treatments for corn were corn fertilized for a grain yield of 8.5 Mg ha (highN), of 5.3 Mg ha (midN), and with no N fertilizer (noN). Total (1990–2000) corn grain yield was not different among rotations at 80.8 Mg ha under highN. Corn yield differences among rotations increased with decreased fertilizer N. Total (1990–2000) corn yields with noN fertilizer were 69 Mg ha under CSWA, 53 Mg ha under CS, and 35 Mg ha under CC. Total N attributed to rotations (noN treatments) was 0.68 Mg ha under CSWA, 0.61 Mg ha under CS, and 0.28 Mg ha under CC. Plant carbon return depended on rotation and N. In the past 10 years, total C returned from above- ground biomass was 29.8 Mg ha under CC with highN, and 12.8 Mg ha under CSWA with noN. Soil C in the top 15 cm significantly increased (0.7 g kg) with perennial grass cover, remained unchanged under CSr, and decreased (1.7 g kg) under CC, CS, and CSWA. C to N ratio significantly narrowed (–0.75) with CSWA and widened (0.72) under grass. Diversified rotations have potential to increase N use efficiency and reduce fertilizer N input for corn. However, within a corn production system using conventional tillage and producing (averaged across rotation and N treatment) about 6.2-Mg ha corn grain per year, we found no gain in soil C after 10 years regardless of rotation.