David A. Laird

The Charcoal Vision : A Win-Win-Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality

The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality David A. Laird USDA, ARS, National Soil Tilth Laboratory 2150 Pammel Dr., Ames, IA 50011 (david.laird@ars.usda.gov). Published online 11 January 2008 in Agron J 100:178-181 (2008) DOI: 10.2134/agrojnl2007.0161

Effects of long-term soil acidification due to nitrogen fertilizer inputs in Wisconsin

Agroecosystems are domesticated ecosystems intermediate between natural ecosystems and fabricated ecosystems, and occupy nearly one-third of the land areas of the earth. Chemical perturbations as a result of human activity are particularly likely in agroecosystems because of the intensity of that activity, which include nutrient inputs intended to supplement native nutrient pools and to support greater biomass production and removal. At a long-term fertility trial in South-Central Wisconsin, USA, significant increases in exchangeable acidity were accompanied by decreases in cation exchange capacity (CEC), base saturation, and exchangeable Ca2+ and Mg2+ with application of ammoniacal N fertilizer. Plant analysis shows that a considerable portion of the alkalinity generated by assimilation of N (and to a lesser extent by S) is sequestered in the above-ground plant parts as organic anions and is not returned to the soil if harvested. Elemental analysis of Ca-saturated soil clays indicates an loss of 16% of the CEC of the soil clay and minor increases in Fe and Al. The reversibility of these changes due to prolonged acidification is doubtful if the changes are due to soil weathering.

Layer change influences on the hydration of expandable 2:1 phyllosilicates

The objective of this study was to investigate the influence of layer charge on the hydration of Mg-saturated expandable 2:1 phyllosilicates. Water retained by 12 Mg-saturated clays at 54% relative humidity was quantified gravimetrically. X-ray diffraction and total chemical analysis were used to determine the hydratable surface area (447–759 m2 g−1) and layer charge [0.327–0.754 electrons per formula unit (e f.u.−1)] of each sample. Water retained by the clays increased with both hydratable surface area and layer charge of the clays. However, the increase in H2O content with layer charge occurred only on external surfaces of the clays. This result suggests that the H2O on external surfaces is localized around the cation/charge sites rather than forming multi-layers as was suggested previously. A model is proposed for the hydration of expandable 2:1 phyllosilicates. The model assumes that interlayer volume controls interlayer hydration and that the number of cation/charge sites on external surfaces controls hydration of external surfaces.

Nitrogen fertilizer effects on soil carbon balances in Midwestern U.S. agricultural systems

A single ecosystem dominates the Midwestern United States, occupying 26 million hectares in five states alone: the corn-soybean agroecosystem [Zea mays L.-Glycine max (L.) Merr.]. Nitrogen (N) fertilization could influence the soil carbon (C) balance in this system because the corn phase is fertilized in 97-100% of farms, at an average rate of 135 kg N x ha(-1) x yr(-1). We evaluated the impacts on two major processes that determine the soil C balance, the rates of organic-carbon (OC) inputs and decay, at four levels of N fertilization, 0, 90, 180, and 270 kg/ha, in two long-term experimental sites in Mollisols in Iowa, USA. We compared the corn-soybean system with other experimental cropping systems fertilized with N in the corn phases only: continuous corn for grain; corn-corn-oats (Avena sativa L.)-alfalfa (Medicago sativa L.; corn-oats-alfalfa-alfalfa; and continuous soybean. In all systems, we estimated long-term OC inputs and decay rates over all phases of the rotations, based on long-term yield data, harvest indices (HI), and root:shoot data. For corn, we measured these two ratios in the four N treatments in a single year in each site; for other crops we used published ratios. Total OC inputs were calculated as aboveground plus belowground net primary production (NPP) minus harvested yield. For corn, measured total OC inputs increased with N fertilization (P < 0.05, both sites). Belowground NPP, comprising only 6-22% of total corn NPP, was not significantly influenced by N fertilization. When all phases of the crop rotations were evaluated over the long term, OC decay rates increased concomitantly with OC input rates in several systems. Increases in decay rates with N fertilization apparently offset gains in carbon inputs to the soil in such a way that soil C sequestration was virtually nil in 78% of the systems studied, despite up to 48 years of N additions. The quantity of belowground OC inputs was the best predictor of long-term soil C storage. This indicates that, in these systems, in comparison with increased N-fertilizer additions, selection of crops with high belowground NPP is a more effective management practice for increasing soil C sequestration.

Model for crystalline swelling of 2:1 phyllosilicates

A macroscopic energy balance model for crystalline swelling of 2:1 phyllosilicates is presented. Crystalline swelling for a static system is modeled by a balance among the potential energies of attraction, repulsion and resistance. The potential energy of attraction is due to both the electrostatic interaction between the interlayer cations and the negative surface charge sites and to van der Waals attraction between layers. The potential energy of repulsion is due to the net hydration energy for the interlayer cations, the net hydration energy for the negative surface charge sites and Born repulsion. The potential energy of resistance represents irreversible work needed to overcome the mechanical resistance of the clay water system to both expansion and collapse. The potential energy of resistance is responsible for both hysteresis and the stepwise nature of crystalline swelling.A numerical solution of the crystalline swelling model is presented and shown to yield reasonable estimates of basal spacings for octahedrally charged clays. Measured and predicted basal spacings are directly compared and are in general agreement (r2 = 0.39). Most of the scatter for the measured vs. predicted basal spacing relationship is attributed to inaccuracies of the assumptions used for the numerical solution. The crystalline swelling model readily accounts for the effects of layer charge and nature of the interlayer cations upon crystalline swelling, but does not account for the effect of charge site location upon crystalline swelling.

Nutrient removal as a function of corn stover cutting height and cob harvest.

One-pass harvest equipment has been developed to collect corn (Zea mays L.) grain, stover, and cobs that can be used as bioenergy feedstock. Nutrients removed in these feedstocks have soil fertility implication and affect feedstock quality. The study objectives were to quantify nutrient concentrations and potential removal as a function of cutting height, plant organ, and physiological stage. Plant samples were collected in 10-cm increments at seven diverse geographic locations at two maturities and analyzed for multiple elements. At grain harvest, nutrient concentration averaged 5.5xa0gu2009Nxa0kg−1, 0.5xa0gu2009Pxa0kg−1, and 6.2xa0gu2009Kxa0kg−1 in cobs, 7.5xa0gu2009Nxa0kg−1, 1.2xa0gu2009Pxa0kg−1, and 8.7xa0gu2009Kxa0kg−1 in the above-ear stover fraction, and 6.4xa0gu2009Nxa0kg−1, 1.0xa0gu2009Pxa0kg−1, and 10.7xa0gu2009Kxa0kg−1 in the below-ear stover fraction (stover fractions exclude cobs). The average collective cost to replace N, P, and K was

RELATIONSHIP BETWEEN CATION EXCHANGE SELECTIVITY AND CRYSTALLINE SWELLING IN EXPANDING 2:1 PHYLLOSILICATES

11.66xa0Mg−1 for cobs,

Vertical Distribution of Corn Stover Dry Mass Grown at Several US Locations

17.59xa0Mg−1 for above-ear stover, and

ELECTRICAL CONDUCTIVITY SPECTRA OF SMECTITES AS INFLUENCED BY SATURATING CATION AND HUMIDITY

18.11xa0Mg−1 for below-ear stover. If 3xa0Mgxa0ha−1 of above-ear stover fraction plus 1xa0Mg of cobs are harvested, an average N, P, and K replacement cost was estimated at

Nature of the illitic phase associated with randomly interstratified smectite/illite in soils

64xa0ha−1. Collecting cobs or above-ear stover fraction may provide a higher quality feedstock while removing fewer nutrients compared to whole stover removal. This information will enable producers to balance soil fertility by adjusting fertilizer rates and to sustain soil quality by predicting C removal for different harvest scenarios. It also provides elemental information to the bioenergy industry.