No abstract

A series of short‐term greenhouse experiments and laboratory incubations were conducted to evaluate the effect of macadamia (Macadamia integrifolia Maiden & Betche) nut shell (MNS) charcoal with varying volatile matter (VM) content on soil properties and plant growth in two tropical soils. Lettuce (Lactuca sativa L.) and corn (Zea mays L.) were planted in an Andisol amended with four rates of MNS charcoal (0, 5, 10, and 20% w/w) containing relatively high VM content (225 g kg−1) with and without N fertilizer. Increasing rates of charcoal without N caused a significant decline in both lettuce and corn growth. Corn growth declined significantly with or without N at the two highest charcoal rates. In a third experiment, corn growth also declined significantly in an Ultisol amended with the MNS charcoal (5% w/w) with and without fertilizers. In a fourth experiment, charcoals with high VM (225 g kg−1) showed negative effects on plant growth while the low‐VM (63.0 g kg−1) charcoal supplemented with fertilizer showed a significant positive effect on corn growth. Results from the 2‐wk incubation experiments showed that high‐VM charcoal caused a significant decline in soil NH4+–N and a significant increase in soil respiration compared with the soil amended with low‐VM charcoal and the soil alone. We propose that phenolic compounds and other products in the high‐VM charcoal stimulated microbial growth and immobilization of plant‐available N. Our results demonstrate that VM content appears to be an important property of charcoal that has short‐term effects on soil N transformations and plant growth. Longer incubation experiments and field trials are needed to further elucidate the role of charcoal VM content on soil processes and plant growth.

No abstract

The difference in pH of a soil suspension prepared with 1N KCl and with water was used to determine net charge of colloids with constant potential type surface. The quantity (pHKCl‐pHH2O) called delta pH had a positive, zero, or negative value corresponding to the net surface charge. Negative and positive adsorption of chloride or nitrate ions were measured in soil suspensions with negative and positive delta pH, respectively. Increasing the nitrate ion concentration increased sulfate adsorption in suspensions with negative delta pH values. Negative adsorption of nitrate and chloride ions was measured when sulfate ions were added to a soil colloidal suspension which was initially net positively charged. This supports the present belief that specifically adsorbed anions render a surface more negative by displacing the zero point of charge to lower pH values. This was substantiated by a measured increase in CEC from an initial value of 26 meq/100 g in a phosphated soil. Each millimole of adsorbed phosphate increased CEC by 0.8 meq.

No abstract

The calculation of hydraulic conductivity by a modified Millington‐Quirk method with a matching factor gave conductivity values closely approximating experimentally measured values. The technique requires knowledge of the moisture characteristic and the saturated conductivity. A number of factors that affect the calculated values and improve the computational results were investigated. Calculated conductivity values decreased with an increasing number of pressure classes at low moisture contents. For all soils tested the calculated conductivities were less than the experimental values at the terminal point of the moisture characteristic. This discrepancy was partially corrected by a small change in the Millington‐Quirk equation, by extending the moisture characteristics to higher suction values, and by reducing the number of pressure classes to approximately 10. A matching factor, the ratio of measured over calculated saturated conductivity, was found necessary for obtaining the best fit of calculated and measured data. Two conductivity functions calculated separately from each moisture characteristic forming a hysteresis loop, converged as the hysteresis loop was translated to higher tensions. All computations were done by computer.

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small-scale and short-term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long-term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field-scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm-scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM-ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country.

Soil properties are usually sampled on some grid or pattern which presumes to represent the unsampled neighborhood. Spatial dependence is a measure of the extent a soil sample represents the unsampled neighborhood. Geostatistics provides procedures to measure spatial dependence. Eighty pedons (Andepts) on the Island of Hawaii were sampled and spatial dependence was measured with semi‐variograms. Areas of soil with similar properties (zones of influence) were delineated by the “range” of the semi‐variogram. Areas of similarity were much greater for soil properties of the 0‐ to 15‐cm depth than of the 30‐ to 45‐cm depth. The ranges of the semi‐variograms for soil pH, Ca, Mg, K, Si, and P sorbed at 0.02 mg P/L were 32 to 42 km while the range of the variogram of rainfall had a similar value of 32 km. Semi‐variograms for Ca, Mg, K, and P based on 30 to 45‐cm‐depth samples demonstrated much greater variability and had smaller zones of influence (Ca, Mg, and K) or were extremely variable (P). Silicon in saturation extract, however, had the same zone of influence in the subsoil as in the topsoil. These results suggest that rainfall has imposed a degree of uniformity on the surface soil properties not apparent in the subsoil. Subsoil properties were highly variable, as might be expected, resulting from great variation over short distances in age and weathering of volcanic ash. The results suggest that soil chemical properties may be spatially dependent and that the spatial dependence in this example represents the imprint of soil‐forming processes and perhaps management. Zones of influence as delineated by semi‐variograms of soil properties may suggest groupings for soil management or soil classification.