William C. Lindemann

Microbial precipitation of pedogenic calcite

Pedogenic calcite in desert soils has become increasingly important as an indicator of paleoclimate, landscape stability, and landscape age. This study indicates that calcic and petrocalcic horizons in desert soils are not simply the result of inorganic precipitation of calcite. Soil microorganisms were found to be involved in calcite precipitation in a typical desert soil near Las Cruces, New Mexico. Fossilized remains of calcified fungal hyphae and Microcodium structures are abundant in the petrocalcic horizon. Soil bacteria and fungi precipitated calcite when cultured on a Ca-rich medium. In an experiment where soil columns were irrigated with Ca-rich solutions, calcite formed in soils containing soil microorganisms, but no calcite formed in sterile soils. Thus, biomineralization of calcite by soil microorganisms appears to be an important mechanism of unknown magnitude.

Microbial diversity and activity of disturbed soil in the northern Chihuahuan Desert

Abstract The effects of intense grazing, seasonal drought, and fire on soil microbial diversity (substrate utilization) and activity in a northern Chihuahuan Desert grassland were measured in summer 1997, winter 1998, and spring 1998. Intense livestock grazing was initiated in winter 1995, burning occurred in August 1994, and drought stresses were imposed from October 1994 to June 1997. Microbial diversity was inferred from the carbon substrate utilization patterns in both gram (+) and gram (–) Biolog plates. Microbial activity was estimated by the activity of selected enzymes. Neither microbial diversity nor activity was affected by grazing. The interaction of intense grazing and stress sub-treatments only occurred in spring for one set of diversity measurements. The maximum microbial diversity and activity occurred in the winter-drought-stress sub-plots in summer and spring. Burning reduced microbial diversity and most enzyme activities as compared to the control in summer and spring. Microbial diversity was also lower in summer-drought-stress sub-plots than in the control in summer and spring. Microbial diversity was highest in summer, intermediate in winter, and lowest in spring. Microbial activity was generally higher in summer and lower in winter. It was concluded that substrate availability was the most important factor affecting the diversity and activity of soil microorganisms within a season. Soil moisture was not the factor causing differences in microbial diversity and activity among the stress treatments, but it was a predictor for some microbial responses under a particular stress.

Nitrogen mineralization in coal mine spoil and topsoil

SummaryN mineralization was compared in fresh topsoil, stockpiled topsoil, coal-mine spoil, and in various mixtures of soil and mine spoil, with and without sludge amendment. N mineralization was slightly lower in stockpiled topsoil than in fresh topsoil or mine spoil. Differences between stockpiled and fresh topsoil were small and were attributed to changes in the relative proportions of readily degradable versus slowly degradable organic fractions. Sludge amendment increased N mineralization, but straw amendment immobilized N through 12 weeks of incubation. More N was leached from mixtures of mine spoil and soil than from soil or mine spoil alone, but net N mineralization decreased with increasing mine-spoil-to-soil ratios, probably as a result of greater denitrification losses. Mixing mine spoil with soil can increase plant available N more than soil or spoil alone, because spoil contributes mineralizable organic N while soil improves the physical and chemical environment of the mine spoil.

Nitrogen Recovery from 15N-Labeled Green Manures: I. Recovery by Forage Sorghum and Soil One Season After Green Manure Incorporation

ABSTRACT This investigation was part of a project to evaluate green manure forage legumes as relay intercrops for sweet corn (Zea mays L.) and chile (Capsicum annuum L.) in north-central New Mexico. The study was carried out under irrigated conditions in 1994 on a Fruitland sandy loam (coarse-loamy, mixed, calcareous, mesic Typic Torriorthent) to evaluate the 15N recovery by forage sorghum (Sorghum bicolor [L.] Moench) and soil after the incorporation of 15N-labeled alfalfa (Medicago sativa L. ‘Nitro’) or hairy vetch (Vicia villosa Roth. ‘Madison’). Two application rates of alfalfa (2.7 or 4.0 Mg dry matter ha□1) or hairy vetch herbage (3.2 or 6.4 Mg dry matter ha□1), were incorporated into soil microplots. Additional treatments consisting of 56, 112, and 168 kg N ha□1 (as urea) were used to compare soil inorganic N concentrations with those released from the legumes. Nitrogen-15 recovery by sorghum tops was 16% of the 15N applied, in two harvests. Of this, 80% was recovered at the first harvest. In soil, 15N recoveries were 50 and 3% of the input at the 0–0.3 and 0.3–0.6 m depths, respectively. Maximum inorganic N concentrations were found 14 d after amendment application. At the end of the growing season, inorganic N concentrations in all treatments were essentially the same as the background (8 mg N kg□1). The low 15N recoveries by crop plus soil and inorganic N concentrations in soil at the end of the season suggest that about 12% and 35–58% of the N applied as green manure was lost from the system for alfalfa and hairy vetch, respectively.

Plant Uptake of Depleted Uranium from Manure-Amended and Citrate Treated Soil

Six plant species were tested for their ability to accumulate depleted uranium in their aboveground biomass from deployed munitions contaminated soil in New Mexico. In greenhouse experiments, Kochia (Kochia scoparia L. Schrad.) and pigweed (Amaranthus retroflexus L.) were grown with steer manure added at rates of 22.4, 44.8, and 89.6 Mg ha−1. Citric acid and glyphosate (N-(phosphonomethyl) glycine) applied at the end of the growing season increased DU concentrations from 2.5 to 17 times. Leaf and stem DU concentrations in kochia increased from 17.0 to 41.9 mg kg−1 and from 3.5 to 18.0 mg kg−1, respectively. In pigweed, leaf and stem DU concentrations increased from 1.0 to 17.3 and from 1.0 to 4.7 mg kg−1, respectively. Manure generally decreased or had no effect on DU uptake. The effect of citric acid and ammonium citrate on DU uptake by kochia, sunflower (Helianthus annuus L.), and sweet corn (Zea mays L.) was also studied. Ammonium citrate was just as effective in enhancing DU uptake as citric acid. This implies that the citrate ion is more important in DU uptake and translocation than the solubilization of DU through acidification. In both experiments, leaves had higher DU concentrations than stems.

Nitrogen Recovery from 15N-Labeled Green Manures: II. Recovery by Oat and Soil Two Seasons After Green Manure Incorporation

ABSTRACT Forage legumes in crop rotations are often used to supply N for succeeding crops. However, the residual effect of forage legume green manures for second crops has not been thoroughly investigated in high desert regions of the Southwestern United States. The objective of this study was to evaluate the 15N recovery by a second subsequent crop (oat [Avena sativa L.]) and soil from microplots amended with 15N-labeled alfalfa (Medicago sativa L. ‘Nitro’) and hairy vetch (Vicia villosa Roth ‘Madison’). In 1994, two application rates of each legume were incorporated into 1 m2 microplots and forage sorghum (Sorghum bicolor [L.] Moench) was used to evaluate the 15N recovery. Above-ground residues were removed from microplots immediately after each of the two sorghum harvests. In 1995, the 15N recovery by the oat crop and soil was determined. Nitrogen-15 recovery by oat averaged 3% of the 15N applied as green manure. Of this, 95% was found in tops and 5% in roots. Averaged across application rates, oat recovery of 15N was 63% greater in treatments amended with alfalfa than with hairy vetch. Green manures did not affect the total N concentration of oat parts. Most of the residual 15N was found in soil at the 0–0.3 m depth at the end of the oat season. The percent of 15N recovery by soil in plots amended with alfalfa was 238% higher than with hairy vetch. Green manures applied in 1994 had little residual effect on the N nutrition of oat.