A new method of assaying microbial biomass in the soil is presented which utilizes separation of a 0.5% NaCl soil extract on the Sephadex SE-C-25 gel. The extract was found to separate into two fractions. The high-molecular fraction correlated with the number of microorganisms determined by the standard plate method

Soil fertility requirements for sweet sorghum [Sorghum bicolor (L.) Moench] as an alcohol fuel crop have not been well defined. The primary objective of this study was to determine the biomass and sugar (% Brix ✕ extracted juice) yield response of sweet sorghum to N-P-K and lime. The study was conducted for 2 years on a Wynnville silt loam (fine-loamy, siliceous, thermic Glossic Fragiudult) soil in the Cumberland Plateau region of northern Alabama. Experimental design was a split-plot with 0 or 8 Mg ha⁻¹ dolomitic limestone and combinations of 0, 45, 90, or 180 kg ha⁻¹ N, 30 or 90 kg ha⁻¹ P, and 40 or 120 kg ha⁻¹ K. Liming significantly increased yields of fresh and dry biomass, grain, and juice sugar extracted from stalks. The lime also greatly reduced exchangeable soil Mn and Al and increased Mg and decreased Mn concentrations of the biomass. Due to the dominant effect of lime and other interactions, biomass and juice sugar yields were not consistently related to applied N, P, or K. In nonlimed soil, biomass and sugar yields decreased with high N in the presence of low P-K, but not with high P or K. This suggests an acidity ✕ P and/or K interaction related to toxicity of soil Mn and/or Al. In the limed soil the maximum dry biomass and sugar yields occurred with 180-90-120 (1981) or 90-90-120 (1982) kg ha⁻¹ N-P-K, however yields from some treatments with lower levels of N, P, or K were often not significantly different at the 0.05 level. Inherent soil acidity and related Mg deficiency must be corrected to obtain maximum response of sweet sorghum to fertilization in Wynnville and associated soils of the Cumberland Plateau region.

Selected microbiological properties of soils receiving different fertilizer management regimes were studied from adjoining wheat farms in the highly productive Palouse region of eastern Washington. Since 1909, the only N input to the soil of Farm Management System 1 has been through leguminous green manure crops consisting most recently of Austrian winter peas (Pisum sativum ssp. arvense L., Poir), plus native soil fertility for N and all other plant nutrients. The soil of Farm Management System 2 received regular applications of anhydrous ammonia, P and S at recommended rates for the last 30 yr. There were no differences in numbers of soil microorganisms as determined by plate counts; however, soil from management system 1 had significantly higher levels of urease, phosphatase and dehydrogenase at all three samplings and significantly higher soil microbial biomass at the first two samplings. The data indicate that management system 1 soil had a larger and more active soil microflora.

Western wheatgrass (Agropyron smithii L.) was grown in a greenhouse study on two Cretaceous coal spoils and a topsoil to describe the short-term behavior of several levels of added ¹⁵N-labeled (NH₄)₂SO₄ (0, 60, 120, and 240 mg N kg⁻¹ soil). Recovery and distribution of fertilizer N was measured at harvest in the soil materials and in the harvested tops, roots, crowns, and rhizomes of the western wheatgrass. Fertilizer N uptake by plants grown in the topsoil increased significantly with increasing fertilizer rate, but a significant increase in aboveground biomass did not occur with the 240 mg N kg⁻¹ treatment. In contrast, aboveground biomass on the two spoils increased significantly with the addition of 60 mg N kg⁻¹, but additional increases in plant biomass with higher fertilizer rates did not occur, and a significant decrease in plant biomass occurred with the 240 mg N kg⁻¹ treatment. Significantly lower water holding capacities and cation exchange capacities resulted in significantly higher NH₄⁺ concentrations in solution in the spoil materials as compared with the topsoil. Thus, suppressed seedling emergence and establishment in the spoil materials was attributed to NH₃ toxicity and/or phytotoxicity due to NO₂⁻ accumulation in the spoil. Substantial fractions of added fertilizer N (65–72%) were immobilized by the plants and into soil organic matter in the topsoil, and only at the highest fertilizer rate did fertilizer N accumulate in mineral form. Under field conditions, this immobilized N should be available for recycling and plant uptake in subsequent years and thus help reestablish a functional N-cycling ecosystem. In comparison, percent recovery of added N decreased in plant biomass and increased in NO₃⁻ form in the two spoils as the rate of fertilizer application increased. Thus, 40 to 50% of added fertilizer N could be susceptible to leaching losses under field conditions.