Dean A. Martens

Plant residue biochemistry regulates soil carbon cycling and carbon sequestration.

Substrate composition is one of the most important factors influencing the decomposition of plant residues in soils. The interaction of organic residue biochemistry with residue decomposition rates, soil aggregation and soil humus composition was determined in a laboratory experiment. Addition of seven diAerent organic residues (2% w/w alfalfa, oat, canola, clover, soybean, corn and prairie grasses) to a Webster soil resulted in a rapid, transient increase in aggregate mean weight diameters (MWD) when incubated for 9 d with residues with low phenolic acid content (alfalfa, canola and clover) and was inversely correlated with soil carbohydrate content Oraˇ0:63). More pronounced improvement in aggregate size was noted upon increased incubation to 84 d with organic residues higher in phenolic acid content (corn, prairie grasses, oat and soybean) and was related to soil phenolic acidOra 0:65U and soil carbohydrate contentOra 0:70). Total plant residue phenolic acid content was related to MWD measured after incubation for 84 d by a quadratic response and plateau functionOra 0:96U and the MWD quadratically increased with an increase in vanillin-vanillic acid concentrations in the plant residuesOra 0:997). Soil organic C after 84 d was related to the MWD Ora 0:82U and the residue’s vanillin-vanillic acid content Ora 0:86), suggesting that C remaining in the soil following decomposition maybe related to the specific phenolic acid content. The results suggest that transient aggregate stability initiated by microbial decomposition of the carbohydrate and amino acid content of the residue, is then strengthened by the interaction with phenolic acids such as vanillin or vanillic acid released by microbial decomposition from residues structural components. Published by Elsevier Science Ltd.

Improved accounting of carbohydrate carbon from plants and soils

Soils have a great potential to accumulate carbon from atmospheric sources, but we possess few quantitative tools to predict and understand the conversion of C from plant sources into stable soil organic matter. Evaluation of present methods used for analyzing the major form of carbon present in plants, carbohydrates, found that development of ‘total carbohydrate’ methods were originally based on colorimetric or gravimetric tests whose accuracy is questionable. Use of ion chromatography found that total carbohydrate extraction and hydrolysis methods based on previously published H2SO4 solublization and hydrolysis techniques released from pure cellulose as little as 0.4% and a maximum of 22% of the glucose equivalents due to a failure to solublize the substrate. Optimum solublization conditions with concentrated H2SO4 (18 M) for 15 – 30 min followed by autoclave hydrolysis (1 – 1.5 M H2SO4) resulted in 82 –97% recovery of purified cellulose – glucose and accounted for a major portion of the plant glucose that was not released by previously published methods. Application of this methodology to soils resulted in additional release of glucose equivalents if the hemicellulose fraction was first extracted with 1.0 M H2SO4 (30 min autoclave digestion). Prolonged hydrolysis times (16 h) recommended by previous methodology resulted in increased formation of carbohydrate degradation products as furan derivatives. Use of improved solublization procedures with autoclave hydrolysis (30 min) accounted for up to 99% of the theoretical carbohydrate content from plant biomass and recovered an additional 2.5 – 3.5 times of soil carbon content as carbohydrate forms while minimizing formation of furan derivatives. q 2002 Elsevier Science Ltd. All rights reserved.

Inhibitory effects of fungicides on hydrolysis of urea and nitrification of urea nitrogen in soil

The influence of 1 and 50 mg active ingredient (AI) kg -1 soil of 17 fungicides on transformations of urea nitrogen in soil was studied by determining the amounts of urea hydrolysed and the amounts of nitrate and nitrite produced when samples of two coarse-textured and two fine-textured soils were incubated aerobically for various times after treatment with urea. When applied at the rate of 1 mg AI kg -1 soil, anilazine, benomyl, captan, chloranil, mancozeb and thiram retarded urea hydrolysis in the two coarse-textured soils and maneb retarded urea hydrolysis in all four of the soils used. Most of the fungicides tested retarded nitrification of urea nitrogen in the two coarse-textured soils when applied at the rate of 1 mg AI kg -1 soil, but only etridiazole markedly retarded nitrification of urea nitrogen in all of the soils used when applied at this rate. When the fungicides were applied at the rate of 50 mg AI kg -1 soil, anilazine, captan, chloranil, fenaminosulf, folpet, maneb, mancozeb and thiram retarded urea hydrolysis in the four soils studied, and all fungicides tested except chloroneb, fenarimol and iprodione retarded nitrification of urea nitrogen in these soils. One-way analysis of variance and correlation analyses indicated that the inhibitory effects of the 17 fungicides tested on nitrification of urea nitrogen in soil increased with decrease in the organic-matter content and increase in the sand content of the soil.

Soil Resources and the Environment

Soil the Earths skin serves many functions. In recent years, scientists and concerned individuals have come to understand that our management of soil resources can have either positive or negative effects on our quality of life. Soil Resources and the Environment provides a very broad-spectrum contextual approach to the many functions of soils, with an emphasis on low external-input sustainable agricultural techniques. Aswathanarayana emphasizes the dynamics of soil processes, provides an overview of how knowledge of soil processes can be put to practical use, and gives a broad overview of the many functions that soil is capable of performing.