Richard J. Haynes

Bio: Richard J. Haynes is an academic researcher from University of Queensland. The author has contributed to research in topics: Organic matter & Soil organic matter. The author has an hindex of 42, co-authored 98 publications receiving 6535 citations. Previous affiliations of Richard J. Haynes include University of KwaZulu-Natal & Canterbury of New Zealand.

Labile Organic Matter Fractions as Central Components of the Quality of Agricultural Soils: An Overview

Abstract: Total soil organic matter content is a key attribute of soil quality since it has far-reaching effects on soil physical, chemical, and biological properties. However, changes in contents of organic carbon (C) and total nitrogen (N) occur only slowly and do not provide an adequate indication of important short-term changes in soil organic matter quality that may be occurring. Labile organic matter pools can be considered as fine indicators of soil quality that influence soil function in specific ways and that are much more sensitive to changes in soil management practice. Particulate organic matter consists of partially decomposed plant litter, and it acts as a substrate and center for soil microbial activity, a short-term reservoir of nutrients, a food source for soil fauna and loci for formation of water stable macroaggregates. Dissolved (soluble) organic matter consists of organic compounds present in soil solution. This pool acts as a substrate for microbial activity, a primary source of mineralizable N, sulfur (S), and phosphorus (P), and its leaching greatly influences the nutrient and organic matter content and pH of groundwater. Various extractable organic matter fractions have also been suggested to be important, including hot water-extractable and dilute acid-extractable carbohydrates, which are involved in stabilization of soil aggregates, and permanganate-oxidizable C. Measurement of potentially mineralizable C and N represents a bioassay of labile organic matter using the indigenous microbial community to release labile organic fractions of C and N. Mineralizable N is also an important indicator of the capacity of the soil to supply N for crops. It is concluded that individual labile organic matter fractions are sensitive to changes in soil management and have specific effects on soil function. Together they reflect the diverse but central effects that organic matter has on soil properties and processes. (c) 2005 Elsevier Inc.

Effects of irrigation-induced salinity and sodicity on soil microbial activity

Abstract: The effects of irrigation-induced salinity and sodicity on the size and activity of the soil microbial biomass in vertic soils on a Zimbabwean sugar estate were investigated. Furrow-irrigated fields were selected which had a gradient of salinity and sugarcane yield ranging from good cane growth at the upper ends to dead and dying cane at the lower ends. Soils were sampled under dead and dying cane, poor, satisfactory and good cane growth and from adjacent undisturbed sites under native vegetation. Electrical conductivity (EC) and sodium adsorption ratio (SAR) of saturation paste extracts was measured, as well as the exchangeable sodium percentage (ESP). There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of organic C present as microbial biomass C, indices of microbial activity (arginine ammonification and fluorescein diacetate hydrolysis rates) and the activities of the exocellular enzymes beta-glucosidase, alkaline phosphatase and arylsulphatase but the negative relationships with SAR and ESP were best described by linear functions. By contrast, the metabolic quotient increased with increasing salinity and sodicity, exponentially with EC and linearly with SAR and ESP. Potentially mineralizable N, measured by aerobic incubation, was also negatively correlated with EC, SAR and ESP. These results indicate that increasing salinity and sodicity resulted in a progressively smaller, more stressed microbial community which was less metabolically efficient. The exponential relationships with EC demonstrate the highly detrimental effect that small increases in salinity had on the microbial community. It is concluded that agriculture-induced salinity and sodicity not only influences the chemical and physical characteristics of soils but also greatly affects soil microbial and biochemical properties. (C) 2003 Elsevier Science Ltd. All rights reserved.

Amelioration of Al toxicity and P deficiency in acid soils by additions of organic residues: a critical review of the phenomenon and the mechanisms involved

Abstract: High rates of lime and fertilizer-P are characteristically required to obtain high crop yields on highly weathered acid soils. Much of the agriculture in the southern tropical belt, where acid soils predominate, is carried out by resource-poor, semi-subsistence farmers who are unable to purchase large quantities of lime and fertilizer. There are, however, a number of reports that additions of organic residues to acid soils can reduce Al toxicity (thus lowering the lime requirement) and improve P availability. The literature regarding these effects is sparse and disjointed and an integrated overview of the probable mechanisms responsible and their implications is presented and discussed. During decomposition of organic residues, a wide range of organic compounds are released from the residues and/or are synthesized by the decomposer microflora. The two most important groups in relation to Al toxicity and P availability are soluble humic molecules and low molecular weight aliphatic organic acids. Both these groups of substances can complex with phytotoxic monomeric Al in soil solution thus detoxifying it and they can also be adsorbed to Al and Fe oxide surfaces consequently blocking P adsorption sites. During residue decomposition, there is often a transitory increase in soil pH and this induces a decrease in exchangeable and soil solution Al through their precipitation as insoluble hydroxy-Al compounds. It also confers a greater negative charge on oxide surfaces and thus tends to decrease P adsorption. The increase in pH has been attributed to a number of causes including oxidation of organic acid anions present in decomposing residues, ammonification of residue N, specific adsorption of organic molecules produced during decomposition and reduction reactions induced by anaerobiosis. There are also mechanisms specific to either Al detoxification or improved soil P status. For example, regular applications of organic residues will induce a long-term increase in soil organic matter content. Complexation of Al by the newly-formed organic matter will tend to reduce the concentrations of exchangeable and soluble Al present. As organic residues decompose, P is released and this can become adsorbed to oxide surfaces. This will, in turn, reduce the extent of adsorption of subsequently added P thus increasing P availability. The practical implication of the processes discussed is that organic residues could be used as a strategic tool to reduce the rates of lime and fertilizer P required for optimum crop production on acidic, P-fixing soils. Further research is, therefore, warranted to investigate the use of organic residues in the management of acid soils.

Soil organic matter content and quality: effects of fertilizer applications, burning and trash retention on a long-term sugarcane experiment in South Africa

Abstract: The effects of crop residue management and fertilizer applications on soil organic matter (SOM) content and labile soil organic fractions were examined on a long-term (59 years) field trial under sugarcane situated at Mount Edgecombe, South Africa. Treatments at the site included pre-harvest burning with harvest residues removed (Bto), burning with harvest residues left at the soil surface (Bt) and green cane harvesting with retention of a trash blanket (T). Plots are either fertilized annually with N, P and K or unfertilized. Soil organic matter content in the surface 10 cm increased with increasing inputs of crop residues (Bto < Bt < T) and with annual fertilizer applications. There were no significant treatment effects on organic C or total N content below 10 cm but for microbial biomass C and N. readily mineralizable C and N, K2SO4-extractable and light fraction C. treatment effects were evident in the 10-20 and 20-30 cm layers. Changes in soil N content were more marked than those for organic C and, as a result, the C-to-N ratios of total SOM, the readily mineralizable fraction and the microbial biomass were all decreased by both increasing crop residue returns and fertilizer additions. By contrast. both crop residue and fertilizer inputs increased the microbial quotient since microbial biomass C was increased to a greater extent than total soil organic C. The results demonstrate that greater inputs of organic matter due to either increased returns of above-ground crop residues or increased deposition due to higher yields (induced by annual fertilizer applications) cause a proportionately greater increase in the size of labile pools of organic matter than in the total organic matter content. (C) 2002 Elsevier Science Ltd. All rights reserved.

Soil enzymes: Kuprevich, V. F. & Shcherbakova, T. A.: Translated from the Russian edition (1966), published by the Indian National Scientific Documentation Centre, New Delhi 1971. 392 pp., offset printing from type script, paper cover. Obtainable from U.S. Department of Commerce, National Technical Information Service, Springfield, Va. 22151

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