Soil Microbial Populations and Activities under Conventional and Organic Management

Abstract

Evaluation of microbial populations and activities, and their relationship to N cycling in soils under organic and conventional farm management was conducted in eastern Nebraska in 1981 and 1982, on an experiment initiated in 1975. The experimental treatments consisted of 3 × 4 factorial with three management systems (organic, fertilizer only, and fertilizer plus herbicide) for a 4‐yr grain/legume crop rotation plus one treatment of continuous corn (Zea mays L.) receiving fertilizer, herbicide, and insecticide (including one subplot without insecticide). Soil physical, chemical, and microbiological characterizations were made at soil depth intervals of 0 to 7.5, 7.5 to 15, and 15 to 30 cm. Soil chemical properties were significantly influenced by chemical management, primarily the application of beef (Bos taurus) feedlot manure in the organic management system. Total organic C, Kjeldahl N, and potentially mineralizable N in manure‐amended surface soils (0–7.5 cm) were 22 to 40% greater than nonmanured soils receiving fertilizer and/or herbicide. Soluble P levels were eightfold greater in manure‐amended surface soils, and soil nitrate levels after harvest in 1981 were two‐ to threefold greater to a depth of 30 cm than nonmanured chemical treatments. Soil microbial biomass, bacterial and fungal counts, dehydrogenase activity, and CO2 evolution were greater in soils planted to oat/clover (Avena sativa L./Trifolium pratense L. + Melilotus officinalis Lam.) and treatments receiving manure. Increases in microbial populations and their activities paralleled increases in soil organic C content, Kjeldahl N, and water‐filled pore space. Differences in N2 fixation and denitrification between crops and management systems were minimal—possibly resulting from suboptimal water availability at midseason sampling. No significant differences were found in measured soil physical, chemical, or biological properties due to herbicide or insecticide at field application rates.

Agricultural Management and Labile Carbon Additions Affect Soil Microbial Community Structure and Interact with Carbon and Nitrogen Cycling

“…In contrast, organic management practices, particularly crop rotations including legumes and cover cropping, can produce a more tightly coupled cycle of C and N and reduce N losses [5]. However, how soil microbial communities, agricultural management, and soil processes, such as decomposition and N mineralization, influence each other are not yet well understood [6][7][8].…”

“…Organic management practices using diverse rotations and additions of organic residues affect microbial community structure over the long term through buildup of soil organic matter (SOM) and changes in SOM chemistry [6,7,[12][13][14]. In addition, greater crop diversity alters plant litter inputs and can presumably increase the number of ecological niches available for soil microbes [7,11].…”

Microbial Community Structure of Paddy Soil Under Long-term Fertilizer Treatment Using Phospholipid Fatty Acid (PLFA) Analysis

“…Therefore, agricultural management practices, particularly inputs of fertilizers, manure, and cover crops, can have large impacts on the size and activity of soil microbial communities (Bolton et al, 1985;Fraser et al, 1988;Powlson et al, 1987). Environmental conditions and perturbations are likely to affect population structures and their functions in soils which may in turn result in a change of overall soil properties (Widmer et al, 2000).…”

Dynamiques paradigmatiques des agricultures écologisées dans les communautés scientifiques internationales

“…L'approche se développe à partir des travaux métro-logiques de la revue Soil Biology & Biochemistry (Jenkinson et Ladd, 1981) avec une forte citation du programme néerlandais sur l'écologie du sol (Kooistra et al, 1989). À la fin des années 1990, l'approche s'étend à d'autres attributs biologiques du sol et à l'évaluation comparée de systèmes (Doran et al, 1987 ;Ferris et al, 1996 ;Fraser et al, 1988 ;Reganold et al, 1993) poursuivant ainsi les travaux fondateurs de Lockeretz.…”