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Seasonal Microbial Biomass Dynamics after Addition of Lentil and Wheat Residues
Author(s) -
Bremer E.,
Kessel C.
Publication year - 1992
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1992.03615995005600040022x
Subject(s) - straw , agronomy , decomposer , green manure , loam , growing season , crop residue , manure , biomass (ecology) , residue (chemistry) , microorganism , chemistry , biology , soil water , agriculture , ecosystem , bacteria , ecology , biochemistry , genetics
The dynamics of soil microbial biomass after the addition of plant residues have a considerable influence on nutrient availability for plants, and can be quantified using the chloroform‐fumigation‐extraction method. The dynamics of microbial C and N following addition of 14 C‐ and 15 N‐labeled lentil ( Lens culinaris Medik.) green manure, lentil straw, and wheat ( Triticum aestivum L.) straw were investigated under field conditions at a site located at Outlook, Saskatchewan, on a Bradwell sandy loam (Typic Boroll). Plant residues were incorporated into microplots on 5 Oct. 1988, and the fraction of added 14 C and 15 N in microbial biomass was determined on four dates during the 1989 growing season. Maximum levels of labeled and unlabeled microbial biomass were observed at the time of planting (8 May) in 1989. Of added 14 C, 26 and 15% was in the microbial biomass in the green manure and straw treatments, respectively, on 8 May; greater microbial accumulation of green‐manure 14 C was due to a higher proportion of 14 C being available rather than to a higher efficiency of 14 C assimilation. Microbial 15 N accounted for 65 to 81% of added residue 15 N on 8 May. Plant‐residue 15 N was readily available to decomposer microorganisms from all residue types, whereas 14 C was more available from green manure than straw. During the 1989 growing season, microbial 14 C declined by 51 and 40% in the green manure and straw treatments, respectively, while microbial 15 N declined by 54% in all treatments. The decline in microbial 15 N during the 1989 growing season was approximately five times greater than the amount of 15 N mineralized in all sampling periods except the first for the green‐manure treatment. The highest levels of labeled and unlabeled microbial biomass observed at the time of planting indicates that microbial biomass may reduce losses of N and other nutrients during periods of low crop demand, and may act as a source of nutrients during active crop growth.