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Organic & Integrated Tree Fruit Production

Wednesday, December 19, 2018

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2331. Gupta, V., and Germida, J.J.. 1988. Distribution of microbial biomass and its activity in different soil aggregate size classes as affected by cultivation.. Soil Biol. Biochem. 20:777-786.
Investigated the effects of 69 yr of cultivation on the nature, distribution, and activity of microbial biomass content in different microaggregate size classes of a native and cultivated soil. Microaggregates (<0.25mm) of both soils contained lower organic-C, microbial biomass, enzymes, and respiration compared to macroaggregates. The negative effects of cultivation were more pronounced on macroaggregates. These results suggest that microbial biomass, especially fungi, plays an important role in the formation of macroaggregates and is the labile organic matter that serves as the primary source of C and nutrients released following cultivation.

10436. Haines, P.J. and N.C. Uren. 1990. Effects of conservation tillage farming on soil microbial biomass, organic matter and earthworm populations, in northeastern Victoria.. Austral. J. Expt. Agric. 30:365-371.
Wheat was grown continuously for 7 years with conventional tillage and direct drilling (no-till). There was a significant gradient of organic matter under no-till. In the surface 2.5 cm, biomass C and N, and N mineralization were 35, 30, and 62% greater, respectively, than under conventional tillage. No-till did not significantly increase soil organic C or N. Of the estimated 7.8 t/ha of C added to the soil from crop residues, 4% was retained in the top 7.5 cm at the time of sampling. Microbial biomass varied considerably with season. The biomass of earthworms in the top 10 cm under no-till was more than twice that of conventional tillage, while total worm numbers increased significantly when wheat residue was retained versus burned.

10556. Follett, R.F. and D.S. Schimel. 1989. Effect of tillage practices on microbial biomass dynamics.. Soil Sci. Soc. Amer. J. 53:1091-1096.
Changes in microbial biomass dynamics and N cycling were studied in soils formed under grassland vegetation in western Nebraska, and farmed under wheat-fallow since 1970. Three tillage treatments were compared: no-till, stubble mulch, and moldboard plow. After 16 yr of cultivation, total N in the top 10 cm of soil had decreased to 73, 68, and 50% of native sod for the three tillages, respectively. Soil microbial biomass levels were decreased to 57, 52, and 36% for the respective tillages, compared to grass. CO2 respiration was proportional to microbial biomass, but N mineralization was not. It appeared that C availability for microbial growth declined with increased tillage intensity, which also decreased the soil's ability to immobilize and conserve mineral N.

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