Donald D. Kaufman

A biologically based indicator of soil quality

Soil quality indices are attempts to classify soil conditions and to compare these conditions to their historical use. From this information it may be possible to determine which uses of soils are better for the long-range goals of agriculture and society. With many factors involved in the profitable production of safe foodstuffs without significant degradation of the environment and soils, an indicator that represents a broad biological perspective of quality is appropriate. Among a group of biological indicators, the ratio of crop N uptake to mineralized N as determined by microbial respiration plus net mineralized N found over a growing season is an useful indicator of soil quality. An evaluation of the 12-year-old Farming Systems Trial at the Rodale Institute Research Center indicated that soils in plots that had been conventionally managed were of lower quality than soil treated with manure or planted with legume-cash grain crops.

Microbial diversity in the rhizosphere of corn grown under conventional and low-input systems

Abstract Microbial processes within the rhizosphere of crop plants are crucial to agriculture. The relation of soil microbial community diversity to cropping system, yield, and soil quality are unclear at present. The Farming Systems Trial at the Rodale Institute Research Center, Kutztown, PA, is a 15-year study in which a conventional corn-soybean rotation has been compared with low-input systems (i.e. animal manure or legumes as nitrogen sources). The effects of the cropping systems on diversity of fast-growing, aerobic, culturable bacteria and fungi were conducted in 1994 by taking 84 cores in between corn plants in June, July, and August. Rhizosphere bacteria and fungi were extracted, plated, and counted. Approximately 6000 bacteria were identified by fatty acid methyl ester analysis, while 18000 fungi were identified by microscopic examination of spores. Microbial diversity and evenness were calculated using several different methods. Total counts, diversity, and evenness were not significantly different for the three cropping systems. These results suggest that conventional agricultural practices may maintain high indices of microbial diversity in the rhizosphere. The functional significance of this needs to be investigated.

Simazine: Degradation by Soil Microorganisms

A soil fungus, Aspergillus fumigatus Fres., is effective in the degradation of the herbicide 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). The degradation of both ring-and chain-labeled (C14) simazine was observed in an unamended and an amended (sucrose) basal medium. A loss of C14 occurred in all culture solutions containing either ring-or chain-labeled simazine, but the decrease in activity observed was greater with chain-labeled than with ring-labeled simazine. Chromatographic evidence indicates that A. fumigatus may possess a degradation mechanism unlike that which occurs in corn plants.