SOIL MICROBIAL-POPULATIONS ANA ACTIVITIES IN REDUCED CHEMICAL INPUT AGROECOSYSTEMS

This study, conducted in the Piedmont of North Carolina, was initiated to determine how reductions in N fertilization and preen-manuring wit h crimson clover (Trifolium incarnatum L. cv. Tibbee) would affect pop ulations and activities of soil microorganisms. Four continuous corn ( Zea mays L.) treatments were used: no-till (receiving herbicides and s oil insecticides) with 0 or 140 kg N ha(-l) as NH4NO3; conventionally tilled, receiving 140 kg N ha(-1), but no pesticides; and conventional ly tilled with a crimson clover preen manure, but no fertilizer or pes ticides. Populations were determined using selective media;for cultura ble bacteria, pram-negative bacteria, fungi, actinomycetes, Bacillus s pp., and Pseudomonas spp. Microbial activities were estimated by enzym e assays for acid and alkaline phosphatase, arylsulfatase, and beta-gl ucosidase. Microbial biomass C was determined by a chloroform fumigati on-extraction procedure and levels of available N were measured after anaerobic incubation Surface soil (0-7.5 cm) from the no-till treatmen t receiving 140 kg N ha(-1) contained significantly more fungi than di d soil from the unfertilized, no-till treatment. Microbial biomass C a nd available N were not affected by N addition, but levels of acid pho sphatase and beta-glucosidase were significantly higher in the fertili zed soil than in the unfertilized soil. Surface soil from a crimson cl over-corn rotation contained sip; nificantly larger populations of Bac illus spp. (260% more), actinomycetes (310% more), and culturable bact eria (120% more) than did soil from the well-fertilized conventionally tilled, no-pesticide treatment. Also, microbial biomass, available N, and levels of alkaline phosphatase, arylsulfatase, and beta-glucosida se were significantly higher in surface soil from the crimson clover t reatment than the nonmanured soil. Although the soil biological proper ties changed significantly during the year, seasonal variations were s imilar across treatments. Microbial numbers and activities were high i n the spring and fall and low during the late summer.