Microbial biomass, S mineralization and S uptake by African millet from soil amended with various composts

Microbial biomass growth, S mineralization after compost amendment (plant s eeding) and S uptake by African millet at d 30, 60 and 120 (first, second, and third cutting, respectively) were monitored in an S-deficient soil amen ded with cattle manure compost (CMC), saw dust compost (SDC) or rice husk c ompost (RHC) at the rate of 20 t ha(-1) in the presence or absence of growi ng African millet. A chemical fertilizer (CF) treatment at the rate of 30 m u g g(-1) soil along with a control (CT) was included for comparison. CMC p roduced a significantly larger microbial biomass-C and -S than SDC or RHC. In the planted soil, during rapid growth of African millet, microbial bioma ss-S decreased more rapidly than in unplanted soil. Both biomass-C and biom ass-S then showed a significant flush particularly at d 60-120 in all the t reatments. CMC, RHC and SDC released 20, 10, and 8 mu g CaCl2 extractable S g(-1) soil, respectively, by d 5. Microbial biomass showed a marked increa se in C-to-S ratio across the treatments which eventually reached 154 in th e unplanted soil and 291 in the planted soil from an initial value of 64. S ubstantial mineralization of soil organic-S in all the treatments was obser ved during the period of greatest plant growth, but not in the absence of p lants. Total S uptake was 37, 81 and 76% lower in the CMC, SDC and RHC amen dment, respectively, than that of CF. CMC improved the S supplying potentia l of the soil, but addition of SDC or RHC (high C-to-S ratio) resulted in s evere S deficiency of plant due to S immobilization in soil. (C) 2000 Elsev ier Science Ltd. All rights reserved.