| Abstrakt: |
A laboratory incubation study was carried out for 8 weeks at 30°C to assess microbial respiration and nitrogen (N) transformation in a sandy loam, Iwo series (Oxic Tropudalf) amended with both inorganic N and cowdung. The treatments consisted of 3 x 3 factorial combinations of manure and inorganic N. Cowdung rates were 0, 12, 24 tha[SUP-1] and rates of (NH[SUB4])[SUB2]SO[SUB4] were 0, 25, and 50mg N kg[SUP-1] (0, 60, and 120 kg N ha[SUP-1]) in soil. Manure, N and their interactions had significant (P = 0.05) effects on soil microbial respiration and N transformation. While inorganic N alone increased acidity, cowdung increased soil pH and thus ameliorated the acidity produced as a result of nitrification. Microbial respiration increased with the rate of cowdung with and without N addition. While N immobilization was evident at the end of the 2nd week, there was net mineralization at the end of the 8th week of incubation. The increases in inorganic N concentrations between the 2nd and 8th week of incubation were 514 and 551% for the cowdung, and between 107 and 329% for the inorganic N amended treatments, in soil that received inorganic N, N immobilization increased with increase in the rate of cowdung addition. Addition of (NH[SUB4])[SUB2]SO[SUB4] caused priming of indigenous organic nitrogen. Microbial respiration was stimulated by factors of 2.6, 2.8, and 1.7 by cowdung, co-applied cowdung and N, and inorganic N, respectively. Terminal pH and inorganic N concentrations were positively correlated (r = 0.69*; 0.89**) with cumulative CO[SUB2] evolved from the treatments. When cowdung was added, the adverse effects of inorganic N application on soil biological and physico-chemical properties could be attenuated. Increasing the stability of manure C through composting and applying it and inorganic N to opposite sides of the seedling should minimize N immobilization and enhance N uptake. [ABSTRACT FROM AUTHOR] |
