Microbial Immobilization and Mineralization of Nutrients during Different Seasons of the Year

A field incubation study with four treatments and five replications in RED was carried out on the typical red loam soil (Alfisol) of Vellayani, Kerala to determine the extent of nutrient immobilization and mineralization by soil microoranisms under the influence of various treatments like glucose, paddy straw, and fertilizers during the rainy, winter and summer seasons in 1988–89. Representative soil samples were collectedfrom the experimental plots before, immediately after and 21 days after the application of treatments. A portion of the soil samples collected after 21 days of incubation under field condition was subjected to chloro form fumigation, reinoculation, incubation. All the above soil samples were analysed and hence quantified the extent of immobilization by soil microflora and subsequent release through mineralization. The immobilization and mineralization of organic carbon was maximum during rainy season in the glucose treatedplots registering a net assimilation of 18.0 to 23.9% and net mineralization of 14.6 to 17.3% respectively of the total organic carbon content of the soil. Nitrogen also followed the same trend with net immobilization and mineralization of 214.6 kg N ha⁻¹ and 26.2 to 34.0 kg N ha⁻¹, respectively on the fertilizer treated plots during rainy season. The immobilization and mineralization of available phosphorus was highest during summer season with values ranging from 4.0 to 16.5 kg P ha⁻¹ and 3.0 to 12.5 kg P ha⁻¹, respectively in the fertilizer treated plots. In the case of exchangeable potassium, the net immobilization and mineralization was maximum during rainy season in the fertilizer treated plots which comes to nearly 14 to 84 and 10.5 to 44 kg K ha⁻¹, respectively. The rates of mineralization of calcium and magnesium followed a random trend about 2 to 15%, 2 to 12% and 5 to 28% and 3 to 15% ofthe total exchangeable Ca and Mg are immobilized and mineralized, respectively.