Abstract
Incubation studies in waterlogged soils were conducted to determine the extent of mineralization of N and P from organic materials and chemical fertilizer, viz., Azolla pinnata R. Brown, Ipomoea sp., Pistia sp., water hyacinth (Eichhornia crassipes Mart Solm), blue-green algae (BGA), farmyard manure (FYM), and urea. Soil samples were analysed at 0, 7, 14, 21, 28, 42, 56, 77, and 100 days after incubation. The results indicated that the maximum amount of N was mineralized during the period between 28 and 42 days of incubation of Azolla and Ipomoea spp and FYM and thereafter declined gradually. However, the highest amount of N was mineralized from Pistia sp., water hyacinth, and BGA between 42 and 56 days of incubation, while in the case of chemical fertilizer (urea) it was during the first two weeks of incubation. Maximum amount of total N (150.5 mg kg-1 of soil) was mineralized when Azolla at 10 t ha-1 was incorporated together with 30 kg of fertilizer N ha-1. Mineralization of P showed an increasing trend until 28 days of incubation, remained static up to 56 days of incubation, and declined thereafter. Urea, when added with Azolla, resulted in the maximum amount of available P at 100 days after incubation. Urea alone registered the lowest amount of P.
