Kinetics of Exchangeable and Water-Soluble Ammonium-N in Soil Growing Rice and Amended with Urea and Sesbania aculeata

Investigations were carried out on a sandy loam Typic Ustochrept soi/under lowland rice condition to study the kinetics of exchangeable and water soluble ammonium-N formation as a result of application of urea with or without Sesbania aculeata as greenmanure over a period of 30 days. The urea treatment produced significantly higher NH_4⁺-N throughout the period as compared with the control and the treatments receiving Sesbania alone. In all the treatments involving urea, with or without Sesbania, NH_4⁺-N level started declining from the third day onwards after fertilizer application. NH_4⁺-N supposedly released from Sesbania (as obtained by difference) increased up to seventh day after fertilizer application and then decreased in cases where Sesbania alone was applied. Application of urea along with Sesbania significantly changed the release pattern of NH_4⁺-N from Sesbania over the period. Barring afew exceptions, 40-day-old Sesbania behaved almost similarlyas 60-day-old Sesbania in these regards.