EFFICIENCY OF SLOW-RELEASE NITROGEN FERTILIZERS IN RICE (ORYZA-SATIVA) ON PARTIALLY RECLAIMED SODIC VERTISOLS

A field experiment was conducted during the rainy season (kharif) of 1 988 and 1983 on a partially reclaimed sodic clay soil (Vertisol) to as sess the relative efficiency of urea-G (phosphogypsum urea 36.8% N), [ neemcake-coated urea (NCU) 34.5% N], ammonium sulphate (20.6% N) and u rea (46.0% N) at 4 levels (40, 80, 120 and 160 kg/ha) applied in 3 spl its. Urea-G and NCU increased the grain yield significantly over urea and ammonium sulphate. The urea-G recorded highest yields (45.0 and 43 .9 qi ha), followed by NCU (43.1 and 41.3 q/ha) in 1988 and 1989 respe ctively. The grain yield increased significantly with the increasing l evel of N, being the highest at 160 kg N/ha. The soil NH4+-N content a t 22, 33 and 56 days after transplanting (DAT) was low in urea-G and N CU-treated plots than that observed under ammonium sulphate and urea. However, at 70 DAT, the NH4+-N content was higher in urea-G and NCU-tr eated plots than in ammonium sulphate and urea. The soil NO3.-N conten t was higher under urea-G and NCU at latter stages. The soil NH4+-N an d NO3.-N contents increased with the increasing levels of N at all the stages of growth.