DIRECT AND RESIDUAL EFFECTS OF PHOSPHATE ROCK ON SOIL NUTRIENT STATUS AND CROP PRODUCTIVITY IN RICE-RICE CROPPING SEQUENCE

Abstract

Two field experiments were conducted in the same plot in rice-rice cropping sequence during 2005 at sher-e-Bangla Agricultural University farm under Madhupur tract (AEZ-28), to study the direct and residual effects of rock phosphate (PR) as compared to TSP on growth, yield and nutrient uptake of Boro rice (BR-29) as first crop and T.aman (BR-30) as residual crop. The experiments were laid out in a Randomized Complete Block Design (RCBD) with five treatments and four replications of each treatment. The treatments used were Tr control (0 kg P ha'1), T2-PR (35 kg P ha'1), T3-TSP (35 kg P ha1), T4-PR (210 kg P ha'1, applied in the previous crop in 2004) and T5-TSP (17.5 kg P ha'1) + PR (17.5 kg P ha'1). The blanket application of recommended doses of N, P, K, S, and Zn was done in all the treatments. In case the first crop, application of full dose of P (35 kg P ha'1) as TSP (T3) and 1:1 mixture of TSP (17.5 kg P ha'1) and PR (17.5 kg P ha'1) (T5) increased dry matter production at panicle initiation stage, grain and straw yield at the harvest over the control. The highest grain yield (6.8 t ha1) and straw yield (7.47 t ha'1) were obtained in the treatment T5 where a judicious mixture of PR and TSP was used. Application of full does of P as PR and 210 kg P applied in the previous crop had no significant effects on yield of rice. The grain yield due to different treatment ranked in the order of T5 > T3 > T2 > T4 > T|. In general these treatments (T3 and T5) increased effective tiller hill'1, filled grains panicle'1 and N, P, K. and S uptake significantly. In case of residual crop, the treatment T3 and T5 had a significant residual effect regarding grain yield and P uptake. The residual effect of the treatment T5 produced the highest grain yield (4.5 t ha'1). After the harvest of two crops in all P treatments, the soil contained significantly higher amount of organic matter, available sulpher. available P and exchangeable K as compared to the control. The treatments had no significant effect on soil PH and total nitrogen content