Availability to wetland rice of nitrogen from cattle manure.

Mineralization and availability of N from organic manure will be affected by its C-to-N ratio, soil management and climatic conditions. Since only a part of organic N will be mineralized during the growing season of rice, a residual effect of manures is expected in the following crop. The availability of N were compared from cattle manure with urea N to wetland rice. Residual effect was evaluated in a following wheat crop. Soil of the experimental field was a Fatehpur loamy sand (typic Ustip-samment) with pH 8.6, 0.34% organic C, 0.05% total N, and a water percolation rate of 4.5 mm/ha. Treatments were four rates of N (0, 60, 120, and 180 kg/ha) applied through urea and through cattle manure. The experiment was laid out in a randomized complete block design with three replications. The cattle manure contained 1.3% total N, 0.38% total P, and had 26:1 C:N. Cattle manure was incorporated into the soil 1 d before transplanting rice. Urea was applied in three equal splits at 7, 21, and 42 d after transplanting. A basal dose of 13 kg P and 5 kg Zn/ha also was applied to rice. Variety PR106 was transplanted 24 Jun 1986. After harvest, all plots were subdivided to accommodate two levels of P (0 and 26 kg/ha). Wheat was fertilized with a uniform 80 kg N and 25 kg K/ha. Both urea and manure N increased rice grain yield and N uptake significantly. Quadratic response curved were fitted to the rice grain yield and N uptake by considering different proportions of the cattle manure N to be as good as urea N. The regression analysis showed that 45% of the N applied as cattle manure and urea N had effects on grain yield; 40% of N as cattle manure and urea N produced similar effects on N uptake by rice. The lower values for N uptake than for grain yield suggest that cattle manure N was more efficiently translated into rice grain yield than was urea N. Both P and K uptake of rice increased significantly with the application of either urea and cattle manure N. Soil organic C content increased only when cattle manure was applied at high rates.