Deep placement of fertilizer solution in puddled soils - Part 1: Nitrogen losses

Deep placement of fertilizer solution in puddled rice fields has been found to be effective in reducing floodwater and volatilization losses of applie d nitrogen (N). However, the effects of the depth and manner of placement o f N solution to losses has not been determined. Determination of N losses w ould help improve mechanical fertilizer application. Placement depths of 3, 7, 11, and 15 cm, and point versus band placement of N solution were evalu ated using a prototype pressurized injector by measuring the ammonium-nitro gen concentration in floodwater and determining the partial pressure of amm onia as the relative indicators of runoff and volatilization losses, respec tively. Results showed high lasses of N at shallower point placement (3 and 7 cm particularly) as the high pressure of injection aided in the diffusio n of N towards the soil surface and high losses with placement holes furthe r exposed to water Deeper point injection at 11 and 15 cm depth resulted in less loss of N, with placement above the hard pan having the least loss wi th depth. Band injection at 7 cm seems to be better in keeping the injected N from the water (with the skid and covered furrows) than point placement at the same depth. However, improvements in the design and performance of t he injection device are necessary to make deep placement more effective and practical.