Nitrogen leaching and N use efficiency after application of zeolite and the nitrification inhibitor DMPP in a pot experiment with spring wheat

In many intensively used agricultural regions nitrate leaching into the groundwater is a major concern. To elucidate the effects of a nitrification inhibitor (3,4-dimethylpyrazole phosphate = DMPP) and a cation binding mineral (zeolite) on nitrogen leaching, yield and nitrogen uptake of spring wheat a pot experiment was conducted. The experiment was arranged based on a randomized complete block design with 7 treatments and 4 replications: control (without N fertilizer), ammonium sulfate alone, ammonium sulfate + DMPP and ammonium sulfate + zeolite (30, 36, 42 and 48 g pot(-1)). Excess water was applied 25, 50, 75 and 100 days after seeding to provoke leaching. While at the first leaching event nitrate leaching was drastically reduced due to the application of DMPP, ammonium leaching was highest. At later leaching events losses for both mineral N forms was rather low with no significant differences between treatments. Contrary to expectations zeolite applications resulted in higher nitrate leaching losses compared to the AS treatment, however, ammonium losses were lower. Neither residual soil mineral N nor grain yield showed any differences between the N treatments. The significantly highest amount of nitrogen uptake by the above ground plant was observed for the AS + DMPP treatment. Overall the effects of zeolite compared to a pure ammonium sulfate application on total N recovery were rather small. It might be worthwhile to get a better understanding of the ammonium adsorption and desorption processes induced after zeolite application during the early phase of the growing period when plant N uptake is less dominating.