Uptake and leaching of sorbed ammonium during early growth of wheat

Purpose: Sorption could be a way to concentrate nutrients in diluted waste streams to bring more nutrients back to agriculture. The aim of this work was to model the fate of sorbed NH4+ content in liquid waste streams by adding nitrogen (N) sorbed to a sorbent, zeolite, and study its effect on early growth and potential leaching losses. Methods: A pot experiment with two soil types and wheat as test crop was conducted. Mineral N in soil was measured, and a leaching experiment performed. 15N labelled ammonium was sorbed to zeolite. The fertilizer effect was then compared to ammonium fertilizer applied the conventional way, with and without zeolite. Results: Early uptake of sorbed ammonium was reduced by 56% compared to ammonium applied conventionally, and soil uptake compensated only very early. Nitrate concentration in leachates was reduced by 12% in sandy soil when N was applied sorbed to zeolite. However, leaching of water through the profile increased 71% when N was applied sorbed to zeolite, so that there was only a tendency to lower N losses when N was applied sorbed to zeolite. Conclusion: Ammonium-N sorbed to zeolite is less plant available than conventionally applied N but may also be less prone to leaching losses.