Effect of Ammonium-Loaded Zeolite Application Rate on Nitrogen Leaching and Plant Nitrogen Uptake in Spring Wheat

Improving nitrogen (N) use efficiency while reducing environmental losses remains a major challenge in crop production. Zeolites, due to their high cation exchange capacity, have been proposed as carriers for ammonium-based fertilizers, potentially modifying N retention and release in soils. However, the effect of varying ammonium-loaded zeolite application rates, while supplying equal amounts of zeolite-derived nitrogen, on soil N dynamics is not well understood. In this study, a greenhouse pot experiment with spring wheat was conducted to investigate the effects of ammonium-loaded zeolite applied at different rates (30, 36, 42 and 48 g pot−1; Zeo30–Zeo48), each supplying 700 mg zeolite-derived N pot−1 in addition to a basal ammonium sulfate application, on N leaching, plant growth and N recovery. Nitrogen leaching was strongly influenced by the amount of zeolite applied. Lower application rates (Zeo30 and Zeo36) resulted in higher nitrate and ammonium leaching losses, particularly during early growth stages, whereas higher application rates (Zeo42 and Zeo48) significantly reduced total N losses. Despite these differences, total aboveground plant N uptake and N recovery (68–71%) did not differ significantly among treatments. However, increasing zeolite application rates tended to improve grain and straw yields and influenced nitrogen partitioning within the plant, as reflected by differences in grain-to-straw N ratios. Residual soil ammonium decreased with increasing zeolite application rate, indicating differences in ammonium retention and release among zeolite treatments. Overall, the results indicate that under the conditions of this greenhouse pot experiment, the amount of zeolite carrier material influenced nitrogen retention patterns and leaching losses. Together, these findings suggest that the effectiveness of ammonium-loaded zeolite depends on the balance between ammonium loading and zeolite mass, although the absence of an equivalent mineral-N control limits the separation of zeolite effects from effects of total N supply.