The properties of clinoptilolite related to cationic exchange and ionic selectivity have motivated us to study its application for agronomic purposes. The high potential of the clinoptilolite has been demonstrated as a vehicle for nitrogen fertilizers, with the aims of decreasing negative impacts on the environment and increasing fertilizer effi ciency. The objective of this study was to evaluate the effects of an exchanged form, clinoptilolite-NH 4 , and an occluded form, clinoptilolite-urea, of nitrogen fertilizer relative to commercial urea on dry matter and the nitrogen uptake effi ciency of Lolium multifl orum under controlled conditions. Lolium multifl orum, sowed in a sandy loam soil, was fertilized with 0, 60, 120, and 180 kg·ha -1 of nitrogen. Yield increased considerably and nitrogen uptake effi ciency was enhanced when clinoptilolite-NH 4 was used, possibly due to its ability to retain and slowly liberate NH 4 + ions. This effect produces time differences in nitrogen disponibility in relation to urea, making the nitrogen available for a longer time for the plant. The clinoptilolite-urea treatments reduced yields signifi cantly in comparison with urea applications only at the lowest dose. In addition, the nitrogen uptake effi ciency was always lower than the other treatments. This behavior is related to the fact that nitrogen liberation dynamics of the occluded form are much slower than for the ionic one.