Clinoptilolite Zeolite Influence on Inorganic Nitrogen in Silt Loam and Sandy Agricultural Soils

Development of best management practices can help improve inorganic nitrogen (N) availability to plants and reduce nitrate-nitrogen (NO3−N) leaching in soils. This study was conducted to determine the influence of the zeolite mineral clinoptilolite (CL) additions on NO3−N and ammonium-nitrogen (NH4−N) in two common Pacific Northwest soils. The effects of CL application rate (up to 26.9 Mg ha−1) either band applied or mixed with a set rate of N fertilizer on masses of NO3−N and NH4−N in leachate and soil were investigated in a column study using a Portneuf silt loam (coarse-silty mixed mesic Durixerollic Caliciorthid) and a Wolverine sand (Mixed, frigid Xeric Torripsamment). All treatments for each soil received a uniform application of N from urea fertilizer, with fertilizer banded or mixed with CL. In the Portneuf soil, band application of CL and N contained 109% more total inorganic N (NO3−N + NH4−N) in the soil/leachate system compared with mixing. In both soils, CL application rate influenced the quantity of NO3−N and NH4−N in the leachate and soil. Application of CL at rates of 6.7 to 13.4 Mg ha−1 resulted in the conservation of inorganic N in the soils. Band applying CL and N seems to conserve available inorganic N in the soil compared with mixing CL and N possibly because of decreased rates of microbial immobilization, nitrification, and denitrification.