DECREASING NITROGEN LEACHING FROM SANDY SOIL WITH AMMONIUM-LOADED CLINOPTILOLITE

Nitrogen (N) loss from irrigated cropland, particularly sandy soils, s ignificantly contributes to nitrate (NO3-) levels in surface and groun dwaters, In this study, as a preface to a plant growth study, we compa red N leaching from NH4+-loaded clinoptitolite (A-Cp) and (NH4)(2)SO4 (AS) in two media: a rounded quartz sand and a sandy soil. We hypothes ized that quartz sand or soil amended with A-Cp would leach significan tly less N than these media amended with AS, and that more N would lea ch from smaller A-CD size fractions than front larger A-Cp size fracti ons. Ammonium sulfate, or one of the three A-CI, size fractions, small (<0.25 mm), medium (0.25-2 mm), or large (2-4 mm), was banded at a de pth of 5 cm in leaching columns filled with inert quartz sand at a rat e of 112, 224, or 336 kg N ha(-1). The experiment was repeated with sa ndy soil in greenhouse pots at rates of 112 and 224 kg N ha(-1). The c olumns and Dots were leached for about 40 d with a simulated irrigatio n water. Significantly more N, as NH4+ and NO3-, leached from AS amend ments than any of the A-Cp amendments in both experiments. Results ind icated that the larger the A-Cp size fraction, the slower NH4+ is rele ased from A-Cp. Ammonium-Cp slowly releases N and could significantly minimize N leaching from sandy soils compared to AS.