Effect of lime or zeolite on N2O and N2 emissions from a pastoral soil treated with urine or nitrate-N fertilizer under field conditions

Abstract

To understand the effect of soil amendments (i.e. lime or zeolite) on nitrous oxide (N2O) and dinitrogen (N2) emissions from pastoral soil, a field experiment was conducted using Topehaehae silt loam soil (Aeric Haplaquent) in a dairy catchment area at Toenepi, Hamilton, New Zealand during late September-November 2003. Field plots were treated with 2 N sources: cow urine or potassium nitrate (KNO3) each applied at 200 kg N ha-1 rate with and without added lime or zeolite (clinoptilonite). The control (no N) plots also received lime or zeolite. Each treatment had 3 replicates. Nitrous oxide and N2 emissions were measured periodically from field plots by taking intact soil cores, followed by incubating them in 1 L gas jars with or without acetylene (C2H2) under field conditions. Soil samples were also taken to determine soil pH and changes in soil ammonium (NH4+) and nitrate (NO3-) concentrations. Total N2O emission was significantly higher from urine treated soils (7622 g N2O-N ha-1) than from KNO3 treated soil (3479 g N2O-N ha-1) probably because of N2O production by both nitrifier-denitrification and denitrification in the former. Zeolite significantly reduced total N2O emissions by 11% from urine treated soils probably because of NH4+ sorption by zeolite; while it had no such effect on N2O emission in KNO3 treated soils. Lime did not have any effect on N2O emission in either urine or KNO3 treated soils. Total N2 emission was significantly higher from urine treated soil (1486 g N2O-N ha-1) than from KNO3 treated soil (795 g N2O-N ha-1). Lime increased N2 emissions by 11%, 6% and 101% in urine, KNO3 treated soils and in the control, respectively; while zeolite had no such effect. N2O:N2 ratios were higher for urine treated soils followed by KNO3 treated soils; while the lowest N2O:N2 ratios were observed in no N treatments. Lime lowered N2O:N2 ratios in urine treated soils and in the control treatment (no N), but had no such effect in KNO3 treated soils. Changes in soil mineral N suggest low soil NH4+ and reduced nitrification with zeolite in urine treated soil, while no such effect was observed in KNO3 treated soils. Lime increased soil pH in all treatments. Lime applied with urine increased both soil NH4+ and NO3- concentrations but no such trend was seen in KNO3 treated soil. The results indicate that zeolite reduced N2O emission while lime increased N2 emissions and lowered N2O:N2 ratios during a short-term field experiment therefore long-term field studies are required to assess zeolite life cycle and its potentials as a mitigating tool for N2O emissions from urine patches in grazed pasture system. © 2009 Elsevier B.V. All rights reserved.