陶瓷杯与蒸渗仪测定硝态氮和氨态氮淋溶的比较

土壤硝态氮（NO₃^--N）和氨态氮（NH4+-N）淋溶量测定方法因草本植物和土壤类型不同而异。试验采用陶瓷杯（ceramic suction cups）和蒸渗仪（lysimeters）分别测定草地土壤NO₃^--N和NH4+-N淋溶量。蒸渗仪直径为50 cm和深度为70 cm，土壤类型分别为新西兰Gorge silt loam、Mataura sandy loam和Lismore stony silt loam，重复4次。陶瓷杯水平插入蒸渗仪不锈钢筒，陶瓷杯插孔中心离不锈钢筒底部距离分别为35 cm（上陶瓷杯）和60 cm（下陶瓷杯）。在试验前，喷灌72 h冲洗蒸渗仪土壤溶液，使淋溶液NO₃^--N浓度接近0 mg·L^-1，然后1次性施加250 kg N·hm^-2尿素溶解液，用喷灌系统喷灌蒸渗仪，每周喷灌1次，喷灌系统误差使Gorge、Mataura和Lismore土壤喷灌强度分别为15.0、19.0和18.7 mm·h^-1，1次喷灌持续时间为3 h。在Gorge和Lismore土壤，陶瓷杯和蒸渗仪测定NO₃^--N淋溶量差异显著。在Gorge土壤，上陶瓷杯、下陶瓷杯和蒸渗仪测定NO₃^--N淋溶累计量分别为64、68和54 kg N·hm^-2，测定NH₄⁺-N淋溶累计量分别为0.43、0.49和0.43 kg N·hm^-2；在Mataura土壤，上陶瓷杯、下陶瓷杯和蒸渗仪测定NO₃^--N淋溶累计量分别为57、68和62 kg N·hm^-2，测定NH₄⁺-N淋溶累计量分别为0.51、0.37和0.23 kg N·hm^-2；在Lismore土壤，上陶瓷杯、下陶瓷杯和蒸渗仪测定NO₃^--N淋溶累计量分别为61、103和99 kg N·hm^-2，测定NH₄⁺-N淋溶累计量分别为1.70、2.24和2.04 kg N·hm^-2。在结构发育良好的Gorge和Lismore土壤，陶瓷杯不适合测定NO₃^--N淋溶量，但适合应用于砂土质地和发育不完善Mataura土壤。NH₄⁺-N淋溶累计量占NO₃^--N淋溶累计量的0.37%～2.93%，在测定和计算氮淋溶时，NH₄⁺-N淋溶可以忽略不计。

Comparison of lysimeters and porous ceramic cups for measuring nitrate and ammonium leaching in different soil types

The measurement of nitrate and ammonium leaching varied with plant species and soil types. This study compared 2 methods of measuring nitrate and ammonium leaching （lysimeters versus ceramic suction cups） using 12 soil monolith lysimeters （50 cm diameter and 70 cm deep） containing 4 replicates of 3 contrasting New Zealand soils：Gorge silt loam，Mataura sandy loam （both stone-free soils） and Lismore stony silt loam. The ceramic suction cups were installed at 35 cm （top cups） and 60 cm （bottom cups） depths. Sprinkler irrigation applied on lysimeters to minimize the NO₃^--N content of drainage water close to 0 mg·L-1，before experiments starting. Urea solution was surface applied at 250 kg N·hm^-2，followed by regular weekly irrigation. Due to small variations in irrigation nozzle application rates，the actual 3 hour irrigation totals measured were 45 mm，57 mm and 56 mm for the Gorge，Mataura and Lismore soils，respectively. There were significant differences between the cumulative leaching loss measured in the lysimeter drainage and values estimated from the cups in the Gorge and Lismore soils. The cumulative leaching loss，measured from the top cups，bottom cups and lysimeter drainage，were 64，68 and 54 kg N·hm^-2 of nitrate and 0.43，0.49 and 0.43 kg N·hm^-2 of ammonium，respectively，in the Gorge soil；57，68 and 62 kg N·hm-2 of nitrate and 0.51，0.37 and 0.23 kg N·hm^-2 of ammonium，respectively，in the Mataura soil; and 61，103 and 99 kg N·hm^-2 of nitrate and 1.70，2.24 and 2.04 kg N·hm^-2 of ammonium，respectively，in the Lismore soil. It was concluded that suction cups were inappropriate for the determination of cumulative leaching in the structured Gorge soil and the Lismore soil，but ceramic cups could provide useful data on cumulative leaching in the Mataura sandy loam soil. The cumulative ammonium leaching accounted for 0.37%-2.93% of the cumulative nitrate leaching in different soil types，and ammonium leaching could be neglected in measuring of nitrogen leaching.