抑制剂NBPT/DCD不同组合对灌区碱性灌淤土中氨挥发及有效氮积累量的影响

脲酶抑制剂N-丁基硫代磷酰三胺(NBPT)和硝化抑制剂双氰胺(DCD)对抑制尿素土壤氨挥发损失和提高土壤有效氮积累量有很大潜力,但2种抑制剂配合施用对灌区强碱性灌淤土尿素施用后氨挥发损失和有效氮积累量的抑制作用尚不明确。为此,选取灌区碱性灌淤土为研究对象开展室内试验,设置NBPT与不同浓度DCD组合下的6个处理,对照为单施尿素,研究NBPT及其与不同浓度DCD组合下的尿素土壤氨挥发和有效氮积累量的变化特征及作用效果。结果表明,在没有添加抑制剂的碱性灌淤土中,尿素施用后短期内(3 d左右)土壤氨挥发速率和NH+4-N积累量达最大值;在施肥后第8 d土壤氨挥发总量和NO-3-N积累量达最大值;添加抑制剂NBPT/DCD可显著降低施肥初期(5 d内)氨挥发速率,且有效减少施肥初期累积氨挥发量;单独添加相当于尿素氮量0.1%的NBPT,累积氨挥发量较CK降低了64%,施肥初期土壤NH+4-N和NO-3-N积累量显著低于CK。NBPT和DCD组合研究结果表明,在NBPT添加浓度为尿素氮量的0.1%,DCD为1%的低浓度水平下,土壤累积氨挥发量较CK降低了16.7%,同时土壤NH+4-N积累量增加趋势缓慢,但硝化抑制率在施肥的第5 d后快速下降,土壤NO-3-N积累量快速增加,氮素淋溶损失的风险加大;随着DCD添加浓度增加(2%~5%),其硝化抑制率显著增加,土壤NO-3-N积累量显著降低,但氨挥发损失量显著增大;相关性分析得出,土壤氨挥发速率与NH+4-N积累量呈正相关,与NO-3-N积累量呈负相关。综合分析得出,0.1%NBPT配施2%~3%的DCD时,土壤氨挥发损失量相对较低,土壤有效态氮积累量较高,且在土壤中滞留时间相对较长,可推荐为灌区碱性灌淤土尿素氮肥与2种抑制剂配施的最佳组合。

Effects of Different NBPT/DCD Combinations on Ammonia Volatilization and Available-N in Alkaline Anthropogenic-alluvial Soil in Irrigated Area

Urease inhibitor, N-(n-butyl)thiophosphorictriamide(NBPT), has potential to reduce urea nitrogen losses via ammonia volatilization(AV), while nitrification inhibitor, dicyandiamide(DCD), could reduce nitrogen loss through leaching, both increasing available-N in soils. A laboratory experiment was conducted to study AV loss and ammonium-N(NH₄⁺-N) and nitrate-N(NO₃^--N) accumulations in alkaline anthropogenic-alluvial soil under different ratios of two inhibitors(NBPT/DCD). Six different rate combinations of NBPT/DCD and CK(without inhibitor) were employed. Results showed that AV rates and NH₄⁺-N accumulation were relatively high in the first a few days after fertilizer application, compared with CK. Addition of NBPT alone at 0.1% reduced AV by 64%. Soil NO₃^--N and NH₄⁺-N accumulations were significantly lower in NBPT treatments than CK during 5 days after urea application. However, such inhibiting effect of NBPT lasted only about 8 days. Combined applications of NBPT and DCD significantly reduced AV loss and NH₄⁺-N accumulation in soil while increased NO₃^--N accumulation in soil. Compared with CK, applying 0.1% NBPT and 1% DCD reduced AV loss by 16.7%, and NH₄⁺-N accumulation in soil slowed down while NO₃^--N accumulation in soil increased after 5 days of fertilization. At 0.1% NBPT, increasing DCD from 2% to 5% decreased soil NO₃^--N concentrations while gradually increased soil NH₃ volatilization. These findings suggest that optimized combined application of inhibitors would be 2%~3% DCD and 0.1%NBPT for reducing nitrogen loss via AV and maintaining higher available-N in alkaline anthropogenic-alluvial soil in irrigated area.