不同施氮量和灌水水平下毛白杨林地土壤矿质氮动态

Dynamics of Soil Mineral Nitrogen in Populus tomentosa Stand under Different Nitrogen and Water Application Levels

【目的】分析不同施氮量和灌水水平对毛白杨林地土壤矿质氮动态的影响,以提高林地生产力和水氮利用效率,降低氮素损失,为林地长期施氮和灌水水平的合理选择提供理论依据。【方法】通过田间试验探究单次施氮周期内,4种施氮量(N0、N1、N2、N3分别为0、101.6、203.2、304.8 kg·hm^(−2))和3种灌水水平(W1、W2、W3分别表示土壤含水量下限为田间持水量的45%、60%、75%)下土壤矿质氮含量、氨挥发速率和脲酶活性的相关关系。【结果】单次施氮周期内,0~100 cm土层硝态氮平均含量为4.84~29.02 mg·kg^(−1),铵态氮平均含量为3.18~13.22 mg·kg^(−1)。硝态氮和铵态氮含量均随土层加深先增大后降低,随时间推移先增大后降低,分别于施氮后第7天和第3天达最大值(26.64~62.34 mg·kg^(−1)和26.61~51.32 mg·kg^(−1))。林地0~100 cm土层硝态氮和铵态氮累积量分别为55.39~331.99 kg·hm^(−2)和31.45~254.21 kg·hm^(−2),土壤矿质氮素主要以硝态氮形式累积,且累积量显著低于农田和果园等,铵态氮含量相对较低且稳定(除表层外)。林地土壤矿质氮含量和累积量与施氮量呈正相关,W3处理更易引起硝态氮向深土层运移。土壤氨挥发总量与施氮量和灌水水平呈显著正相关,且主要发生在施氮后10天内,于施氮后1~2天达到峰值(0.96~3.46 kg·hm^(−2)d^(−1)),单次施氮周期氨挥发损失量为1.57~18.29 kg·hm^(−2),损失率为14.05%~18.97%。土壤脲酶活性受施氮量和灌水水平影响极显著(P<0.01),随施氮量和灌水水平增大而增大,随时间推移先增大后降低,于施氮后第3天达最大值(3.14~4.48 mg·g^(−1))。偏相关分析表明,土壤表层硝态氮含量与铵态氮含量呈显著负相关,铵态氮含量与氨挥发速率呈显著正相关。【结论】不同施氮量和灌水水平显著影响毛白杨林地土壤硝态氮和铵态氮动态、氨挥发特征和脲酶活性。为减少林地氨挥发损失、降低硝态氮淋失风险,建议施氮量为203.2 kg·hm^(−2),土壤含水量控制在田间持水量的60%~75%。

【Objective】This study aims to improve the water and nitrogen(N)use efficiency in fast-growing and high-yield Populus tomentosa stands and to provide a theoretical basis for long-term water and N management.【Method】In a field experiment,four N levels(N0,N1,N2 and N3 represented 0,101.6,203.2 and 304.8 kg·hm^(−2),respectively)with a single application cycle,and three irrigation levels(W1,W2 and W3 represented 45%,60%and 75%of the lower limit of soil water content of field water holding capacity,respectively)were applied.The correlations between soil mineral nitrogen content,ammonia volatilization rate,and urease activity were investigated.【Result】During a single N application cycle,both NO_(3)^(−)-N and NH_(4)^(+)-N contents increased and then decreased with the depth of soil layer,and increased and then decreased with time.They reached the maximum values on the 7th and 3rd day after N application(26.64–62.34 mg·kg^(−1)and 26.61–51.32 mg·kg^(−1)),respectively.The accumulative contents of NO_(3)^(−)-N and NH_(4)^(+)-N from 0 to 100 cm soil layers in the stand was 56.84–104.88 kg·hm^(−2)and 33.53–53.63 kg−1·hm^(−2),respectively.Mineral N in the soil was mainly accumulated in the form of NO_(3)^(−)-N,and the accumulated amount was significantly lower than that in farmland and orchards.The NH_(4)^(+)-N content was relatively low and stable(except for the surface layer).The content and accumulation of soil mineral N were positively correlated with the applied N rates.The W3 treatment was more prone to cause NO_(3)^(−)-N transport to deeper soil layers.Total amount of NH_(3)volatilization was significantly and positively correlated with N and water application levels,and the NH_(3)volatilization mainly occurred within 10 d after N application,reaching a peak(0.96–3.15 kg·hm^(−2)d^(−1))in 1–2 days after N application.The ammonia volatilization loss in a single nitrogen application cycle was 1.57–18.29 kg·hm^(−2),with a loss rate of 14.05%–18.97%.Soil urease activity was significantly(P<0.01)positively correlated with the N and water application levels,and increased and then decreased with the time,reaching the maximum value(3.14–4.48 mg·g^(−1))in 3 days after N application.The partial correlation analysis showed that there was a significantly negative correlation between the NO_(3)^(−)-N content and NH_(4)^(+)-N content in the soil surface layer,and a significant positive correlation between NH_(4)^(+)-N content and NH_(3)volatilization rate.【Conclusion】N and water application levels significantly affect the dynamics of soil NO_(3)^(−)-N,NH_(4)^(+)-N,NH_(3)volatilization characteristics and urease activity in P.tomentosa stand.In order to reduce NH_(3)volatilization loss and NO_(3)^(−)-N leaching risk in forest land,we suggest that N application rate is 203.2 kg·hm^(−2),and the soil water content should be controlled at 60%~75%of the field water holding capacity.