添加尿素和秸秆对三熟制水旱轮作土壤各形态氮素的影响

添加不同外源氮对土壤中不同形态氮素的转化具有十分重要的影响。选取长期耕作土壤,设置对照、添加尿素N 150 kg/hm~2(U150)、添加秸秆(相当于添加N 38 kg/hm~2,Straw)、添加尿素N 150 kg/hm~2+秸秆(相当于添加N188 kg/hm~2,U150+Straw)和添加尿素N 188 kg/hm~2(U188)5个处理进行室内培养试验,研究了添加不同外源氮对土壤铵态氮、硝态氮、可溶性有机氮、微生物生物量氮含量的影响。结果表明,土壤铵态氮随着培养时间的延长表现为先增后减的趋势,添加尿素的两个处理其土壤铵态氮较Straw、U150+Straw处理能够更快地达到峰值;而土壤硝态氮则表现为逐步增加的趋势。添加尿素处理能够显著提高土壤矿质氮的含量,在添加等量氮素的条件下,U188处理矿质氮含量在培养期间始终高于U150+Straw处理;此外,U150+Straw处理矿质氮含量在培养前期均低于U150处理,至培养30天后其含量略高于U150处理。与对照相比,培养结束时添加不同外源氮素处理的土壤矿质氮含量能够提高169.61%~496.75%。对于微生物生物量氮和可溶性有机氮而言,添加不同外源氮素分别在培养10天和30天达到峰值,此后逐渐降低。不同处理而言,添加秸秆+尿素、添加秸秆处理的微生物生物量氮和可溶性有机氮含量在培养前期明显高于仅添加尿素的两个处理,说明添加有机物料氮源主要有益于提高土壤有机态的氮素含量。

Effects of Urea and Straw on Soil Different Nitrogen Forms Under Paddy-Upland Rotation of Triple Cropping System

Adding different nitrogen (N) sources is essential for soil N transformation. In this study, we selected soil under long-term cultivation to conduct the indoor incubation experiment. Five treatments were conducted as control, adding Urea at 150 kg N/hm₂ (U₁₅₀), adding rice straw (equal to adding 38 kg N/hm₂, Straw), adding urea and straw (equal to adding 188 kg N/hm₂, U₁₅₀+Straw), adding urea at 188 kg N/hm₂(U₁₈₈). Our aim was to analyze the effects of adding different N sources on soil ammonium N (NH₄₊), nitrate N (NO_3-), dissolved organic N (DON), and microbial biomass N (MBN). The results showed that soil NH₄₊ increase to peak value and then decrease during the incubation period. Treatments adding with urea reached the peak value more rapidly than the treatments adding with straw. Soil NO_3- content was increase with time. For the total mineral N, the U₁₈₈treatment was higher than that in the U₁₅₀+Straw treatment during the period of incubation. When compared with U150 treatment, soil mineral N content was lower in the U₁₅₀+Straw treatment but was a little higher after 30 days of incubation. Overall, adding urea would increase soil mineral N significantly higher than adding straw, which showed little difference with the control. Compared with control, different N source would increase soil mineral N at the range of 11.21%~302.24%. For the MBN and DON, adding different N source would reach the maximum values at 10 days and 30 days after incubation and then decrease with time, respectively. Treatments with straw and/or straw+urea would yield higher MBN and DON than those treatments with urea only during the prior stage of incubation. The results demonstrated that adding N source of organic material would mainly improve soil organic N.