可溶性有机氮在评价土壤供氮能力中的作用与效果

Effect of Soluble Organic Nitrogen on Evaluating Soil N-Supplying Capacity

【目的】淹水培养法提取态可溶性有机氮在评价土壤供氮能力方面具有重要意义。【方法】通过研究黄土高原物理化学性质差异较大的10种农田土样起始可溶性有机氮(SON)、矿质氮(Nmin)及间歇浸提长期淹水培养期间可溶性有机氮、铵态氮累积量、易矿化和难矿化氮素矿化势(分别ND和NR表示)及其与作物吸氮量的关系,分析SON在评价土壤供氮能力中的作用与效果。【结果】供试土样起始SON平均为23.9mg·kg-1,是起始可溶性总氮的28.8%、全氮的2.4%。淹水培养提取态可溶性氮(TSN)中,SON所占比例更高,几乎与铵态氮相当。经过217d淹水培养,浸提出的SON平均为118.1mg·kg-1,占TSN累积量的46.4%。ND与全氮关系密切:在不包括与包括SON时,二者的相关系数分别为0.92(P<0.01)和0.88(P<0.01)。不同土壤ND和易矿化氮矿化速率(KD)差别很大,干湿砂质新成土和黄土正常新成土的ND小于土垫旱耕人为土。考虑SON后KD值减小,而难矿化氮矿化速率(KR)增加。【结论】淹水培养期间铵态氮累积量是评价可矿化氮的较好指标,不仅适宜于第一季作物,而且也适用于连续两季作物;SON累积量不能单独作为反映可矿化氮的指标,但用ND反映土壤可矿化氮潜势时,包括SON后更加准确;TSN在一定程度上能够反映土壤可矿化氮。铵态氮和TSN累积量及ND在反映两季作物土壤可矿化氮时效果更好,包括SON后TSN及ND在评价土壤供氮持久性时更具意义。

[ Objective ] It is important to study the soluble organic nitrogen （SON） extracting in water-logged incubation for evaluating soil N-supplying capacity. [ Method ] Soil initial SON and mineral nitrogen （Nmi,）, cumulative soluble organic nitrogen and NH4^＋-N in leaching solution during water-logged incubation, mineralization potentials of both decomposable nitrogen （ND） and resistant nitrogen （NR）, and their correlations with crop N-uptake of 10 kinds of farmland soils with different physical and chemical properties on the Loess Plateau were investigated. Effect of SON on evaluating soil N-supplying capacity was studied. [Result] The results showed that mean content of initial SON （23.9 mg.kg-J） of 10 soils was 28.8% of initial total soluble nitrogen （TSN） and 2.4% of total nitrogen （TN）. The percent of cumulative SON in leaching TSNduring incubation was higher than 28.8% and as high as the percent of cumulative NH4^＋-N. After 217 days water-logged incubation, the mean cumulative SON content was 118.1 mg·kg-1, 46.4% of cumulative TSN. NDhad close correlation with TN, the correlation coefficients were 0.92 （P〈0.01, without SON） and 0.88 （P〈 0.01, with SON）, respectively. N mineralization potential（ND） and mineralization rate constant（KD） were different with the soil types. ND of Los-Orthic Entisols and Ust-Sandiic Entisols were lower than that of Eum-Orthrosols. KD decreased and the mineralization rate constant of resistant materials （KR） increased when considering SON. [Conclusion] Cumulative NH4＋^-N is a good evaluating index of soil N-supplying not only for the first season crop, but also for two successive season crops. No is more correct in revealing the potential mineralizable nitrogen when SON was regarded as mineralized N, although cumulative SON alone is not a good index for the potential of mineralizable nitrogen. And cumulative TSN could also be taken as an index for the potential mineralizable nitrogen to some extent. Cumulative NH4＋^-N, TSN and ND are satisfactory indexes for the potential mineralizable nitrogen, especially in estimating the potential mineralizable nitrogen of the soil for two successive season crops. And cumulative TSN and ND in evaluating the permanence of soil N-supply has better effects when SON was included.