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62个表土样品测定表明,农田、草地与林地的全氮含量分别为0.11％,0.14％和0.26％;其δ~(15)N值分别为8.48‰,6.48‰和4.02‰。无论不施氮肥,还是施天然丰度的氮肥或施低丰度~(15)N标记肥,牧草茎叶的δ~(15)N值所发生的变化均反映了施N对它们吸收肥料氮、土壤氮和空气氮的影响。用~(15)N天然丰度法、~(15)N低丰度示踪法与全氮差值法评估了苜蓿共生固氮贡献。比较了三种方法测定％Ndfa值的标准误与变异系数,~(15)N示踪技术优于全氮差值法;少量低丰度~(15)N标记肥的施入降低了茎叶δ~(15)N值测定的变异系数,提高了测定田间苜蓿共生固氮量的精度与准确度。
The determination of 62 topsoil samples showed that the total nitrogen content of farmland, grassland and woodland were 0.11%, 0.14% and 0.26%, respectively. The δ ~ (15) N values were 8.48 ‰, 6.48 ‰ and 4.02 ‰, respectively. The changes of δ ~ (15) N value in the stems and leaves of forage grass, irrespective of not applying nitrogen fertilizer or applying natural abundance nitrogen fertilizer or low abundance ~ (15) N fertilizer fertilizer, all reflect the effects of applying N on their absorption of fertilizer nitrogen , Soil nitrogen and air nitrogen. The contribution of symbiotic nitrogen fixation of Medicago sativa L. was estimated by ~ (15) N natural abundance method, ~ (15) N low abundance tracer method and total nitrogen difference method. The standard error and coefficient of variation of% Ndfa values were compared by three methods. The ~ (15) N tracing technique was superior to the total nitrogen difference method. The application of a small amount of low abundance ~ (15) The variation coefficient of δ ~ (15) N value increased the accuracy and accuracy of determination of symbiotic nitrogen fixation in field.