电超滤浸提土壤养分的研究 Ⅱ.表征旱地土壤有效氮的电超滤—吸光量

STUDIES ON THE EXTRACTION OF SOIL NUTRIENTS BY ELECTRO-ULTRAFILTRATION(EUF)Ⅱ.ELECTRO-ULTRAFILTRATION-ABSORBABILITY(EUF-Q)AS A NEW RELIABLE INDEX FOR CHARACTERIZING THE AVAILABLE NITROGEN IN AERATED SOILS

论述了新的表征旱地土壤有效氮的电超滤-吸光量(EUF-Q)概念、原理和计算法;提出了十分简便、快速、灵敏的测定方法;检定了土壤 EUF-Q 值的精密度和准确性。通过4年62份华北旱地土壤的 EUF-Q 值与盆栽冬小麦对氮肥反应的相关研究,表明土壤 EUF-Q 可以很好地表征旱地土壤有效氮的供应水平,远比通常所用的土壤全氮、碱解氮或有机质等化学法指数优越得多。此外还探讨了土壤 EUF-N 中 NO_3-N 和有机 N 的分配以及 EUF-N 的浸提动态。

The EUF-N value seems to be a reliable index for assessing theavailability of soil nitrogen, but its determination procedure is quite complica-te and tedious. This paper proved that there was a close correlation betweenthe absorbance at 210 nm of a soil EUF-extract and the concentration of NO.-Nand organic一N in the extract. Thus the UV absorbance value might characterizethe content of total available nitrogen in upland soils. On account of the absor-bance of EUF一extract at a particular wavelength (A) is directly related to themass of soil sample used (m),the volume of extract diluted (V),and the opti-cal path length (b),we proposed a new concept 'EUF一absorbability' (EUF-Q)to represent the content of EUF-N in soil. The Q and EUF-Q of soil are definedby the formulas, Q=AV/band EUF-Q of soil=AV1000/bm The unit of soil EUF一Q is 'Absorbability unit/kg',q/kg, with the V inliters, b in centimeters, and m in grams. Within a certain range, the values ofEUF一口possess additive property. By the zinc reduction UV spectrojohotome try, we can easily determineEUF-QT,-Qom, and一QNOa to characterize the EUF-total一N,一organic一N, and-NO。一N of soil respectively. This method is very rapid, simple, inexpensive,sensitive and quite precise and accurate. The results of correlation studies showed that the values of EUF一Q fractionsof 62 upland soils collected from Northern China were closely correlated with of 62 upland soils collected from Northern China were closely correlated withthe relative N一uptake of winter wheat in pot experiments carried out over fouryears.Therefore,the EUF-Q method can reliably characterize the dynamic statusof available nitrogen in upland soils. After calibration studies EUF-Q values of In addition, the contribution of EUF-QNo. and-EUF-Qom To soil EUF-Qr,and the availability of soil EUF-Q,fractions to crops were discussed.