电超滤浸提土壤养分的研究 Ⅰ.石灰性土壤的电超滤特性

STUDIES ON THE EXTRACTION OF SOIL NUTRIENTS BYELECTRO-ULTRAFILTRATION(EUF)Ⅰ.ELECTRO-ULTRAFILTRATION CHARACTERISTICS OF CALCAREOUS SOIL

石灰性土壤的电超滤(EUF)特性主要是浸提时因需控制电流而必须大大降低电压。在一定范围内,降压程度与土壤 CaCO_3%有密切关系。控流限额愈低,电压需成比例地下降,但土壤EUF-值减小不多。电流控制在一定值时,离子的解吸总量亦为定值。控流主要控制了各石灰性土壤解吸/溶解份额特大的 Ca+Mg 量近于定值,对于含量小的其他养分离子则并无多大影响,仍可区辨各土壤间的差别。通过冬小麦盆栽试验和有关化学测试法等方面的相关研究,表明采用国际通用的5g 土样和控电流方法测定 EUF-K 和-P 等有效养分,对于石灰性土壤也是可行的,但其EUF-(Ca+Mg)值则毫无植物营养有效性的意义。土壤 EUF 值只是一种指数,并非真正的解吸离子量。石灰性土壤 EUF-K 值因浸提时降压控流而略低,80℃时5min 内解吸的钾不一定是非交换性钾。由于 Ca-P 和 CaCO_3在高温高电压时浸出较多,故石灰性土壤 EUF-P 和-(Ca+Mg)的80℃值/20℃值之比,与酸性土壤或非石灰性土壤相比要大得多。

The electro-ultrafiltration(EUF)technique might be a promis- ing method for evaluating the status of available nutrients in the soil.When the calcareous soil is used for EUF-extraction,the electric current will be great- ly increased due to the dissolution of CaCO_3 existed in the soil,and then the applied voltage should be depressed to control the current within a certain limit for keeping a given temperature in the soil suspension.The effect of voltage-depression on the determined EUF values in the course of EUF-extra- ction and the feasibility of EUF technique for calcareous soil,are investigated. The voltage should be depressed in proportion as the levels of the contro- lled current,but the amounts of EUF-extractable nutrients are less influen- ced by voltage.For example,if the controlled current in EUF-Ⅱ fraction (10～30 min)is changed from 20 mA to 10 mA,the voltage applied should be depressed from 102 Ⅴ to 44 Ⅴ,while the EUF-P-(0～35 min)value decreases merely 15%,and EUF-K,-Na,and-(Ca+Mg)values decrease only 5-6%. As the controlled current keeps constant,the total amount of cations fil- tered through the semipermeable membrane is also a constant value,in terms of c mol/kg p^+ of soil.The experimental data show that controlling current is mainly to control the desorbed Ca^(2+)Mg^(2+)(the largest share of contribution of desorption or dissolution)at a constant amount for any calcareous soils, but has no great influence on the desorption of other nutrient ions which exist at lower content in the soil.Hence we can't categorize the levels of Ca and Mg among calcareous soils by EUF method,but this can be done for P,K,and other nutrients. The determined EUF value is only an index and not the real amount of EUF desorbed ions,because the total amount of desorbed ions should be inclu- ding the desorbed ions in the soil suspension in central chamber.It seems that EUF-K-(30～35min,80℃)of calcareous soil is not entirely non-exchange- able K,because the EUF-K-(0～35min)value is merely about a half of NH_4OAc- K of soils. Through the correlation studies with pot experiments of winter wheat and relevant chemical soil testings,we have proved that the international traditional EUF practice(current is controlled within 15 mA at 20℃ and 150 mA at 80℃)can be used to determine EUF-P,K-,and other available nutri- ents,but the EUF-(Ca+Mg)value hasn't any significance on availabiliy in plant nutrition for calcareous soils.