The bioavailability of potassium (K) depends on its speciation distribution in the soil. Different methods are commonly used to estimate K speciation including traditional single leaching (TSL) and sequential extraction process (SEP). However, K speciation is largely affected by soil pretreatment methods. The effects of both TSL and SEP soil pretreatment methods were evaluated.
Materials and methods
The TSL method classifies K speciation content based on bioavailability, while the SEP classifies the metal speciation based on the effects of environmental conditions. These two methods, together with a modified sequential single leaching (SSL) scheme, were used to evaluate five types of soil including soil without potassium fertilization, soil with long-term K fertilization, alkaline soil, red soil, and forest soil. The soil samples were gathered randomly at depths varying up to 30 cm before being dried in air at room temperature. The samples were then ground and mixed before passing through a sieve (10 mesh or 100 mesh) in order to perform K speciation analysis via the modified SSL technique, the TSL method, and the four schemes of SEP.
Results and discussion
Soil pretreatment influenced K speciation, with higher concentration in soil samples sieved through 100 mesh than through 10 mesh. In alkaline soil, potassium was observed to be associated with carbonate. For the various SEP schemes, K speciation was found to be greatest in the residual fraction, with only 3% observed in the carbonate, exchangeable, metal organic complex, or amorphous hydroxides of Fe or Mn. After following the first two steps of the SEP schemes, the available K was similar to that of the TSL method. Distribution of non-exchangeable K using the TSL method was comparable with the five combined SEP extraction steps which were all affected by environmental conditions.
Conclusions
Pretreatment affected K speciation distribution and total amount of metal in the soil. The 100 mesh sieve was more effective in estimating K soil speciation. The SEP method was acceptable for estimating K speciation, with the Krishnamurti et al. (Analyst 120:659–665, 1995) scheme as a useful appraisal of K bioavailability. Combination analyses using both TSL and SEP methods are useful techniques to enable a better understanding of K speciation transformation in soil.
To evaluate the impact of mass selection on genetic structure in artificially closed populations of the Pacific oyster Crassostrea gigas, we performed mass selection over six generations on two stocks from Japan and Korea and analyzed their temporal genetic variation and structure using 18 microsatellite makers, which were compared with the base populations of the two selected lines and one wild population from China. The average numbers of alleles (Na), mean observed heterozygosities (Ho), and expected heterozygosities (He) varied over generations in the two selected lines (selected lines of Japan, Na = 10.7–14.9, Ho = 0.757–0.846, He = 0.778–0.871; selected lines of Korea, Na = 9.4–17.3, Ho = 0.736–0.865, He = 0.744–0.854). There was no significant reduction in heterozygosity in the two selected lines. However, the average number of alleles per locus was significantly lower in the fifth and sixth generations of the two selected lines compared with that in the base population and wild population (P < 0.05), suggesting that the successive mass selection in closed populations may increase the sensibility of rare alleles to genetic drift. Equalizing the sex ratio of parents and reducing the selection intensity properly with the increase of selective generations is recommended to minimize the deleterious effect of genetic drift and bottleneck caused by successive mass selection. The information obtained in this study is useful for the design of appropriate management strategies for selective breeding of C. gigas. 相似文献