ABSTRACT Nutrient status of plant affects root exudates of plant. Little is known about effect of potassium status on root exudation. Objective of this study was to identify metabolites in rhizosphere soil of soybean under different potassium conditions. Two soybean cultivars (Satonohohoemi (SAT) and Tachinagaha (TAC)) were grown in soil culture under low (K0, without potassium fertilizer) and normal (K2, 0.42 g K kg−1) soil potassium status. Soil solutions were collected at 15 and 25 DAS. Metabolites in soil solution were detected by CE-TOF MS. Low potassium tolerance was higher in SAT than TAC. Shoot and root K concentration in SAT was lower in K0 than that in K2. Forty-seven metabolites were detected in rhizosphere soil solution of SAT, TAC and without plant. Low K condition increased 6 and 3 metabolites concentration in soil solution without plant and 2 and 4 metabolites concentration with SAT and 2 and 1 metabolites concentration with TAC, at 15 and 25 DAS, respectively. Low K condition decreased 1 and 1 metabolites concentration in soil solution without plant and 6 and 6 metabolites concentration with SAT and 0 and 2 metabolites concentration with TAC, at 15 and 25 DAS, respectively. Increased and decreased metabolites were different between SAT and TAC. These results suggest that K status affect metabolites in root exudate and rhizosphere microbes of soybean and there is cultivar difference in these metabolites.

ABSTRACT To investigate the interactive effects of parent material and topography as soil forming factors, we examined the distribution of soil materials in an alluvial plain, where two types of surface geology were situated upstream and different parent materials supplied accordingly. We hypothesized that these two types of parent material make it possible to trace alluvial processes by analyzing their spatial distribution based on soil physicochemical properties. We collected 101 soil samples from the alluvial plain and nine soil samples from two types of unmixed upstream areas, i.e., granite and mélange. Particle size distributions and total concentrations of 32 elements were analyzed for spatial variabilities. Elemental composition of unmixed upstream samples and isarithmic maps of elemental composition of the soils in the alluvial plain based on geostatistical analysis revealed that gravel, coarse sand and total Na, Al, K, Ca, and Mn concentrations were higher at the southern part close to granite rock areas, whereas silt+clay content and total C, N, Mg, Ti, and Fe concentrations were higher at the northern part close to the mélange area, suggesting strong influence from parent material. In contrast, fine sand content and total P and Si concentrations showed west-east trends, suggesting topography effects reflecting particle size selection. Directional semivariograms suggest coarse sand and silt+clay content, as well as total C, N, Na, Mg, Al, K, Ca, Ti, and Mn concentrations were more strongly affected by parent material, whereas gravel and fine sand and total P concentration were more strongly affected by topography. Accordingly, the combination of elemental composition analysis and geostatistics revealed that the contribution of parent material and topography to total elemental contents in paddy surface soils in the alluvial plain varied among elements. In conclusion, evaluation of the interactive effects of parent material and topography on spatial variability of soil material characteristics enabled better understanding of soil formation processes and their potential fertility.

ABSTRACT Lupinus albus L. (lupin) has a high tolerance for phosphorus deficient conditions as its roots can solubilize the unavailable phosphorus in the rhizosphere soil. The roots may also be able to solubilize other elements, but this requires further investigation. In this study, therefore, we conducted two experiments to comprehensively investigate the effects of lupin roots on the mineral dynamics of the rhizosphere soil. First, a mixed cropping experiment was conducted, in which lupin shared a rhizosphere with soybean (Glycine max (L.) Merr.) in a long-term experimental field with four fertilizer treatments: complete fertilization (+NPK), without nitrogen (−N), without phosphorus (−P), and without potassium (−K). The results of shoot dry weight of plants cultivated alone indicated that lupin is highly tolerant to all N, P, and K deficiencies, while soybean can adapt to N deficiency with the help of rhizobia but is less tolerant to P and K deficiencies than lupin. When mixed-cropped with lupin, the concentrations of many elements in the soybean leaf increased, particularly with the −N and −P treatments. Furthermore, soybean growth was significantly improved when cropped with lupin in the −N and −P treatments. Second, a comparison of the elemental profiles of hydroponically and field-soil-grown plants was conducted. Under hydroponic conditions, the rhizosphere effect is negligible when the culture medium is well circulated. The lupin/soybean ratios for leaf mineral concentrations were considerably larger in the field cultivated plants when compared with the hydroponic cultivations for elements such as sodium, potassium, cesium, phosphorus, iron, copper, and molybdenum, as there were lower concentrations of these elements in the soybean leaves in the field. These results indicate that lupin roots can solubilize a variety of insoluble elements in the soil, which may be the reason why lupin can adapt to various nutrient deficient soils. In the lupin rhizosphere, the solubilization of cesium, which is generally strongly fixed by soil minerals and not easily leached, was particularly pronounced. This implies that the surface structure of clay minerals might be altered in the lupin rhizosphere, resulting in the fixed forms of various elements becoming available.

Abstract The degradation rate of the fungicide chlorothalonil, 2,4,5,6-tetrachloroisoph-thalonitrile, applied at 40 mg kg−1 dry weight of soil was compared among four soils subjected to different types of fertilizer application: unfertilized soil (NF-soil), soil amended with chemical fertilizers (CF-soil), soil amended with the chemical fertilizers and 40 t ha−1 y−1 of farmyard manure (CF+FYM-soil), and soil amended with 400 t ha−1 y−1 of farmyard manure (FYM-soil). Degradation mainly due to microbial activity was faster in the CF+FYM- and FYM-soils than in the non-FYM soils. The microorganisms required other carbon sources for chlorothalonil degradation. The most probable number of chlorothalonil-degrading microorganisms was not significantly different among the four soil treatments. Accelerated degradation was observed in the autoclaved CF+ FYM-soil inoculated with 5% of intact CF-soil but not in the autoclaved CF-soil inoculated with 5% of CF+FYM-soiL Degradation of chlorothalonil increased in the CF- and CF+FYM-soils by adjustment of the soil pH to a neutral value, although the most probable number of degrading microorganisms remained constant. In conclusion, amendment of soil with farmyard manure enhanced microbial degradation of chlorothalonil due to the increase in the degrading capacity by the maintenance of a near neutral pH value in soil and not due to the increase in the number of degrading microorganisms.