Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China.
Methods
Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl2-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point.
Results
The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg?1 to 21.4 mg kg?1, above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg?1 to 90.2 mg kg?1, above which soil CaCl2-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg?1 to 71.8 mg kg?1 among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content.
Conclusions
The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field. 相似文献
Understanding the influences of environmental variation and anthropogenic disturbance on soil respiration (RS) is critical for accurate prediction of ecosystem C uptake and release. However, surprisingly, little is known about how soil respiration and its components respond to grazing in the context of global climate change (i.e., precipitation or nitrogen deposition increase).
Methods
We conducted a field manipulative grazing experiment with water and nitrogen addition treatments in a meadow grassland on the Songnen Plain, China, and assessed the combined influences of grazing and global change factors on RS, autotrophic respiration (RA), and heterotrophic respiration (RH).
Results
Compared with the control plots, RS, RA and RH all exhibited positive responses to water or nitrogen addition in the wet year, while a similar effect occurred only for RH in the dry year. The responses of RS to precipitation regimes were dominated by both frequency and amount. However, grazing significantly inhibited both soil respiration and its components in all subplots. Further analysis demonstrated that the plant root/shoot ratio, belowground biomass and microbial biomass played dominant roles in shaping these C exchange processes.
Conclusion
These findings suggest that changes in precipitation regimes, nitrogen deposition, and land utilization may significantly alter soil respiration and its component processes by affecting local carbon users (roots and soil microorganism) and carbon substrate supply in meadow steppe grasslands. The future soil carbon sequestration in the studied meadow steppe will be benefited more by the moderate grazing disturbance.
An alkaliphilic, moderately halophilic, bacterium, designated strain X10-1T, was isolated from saline-alkaline soil inDaqing, Heilongjiang Province, China. Strain X10-1T was determined to be a Gram-positive aerobe with rod-shaped cells. The isolate was catalase-positive, oxidase-negative, non-motile, and capable of growth at salinities of 0–16% (w/v) NaCl (optimum, 3%). The pHrange for growth was 7.5–11.0 (optimum, pH 10.0). The genomic DNA G+C content was 47.7 mol%. Itsmajor isoprenoid quinone was MK-7 and its cellular fatty acid profile mainly consisted of anteiso-C15:0, anteiso-C17:0, iso-C15:0, C16:0, and iso-C16:0. The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. The predominant polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylglycerol. Phylogenetic analysis based on 16S rRNA gene sequences showed that X10-1T is a member of the genus Bacillus, being most closely related to B. saliphilus DSM15402T (97.8% similarity) and B. agaradhaerens DSM 8721T (96.2%). DNA-DNA relatedness to the type strains of these species was less than 40%. On the basis of the phylogenetic, physiological, and biochemical data, strain X10-1T represents a novel species of the genus Bacillus, for which the name Bacillus daqingensis sp. nov. is proposed. The type strain is X10-1T (=NBRC 109404T = CGMCC 1.12295T). 相似文献