Regression procedures were used to study the relation between yield of soybean and rates of P 2 O 5. When phosphate rocks PR are acidulated to form more soluble P fertilizers, P compounds are formed other than the desired NH 4 and Ca phosphates. Exhaustion of high-grade phosphate rock throughout the world will certainly increase the levels of impurity compounds, generally water-insoluble, in the final acidulated P fertilizers Lehr, In Brazil, acidulated P fertilizers have been produced from low-grade PR due to high amounts of impurities, especially iron-aluminum oxides, present in the ore.
Prochnow et al. The authors concluded that the P availability of the water-insoluble fraction was generally lower than the original P source and that higher amounts of iron and aluminum oxides lead to lower performance of the water-insoluble fraction. These standards discard some PRs or apatite concentrates as potential sources to produce acidulated P fertilizers.
Furthermore, some materials or industrial processes utilized in order to produce SSP with better physical properties, or containing micronutrients, interfere with the water solubility of the final product and these processes should also be evaluated concerning the performance of the modified products in terms of P availability to plants. The objective of this study was to evaluate the effectiveness of various commercial and experimental acidulated P fertilizers, varying in water and citrate solubility, and produced following the procedure to obtain single superphosphates, in order to provide P to soybean plants under field condition.
Ten P sources 1 1 The term P source was preferred since many of the fertilizers tested do not follow the standards to be classified as single superphosphates according to the current Brazilian legislation Brasil, ,. The term P source was preferred since many of the fertilizers tested do not follow the standards to be classified as single superphosphates according to the current Brazilian legislation Brasil, ,.
Cation-exchange capacity was 5. Potassium was added as basal dressing at a rate of kg ha -1 K as KCl. These fertilizers were broadcast and incorporated to a soil depth of 8 cm. The amounts of nutrients applied as basal application were adequate to discard any potential side-effect when comparing the P sources. In order to test some of the products in a range of rates response curve the P sources FL, FS and the standard source of P were also applied in rates of 40 and kg ha -1 P 2 O 5.
A check plot control no P applied was also included. The P sources and rates were arranged in a randomized complete-block design with three replications. Field plots consisted of four rows, 4 m long and spaced at 0. Seeds of soybean Glycine max, cultivar FT were inoculated with Rhizobium japonicum and treated with 17 g of Mo and 2 g Co per 50 kg of seeds and sown in november 24, , at the rate of 15 seeds per meter. Soybean grain was manually harvested in April 08, , from the 2 meters of the two central rows and the yield calculated.
For the relation between yield of soybean and rates of P 2 O 5 a dummy variable multiple regression analysis was performed. This resulted in a common intercept and a single value of MSE and R 2 for the three regression equations one for each P source. Three models linear, semi-log and square root were tested to describe the relationship between the parameters studied, and the one presenting the higher R 2 chosen.
The relative agronomic effectiveness RAE was calculated for each P source. RAE was definied as the ratio of the two slopes:. Phosphorus occurs naturally in most geological formations and soils in varying amounts and forms; the main source of agricultural and industrial phosphate is deposits of the mineral apatite—known as rock phosphate. Municipal and agricultural pollution is a major source of phosphorus to many water bodies.
Most dissolved inorganic phosphorus in aquatic ecosystems is an ionization product of orthophosphoric acid H 3 PO 4. Despite its biological significance, the dynamics of phosphorus in ecosystems are dominated by chemical processes. Phosphate is removed from water by reactions with aluminum, and to a lesser extent, with iron in sediment.
In alkaline environments, phosphate is precipitated as calcium phosphate. Aluminum, iron and calcium phosphates are only slightly soluble, and sediments act as sinks for phosphorus. Concentrations of inorganic phosphorus in water bodies seldom exceed 0. Phosphorus is not toxic at elevated concentration, but along with nitrogen, it can lead to eutrophication. K represents all the samples of rocky desertification areas karst areas. NK represents all the samples of non-rocky desertification areas non-karst areas.
Alpha diversity analysis of the bacterial community structure Table 4 showed that the Shannon, Chao1, ACE, and PD indices of the soil samples in the rocky desertification areas were significantly lower than those for the non-rocky desertification areas. The observed species of the soil samples in the rocky desertification areas were significantly lower in number than for the non-rocky desertification areas.
A diagram of petals with shared and unique OTUs was generated to compare the similarity and dissimilarity in bacterial community composition between the soil samples in rocky and non-rocky desertification areas Supplemental Fig. The average number of unique OTUs in rocky desertification areas was lower than that in non-rocky desertification areas These data indicate that the diversity and abundance of the bacterial community in the rocky desertification areas are lower than those in the non-rocky desertification areas.
Distance-based redundancy analysis db-RDA Fig. Longitude, pH, and TP did not significantly influence the soil bacterial community structure. As WSP is derived from insoluble phosphorus minerals, the solubility of soil phosphorus is crucial to soil fragility. Accelerating the dissolution of insoluble phosphorus minerals by PSB is of great significance for improvement the agricultural production and ecological environment in rocky desertification areas.
The correlation between the environmental factors and bacterial community structure by distance-based redundancy analysis db-RDA. Microorganisms play important roles in soil improvement, and microbial community structure affects soil fertility and plant growth. In this study, high-throughput sequencing was performed to analyse the bacterial community structure of fruit tree rhizosphere soil in rocky and non-rocky desertification areas.
Significant differences in bacterial community structures were revealed for different soil types. However, no significant difference in bacterial community structure was found between the root and non-root surfaces in the same rhizosphere soil Figs.
This result may be due to the environmental similarity in the root surface and non-root surface soil as the developed roots couple with the natural growth of fruit trees for many years. This conclusion is similar to that found by Xiao et al. In this study, significant differences in the bacterial community structures in the rhizosphere soils of rocky and non-rocky desertification areas were identified Table 3.
At the phylum level, Proteobacteria predominated in rocky desertification areas, while Actinobacteria predominated in non-rocky desertification areas Fig. It has been reported that Proteobacteria dissolve insoluble phosphorus minerals and participate in the phosphorus cycle 13 , 33 , Betaproteobacteria belonging to Proteobacteria are also reported to have a role in apatite dissolution and nutrient cycling Therefore, isolating these dominant bacteria and applying them back to the soil may be beneficial for improving soil quality.
Biogeographical and unique environmental conditions generally affect the distribution of Actinobacteria in soil In this study, it was found that the proportion of Actinobacteria This result could be attributed to the low adaptation of Actinobacteria to the harsh rocky desertification environment. Differences in the bacterial community structures of KHT1 and KNY2 from those in other rocky desertification areas suggest that other environmental factors may also affect the bacterial community structure of rhizosphere soil.
In this study, it was also revealed that the diversity and abundance of bacteria in rocky desertification areas is significantly lower than those in non-rocky desertification areas Table 4 and Fig. It has been reported that the degree of rocky soil desertification and vegetation restoration affects the physicochemical properties and then the growth of microorganisms and plants 3 , 30 , Therefore, it is quite logic that the soil fertility, particularly WSP content, affects the diversity and abundance of bacteria in rocky and non-rocky desertification areas.
Phosphorus is indispensable for plant growth and development, as well as for microorganisms. The relationship between available phosphorus and microbial community dynamics is complex and current knowledge regarding these mechanisms is incomplete In karst broadleaf forests, TP content has a greater effect on the microbial community than available phosphorus content 39 ; while in the Black soil of northeast China, the microbial community structure is mainly affected by soil phosphorus, including both TP and available phosphorus, which are significantly increased by chemical fertilization Therefore, different forms of phosphorus have inconsistent effects on the microbial communities in different types of soil.
These data indicate that WSP is an important indicator of soil fertility in rocky desertification areas, and the solubility of phosphorus is crucial for soil vulnerability. Therefore, supplementing PSBs to soil is an important measure to accelerate the dissolution of insoluble phosphorus minerals in soil and thus improve the agricultural production and ecological environment in rocky desertification areas.
The relationship between microbial structure and altitude is not considered to be significant The correlation between latitude and bacterial community structure is not consistent. Some studies have previously reported that soil bacterial diversity is higher in low latitudes 42 , while others have reported that soil bacterial diversity has no 43 or a parabolic relationship 44 with latitude.
However, no significant influence of longitude on bacterial community structure was identified, which may be due to the minute difference in longitudes of the soil sampling areas. The growth and developmental stages of two cultivated legume plants have also been reported to affect the microbial community structures in rhizosphere soil 32 , which is consistent with the findings of the present study, i.
Bacteria grow effectively in a suitable pH; it has previously been reported that pH significantly affects the bacterial community structure in soil 11 , 45 , However, pH did not significantly affect the bacterial community structure in this study Fig.
In these studies, soil texture and heavy metals Cd, Cr, Pb, and Cu have greater effects on soil bacterial community structure than other physicochemical properties, such as pH value.
The effect of pH value on the bacterial communities in these studies may have been masked by other prevailing factors, such as WSP, latitude, altitude, and the age of fruit trees. In summary, the results of this study demonstrate that the bacterial community structures were significantly different between rocky and non-rocky desertification areas. Proteobacteria was the dominant phylum in the rocky desertification areas, while Actinobacteria was dominant in non-rocky desertification areas.
No significant difference in bacterial community was found between the root surface and non-root surface in the same rhizosphere soil. WSP was found to be the primary factor shaping bacterial community structures in fruit tree rhizosphere soils. Latitude, altitude, and the age of fruit trees also had significant influences on the bacterial community structures in soils. Longitude, pH, and TP did not significantly influence the bacterial community structure in soils.
These data contribute to the development of agricultural production and the restoration of ecological environments in rocky desertification areas from a microorganism aspect. Fruit trees that had not been affected by weeds, fertilizers, or pesticides for many years, had grown normally, and were producing healthy fruit were selected. The sampling time, latitude, longitude, and altitude of the sampling sites, as well as species and age of fruit trees, were recorded.
Meanwhile, the fruit tree rhizosphere soil in two sites NCX2 and NCX3 Table 1 from the non-rocky desertification areas in northeast China were also selected for sampling, as described above.
The extraction of WSP was slightly modified. The fruit tree roots in the rhizosphere soil were picked out. Each soil sample 0. This procedure was repeated two-three times until the soil colour in the supernatants was not obvious. The lysis solution was then transferred to a grinding tube containing 0. The purity and concentration were detected using agarose gel electrophoresis. Quality filtering on the raw tags was performed under specific filtering conditions 53 to obtain high-quality clean tags according to the QIIME quality-controlled process Then, the effective tags were finally obtained.
The representative sequence for each OTU was screened for further annotation. Based on the RDP classifier algorithm 58 , the GreenGene Database 59 was used to annotate the taxonomic information of each representative sequence. OTU abundance information was normalized using a standard of the sample with the least sequences. Alpha diversity and beta diversity were subsequently performed based on this output normalized data.
According to the results of the OTU clustering analysis, the shared and unique OTUs among different samples were analysed, and the petal diagram was plotted. An analysis of similarities ANOSIM was performed using the anosim function of the R vegan package to determine whether different soil samples had significantly different bacterial communities The relevance of the environmental factors in explaining the distribution patterns of bacterial communities in different soil samples was conducted through distance-based redundancy analysis db-RDA using R software Jiang, Z.
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