Effectiveness of phosphate and potash rocks with <Emphasis Type="Italic">Acidithiobacillus</Emphasis> on sugarcane yield and their effects on soil chemical attributes

Experiments were conducted to evaluate the effectiveness of biofertilizers produced from phosphate and potash rocks mixed with sulfur inoculated with Acidithiobacillus oxidizing bacteria on sugarcane yield and their effects on some chemical attributes of a Brazilian tableland soil. The experiment was arranged in a completely randomized factorial design 2 × 4 × 3 + 1, with four replicates. Two varieties of sugarcane, four rates of three sources of P and K (apatite + biotite, P + K biofertilizers with Acidithiobacillus, and soluble fertilizers—triple superphosphate and potassium chloride) were tested. A control without P and K fertilization was applied. A significant reduction in soil pH was observed with biofertilizers, especially when applied at higher rates, although no harmful effect on sugarcane yield was observed. Available P and K and exchangeable Ca and Mg increased with biofertilizer application compared to mineral fertilizers and P and K rocks. Biofertilizers may be used as an alternative source of P and K for sugarcane grown in soils with low available P and K.     

Effect of rhizobia and rock biofertilizers with <Emphasis Type="Italic">Acidithiobacillus</Emphasis> on cowpea nodulation and nutrients uptake in a tableland soil

Chemical fertilizers have been used in the cultivation of plants due to their high solubility and effect on crops yield. Biofertilizers with phosphate rock (PR) and potash rock (KR) plus sulfur inoculated with Acidithiobacillus may improve plant growth and contribute to addition of available P and K in soil. The effectiveness of biofertilizers from phosphate and potash rocks mixed with sulfur and Acidithiobacillus was studied in a Typic Fragiuldult soil of the Brazilian Northeast Tableland. Cowpea (cv. “IPA 206”) was grown with and without rhizobia inoculation. Treatments were: (a) phosphate rock (1000 kg ha⁻¹); (b) Biofertilizers-B_P (250 and 500 kg ha⁻¹); (c) triple superphosphate-TSP (250 kg ha⁻¹); (d) potash rock (1000 kg ha⁻¹); (e) biofertilizer-B_K (250; 500 and 750 kg ha⁻¹); (f) potassium chloride-KCl (250 kg K₂0 ha⁻¹); (g) control without P or K fertilization (P₀K₀). The soil was maintained under water submersion covered with black plastic (solarization process) for a period of 30 days. Biofertilizers (B_p and B_K) and soluble fertilizers increased plant growth and NPK uptake. Biofertilizers reduced soil pH, especially when applied in highest rates. Biofertilizers and TSP+KCl showed the best values of available P and K in soil. Rhizobial inoculation was effective on cowpea, but no nodules were formed by bacteria native from the soil, probably due to the effect of the solarization process. From obtained PK biofertilizers could be used as alternative for cowpea fertilization in Tableland soils.     

Agronomic effectiveness of biofertilizers with phosphate rock, sulphur and Acidithiobacillus for yam bean grown on a Brazilian tableland acidic soil

Phosphate rocks have low available P and soluble P fertilizers have been preferably used in plant crop production, although economic and effective P sources are needed. Experiments were carried out on a Brazilian Typic Fragiudult soil with low available P to evaluate the agronomic effectiveness of phosphate rock (PR) compared with soluble phosphate fertilizer. Yam bean (Pachyrhizus erosus) inoculated with rhizobia (strains NFB 747 and NFB 748) or not inoculated was the test crop. Biofertilizers were produced in field furrows by mixing phosphate rock (PR) and sulphur inoculated with Acidithiobacillus (S+Ac) in different rates (50, 100, 150 and 200 g S kg(-1) PR), with 60 days of incubation. Treatments were carried out with PR; biofertilizers B(50), B(100), B(150), B(200); triple super phosphate (TSP); B(200) without Acidithiobacillus and a control treatment without P application (P(0)). TSP and biofertilizers plus S inoculated with Acidithiobacillus increased plant growth. Soil acidity and available P increased when biofertilizers B(150) and B(200) were applied. We conclude that biofertilizers may be used as P source; however, long term use will reduce soil pH and potentially reduce crop growth.     

Phosphorus fertilizer recovery from calcareous soils amended with humic and fulvic acids

Precipitation of Ca phosphates negatively affects recovery by plants of P fertilizer applied to calcareous soils, but organic matter slows the precipitation of poorly soluble Ca phosphates. To study the effect of high molecular weight organic compounds on the recovery of applied P, a mixture of humic and fulvic acids was applied to calcareous soils with different levels of salinity and Na saturation which were fertilized with 200 and 2000 mg P kg^–1 as NH₄H₂PO₄. Recovery was measured as the ratio of increment in Olsen P-to-applied P after 30, 60 and 150 days, and associated P forms were studied using sequential chemical fractionation and ³¹P NMR spectroscopy. Application of the humic-fulvic acid mixture (HFA) increased the amount of applied P recovered as Olsen P in all the soils except in one soil with the highest Na saturation. In soils with high Ca saturation and high Olsen P, recovery increased from < 15% in the absence of amendment to > 40% at a 5 g HFA kg^–1 amendment rate (30 days incubation and 200 mg P kg^–1 fertilizer rate). This is ascribed to inhibition of the precipitation of poorly soluble Ca phosphates, consistent with the sequential chemical extraction (reduction of the HCl extractable P) and P concentration in 0.01 M CaCl₂ (1:10 soil:solution ratio) extracts. ³¹P NMR spectra revealed that in non-amended samples, most spectral shifts were due to poorly soluble P compounds (carbonate apatite); on the other hand, at the 5 g HFA kg^–1 rate, significant amounts of amorphous Ca phosphate and dicalcium phosphate dihydrate (DCDP) were identified. The increase in the recovery of applied P due to HFA reveals a positive effect of the application of organic matter as soil amendments on the efficiency of P fertilizers and also explains that manures and other organic sources of P were more efficient increasing available P than inorganic P fertilizers in calcareous soils.     

Enhancing crop growth, nutrients availability, economics and beneficial rhizosphere microflora through organic and biofertilizers

Field experiment was conducted on fodder maize to explore the potential of integrated use of chemical, organic and biofertilizers for improving maize growth, beneficial microflora in the rhizosphere and the economic returns. The treatments were designed to make comparison of NPK fertilizer with different combinations of half dose of NP with organic and biofertilizers viz. biological potassium fertilizer (BPF), Biopower, effective microorganisms (EM) and green force compost (GFC). Data reflected maximum crop growth in terms of plant height, leaf area and fresh biomass with the treatment of full NPK; and it was followed by BPF+full NP. The highest uptake of NPK nutrients by crop was recorded as: N under half NP+Biopower; P in BPF+full NP; and K from full NPK. The rhizosphere microflora enumeration revealed that Biopower+EM applied along with half dose of GFC soil conditioner (SC) or NP fertilizer gave the highest count of N-fixing bacteria (Azotobacter, Azospirillum, Azoarcus andZoogloea). Regarding the P-solubilizing bacteria,Bacillus was having maximum population with Biopower+BPF+half NP, andPseudomonas under Biopower+EM+half NP treatment. It was concluded that integration of half dose of NP fertilizer with Biopower+BPF / EM can give similar crop yield as with full rate of NP fertilizer; and through reduced use of fertilizers the production cost is minimized and the net return maximized. However, the integration of half dose of NP fertilizer with biofertilizers and compost did not give maize fodder growth and yield comparable to that from full dose of NPK fertilizers.     

Estimation of N2-fixation by sugarcane,Saccharum sp., and soybean,Glycine max,grown in soil with15N-labelled organic matter

Summary Two varieties of sugarcane, and nodulated and non-nodulated soybean isolines, were planted in a soil previously mixed with¹⁵N-labelled plant material. 45 days was allowed to elapse before planting, to permit initiation of organic matter mineralization. Plants were grown for 60 days, then harvested, dried, weighed and analysed for total N. Analysis of soil samples pre-incubated in the laboratory was carried out to evaluate ammonium and nitrate from added organic matter. Dry weights of the soybean isolines were similar, but total N was higher for the nodulated line. Both sugarcane varieties showed similar weight and total N. Nitrogen derived from applied organic matter (NdfOM) was higher in non-nodulated soybean than in all other plants. Although there is the possibility of different¹⁵N availabilities between species, nitrogen derived from fixation (Nfix) was calculated based on the¹⁵N enrichment of the non-nodulating soybean. Nfix was 72% for nodulating soybean and ranged from 19 to 39% for different parts of sugarcane plants, despite high levels of available-N. Nitrogen derived from soil was calculated by difference. NdfOM was lower in roots than in upper parts (leaves+stalks) of plants. Use of¹⁵N labelled organic matter seems a useful approach to the longer term measurement of N₂-fixation.IAEA Project BRA/5/009-CENA.     

Environmental and energy assessment of the substitution of chemical fertilizers for industrial wastes of ethanol production in sugarcane cultivation in Brazil

Purpose

Vinasse and filter cake are residues of bioethanol processing that are used to be recycled as fertilizers in sugarcane plantation. Studies related to the environmental dimension on this practice are concerned only with the effects on water and soil. The present study examines the systemic effects of replacing chemical fertilizers with vinasse and filter cake on the environmental performance of ethanol, via life cycle assessment (LCA).

Methods

The analysis was carried out by comparing various scenarios structured from two control variables: crop management techniques (manual and mechanized harvesting) and source of nutrients (for supplying the nutritional needs of sugarcane crops): chemical fertilizers, chemical fertilizers + vinasse, and chemical fertilizer + vinasse + filter cake. Impact assessment was carried out in terms of primary energy demand, climate change, terrestrial acidification, freshwater eutrophication, human toxicity, and terrestrial ecotoxicity. LCA has been applied according to both attributional and consequential perspectives. Moreover, a sensitivity analysis was performed in order to verify the effects of the varying amounts of nitrogen (N), phosphorus (P), and potassium (K) in the composition of vinasse on the results obtained for the impact profile.

Results and discussion

From the attributional LCA perspective, the most expressive contributions regarding primary energy demand occurred in terms of depletion of non-renewable fossils. Replacing chemical fertilizers with vinasse and filter cake was beneficial for the environmental performance of ethanol as it reduces climate change, terrestrial acidification, and human toxicity impacts and sustains freshwater eutrophication and terrestrial ecotoxicity unaltered in relation to scenarios using only fertilizers. In terms of consequential LCA, ethanol’s environmental performance is influenced by the inclusion of the production of calcium fluorite to compensate the hexafluorosilicic acid deficit occurring in conjunction to the decrease of phosphate fertilizer and is compensated by the benefits provided by the general reduced consumption of chemical fertilizers for most of the impact categories. The exception occurred for primary energy demand.

Conclusions

The reuse of residues from bioethanol production—vinasse and filter cake—as primary nutrient suppliers for the cultivation of sugarcane instead of chemical fertilizers is a valid practice that improves the environmental performance of ethanol, even if it is analyzed under a consequential LCA perspective. The transport of these inputs to the field must be managed, however, in order to minimize primary energy demand and climate change impacts.

     

氮磷添加与不同栽植密度交互对樟树幼苗土壤化学性质的短期影响

研究氮磷添加对不同密度樟树(Cinnamomum camphora)幼苗土壤化学性质的影响,以期为全球化背景下樟树人工林生态系统的土壤养分管理提供依据。以1年生樟树幼苗为试验材料,选择氯化铵(NH4Cl)作为氮肥模拟大气氮沉降,以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加。氮磷处理设置CK、施N、施P和施N+P 4个水平,其中N、P和N+P施肥量分别为40 g m~(-2)a~(-1)(NH_4Cl)、20 g m-2a-1(NaH_2PO_4·2H_2O)和40g m~(-2)a~(-1)(NH_4Cl)+20 g m~(-2)a~(-1)(NaH_2PO_4·2H_2O)。种植密度设置4个水平:10、20、40和80株/m~2,试验时间为2017年6月至9月。研究结果表明,在各密度幼苗土壤中,N和N+P处理引起pH值的显著下降,N、P和N+P处理的土壤有机质和碱解N含量的变化规律不明显,P处理的幼苗土壤全P含量上升,P和N+P处理的土壤有效P含量增加,N+P处理的土壤全K含量以及N、P和N+P处理的土壤速效K含量均下降。在10、20和40株/m~2幼苗的土壤中,P处理的土壤全N含量高于N和N+P处理的,而80株/m~2幼苗的土壤全N含量低于其他密度幼苗。随着种植密度的增加,各施肥处理的土壤pH、全P、有效P、全K和速效K含量均呈现上升趋势,而施N和施P处理的土壤有机质呈现下降趋势,各施肥处理的土壤碱解N含量变化规律不明显。施肥和密度处理对樟树幼苗土壤有机质、碱解氮和速效钾含量有显著的交互作用。     

Effect of nitrogen form and phosphorus source on the growth,nutrient uptake and rhizosphere soil property of Camellia sinensis L.

The effects of nitrogen form and phosphorus source on the growth, nutrient uptake and rhizosphere soil property of tea (Camellia sinensis L.) were investigated in a pot experiment. The experiment was performed with a compartmental cropping device, which enables the collection of rhizosphere soil at defined distances from the root of tea plant. Nitrogen was supplied as nitrate or ammonium in combination with soluble phosphorus as Ca(H₂PO₄)₂ or insoluble P as rock phosphate. The leaf dry matter production of tea was significantly greater in the treatments with NH₄ ⁺ than NO₃ ^-, whereas dry matter production of root and stem was not significantly affected. Addition of phosphorus as either source did not influence the dry matter production. The concentrations of K in root, Mg and Ca in both the shoot and root supplied with NO₃ ^- were significantly higher than in NH₄ ⁺ and influence of P sources was minor. On the contrary, Al and Mn concentrations were significantly larger in NH₄ ^--fed plants which could be attributed to remarkably increased availability of Al and Mn caused by acidification of the rhizosphere soil (the first 1-mm soil section from the root surface) with NH₄–N nutrition. The concentration of N in shoot was also significantly higher in NH₄- than in NO₃-fed plants, indicating higher use efficiency of NH₄–N. Whatever the phosphate source, rhizosphere pH declined in ammonium compared to in nitrate treatment. The pH decrease was much larger when no P or soluble P were applied and reached 0.85–1.30 units which extended to 3–5 mm away from the root surface. Exchangeable acidity, content of exchangeable Al and Mn were also considerably higher in the rhizosphere soils of NH₄ ⁺ fed tea plants. Significant amounts of P dissolved from rock phosphate accumulated in rhizosphere of NH₄ ⁺, not NO₃ ^-, suggesting that the dissolution of rock phosphate was induced by the proton excreted by tea root fed with ammonium. With soluble P addition, shoot and root P concentrations were greater in NH₄ ⁺ than in NO₃ ^- treatment and it appeared that this difference could not be sufficiently explained by the available P content in soil which was only slightly higher in NH₄ ⁺ treatment. With rock phosphate addition, the shoot and root P concentrations were hardly affected by nitrogen form, although the available P content was much higher and accumulated in the rhizosphere soil supplied with ammonium. The reason for this was discussed with regard to the inter-relationship of Al with P uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth and nutrient status of citrus plants as influenced by mycorrhiza and phosphorus application

To test the hypothesis that high levels of soluble phosphate applied in combination with VAM fungi, to citrus plants, can cause growth depression even in the absence of other limiting factors, and also to test if rock phosphate, under these conditions, may be a satisfactory P source, a greenhouse experiment was conducted using sterilized soil with four levels of phosphate (0, 50, 100 and 200 ppm P) supplied either as soluble P or as rock phosphate. Citrus seedlings were either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or left uninoculated. Six months after the start of the experiment, the plants were harvested and shoot dry weight, P and K uptake, root colonization and the number of spores in 50 cm³ of soil were determined. Significant increases were found in dry matter yields and in P and K contents, due to VAM fungus inoculation, at the zero and 50 ppm soluble P levels and at all rock phosphate levels. At 100 ppm soluble P, the development of VAM plants was equilvalent to that of non-VAM plants, and at 200 ppm, growth was significantly less than that of non-VAM plants. Root colonization and sporulation were reduced at higher P levels. The absolute growth depression of VAM plants at the higher P level was likely due to P toxicity. In addition, high leaf P and K concentrations may have interfered with carbohydrate distribution and utilization in these symbioses. Rock phosphate may be used with VAM citrus to substitute for medium amounts of soluble phosphate.     

Phosphorus and phosphate solubilizing bacteria: Keys for sustainable agriculture

Abstract

Phosphorus (P) is one of the most important minerals required for plant growth occupying a strong position among soil macro nutrients. Soil P deficiency is often fulfilled by phosphate fertilizers. P deficiency in soils is due to less total P contents in the soil and fixation of added P from chemical fertilizers as well as other organic sources like manures. The response of plant under P stress or even when it is present in adequate amount is very mild. The basic constraint in the availability of P is its solubilization as it gets fixed both in acidic and alkaline soil. Soil fixed P can only be solubilized by phosphate solubilizing microorganisms (PSMs).These bacteria released different types of organic acids in the soil which make P soluble and available to plants. The potential of these PSMs to solubilize P varies and mainly depends upon mechanism adopted for solubilization, their molecular genetics as well as their ability to release P in soil. The PSMs, having all the characteristics of phytohormone production, nitrogen fixation, as well as, heavy metal decontamination and creating salt stress tolerance in plants, are quite rare for sustainable agriculture. Application of this environment friendly approach for increasing crop productivity as well as its impact on soil and plant health is discussed in this review which will not only open new avenues of research but also provide fruitful information about phosphate solubilizing microbes for sustainable agriculture development.     

长期施肥对麦田大型土壤动物群落结构的影响

于2007、2008年春季在中国科学院封丘农业生态实验站,研究长期定位施肥对麦田大型土壤动物群落结构的影响。调查共获得大型土壤动物3068头,隶属8纲,19目,28科。不同施肥处理条件下土壤动物类群数差异显著(F=2.51, P＜0.05, df=55),个体数差异极显著(F=8.99, P＜0.01, df=55)。结果显示,大型土壤动物的类群数和个体数在有机肥和营养均衡条件下较高,缺磷条件下较低。土壤动物多样性指数(H')以有机肥和营养均衡条件下显著高于营养不均衡和不施肥处理(P＜0.05)。主成分分析结果显示,第一主成分贡献值47.14%,第二主成分贡献值30.10%。经线性检验第一主成分与土壤动物个体数(y=0.335x-2.163,R²=0.51)和类群数(y=0.042x-1.25,R²=0.67)均呈线性关系。总之,长期施用有机肥和营养均衡大型土壤动物群落构成相似。土壤有机质和磷含量是影响土壤动物群落构主要生态因子。     

Native soil and fresh fertilizer phosphorus uptake as affected by rate of application and P fertilizers

³²P labelled fertilizers were used to measure native soil and fresh fertilizer phosphorus uptake byLolium perenne L. in greenhouse experiments. The P source evaluation was carried out for multiple rates of application for a standard P fertilizer (DAP) on low and medium soil P levels and for North Carolina rock phosphate (RP) at the medium soil P level only. At the low soil P level, the native P uptake increase was independent of P-DAP applied, and represented 19% of the nil P uptake. At the medium soil P level, the variability of the native soil as a nutrient P source depended on the phosphate fertilizer applied, and the rate of application. Consequently the amount of total P uptake could conceal differences in P fertilizer evaluations as the nutrient P source. Fresh P uptake increased linearly with the rates of P applied as standard or tested P fertilizer. The comparison of various P sources by means of fresh P uptake ratio (i.e. fresh P uptake from tested phosphate divided by fresh P uptake from standard phosphate) was independent of the rate of application. It was therefore suggested that various phosphorus sources be evaluated by measuring the fresh P uptake for a single rate of application.     

Simultaneous phosphate solubilization potential and antifungal activity of new fluorescent pseudomonad strains, Pseudomonasaeruginosa, P. plecoglossicida and P. mosselii

Of 80 fluorescent pseudomonad strains screened for phosphate solubilization, three strains (BFPB9, FP12 and FP13) showed the ability to solubilize tri-calcium phosphate (Ca₃(PO₄)₂). During mineral phosphate solubilization, decrease of pH in the culture medium due to the production of organic acids by the strains was observed. These phosphate solubilizing strains produced indole-3-acetic acid (IAA) and protease as well as exhibited a broad-spectrum antifungal activity against phytopathogenic fungi. When tested in PCR using the gene-specific primers, strain BFPB9 showed the presence of hcnBC genes that encode hydrogen cyanide. On the basis of phenotypic traits, 16S rRNA sequence homology and subsequent phylogenetic analysis, strains BFPB9, FP12 and FP13 were designated as Pseudomonas aeruginosa, P. plecoglossicida and P. mosselii, respectively. Present investigation reports the phosphate solubilization potential and biocontrol ability of new strains that belong to P. plecoglossicida and P. mosselii. Because of the innate potential of phosphate solubilization, production of siderophore, IAA, protease, cellulase and HCN strains reported in this study can be used as biofertilizers as well as biocontrol agents.     

Solubilization of organic and inorganic phosphates by three highly efficient soil bacterial isolates

Screening soil samples collected from a diverse range of slightly alkaline soil types, we have isolated 22 competent phosphate solubilizing bacteria (PSB). Three isolates identified as Pantoea agglomerans strain P5, Microbacterium laevaniformans strain P7 and Pseudomonas putida strain P13 hydrolyzed inorganic and organic phosphate compounds effectively. Bacterial growth rates and phosphate solubilization activities were measured quantitatively under various environmental conditions. In general, a close association was evident between phosphate solubilizing ability and growth rate which is an indicator of active metabolism. All three PSB were able to withstand temperature as high as 42°C, high concentration of NaCl upto 5% and a wide range of initial pH from 5 to 11 while hydrolyzing phosphate compounds actively. Such criteria make these isolates superior candidates for biofertilizers that are capable of utilizing both organic and mineral phosphate substrates to release absorbable phosphate ion for plants.     

Direct N2O emission factors for synthetic N‐fertilizer and organic residues applied on sugarcane for bioethanol production in Central‐Southern Brazil

The production and use of biofuels have increased rapidly in recent decades. Bioethanol derived from sugarcane has become a promising alternative to fossil fuel for use in automotive vehicles. The ‘savings’ calculated from the carbon footprint of this energy source still generates many questions related to nitrous oxide (N₂O) emissions from sugarcane cultivation. We quantified N₂O emissions from soil covered with different amounts of sugarcane straw and determined the direct N₂O emission factors of nitrogen fertilizers (applied at the planting furrows and in the topdressing) and the by‐products of sugarcane processing (filter cake and vinasse) applied to sugarcane fields. The results showed that the presence of different amounts of sugarcane straw did not change N₂O emissions relative to bare soil (control). N‐fertilizer increased N₂O emissions from the soil, especially when urea was used, both at the planting furrow (plant cane) and during the regrowth process (ratoon cane) in relation to ammonium nitrate. The emission factor for N‐fertilizer was 0.46 ± 0.33%. The field application of filter cake and vinasse favored N₂O emissions from the soil, the emission factor for vinasse was 0.65 ± 0.29%, while filter cake had a lower emission factor of 0.13 ± 0.04%. The experimentally obtained N₂O emission factors associated with sugarcane cultivation, specific to the major sugarcane production region of the Brazil, were lower than those considered by the IPCC. Thus, the results of this study should contribute to bioethanol carbon footprint calculations.     

Improving fertility and productivity of a highly-weathered upland soil in subtropical China by incorporating rice straw

The transfer of rice straw from paddy fields to upland areas was proposed in our study as an innovative practice to improve the fertility of the highly-weathered and poor upland soils, as well as to mitigate environmental impacts from rice production system (e.g., the large application of chemical fertilizers, straw burning, CH₄ emission from decomposed straw) in the subtropical China. Data from an 8-year field experiment with sweet potato and rapeseed show that, the contents of organic matter and total nitrogen (N) in the surface soil (0–20 cm) with rice straw incorporation were increased by 13%, and the amounts of soil microbial biomass carbon (C), N, and phosphorus (P) by 18–43%, compared with the values when chemical fertilizers (NPK) were applied alone. Physical conditions and crop productivity of the test soil were effectively promoted with the straw incorporation, as indicated in significant changes in soil field water-holding capacity, total porosity, and bulk density in the 10–15 cm soil layer, and the rise (about 10% and 20%, respectively) of sweet potato and rapeseed yields. In conclusion, these results suggest that the practice shift from conventional rice straw management (‘on the spot’ incorporation) to upland incorporation is effective in improvement in fertility and productivity of the upland soil, which has potentials to reduce the amounts of chemical fertilizers applied and to increase soil C storage in farmlands in the region.     

Long-term availability of nutients in forest soil derived from fast- and slow-release fertilizers

The availability of P, K and Mg was studied in boreal forest soil treated 10 years earlier with slow- and fast-release fertilizers. Fast release superphosphate, potassium chloride and magnesium sulphate and slow-release apatite (P) and biotite (K, Mg) were applied alone or together with urea or urea+limestone. The concentrations of total and exchangeable nutrients in the organic horizon and the concentration of exchangeable nutrients in the uppermost mineral horizon were measured. CO₂ production during aerobic laboratory incubation was used to estimate the microbial activity and substrate-induced respiration to determine the microbial biomass C in soil. Biotite caused a moderate but persistent increase in pH in the organic horizon, but this increase was smaller than with lime. The fast-release fertilizers had no effects on the nutrient status of the soil 10 years after the fertilization. However, apatite and biotite still increased the total content of Mg, K and P and the concentrations of exchangeable Mg and soluble P in soil. On the other hand, simultaneous addition of lime and biotite reduced the release of soluble P from apatite. The reduction in soil microbial activity found with urea and the fast-release salts soon after application was no longer evident 10 years later. There was no increase in nitrification in the fertilized soils, not even with the urea+lime treatment. The previous results right after the application and the results presented here do not indicate major leaching of nutrients from the slow-release fertilizers to the deeper soil profiles.     

Evaluation of synergistic effects of bacterial and cyanobacterial strains as biofertilizers for wheat

An investigation was undertaken to screen, select and evaluate a set of bacterial and cyanobacterial isolates from the wheat rhizosphere for their role as biofertilizers in wheat. From an initial set of 23 cyanobacterial strains and 110 bacterial isolates from wheat rhizospheric soil, 3 bacterial and 3 cyanobacterial strains were selected based on their plant growth promoting potential under laboratory and controlled greenhouse conditions. In vitro compatibility studies revealed positive interactions among the six strains. Pot experiments were conducted with wheat variety HD 2687, with a total of 51 treatments, along with recommended fertilizer controls. Various combinations of the selected set of three bacterial (PW1, PW5 and PW7) and three cyanobacterial isolates (CW1, CW2 and CW3) were used along with 1/3 N and full dose of P and K fertilizers. Significant enhancement in the soil microbiological (Dehydrogenase activity, FDA hydrolase, Alkaline phosphatase and microbial biomass) and plant growth/yield parameters were recorded. Observations revealed a two-fold increase in panicle weight in selected combinations (PW1+PW7+CW3; PW1+ CW1+CW2/CW1+CW3; CW2+CW3), as compared to control treatment involving full dose of chemical fertilizers. Such combinations, which also provided N savings of 40–80 kg N/ha are being further evaluated in field experiments. This study for the first time illustrated the positive and dynamic interactions among bacterial and cyanobacterial strains and their promise in integrated nutrient management of wheat crop.     

Low recovery frequency of <Emphasis Type="Italic">Gluconacetobacter diazotrophicus</Emphasis> from plants and associated mealybugs in Cuban sugarcane fields

This study was aimed to isolate and identify the N₂-fixing bacterium Gluconacetobacter diazotrophicus from 11 sugarcane varieties, grown under field conditions in four Cuban provinces, and from their associated mealybugs Saccharicoccus sacchari. Identification was based on morphological and biochemical tests and PCR-amplification of 16S rRNA genes using species-specific primers. From all sugarcane varieties and numerous mealybug colonies sampled, G. diazotrophicus isolates were recovered from inside sugarcane stems of only three varieties, and one from S. sacchari colony. These four isolates showed acetylene reduction activity in nitrogen-free media and contained nifH genes which were PCR-amplified using specific primers. ERIC-PCR fingerprinting was used to compare the Cuban G. diazotrophicus isolates with type and reference strains of N₂-fixing Gluconacetobacteria. The very low frequency of G. diazotrophicus isolates recovered is probably related with the high doses of nitrogen fertilizers applied to the sugarcane in the Cuban fields for almost 30 years. Some genetic differences, using ERIC-PCR, were detected among G. diazotrophicus strains, which could be related with its source.