Agronomic effectiveness of partially acidulated phosphate rock as influenced by soil phosphorus-fixing capacity

A greenhouse study compared the effect of soil P-fixing capacity on the relative argonomic effectiveness (RAE) of partially acidulated phosphate rock (PAPR) and water-soluble P. Such information is lacking in the literature. Six soils varying widely in P-fixing capacity (5.6%–56.1%) were used. A phosphate rock (Huila PR) from Colombia was acidulated with H₂SO₄ at 50% of the level necessary to achieve full conversion to single superphosphate (SSP). Rates of P applied from PAPR or SSP were 0,05, 100, and 300 mg P kg⁻¹. The P fertilizers were mixed with the soils, and maize was grown for 6 weeks before harvest. The results show that the effectiveness of PAPR in increasing dry-matter yield and P uptake over yield and uptake obtained with SSP linearly increased as the soil P-fixing capacity increased. PAPR and SSP were equally effective in increasing dry-matter yield or P uptake at P-fixing capacities of 28% or 36%, respectively. PAPR was found to be more effective than SSP in soils (treated with Fe-gel) with P-fixing capacity higher than these values. The internal efficiency, which is defined as the ratio between dry-matter yield and P uptake, was the same for both PAPR and SSP in all the soils.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Risk of municipal solid waste compost and sewage sludge use on photosynthetic performance in common crop (<Emphasis Type="Italic">Triticum durum</Emphasis>)

The effect of composted municipal solid waste (MSW) and sewage sludge (SS) on photosynthetic activity of wheat (Triticum durum L.) was investigated. Chlorophyll fluorescence and gas exchange parameters were assessed following application of up to 300 t ha^?1 of MSW compost or SS. 100 t ha^?1 MSW compost was optimal for the plant growth, which showed 78% stimulation as compared to the control. This was associated with higher maximum quantum efficiency (F _v /F _m) of photosystem II (PSII) and the actual quantum efficiency of PSII open centers at light adapted state (ΔF/\(F_{\rm m}^{\prime}\)). Maximal values of net photosynthetic rate and stomatal conductance were recorded at 100 t ha^?1 MSW compost (+40 and +116%, respectively). Ribulose bisphosphate carboxylase/oxygenase (RubisCO) activity was also significantly stimulated at 100 t ha^?1, while less significant impact was found in SS treatment. A marked accumulation of Ni, Pb, Cu, and Zn in concomitance with membrane lipid peroxidation were observed at 200–300 t ha^?1 MSW compost and SS, resulting in lower photosynthetic activity and altered PSII functional integrity. Altogether, these results suggest that the MSW compost at 100 t ha^?1 would be suitable for wheat cultivation, within the critical limits of heavy metal accumulation. However, long-term field experiments seem necessary to more accurately evaluate the safety of MSW application.     

Phosphorus intensity determines short-term P uptake by pigeon pea (<Emphasis Type="Italic">Cajanus cajan</Emphasis> L.) grown in soils with differing P buffering capacity

Phosphorus (P) uptake by plant roots depends on P intensity (I) and P quantity (Q) in the soil. The relative importance of Q and I on P uptake is unknown for soils with large P sorption capacities because of difficulties in determining trace levels of P in the soil solution. We applied a new isotope based method to detect low P concentrations (<20 μg P l⁻¹). The Q factor was determined by assessment of the isotopically exchangeable P in the soil (E-value) and the I factor was determined by measurement of the P concentration in the pore water. A pot trial was set up using four soils with similar labile P quantities but contrasting P buffering capacities. Soils were amended with KH₂PO₄ at various rates and pigeon pea (Cajanus cajan L.) was grown for 25 days. The P intensity ranged between 0.0008 and 50 mg P l⁻¹ and the P quantity ranged between 10 and 500 mg P kg⁻¹. Shoot dry matter (DM) yield and P uptake significantly increased with increasing P application rates in all soils. Shoot DM yield and P uptake, relative to the maximal yield or P uptake, were better correlated with the P concentration in the pore water (R ² = 0.83–0.90) than with the E-value (R ²=0.40–0.53). The observed P uptakes were strongly correlated to values simulated using a mechanistic rhizosphere model (NST 3.0). A sensitivity analysis reveals that the effect of P intensity on the short-term P uptake by pigeon pea exceeded the effect of P quantity both at low and high P levels. However, DM yield and P uptake at a given P intensity consistently increased with increasing P buffering capacity (PBC). The experimental data showed that the intensity yielding 80% of the maximal P uptake was 4 times larger in the soil with the smallest PBC compared to the soil with the largest PBC. This study confirms that short-term P uptake by legumes is principally controlled by the P intensity in the soil, but is to a large extent also affected by the PBC of the soil. Section Editor: N. J. Barrow     

Soil phosphorus levels needed for equal P uptake from four soils with different water contents at the same water potential

Soil volumetric water contents, , at –33 kPa potential may vary with soil from 0.06 to 0.70. Because P diffusion depends on , most economic P fertilizer rates required for different soils may require adjusting according to their soil-water relationships. The objective of this study was, after experimentally verifying a mechanistic nutrient uptake model on a series of soils varying in at –33 kPa potential, to use the model to predict labile P levels needed for each of these soils to achieve equal P uptake by maize (Zae mays L.) and verify these predictions. Maize was grown in a pot experiment using four soils having of 0.13, 0.20, 0.26, and 0.40 at –33 kPa each at 0, 200, and 400 mg kg^-1 of added P. When root parameters obtained experimentally were used, predicted P uptake with the uptake model agreed with observed P uptake, y=0.99x+9.08 (r²=0.98). When P uptake was plotted vs. soil solution P, C_li, the relation varied with soil. The higher the the lower the C_li needed for equal P uptake. A similar relation was found between P uptake and diffusible soil P, C_si. Differences between the two plots occurred because of differences among soils in buffer power, C_si/C_li. The C_si vs. P added relation was used to calculate differences among soils in the C_si needed to obtain equal P uptake. The C_si values ranged from 1.3 to 4.0 mmol kg^–1. The calculated values were used in a second pot experiments to verify the predictions. No significant difference (=0.05) in P uptake occurred. The results of this research indicate that the mechanistic nutrient uptake model can be used to predict the degree of adjustments in C_si needed to obtain the most economic P fertilizer rates among soils varying in .Journal Paper No. 13072. Purdue Univ. Agric. Exp. Stn., West Lafayette, IN 47907.     

Isolation of Phosphate Solubilizing Bacteria from Maize Rhizosphere and Their Potential for Rock Phosphate Solubilization–Mineralization and Plant Growth Promotion

Phosphate solubilizing bacteria (PSB) play a significant role in plant P nutrition by their effect on soil P dynamics and their subsequent ability to make P available to plants via solubilization and mineralization processes. This study aimed to evaluate the effect of separate and combined use of indigenous PSB, poultry manure (PM) and compost on solubilization and mineralization of rock phosphate (RP) and their subsequent effect on growth and P accumulation of maize (Zea mays L.). A group of fifty seven bacteria were isolated from the rhizosphere/rhizoplane of maize that had been grown in soils collected from varying altitudes (655–2,576 m) of the mountain region of Rawalakot, Azad Jammu and Kashmir, Pakistan. After screening, the capacity of eleven isolates to solubilize mineral phosphate was quantitatively evaluated using insoluble Ca₃(PO₄)₂ in culture medium as a time course study through spectrometer. The growth hormone producing (IAA) capacity of the isolates was also determined. Furthermore, five potential isolates were tested for their ability to increase P release capacity (mineralization) of insoluble RP in an incubation study. The effect of PSB inoculation on maize was determined in a completely randomized greenhouse experiment where root and shoot biomass and P accumulation in plants were assessed. The P solubilization index of selected isolates varied from 1.94 to 3.69, while the P solubilization efficiency ranged between 94.1% and 269.0%. The isolates MRS18 and MRS27 displayed the highest values. The P solubilization in the liquid medium was maximum at 6 and 9 days of incubation ranging between 9.91 and 44.04 µgmL^?1 and the isolates MRS27 and MRS34 exhibited the highest solubilization. Six isolates showed additional capability of producing IAA ranging between 2.66 and 28.41 µgmL^?1. Results of the incubation study indicated that P release capacity (P mineralization) of RP-amended soil varied between 6.0 and 11.8 µgPg^?1 that had been significantly increased to 30.6–36.3 µgPg^?1 (maximum value) when PSB were combined with RP. The combined application of PSB and organic amendments (PM, compost) with RP further increased P mineralization by releasing a maximum of 37.7 µgPg^?1 compared with separate application of RP (11.8 µgPg^?1) and organic amendments (21.5 and 16.5 µgPg^?1). The overall effect of PSB (as a group) with RP over RP alone on maize growth showing a relative increase in shoot length 21%, shoot fresh weight 42%, shoot dry weight 24%, root length 11%, root fresh weight 59%, root dry weight 35% and chlorophyll content 32%. This study clearly indicates that use of PSB, and organic amendments with insoluble RP could be a promising management strategy to enhance P availability in soil pool and improve plant growth in intensive cropping systems.     

The Ultuna long-term soil organic matter experiment

In 1991, soil samples were taken from the long-term (40 years old) field trial at Ultuna in order to investigate soil P status and the distribution of its various forms. Among the treatments investigated, two were inorganic PK additions only – one to continuous fallow (PK-fallow) and the other to cropped fields (PK). There were also treatments amended with PK in combination with applications of straw, green manure composed of grass (GM), farmyard manure (FYM) or sewage sludge (SS). A total of 720, 720, 883, 1154, 1941 and 6617 kg P h^-1 had been supplied in the PK-fallow, PK, Straw, GM, FYM and SS treatments, respectively up to 1991. The soil P distribution was determined by step-wise fractionation using anion exchange resin (resin-P), sodium bicarbonate (bicarb-P), sodium hydroxide (hyd-P), and HCl (HCl-P). Finally, the soil was digested to obtain residual P (resid-P). The amendments resulted in a significant (p=0.05) enrichment of total P in soils relative to the initial value. A breakdown of the bicarb-P and hyd-P into inorganic P (P_i) and organic P (P_o) was manifested as considerable transformations within these P compartments compared with the initial values. Thus, total P_i (resin-P, bicarb-P_i, hyd-P_i, HC1-P, resid-P)/total P_o (bicarb-P_o, hyd-P_o) ratios markedly decreased in all treatments relative to control. The two P compartments were significantly and negatively (p =0.05) correlated. On average, the total P_o increase was about 380 mg kg^-1 (range 270–715). The results suggested that an equilibrium between P_i immobilization and P_o mineralization was difficult to attain under any of the experimental management regimes used, which exclude inorganic N application. The balance sheet calculations revealed P deficits ranging from about 10 to 60 kg ha^-1, indicating that some P had migrated to the subsoil.     

Changes and availability of P fractions following 65 years of P application to a calcareous soil in a Mediterranean climate

The fate and availability of P derived from granular fertilisers in an alkaline Calcarosol soil were examined in a 65-year field trial in a semi-arid environment (annual rainfall 325 mm). Sequential P fractionation was conducted in the soils collected from the trial plots receiving 0–12 kg P ha⁻¹crop⁻¹, and the rhizosphere soil after growing wheat (Triticum aestivum L. cv. Yitpi) and chickpea (Cicer arietinum L. cv. Genesis 836) for one or two 60-day cycles in the glasshouse. Increasing long-term P application rate over 65 years significantly increased all inorganic P (Pi) fractions except HCl–Pi. By contrast, P application did not affect or tended to decrease organic P (Po) fractions. Increasing P application also increased Olsen-P and resin-P but decreased the P buffer capacity and sorption maxima. Residual P, Pi and Po fractions accounted for an average of 32, 16 and 52% of total P, respectively. All soil P fractions including residual P in the rhizosphere soil declined following 60-day growth of either wheat or chickpea. The decreases were greater in soils with a history of high P application than low P. An exception was water-extractable Po, which increased following plant growth. Changes in various P fractions in the rhizosphere followed the same pattern for both plant species. Biomass production and P uptake of the plants grown in the glasshouse correlated positively with the residual P and inorganic fractions (except HCl–Pi) but negatively with Po in the H₂O-, NaOH- and H₂SO₄-fractions of the original soils. The results suggest that the long-term application of fertiliser P to the calcareous sandy soil built up residual P and non-labile Pi fractions, but these P fractions are potentially available to crops.     

Potential growth of alfalfa (Medicago sativa L.) in the desert of Southern Peru and its response to high NPK fertilization

Irrigated and highly fertilized alfalfa growing in the deserts of Southern Peru reached maximum growth rates of about 200 kg dry forage ha^?1 d^?1 during the summer period and of 150 kg ha^?1 d^?1 during winter. These high rates were maintained for 10 to 20 days, after which growth rates declined. ‘Ceiling’ yields of about 5000 kg dry forage ha^?1 in summer and 3500 kg ha^?1 in winter were obtained in a growth period of 53 days. Simulations with an adapted model indicate that a decreased photosynthetic rate for aging leaves is a probable cause for the decrease. Growth curve simulations were also very sensitive to the level of carbohydrate reserves in the root system at harvest. High NPK fertilization (420, 280 and 420 kg ha^?1 yr^?1 of urea-N, P and K respectively) increased NO₃?N in soil 2.5 fold, available-K 1.6 fold, and available-P 4.3 fold. NH₄?N content did not increase. The higher amounts of available nutrients resulted in only about 10 percent increases in maximum growth rate and maximum yields. With respect to plant composition (%N, %P and %K), a significant response only to the higher P level was observed and a very slight, non-significant response to the higher K level was also noted. High N-fertilization did not increase the N-content of the plant, indicating that the rhizobia present are able to fix up to 900–1000 kg N ha^?1 yr^?1 in the aboveground herbage. Commercial inoculants did not improve this N-fixation capacity; even in virgin desert soils after only a few harvests, yields as well as N-contents of non-inoculated alfalfa were of the same order of magnitude as inoculated alfalfa.     

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.     

Phosphorus benefits from grain-legume crops to subsequent maize grown on acid soils of southern Cameroon

We conducted field experiments over 2 years on two acid soils of southern Cameroon to test whether efficient uptake and use of phosphorus (P) from less available sources by grain legume genotypes could benefit subsequent rotational maize. We grew two crops each year. For the first crop we grew 4 genotypes of soybean and of cowpea, plus maize. For the second crop we grew maize. The first crops were fertilized with 0, 90 kg P ha⁻¹ as phosphate rock (PR) or 30 kg P ha⁻¹ as triple super phosphate (TSP). P application highly significantly increased shoot dry matter, P uptake, N₂ fixation and grain yields of the grain legumes with TSP generally more effective than PR. Two of the soybean and two of the cowpea genotypes were more efficient at using P. Only the P-efficient soybean and cowpea genotypes increased subsequent maize yields. Yields of the subsequent maize grown in rotation were significantly correlated with shoot P uptake for which the quantity of P applied with the crop residues of the pre-crop appeared to be a major factor. We also grew the grain legumes in nutrient solutions and measured organic acid-anion exudation from roots, root-surface phosphatase-activity, and root morphological characteristics. Enhanced exudation of organic acid anions from roots of P-deprived plants might have contributed to the P acquisition efficiency under field conditions of the P-efficient cowpea genotypes and one of the P-efficient soybean genotypes. A higher activity of root-surface acid phosphatase might have been important for the other P-efficient soybean genotype. The results show, that the potential positive rotational effect of cowpea and soybean on the acid, highly P-sorbing soils of southern Cameroon depends on breeding and using P-efficient genotypes when sparingly soluble and suboptimal rates of soluble P fertilizers are used. Section Editor: N. J. Barrow     

Municipal solid waste compost dose effects on soil microbial biomass determined by chloroform fumigation-extraction and DNA methods

We evaluated the relationship between microbial biomass C and N (B_C and B_N) as estimated by the chloroform fumigation-extraction (CFE) method and microbial biomass DNA concentration in a loam-clayey wheat cultivated soil. The soil received municipal solid waste compost at rates of 40 or 80 t ha^?1 and farmyard manure at 40 t ha^?1. Microbial biomasses C and N and DNA concentration centration showed the highest values for microorganisms counts with compost and farmyard manure at 40 t ha^?1. Compost applications at 40 t ha?1 improve the micro-organisms growth than that of 80 t ha^?1. Moreover a significant decrease of soil microbial biomass was noted after fertilisation for three years. The presence of humic acid and proteins impurities in DNA extracts; even in important level as in F-treated soil; did not affect the microbial biomass. The decrease of microbial biomass was due to heavy metals content elevation in compost at 80 t ha^?1 treated soil. Thus the highest rate of municipal solid waste compost induced the lowest ratio of biomass C to soil organic carbon and the lowest ratio of biomass N to soil organic nitrogen. There was a positive relationship between B_C, B_N and DNA concentration. DNA concentration was significantly and positively correlated with B_C and with B_N. However there was a negative correlation between either micro-organisms numbers and DNA concentration, or B_C and B_N. The comparison of the two used methods DNA extraction and CFE showed the lowest coefficient of variation (cv %) with DNA extraction method. This last method can be used as an alternative method to measure the microbial biomass in amended soils.     

Transformations between organic and inorganic sediment phosphorus in Lake Balaton

In order to estimate microbial P content and biological P uptake in sediments, the tungstate precipitation method of Orrett & Karl (1987) was used in sediment extracts. This method allows a simple and rapid separation of organic and inorganic ³²P radioactivity. Either inorganic ³²P (as carrierfree H₃ ³²PO₄) or organic ³²P (as ³²P-labelled algal material) was added to surface sediment suspensions of shallow Lake Balaton. Inorganic ³²P was rapidly transformed into organic ³²P, and this process was completely inhibited by formaline. P content of living benthic microorganisms was estimated from steady state distribution of the radioactivity. Transformation of algal organic P into inorganic P could also be detected.In extremely P limited Lake Balaton benthic microorganisms were shown to supplement their high P requirements by inorganic P uptake. The velocity of the inorganic into organic P transformation, i.e. the rate of microbial P uptake, was comparable to P uptake in the water column. Microbial P uptake contributed significantly to total P fixation by sediments, particularly at low ( 100 µg P l^–1) phosphate additions.     

Photosynthetic rates in relation to leaf phosphorus content in pioneer versus climax tropical rainforest trees

In Guyana dense rainforest occurs on intensely weathered acid soils, low in soil phosphorus. To investigate whether low P availability limits photosynthesis of trees growing on these soils more than N does, leaf P and N content, and their relationship with the photosynthetic capacity (A _sat, mol CO₂ m^-2 s^-1) were studied for nine pioneer and climax tree species in a range of light climates. Light environment was described using hemispherical photographs. For both pioneer and climax species, leaf P content (r ²=0.71 and 0.23, respectively) is a more important determinant of A _sat than leaf N content (r ²=0.54 and 0.12, respectively). Pioneer species have a higher leaf P and N content than climax species. At similar P or N content, pioneers have a higher A _sat than climax species. The saplings studied had a relatively high A _sat, considering their low P concentration (15–30 mol P g^-1). All species studied had a constant leaf P and N concentration and photosynthetic capacity across light climates, because specific leaf mass (g m^-2) increased similarly with light availability. This acclimation to a change in light environment makes a possible limitation of A _sat by P or N independent of light environment.     

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pb_total were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56 mg Pb ha^–1 for TML and 222 kg Pb ha^–1 for Pb_total. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pb_total (>90%) was found in the upland soils. In upland soils, TML was only detectable in the forest floor. The annual total deposition from the atmosphere, estimated as throughfall + litterfall fluxes, amounted to 3.7 mg Pb ha^–1 year^–1 for TML and 52 g Pb ha^–1 year^–1 for Pb_total. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pb_total in wet precipitation were: fog > throughfall > bulk precipitation. The annual fluxes with runoff from the catchment was 0.5 mg Pb ha^–1 year^–1 for TML and 2.8 g Pb ha^–1 year^–1 for Pb_total. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t _1/2) of 33.5 days. The degradation of TML in Fen (t _1/2 = 421 days) and in the mineral soil (Bw-C horizon, t _1/2 = 612 days) was much slower. Emission of tetramethyllead from wetland soils was not observed during the 1 year incubation. The adsorption affinity of TML to different soils was Fen > Oa > A Bw-C. The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pb_total are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pbtotal. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for a long time. In upland soils, TML decomposes rapidly. Only small amounts of TML are transferred from soils into runoff.     

Using municipal biosolids in combination with other residuals to restore metal-contaminated mining areas

High metal waste materials from historic mining at the Bunker Hill, Idaho (ID) Superfund site was amended with a range of materials including municipal biosolids, woody debris, wood ash, pulp and paper sludge, and compost. The existing soil or waste material has elevated metal concentrations with total Zn, Pb and Cd ranging from 6000 to 14700, 2100 to 27000 and 9 to 28 mg kg^–1, respectively. Surface application of certain amendments including biosolids mixed with wood ash resulted in significant decreases in subsoil acidity as well as subsoil extractable metals. This mixture was sufficient to restore a plant cover to the contaminated areas. At the Bunker Hill site, a surface application of high N biosolids (44 or 66 tons ha^–1) in combination with wood ash (220 tons ha^–1) with or without log yard debris (20% by volume) or pulp and paper sludge (44 tons ha^–1) was able to restore a vegetative cover to the metal contaminated materials for 2 years following amendment application. Plant biomass in 1999 was 0.01 mg ha^–1 in the control versus a mean of 3.4 tons ha^–1 in the residual amended plots. Metal concentrations of the vegetation indicated that plants were within normal concentrations for the 2 years that data were collected. Surface application of amendments was also able to reduce Ca(NO₃)₂ extractable Zn in the subsoil from about 50 mg kg^–1in the control to less than 4 mg kg^–1in two of the treatments. Use of conventional amendments including lime alone and microbial stimulants were not sufficient to support plant growth. These results indicate that surface application of biosolids in combination with other residuals is sufficient to restore a vegetative cover to high metal mine wastes.     

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

Backgrounds and aims

In Mediterranean frequently burnt areas, the decrease of soil fertility leads to regressive vegetation dynamics. Organic amendments could help to accelerate post-fire ecosystem resilience, by improving soil properties and plant nutrition. This study was conducted to assess the potential of a composted biosolid to restore an early post-fire shrubland.

Methods

About 50 Mg.ha^?1 of fresh co-composted sewage sludge and green wastes were surface applied 7 months after fire on a silty-clayey soil. We monitored over a 2-year period organic matter and nutrient transfers to soil, nutrient responses of dominant plant species, and ecosystem contamination by potentially toxic trace elements.

Results

Over the experimental survey, compost rapidly and durably improved soil P₂O₅, MgO and K₂O content, and temporarily increased N-(NO₃ ^? + NO₂ ^?) content. Plant nutrition was improved more or less durably depending species. The most positive compost effect was on plant and soil phosphorus content. Plant nutrient storage was not improved 2 years after amendment, suggesting luxury consumption. No contamination by trace elements was detected in soil and plant.

Conclusions

The use of compost after fire could help for rapidly restoring soil fertility and improving plant nutrition. The increase of soil nutrient pools after amendment emphazised the diversity of plant nutritional traits. Eutrophication risk could occur from high compost and soil P₂O₅ content.     

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.     

Controls and models for estimating direct nitrous oxide emissions from temperate and sub-boreal agricultural mineral soils in Europe

Based on a review of N₂O field studies in Europe, major soil, climate and management controls of N₂O release from agricultural mineral soils in the European Union have been identified. Data for these N₂O emission drivers can easily be gathered from statistical services. Using stepwise multivariate linear regression analysis, empirical first order models of N₂O emissions have been established which allow – in contrast to existing large-scale approaches – a regionally disaggregated estimation of N₂O emissions at sub-national, national and continental level in the temperate and boreal climate regions of Europe. Arable soils showed lower mean and maximum emissions in oceanic temperate climate (Temperate West) than in pre-alpine temperate and sub-boreal climate (Sub-boreal Europe). Therefore, two separate regression models were developed. Nitrous oxide emissions from arable soils the Temperate West amount to an average flux rate below 2 kg N₂O-N ha^–1 yr^–1 and rarely exceed 5 kg N₂O-N ha^–1 yr^–1. They are modelled by the parameters fertiliser, topsoil organic carbon and sand content. In Sub-boreal European arable soils, N₂O emissions vary in a much wider range between 0 and 27 kg N₂O-N ha^–1 yr^–1 in dependence of available nitrogen, represented in the model by fertiliser and topsoil nitrogen content. Compared to existing methods for large scale inventories, the regression models allow a better regional fit to measured values since they integrate additional driving forces for N₂O emissions. For grasslands, a fertiliser-based model was established which yields higher emission estimates than existing ones. Due to an extreme variability, no climate, soil nor management parameters could be included in the empirical grasslands model.     

Towards an understanding of the dynamics of compost N in the soil-plant-atmosphere system using 15N tracer

Aims

The principal aim of the present review is to synthesize and evaluate published information on the N fertilizer value of composts, and their effect on the utilization of conventional N fertilizers by crops.

Methods

We have examined the literature where the dynamics of N in the soil-plant-atmosphere continuum are traced using composts that were either artificially enriched in the ¹⁵N stable isotope (in units of atom % ¹⁵N excess) or had a natural ¹⁵N abundance (δ¹⁵N in units of ‰ or per mil) due to isotope discrimination processes that occur during composting. The methods used to produce artificially-enriched composts and to test uniformity of labelling are reviewed.

Results

Limited data show that composts are generally inferior sources of N for crops compared with their raw materials due to a lower N mineralization capacity. Immobilization of fertilizer N increases in compost-amended soils and may reduce recovery by a crop, but fertilizer N losses are reduced overall. However, co-application of compost and urea should be avoided due to the risk of increased NH₃ volatilization due to the action of compost-derived urease. High annual rates of compost application can exacerbate environmental problems including nitrate contamination of groundwater.

Conclusions

Efforts are required to improve the N fertilizer value of composts by minimizing NH₃ volatilization losses during composting. More attention should also be given to the use of the natural ¹⁵N abundance of compost as a tracer.