Long-term changes in phosphorus fractions in growers’ paddocks in the northern Victorian grain belt

Increases in P fertiliser use in Australian grain production systems over the past decades have not necessarily coincided with improved nutrient-use efficiency by crops because only a small proportion of applied P has been directly used by crops, leaving large amounts of the P in soil. Information on the transformation of applied P and the residual effectiveness of P fertiliser in growers’ paddocks under their crop rotations in a wide range of soil types may help to develop improved management practises for P fertilisers. The present study examined the size and changes of P pools in soils in the major regions used for grain production across northern Victoria. Soil samples were collected from 43 sites representing all the major soil types. In addition, samples were collected from adjacent ‘reference’ areas across fence-lines where remnant native vegetation was present to examine long-term changes in soil fertility as a result of cropping. Highly positive P balance in 27 growers’ paddocks indicates potentially high rates of P fertilization in excess of that exported/lost from these paddocks. The accumulated P was transformed into both labile and non-labile pools depending on the general chemical–physical properties of a particular soil. In particular, in soils with a sandy texture and low oxalate-extractable Al and Fe such as the sandy Calcarosols, the residual P fertilizer was preferentially transformed into labile and moderately labile pools. These P fractions can be available for subsequent crops. In contrast, a large proportion of P fertilizer applied to other soil types has been transformed into the non-labile P pools where crops have difficulty in accessing. It is suggested that P application rates should be reduced to avoid the loss of P through sorption/precipitation, leaching or run-off while still meet crop demand.     

Yield,nitrogen recovery efficiency and quality of vegetables grown with organic waste-derived fertilisers

More sustainable production of high-quality, nutritious food is of worldwide interest. Increasing nutrient recycling into food systems is a step in this direction. The objective of the present study was to determine nitrogen (N) fertiliser effects of four waste-derived and organic materials in a cropping sequence of broccoli, potato and lettuce grown at two latitudes (58° and 67°N) in Norway during 3 years. Effects of anaerobically digested food waste (AD), shrimp shell (SS), algae meal (AM) and sheep manure (SM) at different N application rates (80 and 170 kg N ha^?1 for broccoli, and 80 and 60 kg N ha^?1 for potato and lettuce, respectively) and residual effects were tested on crop yield, N uptake, N recovery efficiency (NRE), N balance, N content in produce, mineral N in soil, product quality parameters and content of nitrate in lettuce. Mineral fertiliser (MF) served as control. Effects on yield, N uptake, NRE, N balance and product quality parameters could to a great extent be explained by estimated potentially plant-available N, which ranked in the order of AD > SS > SM > AM. Results for crops fertilised with AD and SS were not significantly different from MF at the same N application rate, while AM, in agreement with its negative effect on N mineralisation, gave negative or near-neutral effects compared to the control. No residual effect was detected after the year of application. The results showed that knowledge about N dynamics of relevant organic waste-derived fertilisers is necessary to decide on the timing and rate of application.     

A process for the introduction of elemental sulphur into high analysis phosphate fertilisers

A method for producing and incorporating fine elemental sulphur into high analysis fertilisers based on phosphoric acid is described. Molten sulphur is added to phosphoric acid under high shear conditions to produce a slurry containing fine sulphur. The slurry is subsequently used to acidulate phosphate rock and the resultant high analysis fertiliser contains sulphur which is sufficiently fine to ensure reasonably rapid oxidation to sulphate by soil micro-organisms. A small pilot plant has been used to produce a triple superphosphate containing 15% elemental sulphur which has a particle size distribution of: 95% < 0.5 mm, 76% < 0.25 mm and 57% < 0.15 mm.     

Modelling the oxidation of elemental sulfur in soils

Direct and recursive estimation models for the oxidation rate of elemental sulfur (S°) in soil have been proposed, both essentially based on a constant oxidation rate per unit area of exposed surface. Fertilizer S° is taken to consist largely of blocky shaped particles, i.e. having similar dimensions along three axes, which can be treated as equivalent spheres. The most important implication in applying the rate assumption to these shaped particles is that the mass at any time is related to the cube of the time. This has been verified experimentally for oxidation by thiobacilli. Although the assumption is less likely for heterotrophs, experiments involving four soils conformed to the cubic relation. Implications for the particle variables of size and size distribution have been given more limited testing. The data are generally consistent with theory, such as independence of the rate constant with particle size. Assuming an activation energy for the oxidation process implies, in addition to the above, an exponential relation of rate constant with temperature. This is supported by experiment. Values for the activation energy are approximately 85 kJ mol⁻¹, and therefore consistent with the rate limiting step for the oxidation being a chemical or biochemical reaction, rather than a diffusion process. Because absolute rate constants are generated by the models, they are useful for examining the effects of environmental variables not hitherto included. Empirical relationships, once established, can then be included in the model, such as the quadratic relation between rate constant and soil moisture, with the maximum at approximately field capacity. The delay time (the time to reach maximum oxidation rate) was useful, together with the rate constant, for distinguishing species of oxidizing microorganisms. Typically, under optimum conditions at 25°C, thiobacilli have a delay time of several days and a rate constant of 50μg cm⁻² day⁻¹ S, while heterotrophs have a negligible delay time but a rate constant of only 5μg cm⁻² day⁻¹ S. The cubic model with a single rate constant gave a surprisingly good fit to the oxidation rate over 12 months in New Zealand pastoral soils under field conditions of varying temperature and moisture. This was attributed to the balancing effect of moisture and temperature on the rate constant under the cool temperate climate. A knowledge of the annual average soil temperature is sufficient to provide advice on the optimum particle size for S° fertilizer.     

Assessing internal crop nitrogen use efficiency in high-yielding irrigated cotton

Improving the efficiency of nitrogen (N) fertiliser use is one means of reducing greenhouse gas emissions, particularly in irrigated crops such as cotton (Gossypium hirsutum L.). Internal crop N use efficiency (iNUE) was measured within two N fertiliser rate experiments that covered a wide range of N fertility over six cropping seasons. Crop iNUE was determined by dividing lint yield by crop N uptake. No nutrients other than N limited cotton growth or yield and the crops were irrigated to avoid drought stress. The optimal N fertiliser rates were determined from fitted quadratic functions that related lint yields with N fertiliser rates for each cropping system in each year. When the optimal N fertiliser rate was applied, crop iNUE averaged 12.5 ± 0.2 kg lint/kg crop N uptake. The crop iNUE was then used to determine the degree to which N fertiliser was under or over-applied, with respect to the economic optimum N fertiliser rate. Low iNUE values were associated with excessive N fertiliser application. Crop iNUE was determined in 82 commercial cotton crops in six valleys over the final 4 years of this study. The crop iNUE value was high in 8 fields (10%), optimal in 9 fields (11%) and low in 65 fields (79%). Crop N uptake averaged 247 kg N/ha, yield 2,273 kg lint/ha and crop iNUE 10.1 kg lint/kg crop N uptake for these sites. Averaged over all sites and years, about 49 kg N/ha too much N fertiliser was applied. Apparent N fertiliser recovery by cotton in the N rate experiments ranged from <20% in N-fertile treatments where legume crops had been grown, to more than 60% following winter cereal crops. Information on crop iNUE will enable cotton producers to assess their N fertiliser management and adjust N fertiliser rates for future crops. This study has demonstrated that there is scope to substantially reduce N fertiliser inputs to Australian cotton fields without reducing yields.     

Effect of sulphur content of phosphate rock/sulphur granules on the availability of phosphate to plants

Greenhouse studies were conducted to evaluate the agronomic effectiveness of phosphate rock/sulphur granules (PR/S) as influenced by (1) phosphate rock: sulphur ratio (2) the granule size and (3) the particle size of the rock used. In addition the effect of two methods of fertiliser application was determined. The reactive phosphate rock Sechura from Peru and a highly P retentive volcanic ash soil were used. Perennial ryegrass was grown as the test plant for 9 months. Herbage yield and phosphate uptake data indicated that PR/S of 5:1 ratio was as effective as single superphosphate. The uptake but not the yield decreased a little when the PR:S ratio was 6:1 whereas both were considerably reduced when the ratio was 7:1. With the 5:1 ratio product, 0.2–2 mm granules were more effective than 2–4 mm granules. With the 6:1 product this difference decreased and with the 7:1 the 2–4 mm granules were more effective. PR/S prepared using unground Sechura gave the same yield as that prepared using ground Sechura. Fractionation of inorganic soil phosphate at the end of the experiment indicated no accumulation of Fe-P plus Al-P when PR/S fertilisers were used. Ca-P values suggested a greater residual effect of these products compared to superphosphate. Mixing the PR/S with soil apparently increased the rate of sulphur oxidation compared to its application as a layer but the total herbage production for 10 cuts in the mixing treatment was greater only at the highest rate of fertiliser application.     

Nitrogen use efficiency of <Superscript>15</Superscript>N-labelled sheep manure and mineral fertiliser applied to microplots in long-term organic and conventional cropping systems

Nitrogen (N) utilisation by crops has to be improved to minimize losses to the environment. We investigated N use efficiency of animal manure and mineral fertiliser and fate of fertiliser N not taken up by crops in a conventional (CONMIN) and a bio-organic (BIOORG) cropping system of a long-term field experiment over three vegetation periods (winter wheat–soybean–maize). Microplots planted with wheat received a single application of ¹⁵N-labelled slurries (either urine or faeces labelled) or mineral fertiliser. At the end of each vegetation period we tested whether higher microbial activity and larger microbial biomass in BIOORG than CONMIN soils, and lower long-term N input level in BIOORG, affected use efficiency and fate of fertiliser N not taken up by crops. Recovery of ¹⁵N in wheat was 37%, 10% and 47% from urine, faeces and mineral fertiliser, respectively, and decreased strongly in the residual years. In total 41%, 15% and 50% of ¹⁵N applied as urine, faeces and mineral fertiliser was recovered by the three crops. ¹⁵N recovered from originally applied urine, faeces and mineral fertiliser in the topsoil (0–18 cm) at the end of the third vegetation period was 19%, 25% and 20%, respectively. Of urine-, faeces- and mineral fertiliser-¹⁵N, 40%, 61% and 29%, respectively, was not recovered by the three crops and in topsoil suggesting significant transport of ¹⁵N-labelled components to deeper soil layers. CONMIN and BIOORG differed neither in fertiliser N use efficiency by crops nor in ¹⁵N recovery in soil indicating insignificant difference in the turnover and utilization of the applied manure nitrogen in the conventional and the bio-organic cropping systems.     

Evaluation of partially acidulated phosphate fertilisers and reactive phosphate rock for hill pastures

The initial and residual effectiveness of two partially acidulated fertilisers, a single superphosphate (SSP): reactive phosphate rock (RPR) physical mix (SSP:RPR) and a partially acidulated phosphate rock (PAPR), and a RPR, North Carolina, were compared with SSP at two phosphate (P)-responsive sites in hill country. One site had received small annual inputs of SSP (125 kg ha^–1 y^–1) fertiliser for 10 years (LF) and the other site no SSP in the past 5 years (NF). The SSP, PAPR and RPR were applied at 3 rates (20, 40 and 60 kg P ha^–1) and SSP:RPR at one rate (40 kg P ha^–1) once only in the first year. Fertiliser treatments were applied with or without Grasslands Huia white clover (Trifolium repens L.) seed. Initial and residual pasture and legume responses were measured over two years.In the first year, pasture and legume response to applied P was much greater at the LF than NF site. A deterioration in legume content and vigour brought about by withholding fertiliser, rather than a difference in soil-fertiliser reactions, appears to be the main reason for the different response at the two sites in the first year. At the LF site the fully (SSP) and partially (SSP:RPR and PAPR) acidulated fertilisers were far more effective in stimulating legume growth than the RPR, while at the NF site no differences in pasture or legume production were found between fertilisers in the first year. Where fertiliser has been withheld for a number of years the use of SSP appears to be a wasteful and inefficient use of a processed fertiliser.Residual effects of RPR were greater than those of SSP, as shown by the greater yield of legume at both sites in the second year. The residual effectiveness of both the partially acidulated materials was much less than that of the RPR. Mixing and sowing white clover with the fertilisers had some beneficial effects on legume content at the NF site in both years and improved legume production at this site in the second year.     

Kinetics of chemical desulphurization of coal in aqueous ferric chloride

The kinetics of the chemical desulphurization of Lafia coal by the oxidation of the pyritic sulphur component with aqueous ferric chloride has been investigated. The oxidation rate was found to increase significantly with increasing temperature (60 to 102°C) and ferric chloride concentration (0.2 to 1.0M) but decreased with increasing coal particle size (-0.210 mm to +0.841 mm). The kinetic data were well described by the unreacted shrinking core model with the indication that the desulphurization was predominantly chemical reaction controlled. The rate of reaction was also found to be well correlated by a two-parameter pseudo-homogeneous kinetic model. The specific rate constant obtained showed a true Arrhenius temperature dependence.     

Simulating phosphorus responses in annual crops using APSIM: model evaluation on contrasting soil types

Crop simulation models have been used successfully to evaluate many systems and the impact of change on these systems, e.g. for climatic risk and the use of alternative management options, including the use of nitrogen fertilisers. However, for low input systems in tropical and subtropical regions where organic inputs rather than fertilisers are the predominant nutrient management option and other nutrients besides nitrogen (particular phosphorus) constrain crop growth, these models are not up to the task. This paper describes progress towards developing a capability to simulate response to phosphorus (P) within the APSIM (Agricultural Production Systems Simulator) framework. It reports the development of the P routines based on maize crops grown in semi-arid eastern Kenya, and validation in contrasting soils in western Kenya and South-western Colombia to demonstrate the robustness of the routines. The creation of this capability required: (1) a new module (APSIM SoilP) that simulates the dynamics of P in soil and is able to account for effectiveness of alternative fertiliser management (i.e. water-soluble versus rock phosphate sources, placement effects); (2) a link to the modules simulating the dynamics of carbon and nitrogen in soil organic matter, crop residues, etc., in order that the P present in such materials can be accounted for; and (3) modification to crop modules to represent the P uptake process, estimation of the P stress in the crop, and consequent restrictions to the plant growth processes of photosynthesis, leaf expansion, phenology and grain filling. Modelling results show that the P routines in APSIM can be specified to produce output that matches multi-season rotations of different crops, on a contrasting soil type to previous evaluations, with very few changes to the parameterization files. Model performance in predicting the growth of maize and bean crops grown in rotation on an Andisol with different sources and rates of P was good (75–87% of variance could be explained). This is the first published example of extending APSIM P routines to another crop (beans) from maize. Dr R. J. Delve has recently left CIAT and joined Catholic Relief Services, Kenya.     

The long-term effects of manures and fertilisers on soil productivity and quality: a review

The results from 14 field trials comparing the long-term (20 to 120 years) effects of fertilisers and manures (farmyard manure, slurry, and green manure) on crop production and soil properties are reviewed. In total there were 24 paired comparisons of the effects of manure and fertiliser. Some of the trials also contained a control (no nutrient inputs) treatment. The input of nutrients as either fertilisers or manures had very large effects (150–1000%) on soil productivity as measured by crop yields. Manured soils had higher contents of organic matter and numbers of microfauna than fertilised soils, and were more enriched in P, K, Ca and Mg in topsoils and nitrate N, Ca and Mg in subsoils. Manured soils also had lower bulk density and higher porosity, hydraulic conductivity and aggregate stability, relative to fertilised soils. However, there was no significant difference (P < 0.05) between fertilisers and manures in their long-term effects on crop production. In the context of this set of international trials, the recent evidence from the Rothamsted classical long-term trials appears to be exceptional, due to the larger inputs of manures and larger accumulation of soil OM in these trials. It is suggested therefore that manures may only have a benefit on soil productivity, over and above their nutrient content, when large inputs are applied over many years. The evidence from these trials also shows that, because the ratio of nutrients in manures is different from the ratio of nutrients removed by common crops, excessive accumulation of some nutrients, and particularly P and N, can arise from the long-term use of manures, relative to the use of fertilisers. Under these conditions greater runoff of P, and leaching of N may result, and for soils with low P retention and/or in situations where organic P is leached, greater P leaching losses may occur. The use of manures, relative to fertilisers, may also contribute to poor water quality by increasing its chemical oxygen demand. It is concluded therefore that it cannot generally be assumed that the long-term use of manures will enhance soil quality – defined in terms of productivity and potential to adversely affect water quality – in the long term, relative to applying the same amounts of nutrients as fertiliser.     

Fertiliser influence on alkali release during straw pyrolysis

Comparative studies of alkali release from wheat and oat straws cultivated in the laboratory with chloride-rich and sulphate-rich fertilisers are reported. The release of alkali during pyrolysis in the temperature range 25-1060°C is measured using the sensitive surface ionisation technique. Straw cultivated with a chloride-rich fertiliser releases two to four times more alkali than straw fertilised with a sulphate-rich fertiliser, and the release takes place at lower temperatures. The temperatures for maximum alkali release are ∼800°C for straw cultivated with a chloride-rich fertiliser, and ∼870°C for straw supplied with a sulphate-rich fertiliser. The samples were also subject to simple water leaching, and alkali was observed to be easily removed by leaching irrespective of fertiliser. Application of chloride-free fertilisers is concluded to be a simple and efficient way to reduce the alkali release from the fuels, and the method can easily be combined with other methods in order to improve fuel quality.     

Identification of opportunities for improved nitrogen management in sugarcane cropping systems using the newly developed Canegro-N model

Sugarcane (Saccharum spp. L.) cropping systems require the application of substantial amounts of fertiliser nitrogen (N), especially under irrigated conditions and in areas where rainfall is sufficient for high dry matter production. Inadequate N applications can reduce yields, while excess N or inappropriately timed applications can result in the export of significant quantities of N to the environment as a pollutant. An N subroutine has now been included into the Canegro crop model which is based in the DSSAT (Decision Support System for Agrotechnology Transfer) framework. Data from a field and lysimeter trial conducted in Pongola, South Africa were used to calibrate and evaluate the model, following which the model was used to investigate two potential approaches to improve fertiliser N management. Findings were, firstly, that measured and simulated results show on-farm monitoring of soil inorganic N levels and adjusting fertiliser applications accordingly has considerable potential for reducing fertiliser requirements and N losses. Secondly, during the periods between active crop growth cycles, significant amounts of inorganic N can accumulate in a soil as a result of mineralisation. Accounting for this N enables fertiliser N application to be delayed to some time after planting or commencement of ratoon growth, thereby significantly reducing the risky period during which applied N may be leached. For the system modelled in this study, inorganic N made available through organic matter mineralisation was sufficient to match initial crop demand for ~55 days following ratooning. When ammonium-based fertilisers are used, lower volatilisation losses can also be expected with this strategy. These findings now need to be confirmed in field trials. Modelling, combined with adequate measured data for calibration purposes, can be a powerful tool to identify improved N management practices for a particular cropping system. In its current form, Canegro-N can be used to improve our understanding of N dynamics in sugarcane production systems and to guide management practices and future research.     

Crop production,soil carbon and nutrient balances as affected by fertilisation in a Mollisol agroecosystem

A 19-year field experiment on a Mollisol agroecosystem was carried out to study the productivity of a wheat-maize-soybean rotation and the changes in soil carbon and nutrient status in response to different fertiliser applications in Northeast China. The experiment consisted of seven fertiliser treatments: (1) unfertilised control, (2) annual application of P and K fertilisers, (3) N and K fertilisers, (4) N and P fertilisers, (5) N, P and K fertilisers, (6) N, K and second level P fertilisers, and (7) N, P and second level K fertilisers. Without fertiliser, the Mollisols could support an average yield of 1.88 t ha⁻¹ for wheat, 3.89 t ha⁻¹ for maize and 2.12 t ha⁻¹ for soybean, compared to yields of 3.20, 9.30 and 2.45 t ha⁻¹ respectively for wheat, maize and soybean if the crop nutrient demands were met. At the potential yield level, the N, P and K removal by wheat are 79 kg N ha⁻¹, 15 kg P ha⁻¹, and 53 kg K ha⁻¹, by maize are 207 kg N ha⁻¹, 47 kg P ha⁻¹, and 180 kg K ha⁻¹, by soybean are 174 kg N ha⁻¹, 18 kg P ha⁻¹, and 55 kg K ha⁻¹. Crop yield, change in soil organic carbon (SOC), and the total and available nutrient status were used to evaluate the fertility of this soil over different time periods. This study showed that a fertiliser strategy that was able to maintain yields in the short term (19 years) would not maintain the long term fertility of these soils. Although organic carbon levels did not rise to the level of virgin soil in any treatment, a combination of N, P and K fertiliser that approximated crop export was required to stabilise SOC and prevent a decline in the total store of soil nutrients.     

Can nitrogen fertiliser and nitrification inhibitor management influence N2O losses from high rainfall cropping systems in South Eastern Australia?

Nitrous oxide (N₂O) is a potent greenhouse gas released from high rainfall cropping soils, but the role of management in its abatement remains unclear in these environments. To quantify the relative influence of management, nitrogen (N) fertiliser and soil nitrification inhibitor was applied to separate but paired raised bed and conventionally flat field experiments in south west Victoria, to measure emissions and income from wheat and canola planted 2 and 3 years after conversion from a long-term pasture. Management included four different rates of N fertiliser, top-dressed with and without the nitrification inhibitor Dicyandiamide (DCD), which was applied in solution to the soil in the second year of experimentation. Crop biomass, grain yield, soil mineral N, soil temperature and soil water and N₂O flux were measured. Static chamber methodology was used to identify relative differences in N₂O loss between management. In the second crop (wheat) following conversion, N₂O losses were up to 72 % lower (P < 0.05) in the furrows, receiving the lower rate of N fertiliser compared with the highest rate, with less frequent reductions observed in the third crop (canola); losses of N₂O from the beds was unaffected by N rate, perhaps from nitrate leakage into the adjacent furrow of the raised bed experiment. On the nearby flat experiment, nitrate leaching may have diminished the effects of N rate and DCD on N₂O flux. Furthermore the extra N did not significantly increase grain yield in either the wheat or canola crops on both experiments. The application of DCD in the canola crop temporarily reduced (P < 0.05) N₂O production by up to 84 % from the beds, 83 % in the adjacent furrows and 75 % on the flat experiment. Grain yield was not significantly (P < 0.001) affected however, canola income was reduced by $1407/ha and $1252/ha, compared with no addition of inhibitor on the respective bed and flat experiments. Although N₂O fluxes are driven by environmental episodic events, management will play a role in N₂O abatement. However, DCD currently appears economically unfeasible and matching N fertiliser supply to meet crop demand appears a better option for minimising N₂O losses from high rainfall cropping systems.     

Performance of Pb/Zn tolerantFestuca rubra on metalliferous spoil in relation to nitrogen source

In a glasshouse bioassay of acid and calcareous Pb/Zn mine waste, relationships between dry matter yield of Pb/Zn tolerantFestuca rubra L. cv. Merlin, and seven conventional and slow-release nitrogen fertilisers applied as single and split applications were examined against a standard background of phosphate and potassium levels. No significant advantages were found to justify the use of slow release N sources over standard formulations, despite losses due to volatilisation, leaching and immobilisation processes. The fate of the applied nitrogen fertiliser is greatly influenced by the physical and chemical properties of the substrate which must be taken account of in formulating establishment and management specifications.     

Effect of phosphate fertiliser type on the accumulation and plant availability of cadmium in grassland soils

Cadmium (Cd), a potentially toxic heavy metal for humans and animals, accumulates in the liver and kidneys of older animals grazing New Zealand and Australian pastoral soils. Phosphorus (P) fertiliser is the major input of Cd into these farming systems. A study was conducted to evaluate the effects, over 10 years, of annual application (30 kg P ha^–1 yr^–1) of four forms of P fertilisers having different solubilities and Cd contents [41, 32, 10 and 5 g Cd g^–1 for North Carolina phosphate rock (NCPR), single superphosphate (SSP), diammonium phosphate (DAP) made from low Cd phosphate rocks and Jordan phosphate rock (JPR) respectively] on soil and herbage Cd concentrations. Ten years of fertiliser application caused a marked increase in surface soil Cd concentrations. Total soil Cd was significantly higher in SSP and NCPR treatments compared to control (no P fertiliser), JPR and DAP treatments in the 0–30 and 30–75 mm soil depths. Plant-available Cd (0.01 M CaCl₂ extractable Cd) was higher in SSP treatments than in control and other fertiliser treatments. Chemical analysis of herbage samples showed that there was no significant difference in Cd concentration in pasture grasses between treatments in the second year of the trial but in the eighth and tenth year, plots fertilised with SSP and NCPR had significantly higher Cd in pasture grasses in most of the seasonal cuts compared to control, JPR and DAP. Cadmium recovery by both grasses and clover was less than 5% of Cd applied in fertiliser. Clover Cd concentration and yield were much lower than those for grass and therefore its contribution to pasture Cd uptake was very low (< 7%). A strong seasonal effect on grass Cd concentration, which is inversely related to pasture growth rate, was observed in all three sampling years — Cd concentration was highest during autumn and lowest in spring. Total Cd contents of the fertilisers and their rate of dissolution rather than soil pH [pH (H₂O) at 30–75 mm depth of 5.39, 5.20, 5.11 and 5.36 for NCPR, SSP, DAP and JPR treatments respectively]influenced soil and herbage Cd. These results showed that the use of P fertilisers with low Cd contents will reduce herbage Cd levels and has the potential of reducing Cd levels in grazing animals and their products.     

Controlling soil water content in fertiliser dissolution experiments

Phosphorus lost in runoff from agricultural land leads to the enrichment of surface waters and contributes to algal blooms. Fertilisers are one source of this P. To compare the water available P of different fertiliser formulations in the laboratory it is necessary to control environmental conditions, temperature, relative humidity and soil water content, prior to simulating rainfall. Two chambers were designed in which relative humidity and soil water content were controlled using salt solutions. An initial design comprising a sealed chamber with three layers of soil samples over a salt bath was found to be inferior to a single layer design. The changes in water content of soil samples were used to test the single layer chamber in a constant temperature environment (15 °C) using a saturated KCl solution (90% relative humidity). Based on the final soil water content of the samples, the spatial variation within the chamber was within tolerable limits. The single layer chamber was used for a simulation experiment comparing the water available P of two commercial fertilisers. Using a saturated resorcinol solution (95% relative humidity) soil samples were equilibrated at 15 °C for 21 days, fertiliser added, and the water available P measured up to 600 h after fertiliser application. The results indicate that the amount of water available P was related to the fertiliser compound and exponentially related to the time since fertiliser application. It was concluded that the single layer chamber is suitable for controlling relative humidity and soil water content in trials such as these where the water available P of fertilisers are being compared.     

The influence of controlled release fertilisers and the form of applied fertiliser nitrogen on nitrous oxide emissions from an andosol

A laboratory experiment was conducted to determine whether applying controlled release nitrogen fertilisers could reduce nitrous oxide emissions from an andosol maintained at different water contents, compared with applying standard nitrogen fertiliser. The effect of the form of N applied (NH₄-N or NO₃-N) was also investigated. Soil was collected from an arable field and sub-samples were treated with controlled release or standard fertiliser, applied at a rate of 200 g N g^–1 dry soil either as NH₄ ⁺ or NO₃ ^–. The soils were maintained at 40%, 55%, 70% or 85% water filled pore space (WFPS) and incubated at 25 °C for 50 days. Gas samples were collected and analysed every 3–4 days and soil samples were analysed on five occasions during the incubation. Emissions of N₂O were much greater from ammonium sulphate than from calcium nitrate fertiliser, indicating that nitrification was the main source of the N₂O. Emissions at 85% WFPS were greater than at the lower water contents in all treatments. The use of controlled release NH₄-N fertilisers reduced and delayed the maximum peak of emissions, but at 55% and 70% WFPS this did not always result in lower total emissions. Emissions from the controlled release NO₃-N fertiliser were very low, but only significantly lower than from standard NO₃-N fertiliser at water contents below 85% WFPS. The results demonstrate that choosing the appropriate form of fertiliser in relation to expected soil moisture could significantly reduce N₂O emissions. Applying the fertiliser in a controlled-release form could further reduce emissions by reducing the length of time that fertiliser nitrogen is present in the soil and available for nitrification or denitrification.     

Comparison of Titania Particles Between Oxidation of Titanium Tetrachloride and Thermal Decomposition of Titanium Tetraisopropoxide

Thermal decomposition of TTIP was compared with oxidation of TiCl 4 in morphology and primary particle size of produced TiO 2 particles in a tubular reactor 2.7 cm in diameter and 54 cm in length under equal rate constants. The reactor temperature was varied from 850 to 1000°C for TiCl 4 oxidation and from 492 to 579°C for TTIP decomposition. The lower and upper limits of decomposition temperature for TTIP were determined so that the rate constants become equal, at corresponding limits, between TiCl 4 oxidation and TTIP decomposition. In order to maintain constant concentration with variation of reactor temperature, the flow rate of dilution gas was adjusted to compensate for the volume change of gas with temperature. The precursor concentration at the reaction condition was in the range of 1.09 2 10 m 6 to 1.09 2 10 m 5 mol/L, and the residence time of 3.1 to 10.8 s was based on the reactor set temperature. Particles from TTIP were spherical, while those from TiCl 4 were polyhedral. A considerable fraction of the precursor admitted to the reactor was consumed on the tube wall by surface reaction to form a zone coated with TiO 2 . The loss of precursor to the wall was greater with TiCl 4 oxidation. The particle size was, however, larger by 20% with TiCl 4 oxidation. By replacing the straight reaction tube with a concentric tube, the loss could be reduced, thereby increasing the amount of TiCl 4 available for particle formation significantly; the particle size was similar, however. With the straight tube a mixture of TiCl 4 and oxygen entered the reactor and the reaction occurred over the gradual increase from 650°C to a reactor set temperature of 900°C. With the concentric tube, the reactants had been preheated separately and then brought into contact right at the set temperature. The difference in the history of temperature for reaction may have brought about a difference in nucleation rate and consequently yielded particles of similar size. By analyses of BET surface area, X-ray diffraction patterns, and thermogravimetric data, TiO 2 particles from both routes were nearly nonporous, showed anatase peaks in majority, and contained no appreciable volatiles.