Anthony J. Weatherley

Risk of nitrate leaching from two soils amended with biosolids

High concentrations of N and P in biosolids are one of the strongest appeals for their agronomic use. However, it is essential to understand the fate of N in soils treated with biosolids for both plant nutrition and managing the environmental risk of NO3−-N leaching. This work aims to evaluate the risk of nitrate leaching from a sandy Podosol soil and from a clay Ferrosol soil, each one amended at the range 0.5–8.0 dry Mg/ha rates of freshly tertiary sewage sludge, composted sludge, limed sludge, heating-dried sludge and solar-irradiated sludge. Results showed that for similar biosolids application rates NO3−-N accumulated up to 3 times as much in the Ferrosol than in Podosol soil. However, there was a fixed 20% NO3−-N loss from the 20 cm amended-Ferrosol topsoil, whilst the N-nitrified expected to leach down from 20 cm amended-Podosol topsoil layer ranged from 42% to 76% of the accumulated NO3−-N, depending on the biosolid type. After all, NO3−-N expected to leach from Podosol soil ranged from 0.6 (heating-dried sludge) to 3.9 times (limed sludge) relative to Ferrosol soil at similar biosolid application rates. Nevertheless, the risk of NO3−-N groundwater contamination caused by biosolids applied at 0.5−8.0 dry Mg/ha rates could be considered very low.

The long-term residual value of rock phosphate and superphosphate fertilizers for various plant species under field conditions

In three, long-term field experiments on different lateritic soils in south-western Australia, the effectiveness of superphosphate and rock phosphate fertilizers applied 10 years (one experiment) or 4 years previously was measured relative to the effectiveness of freshly-applied superphosphate (relative effectiveness or RE) using several different plant species. For the species comparisons, RE values were estimated using the initial slope of the relationship between yield and the level of P applied. In addition, RE values were also determined for different levels of application to test whether RE values for previously-applied fertilizer changed with increasing level of application. Soil samples were collected 3–5 months before sowing for a soil test for phosphate (P) and the soil test values were related to plant yields measured later that year.At each site, the RE value of previously-appliedrock phosphate was calculated using initial slopes and was mostly consistently low and was similar (0.04–0.18) for all plant species. The exceptions were that the RE value about doubled for barley in one experiment and for another experiment the effectiveness of calcined (heated) C-grade ore (Calciphos) was about 2–3 times that of the untreated (i.e. unheated) fertilizer. In most cases, the RE value of previously appliedsuperphosphate at each site was similar (0.23–0.34) regardless of plant species. The exceptions were that the RE value was about double for barley in one experiment and about half for triticale in another. Rock phosphates applied 4 or 10 years previously were between about one twentieth to one quarter as effective as freshly applied superphosphate. Superphosphate applied 4 or 10 years previously was between about a quarter to one third as effective as freshly-applied superphosphate. At each site, the yield of each species was closely related to the P content of plant tissue and the relationship was independent of the fertilizer type or when the fertilizer was applied.At each site and for each plant species, the RE value of the previously-applied rock phosphate was estimated for different levels of application and generally decreased with increasing level of application, whereas the RE value for previously-applied superphosphate mostly remained approximately constant.At each site, the relationship between yield and soil test values (i.e. soil test for P calibrations) differed depending on the fertilizer type and the plant species.

Opportunities and constraints for biochar technology in Australian agriculture: looking beyond carbon sequestration

The application of biochar technology for soil amendment is largely based on evidence about soil fertility and crop productivity gains made in the Amazonian Black Earth (terra preta). However, the uncertainty of production gains at realistic application rates of biochars and lack of knowledge about other benefits and other concerns may have resulted in poor uptake of biochar technology in Australia so far. In this review, we identify important opportunities as well as challenges in the adoption of biochar technology for broadacre farming and other sectors in Australia. The paper highlights that for biochar technology to be cost-effective and successful, we need to look beyond carbon sequestration and explore other opportunities to value-add to biochar. Therefore, some emerging and novel applications of biochar are identified. We also suggest some priority research areas that need immediate attention in order to realise the full potential of biochar technology in agriculture and other sectors in Australia.

Biosolids effectiveness to yield ryegrass based on their nitrogen content

Biosolids have been reported to increase yields and supply plant nutrients. However, complying with health and environmental standards is necessary before applying biosolids to land. Thus, sludge stabilization is required to make biosolids safe enough for their agricultural use. Side effects of stabilization processes on agronomic features of sewage sludge are not quite known, although their understanding is essential for biosolids management. Based on a model equivalent to the Mitscherlich equation, effects of the most common processes for sludge stabilization were evaluated (composting, liming, heat-drying and solar irradiation) in relation to the agronomic effectiveness of biosolids to yield Lolium perenne L. on two tropical soils, with NH4H2PO4 as a reference. Sewage stabilization processes have affected the ability of biosolids to promote plant growth. Their effectiveness was usually higher than fertilizer in a Spodosol and lower in an Oxisol. Solar-irradiated sludge presented the highest effectiveness among the biosolids and reached peak yields at the lowest application rate independent on soil type. Biosolids could efficiently substitute fertilizers and even yield more plant dry matter than the NH4H2PO4 reference, depending on the biosolid and soil type.

A novel substance flow analysis model for analysing multi-year phosphorus flow at the regional scale

Achieving sustainable management of phosphorus (P) is crucial for both global food security and global environmental protection. In order to formulate informed policy measures to overcome existing barriers of achieving sustainable P management, there is need for a sound understanding of the nature and magnitude of P flow through various systems at different geographical and temporal scales. So far, there is a limited understanding on the nature and magnitude of P flow over multiple years at the regional scale. In this study, we have developed a novel substance flow analysis (SFA) model in the MATLAB/Simulink® software platform that can be effectively utilized to analyse the nature and magnitude of multi-year P flow at the regional scale. The model is inclusive of all P flows and storage relating to all key systems, subsystems, processes or components, and the associated interactions of P flow required to represent a typical P flow system at the regional scale. In an annual time step, this model can analyse P flow and storage over as many as years required at a time, and therefore, can indicate the trends and changes in P flow and storage over many years, which is not offered by the existing regional scale SFA models of P. The model is flexible enough to allow any modification or the inclusion of any degree of complexity, and therefore, can be utilized for analysing P flow in any region around the world. The application of the model in the case of Gippsland region, Australia has revealed that the model generates essential information about the nature and magnitude of P flow at the regional scale which can be utilized for making improved management decisions towards attaining P sustainability. A systematic reliability check on the findings of model application also indicates that the model produces reliable results.

Runoff losses from irrigated dairy pastures treated with phosphorus fertilisers of differing solubility in south-eastern Australia

In response to increasing concern about environmental quality, water authorities in many countries are imposing legislation limiting phosphorus (P) concentrations in water, which is having an impact on farming practice. This experiment investigated the agronomic effects and runoff losses associated with different forms of P fertiliser applied to an irrigated dairy pasture (soils were Vertic Calcic Red Chromosols; average Olsen P, 50 mg P/kg) in north-central Victoria, Australia. Single superphosphate (SSP), a sulfurised diammonium phosphate, or partially acidulated phosphate rock was surface-applied at 50 kg P/ha in March 2005 to a border-check, flood-irrigated dairy pasture (ryegrass–white clover) ten days before a scheduled irrigation. Dissolved reactive P (DRP) and total P (TP) were measured in runoff from whole bays on one replicate and from microplots on all three replicates for a period of 9 weeks. In all runoff events and all treatments, concentrations of DRP and TP in runoff greatly exceeded water quality guidelines for acceptable limits (0.045 mg P/L). The SSP resulted in significantly higher concentrations of P in runoff than the less water-soluble fertilisers. Even after the fifth irrigation, runoff from all fertilisers still exceeded the control. These results suggest that: (i) P fertilisers should not be applied in high-risk situations as insurance against yield loss; (ii) the current recommendation of withholding irrigation for 3 days after fertiliser application is insufficient to prevent potentially significant losses occurring; and (iii) runoff losses were dependent on the type of fertiliser applied, with a smaller proportion of P applied as sulfurised DAP lost in runoff.

Socio-environmental consideration of phosphorus flows in the urban sanitation chain of contrasting cities

Understanding how cities can transform organic waste into a valuable resource is critical to urban sustainability. The capture and recycling of phosphorus (P), and other essential nutrients, from human excreta is particularly important as an alternative organic fertilizer source for agriculture. However, the complex set of socio-environmental factors influencing urban human excreta management is not yet sufficiently integrated into sustainable P research. Here, we synthesize information about the pathways P can take through urban sanitation systems along with barriers and facilitators to P recycling across cities. We examine five case study cities by using a sanitation chains approach: Accra, Ghana; Buenos Aires, Argentina; Beijing, China; Baltimore, USA; and London, England. Our cross-city comparison shows that London and Baltimore recycle a larger percentage of P from human excreta back to agricultural lands than other cities, and that there is a large diversity in socio-environmental factors that affect the patterns of recycling observed across cities. Our research highlights conditions that may be “necessary but not sufficient” for P recycling, including access to capital resources. Path dependencies of large sanitation infrastructure investments in the Global North contrast with rapidly urbanizing cities in the Global South, which present opportunities for alternative sanitation development pathways. Understanding such city-specific social and environmental barriers to P recycling options could help address multiple interacting societal objectives related to sanitation and provide options for satisfying global agricultural nutrient demand.

Agronomic effectiveness of urban biochar aged through co-composting with food waste

Terra preta soils have been shown to develop after considerable modification of soil through char addition and over time natural ageing has led to increase in fertility of those soils. A co-composting experiment was conducted to accelerate the artificial ageing of urban biochar (UB) with the aim of achieving similar terra preta effect. UB was produced through the pyrolysis of 2:1 ratio of biosolids and green waste and then composted with food waste (10% v/v) until compost maturity at around 75 days. A portion of the UB was placed in litterbags within the composting biomass in order to examine the effects of co-composting more closely. Addition of 10% UB to food waste accelerated the composting process. As measured from the litter bags, co-composting UB with foodwaste increased CEC, pH, EC and nitrogen loading of composted UB relative to the un-composted UB. However, the composting process reduced BET surface area and porosity of UB most probably due to clogging of pores by the organics released during composting. The agronomic value of UB, UB co-composted with foodwaste and foodwaste compost was evaluated in a greenhouse pot experiment with sorghum plants on a sandy acidic topsoil. Results of the pot experiment showed higher plant growth, lower emissions of N2O and higher nitrogen use efficiency in soil amended with UB than the soil amended with compost and co-composted UB.

Urban biochar improves nitrogen and phosphorus availability in growing media

The purpose of this study was to substitute sphagnum peat from plant growing media with urban biochar (UB) and evaluate its impact on nitrogen (N) and phosphorus (P) availability. The UB was produced from the pyrolysis (650°C) of a 2 : 1 ratio of biosolids to green waste. We compared three mixes – 20% sphagnum peat mixed with composted pine bark (B0), 20% UB mixed with composted pine bark (B20) and 60% UB mixed with composted pine bark (B60) – for their ability to promote plant growth and minimise leaching losses in a greenhouse experiment using silverbeet (Beta vulgaris ssp. cicla). Plants were grown in 4.0-L custom-made chambers with the capacity to collect leachate and measure nitrous oxide gas flux. Both biochar mixes increased media pH, air filled porosity, bulk density and nutrient content relative to B0. The B0 had the highest cation exchange capacity and electrical conductivity. The UB-based mixes, B20 and B60, had no significant effect on silverbeet biomass after 11 weeks of growth but had higher N use efficiency and P availability than B0. These results indicate that UB can completely replace sphagnum peat from growing media and can be used at the rate of 60% on volume basis while improving N and P availability. Using a higher rate of biochar in growing media has the additional advantage of sequestering more carbon and reducing urban waste streams and landfill costs.