Inorganic phosphorous availability and mobility in a manufactured soil.

Manufactured soils, created by combining various organic and inorganic waste materials and byproducts, may be tailored to specific applications, providing an alternative to the extraction of natural soils. It is important for them to be capable of supporting plant growth without the need for significant management or fertiliser applications, the over-application of which can have adverse environmental effects. We examined the dynamics of phosphorus (P) transformations within a manufactured soil and the implications for nutrient cycling. A freshly prepared manufactured soil (32.5 % composted green waste, 32.5 % composted bark, 25 % horticultural grit, and 10 % lignite clay) was studied over one year in temperature and moisture controlled mesocosms. Leachate was collected to achieve high-resolution monitoring of leached phosphate concentrations. Initially, leached dissolved inorganic phosphorus (DIP) concentrations were low (0.02 ± 0.01 mg P L-1), before increasing by 160 µg P L-1 d-1 over the first 42 days to 5.57 ± 1.23 mg P L-1. After reaching a maximum concentration, DIP concentrations remained relatively consistent, varying by only 1.67 mg P L-1 until day 270. The increase in leached DIP was likely driven by soil organic matter mineralisation and the cleavage of carbon­phosphorus bonds by the soil microbes to satisfy carbon demand with mineralogical influences, such as a decrease in apatite content, also contributing. Sorption and desorption from soil particles were the processes behind the P loss from the soil, which was followed by slow diffusion and eventual loss via leaching. The fertiliser application on phosphate dynamics resulted in increased DIP leaching. P concentrations observed in the manufactured soil were within the range considered sufficient to support plant growth. However, the mean leached phosphorus concentrations were higher than reported eutrophication thresholds suggesting that these soils may pose a risk to surface waters in their current form.

Biochar improves fertility in waste derived manufactured soils, but not resilience to climate change.

We present a soil manufactured from waste materials, which could replace the use of peat and topsoil in plant production and reduce the pressure on natural soil resources. We tested the effect of the manufactured soil on ecosystem functions and microbial communities with and without plants present, and with and without biochar addition (Experiment 1). The resilience of the soil in response to drought and flooding, and also the effect of biochar was also tested (Experiment 2). Biochar increased soil C and N regardless of plant presence and negated the effect of the plant on soil peroxidase enzyme activity. The manufactured soil was largely resilient to drought, but not flooding, with negative impacts on microbial communities. Results indicate that biochar could improve soil properties, but not resilience to climatic perturbations. Results suggest that manufactured soils amended with biochar could offer a useful alternative to natural soil in many contexts.

Different feedstocks of biochar affected the bioavailability and uptake of heavy metals by wheat (Triticum aestivum L.) plants grown in metal contaminated soil.

Heavy metals (HMs) contamination of agricultural soils is an emerging food safety challenge at world level. Therefore, as a possible treatment for the remediation of a HMs contaminated soil (sewage water irrigation for 20-years), the impact of biochar (BC) was investigated on the uptake of HMs by wheat (Triticum aestivum L.) plants. The BC was produced from seven different feedstocks (cotton stalks (CSBC), rice straw (RSBC), poultry manure (PMBC), lawn grass (LGBC), vegetable peels (VPBC), maize straw (MSBC), and rice husks (RHBC)). Each BC was applied at 1.25% (dry weight basis, w/w) in contaminated soil and a control was maintained without BC addition and wheat was grown in potted soil and harvested at maturity. Results revealed that the properties of different biochars regulated their effects on soil nutrient and HMs mobility and uptake by plants. The maximum plant phosphorous and potassium uptake and translocation to grain (173.4% and 341%, respectively) was found in RSBC treatment over control. The RHBC, PMBC, and MSBC treatments showed a maximum decrease in grain Cd concentration (32.9%, 33.8%, and 34.1%, respectively) compared to the control. The grain Pb (-41% to -51%, with no significant differences among different treatments) and Ni (-63%) concentrations were also reduced significantly following BC treatments compared to control. The daily intake and health risk index of Cd were significantly decreased due to PMBC (-28.1% and -33.8%, respectively), and MSBC (-28.3% and -34.1%, respectively) treatment over control. The BC treatments significantly increased the translocation factor of Cd in the order of VPBC (52.1%) > LGBC (25.4%) > CSBC (13.6%) > RSBC (12.1%) compared to control. The study demonstrated that the effects of BC on metal uptake in plants varied with feedstocks and suitable BC can be further exploited for the rehabilitation of contaminated soils and thereby ensuring food safety.

Physico-chemical factors controlling the speciation of phosphorus in English and Welsh rivers.

Phosphorus is a finite resource essential for global food production. However, excessive loss to river systems from diffuse sources (typically agricultural) and point sources (e.g. waste water treatment works and industrial effluent) can lead to negative environmental impacts, including changes to diatom and invertebrate community structure. Current environmental quality standards for phosphorus in the UK have been based on reactive phosphorus, which is poorly defined and comprises an unknown proportion of soluble reactive phosphorus and chemically extractable particulate phosphorus. This research assesses the influencing factors that may control soluble reactive phosphorus concentrations in rivers, including dissolved iron, as well as partitioning processes associated with the presence of total suspended solids, and questions the reliability of the assumptions used when setting environmental quality standards. The extensive phosphorus speciation monitoring carried out across a wide geographic area of England and Wales shows that not all phosphorus as measured by the molybdenum blue method is either soluble or necessarily bioavailable, particularly at concentrations in the range in which the Environmental Quality Standard for 'Good' status (typically less than 100 µg P L-1) has been set. Phosphorus speciation can change due to physico-chemical processes which vary spatially and/or temporally, including precipitation with iron and partitioning with suspended solids.

Biochar incorporation increased nitrogen and carbon retention in a waste-derived soil.

The synthesis of manufactured soils converts waste materials to value-added products, alleviating pressures on both waste disposal infrastructure and topsoils. For manufactured soils to be effective media for plant growth, they must retain and store plant-available nutrients, including nitrogen. In this study, biochar applications were tested for their ability to retain nitrogen in a soil manufactured from waste materials. A biochar, produced from horticultural green waste, was added to a manufactured soil at 2, 5 and 10 % (by weight), then maintained at 15 °C and irrigated with water (0.84 mL m-2 d-1) over 6 weeks. Total dissolved nitrogen concentrations in soil leachate decreased by 25.2, 30.6 and 44.0 % at biochar concentrations of 2, 5 and 10 %, respectively. Biochar also changed the proportions of each nitrogen-fraction in collected samples. Three mechanisms for biochar-induced nitrogen retention were possible: i) increased cation and anion exchange capacity of the substrate; ii) retention of molecules within the biochar pore spaces; iii) immobilisation of nitrogen through microbial utilisation of labile carbon further supported by increased soil moisture content, surface area, and pH. Dissolved organic carbon concentrations in leachate were reduced (-34.7 %, -28.9 %, and -16.7 %) in the substrate with 2, 5 and 10 % biochar additions, respectively. Fluorescein diacetate hydrolysis data showed increased microbial metabolic activity with biochar application (14.7 ±â€¯0.5, 25.4 ±â€¯5.3, 27.0 ±â€¯0.1, 46.1 ±â€¯6.1 µg FL g-1 h-1 for applications at 0, 2, 5, and 10 %, respectively), linking biochar addition to enhanced microbial activity. These data highlight the potential for biochar to suppress the long-term turnover of SOM and promote carbon sequestration, and a long-term sustainable growth substrate provided by the reuse of waste materials diverted from landfill.