Waste recovered by-products can increase growth of grass-clover mixtures in low fertility soils and alter botanical and mineral nutrient composition

The effectiveness of four by-products (biogas digestate, pot ale, rockdust and wood ash) as fertilisers of a perennial ryegrass (Lolium perenne)-red clover (Trifolium pratense) mixture in terms of biomass production, botanical composition and macro- and micronutrient concentrations was tested in an outdoor pot trial. This was carried out over two growing seasons using two inherently low-fertility soils used for forage production. Macro- and micronutrients (N, P, K, Ca, Mg, Co, Cu, Mn, Mo and Zn) relevant for crops and livestock were determined in soils and plants. All the by-products increased overall biomass production and affected nutrient concentrations of the individual plant species to varying degrees. In addition the competitive balance between grass and clover was altered leading to different botanical composition in the different treatments and consequently differences in the nutrient concentrations of the species mixture. Changes were due to the nutrients applied in the by-products per se and/or to changes in the soil chemistry caused by the by-products. The results suggest a potential to enhance agricultural productivity through improved production and quality of forage on less fertile land by matching of by-products and soil properties

Influence of soil amendments and soil properties on macro– and micronutrient availability to microorganisms and plants

Utilising by-products from industrial and domestic activities and from bioenergy production is one of the new ways of recovering and re-using nutrient resources in agriculture. However, these by-products can potentially add toxic elements or alter soil properties in ways that harm the soil and related environments. This thesis investigated the efficacy and potential adverse effects of using organic (biogas digestate, pot ale) and inorganic (rockdust, wood ash) by-products as amendments on the supply of nutrients to crops (wheat, mixed perennial ryegrass and red clover) and the impact on community-level physiological and genetic profiles of soil microorganisms. The influence of the inherent soil macro –and micronutrient concentration relative to a range of environmental variables was also investigated to explain the variation in physiological profiles of the microbial communities and the genotypic variation in Rhizobium/Agrobacterium in a landscape-scale study of pasture and arable soils. The nutrient status of soils proved to be an important factor for the efficacy of amendment application. The by-products studied generally enhanced crop biomass and the content of some macronutrients and micronutrients in soils and plants when applied to nutrient-poor soils. The concentration of potentially toxic elements (Cd, Pb) was not increased in soils or plants due to amendment application. The botanical composition of mixed ryegrass-red clover stands was also affected by amendments, with biogas digestate, rockdust and wood ash producing more clover than grass. Soil microorganisms were largely unaffected by these amendments. However, the soil microbial community composition was altered by increasing the availability of nutrients through a fully-fertilised treatment. The landscape study showed that aqua regia-extractable manganese and rainfall, respectively, were the main factors explaining the variation in microbial physiological profiles and Rhizobium/Agrobacterium genotypes

Revisiting herbage sample collection and preparation procedures to minimise risks of trace element contamination

A renewed interest in trace elements (TE), as micronutrients as well as potentially toxic elements, and new options for multi-element analysis has led to an increased number of scientists engaging in TE studies. Accreditation, certification and quality control of TE analyses often applies only to the last step in the sample chain when prepared samples are sent to the laboratory for digestion/extraction and subsequent analysis. However, all stages of the chain from initial sampling to final analysis require an understanding of the specific challenges involved in TE studies and an awareness of the contamination risks as well as approaches to limit these. Contamination can potentially be introduced during all stages of handling and preparation of plant samples, e.g. through dust and the materials that make up the different work surfaces, tools and containers used. Milling devices originally used during preparation of two sets of archived herbage samples were tested to indicate the degree of contamination that can arise from milling. For example, some of the milling devices tested showed effects on several TE concentrations while also increasing the variability between samples. A titanium knife mill which was included for comparison gave the best results, showing no measurable contamination by TE of primary interest, while it allowed a high throughput of samples. To enhance the quality of data on TE in bulky plant material such as herbage and to ensure future usability of newly archived samples, we suggest that field handbooks and sample preparation protocols (where needed) are revised to include precautions against TE contamination in all handling steps. This will ensure reliable data on concentrations of micronutrients and potential toxic TE in plant material