Soil sample storage conditions affect measurements of pH, potassium, and nitrogen

AbstractSoil quality monitoring schemes are a useful tool for assessing the potential of soils to perform desired services such as agricultural productivity. When researchers or other stakeholders wish to compare results between different schemes or studies, failure to consider differences in soil sample storage conditions presents a significant potential for error. Here, we compared levels of nitrogen and potassium, as well as pH, in agricultural soil samples stored under three different conditions (refrigerated, frozen, and oven‐dried). All tests were performed after 7 and 24 weeks of storage. Nitrate decreased significantly in dried (p < 0.001) samples. When refrigerated, nitrate first increased (p < 0.01) and then decreased (p < 0.001). Nitrate levels where unchanged at Week 7 in the freezer but decreased significantly at Week 24 (p < 0.001). Nitrite and ammonium increased after drying (p < 0.001) and when frozen (p < 0.001 and p < 0.05) but remained stable when refrigerated. There was no significant difference in potassium levels between the fresh control and Week 7 in the freezer, but potassium had increased at Week 24 (p < 0.05). Potassium concentration increased in refrigerated samples (p < 0.001) and fluctuated up and down in dried samples (p < 0.01). pH measurements fluctuated significantly in refrigerated and frozen samples (p < 0.001 and p < 0.01, respectively) but were unchanged in dried samples. We suggest that soil monitoring schemes standardize their sample storage, and we encourage researchers to clearly report soil sample storage conditions in publications, to improve transparency and reproducibility

Written evidence submitted by Canterbury Christ Church University (SH0097) to the House of Commons Environment, Food and Rural Affairs Committee on Soil health. First Report of Session 2023–24, HC 245.

Executive summary Soils are fundamental to ecosystem functioning in agricultural soils and therefore their ability to provide public goods. Agri-environment policy measure progress towards improving soil health through various physio-chemical or biological means; however, these are no longer fit for purpose. This paper is split into two sections: soil health indicators, covering physio-chemical characteristics and biodiversity, and soil contamination, dealing with heavy metals, pharmaceuticals and microplastics. Within this document, we make a series of recommendations to improve monitoring and subsidy schemes under the new Environmental Land Management schemes. New policy frameworks also need to consider known and emerging contaminants if they are to be a true representation of the health of our soils. Recommendations are given below, split into: physio-chemical characteristics, biodiversity, heavy metals, pharmaceuticals and microplastics. Physio-chemical indicators: 1. Expand on the soil health indicators quantified under the ELMS to include several more that are mentioned under the Countryside Survey (i.e. pH, bulk density, soil carbon, organic matter, total nitrogen, mineralizable nitrogen and total phosphorous), and offer a set of relevant tests related to soil health, taking into account basic soil characteristics, cropping systems and/or climate. 2. Subsidise costs of soil testing under the ELMS so that farmers can collect good quality data on soil health before and after management interventions to demonstrate if soil health has been improved. 3. Ensure that all tests have a standardised method for soil sampling, storage and testing to enable comparisons and accurately track long-term changes. 4. There is a risk of low farmer participation due to the loosely defined soil assessment methods. There is a need for clear guidance and defined, but easy to use, methodologies and farmers need to have access to expert advice and guidance. 5. Soil quality indicators should be relatable to a specific ecosystem services/public goods, and farmers need clear guidance on how to interpret the results of their soil tests in this context. 6. Conduct a large-scale monitoring scheme to provide a reference dataset for farmers to compare their soil physio-chemical data to, or create a scoring system that is easy for farmers to interpret to use as a comparison or demonstrate changes in soil health. Biological indicators: 1. Any agreements attaching subsidy payments to improvements in soil biodiversity need to be long-term and might need to include staged and proxy payments. This is to account for the longer timeframe that soil communities may take to respond to new land management approaches compared to physio-chemical characteristics. 2. Current measurements of biological health are no longer appropriate. Since soil biodiversity – especially microbial biodiversity – drives soil functioning and is a key component of soil health, this needs to be included as a soil health indicator under the new ELMS. 3. Although methods for biodiversity assessment using metagenomics are complex, schemes ot monitor soil must be cooperative. Thus, farmers have to be able to on collecting soil samples and sending these for analysis. Similarly, the biodiversity data that is sent back to the farmer also needs to be easily interpreted (i.e. using a simple summary of findings or scoring system). Heavy metals: 1. Expand on heavy metals that are used as soil health indicators under the Countryside Survey (total copper, zinc, cadmium, and nickel) to include several more that are prevalent in agricultural soils. 2. Include contamination as a soil threat and add Action(s) within the ELMS that targets remediation of contaminated soils. Pharmaceuticals: 1. First, there is a need for prioritization: there are more than 1,900 active pharmaceutical compounds in use, making it a challenge to study all of them at once. Prioritization will allow identifying those compounds that can pose the greatest risk to the UK soil, plants, environment, and public health. 2. Soil microbiome is diverse and varies with location, soil type, plants, environmental conditions, and human activities. There is a need to understand the effect of prioritized CECs pharmaceuticals on soil microbiome and its interaction with the rhizosphere in different agroecological zones of the UK. 3. How the presence of prioritized CECs in the soil affects the growth, productivity, and nutritional quality of main UK crops needs to be assessed. This will be achieved by evaluating the mechanisms of absorption, plant uptake and metabolism of CECs in main UK crop species. 4. With the anticipated negative effects of the CECs on agriculture and the environment, strategies for the remediation of prioritized CECs from contaminated soils should be developed. Different available bioremediation approaches need to be tested to identify those who would work on those CECs and in the UK context. 5. Considering the current development of climate change and its impact on agriculture, it is inevitable to assess how climate change is affecting / will affect the prioritized CECs in their interaction with plants and soil. Microplastics: 1. Define ‘microplastics’ clearly as an environmental contaminant in policy documents. 2. More accurate estimates of deliberate and accidental release of plastics are required to reduce uncertainty in approximations of the quantity of plastics entering soils. 3. Well-aligned initiatives, best management practices, more stringent policies and co-operative efforts of the public, manufacturers and government officials are urgently needed to reduce illegal disposal of plastic waste, moderate improper use of plastic products in the agriculture and increase the proportion of plastics undergoing waste management or recycling processes. 4. Better characterisation of MPs (i.e. origin, shape, size, and composition) and evaluation of their in soils (i.e. distribution, transport and degradation) is required, with reference to specific soil characteristics, agricultural systems and climates. 5. Understand how the presence of MPs in the soil affects soil biota and the growth, productivity and nutritional quality of crops, and determine soil guideline values for MPs in soils. 6. Develop a standard set of low-cost, high-efficiency protocols to collect and process soil samples, and then to isolate, identify and quantify microplastics in soils, depending on both the soil characteristics and the type of MPs being quantified

Agroforestry benefits and challenges for adoption in Europe and beyond

Soil degradation is a global concern, decreasing the soil’s ability to perform a multitude of functions. In Europe, one of the leading causes of soil degradation is unsustainable agricultural practices. Hence, there is a need to explore alternative production systems for enhanced agronomic productivity and environmental performance, such as agroforestry systems (AFS). Given this, the objective of the study is to enumerate the major benefits and challenges in the adoption of AFS. AFS can improve agronomic productivity, carbon sequestration, nutrient cycling, soil biodiversity, water retention, and pollination. Furthermore, they can reduce soil erosion and incidence of fire and provide recreational and cultural benefits. There are several challenges to the adoption and uptake of AFS in Europe, including high costs for implementation, lack of financial incentives, limited AFS product marketing, lack of education, awareness, and field demonstrations. Policies for financial incentives such as subsidies and payments for ecosystem services provided by AFS must be introduced or amended. Awareness of AFS products must be increased for consumers through appropriate marketing strategies, and landowners need more opportunities for education on how to successfully manage diverse, economically viable AFS. Finally, field-based evidence is required for informed decision-making by farmers, advisory services, and policy-making bodies