Abstract
This research proposal has two components: 1. To develop a cost curve for mitigation of soil compaction on agricultural land The use of heavy machinery or trampling by livestock can cause compaction of soil; a greater mass of minerals and less space for air occupying the same volume. In contrast to some of the other soil degradation threats, the costs associated with soil compaction across Europe cannot currently be estimated, but they are widely considered to be very substantial. Compaction is considered among the top seven threats to our use of the soil across England and Wales. The degree of compaction in agricultural soil largely depends on the which type of impact the soil is exposed to (machinery or the number of grazing animals), the timing of these impacts (how wet the soil is) and the soil type. Some soils are more prone to compaction than others. There are ways in which soil compaction can be avoided or rectified. For example, a farmer can restrict access to fields under certain conditions, alter the number of grazing animals or use a plough to break up compacted soil layers. The government and farmers need evidence to decide whether attempts to prevent or address soil compaction problems are likely to be cost effective. We need to know if the benefits outweigh the costs? This project will assemble information on both the value of benefits and costs using information from previous studies, agricultural companies who provide the machinery, and relevant farming groups. These data will then be used by the project economist to determine whether there are compelling financial and/or social benefits to rectifying or preventing compaction. This will be done in conjunction with expert knowledge from soil scientists on the types of soil across England and Wales, and agricultural engineers who know about the types of farm machinery used. The analysis will include an assessment of the topmost and deeper layers of the soil for different types of farming, and new technologies and future trends in farming which may alter both the costs associated with compaction and new techniques which might help to avoid it. The report will also describe if there is insufficient information for clear decisions to be made on the balance between costs and benefits, and the potential impacts of climate change on measures to prevent soil compaction. 2. To assess methods which are used to determine soil bulk density and their influence on estimates of soil carbon stocks It is estimated that the global soil carbon stock is equivalent to about 300 times the amount of carbon released annually through the burning of fossil fuels. Because the soil is a living system, responsive to environmental change, this carbon is not inert, it is not 'locked up' in the soil. It is therefore important that we can measure and monitor the soil carbon stock to detect any trends in its status. This task is not simple. The soil is very variable in time and space (both laterally and with depth) which means that estimates of its properties are uncertain. Furthermore, while it is relatively straightforward to measure the concentration of carbon, or other soil constituents, measured in units of mass per unit mass of soil, converting this to a stock of carbon (e.g. tonnes of carbon in the top metre of soil per hectare) requires that we also estimate the bulk density of the soil (the mass of soil per unit volume). This depends on the composition and structure of the soil, and is also variable in time and space. The objective of this subproject is to address the problem of how soil bulk density can be determined sufficiently accurately and precisely so that we can determine stocks of soil constituents (most immediately carbon) with sufficient confidence. Our research will cover both mineral soils and peat soils, since these behave rather differently. To achieve this objective we shall review how soil bulk density has been predicted in the past, and test the predictive methods with available data, and refine them where necessary. We shall also conduct field work to study uncertainty in bulk density measurement by more than one method, and the joint uncertainty in measurements of bulk density and soil carbon. In an optional component of the project (total cost £10,000) we propose to use computerised x ray tomography, a powerful method to study fine structure of materials, to examine how bulk density of mineral soils varies with depth, and the implications of this for uncertainty in our measurements. In summarizing our results we shall be able to identify a protocol to determine soil bulk density which is efficient and adequate for our purposes, resulting in acceptable levels of error in our estimates of soil carbon stock. As a result we will have confidence that our field procedures are producing reliable data but without wasting effort through more intensive sampling than is strictly necessary.
United Kingdom