The effects of agriculture on soil structure can range from minor alterations to significant changes, and can result in serious problems such as erosion or water logging. In counties where agriculture has replaced rainforest, desertification can rapidly occur because of the poor structure of rainforest soils. In more temperate climates the effects are less dramatic but still occur for example in areas such as East Anglia repeated cultivation has lead to the removal of organic matter and structure resulting in significant erosion by the wind and rain.
I intend to investigate the effects of various agricultural land uses on the infiltration rates of soils. This will allow comparisons to be made with the natural biome therefore indicating any changes that have occurred and allow the major factors, which affect the rate of infiltration. Location The study will be carried out on a mixed farm near Exeter in Devon in the Southwest of the UK. Map1 Map 2 shows the boundary of the farm. Map 3 showing local geology Index for map 3 Introduction There are many factors which affect the infiltration rate of soils such as the composition of the soil its self, i.
e. the percent of each of the 3 major inorganic components which are sand, clay and silt in order of particle size. The underlying bedrock has an effect and determines the type of soil that can be present. The slope angle has an effect as does the regional climate. Agricultural management controls none of theses conditions so their effect is not under investigation. However they still affect the rates of infiltration, which means that in order to eliminate them from the investigation all these factors must be kept constant.
I have done this by limiting the study to one specific farm which as map 3 the geological map shows the under lying rock type is the same through out the farm. The underlying rock is Permian: Sandstone and conglomerate, which results in a soil, which is generally a sandy loam. The farm is in the exe river valley and has one gently sloping gradients which therefore limits the affect of gradient and prevents the occurrence of soils such as podsol which are created on major slopes.
I investigated the effect of gradient on infiltration in a preliminary field trial and found that there was a noticeable increase in the rate of infiltration on the steeper sections of the farm and so to prevent this from affecting the results I will have to choose areas, which have little or no slope. The factors which agriculture can affect are the vegetation that is grown and the cultivation/physical land use, which occurs i. e. grazing, ploughing, dirt tracks for machinery. The use of the land will affect the soil structure of the organic layer and the A-horizon.
The infiltration rate depends upon the size and number of air spaces between the soil partials and between the peds and other soil structures. Changing the porosity of the soil therefore alters the permeability of the soil. Hypothesis I would expect that grazing of animals especially cattle would compact the soil and break down the ped structure of the soil compacting the air spaces and so reducing the rate of infiltration and that cultivation methods such as ploughing improve the soil structure and increase the porosity so increasing the rate of infiltration.
The excessive use of heavy machines on particular areas such as tracks would seriously compact the soil structure and result in a serious reduction in infiltration rates. Data requirements. I will require from each location the average infiltration rates, the % vegetation ground cover, the number of plant species that are present, an observation of the level of soil compaction and a record of the general agricultural use of the land. I will investigate 12 different locations, which are: 1 a storage area for round bale silage 2 a grass paddock that has been grazed over the winter
3 a potato crop 4 an area of spring barley 5 an area of winter barley 6 a heavily used dirk track 7 a recently ploughed field 8 an area, which has been set-aside for 1 year 9 grassland 10 an area, which has been set-aside for 10 year 11 a small oak wood 12 marshland Fieldwork Schedule: Saturday 6th to Sunday 7th research of Internet and of textbooks and investigation planning. Monday 8th field recce to determine locations for analysis, and testing of equipment. Tuesday 9th data collection from chosen locations. Wednesday 10th to Sunday 14th analysis of data and completion of written report.
Risk assessment of fieldwork The fieldwork is generally a safe activity and the risk is generally low. There are however certain risks and precautions that must be observed. As the study is taking place on private farmland permission must be acquired from the owner. Information must also be obtained as to whether there has been any application of toxic chemicals to the area in question or whether the is going to be heavy machinery operating near by and also the location of potentially dangerous animals such as cattle. This should prevent the risk of poisoning or serious injury from livestock/machinery.
It is also necessary to inform a family member/friend on the location and estimate time to complete the fieldwork. A mobile phone is a useful item but must not be relied upon, as reception can be poor. Fieldwork also has a risk of minor injuries such as sprained ankles from uneven ground. Method of Data Collection Primary data is the main source of data for the investigation and is obtained from the fieldwork. Secondary data that is required is the location and farm plan maps, the geological maps and the recent history of the field use from the farm records.
Use of measuring equipment. The main data that is measured is the rate of infiltration. This requires an infiltration tube, which is made from a section of strong section of plastic drainpipe that measures 10cm in diameter and 30 cm in length. Also required is a 30cm ruler a stop watch a hammer a piece of wood and a source of water. Method for measuring the rate of infiltration; the infiltration tube is to be hammered into the ground to a depth of 10cm to prevent damage to the tube whist it is being hammered into the ground a piece of wood will be placed on the top of the tube.
Once the tube is firmly in place and good seal between the tube and the soil has been achieved place the ruler in side the tube and pour water into the tube so that it is nearly full. The timer is to be started and the height of the meniscus above the ground is to be recorded. The height is then to be taken at minute intervals up to 4 minutes. To ensure greatest accuracy the initial height of the water should be maintained on each measurement taken. The vegetation height is simply recorded be measuring the height above the ground.
Percent vegetation cover can be observed with the aid of a quadrate place on the ground, this also enables the number of plant species to be recorded, it may be necessary to use a text book in order to identify different species, a although the species present are not being investigated. A measure of ground compaction can be given using a scale of 1-10 where 1 is the s=least amount of compaction, visual observations and the amount of force required to insert the infiltration tube will be required to give a figure for this measurement. Sampling Methods.