Reply #3 on: May 11, 2008, 13:42:51 PM
Ecological value of farmland Factors (Organic farming)
Modernisation of agricultural practices has lead to an intensification of agriculture on the land. This has resulted in a decline in biodiversity and species abundance in much of the UK countryside. To combat this, the government and NGOs are increasingly supporting "organic farming" practices, which go further than the assumption that the produce is GMO free, but also produced in an environmentally friendly way.
Before exploring the methods and tools available for farmers seeking an organic solution, the pressures and issues that organic farming tackles must be addressed.
The core of the problem lies with overuse or misuse of chemicals, and overstocking of land with cattle.
Chemical use can be broken down into pesticides (herbi/insecti/fungicides) and fertilisers.
Pesticides are responsible for a large decline in biodiversity, both directly and indirectly. Originally, many pesticides were created using organochlorines, which persist in the habitat and can accumulate trophically. Modern pesticides are based off organophosphates, which are less likely to accumulate trophically (though still have associated risks) or natural chemicals, such as pyrethins, which are bassed of a chemical found in Crysanthemums. Herbicides generally target broad leaved ruderal species, reducing the diversity of flora in a field. This in turn reduces the diversity and abundance of invertebrates, which are important food sources for many birds. The grey partridge (Perdix perdix) has particularly been affected from a combination of factors, which will be discussed later. Foliar applications of herbicides also impact wildlife indirectly through the ingestion and accumulation of toxic compounds.
Insecticides directly impact the invertebrate diversity/abundance, and as a result any invertebrate feeding fauna (both by lack of food and by ingesting contaminated prey). Fungicides additionally may contain insecticidal properties. A basic solution to pesticide propblems is to apply the pesticides to seeds, and then drill the seeds into the soil to avoid the risk of grain-feeding birds from ingesting the treated seed stock.
Chemical fertilisers are also responsible for the nutrient loading of agricultural land. Additionally, as with pesticides, there is the risk of run-off into water systems, which would cause eutrophication and toxic effects. The use of slurry is now known to result in the accumulation of toxic elements, such as Cd, which is xenobiotic and may bioaccumulate in flora and fauna. Additionally slurry is toxic to earthworms. This as a result reduces the value of arable, nutrient enriched fields, as an invertebrate food source for many birds such as the black bird.
Another practice that has impacted wildlife include the change from spring sown crops to winter sown crops. As a result, stubble in fields was lost, which provides a vital food source for wood pidgeons, pheasant, and grey partridge. The advent of combine harvesters additionally removed more food by being more efficient at harvesting grain, with less waste grain available to the birds. Silage bales further prevented access to vital grain for these animals.
Organic solutions
The aim of organic farming practices is to help reduce the impact of agricultural practices on biodiversity. The range of techniques and tools cover all farming areas. Many techniques result in a slight loss of crop yield (5-10%), however due to the labelling/certification system, this loss of yield can be compensated through increased prices. Additionally, farmers have available to them a range of bursaries and grants for following specific organic farming best practice guides.
A driver of organic farming is in the decline of many farmland bird species, such as the grey partridge, pheasant, stone curlew etc. These species have declined as a result of the change in agricultural practices mentioned above. As a result, many organic techniques are aimed at increasing the population numbers of these birds. This can be achieved by providing food and shelter for the birds, by improving hedgerows and creating conservation headlands.
hedgerows can be improved by more careful management. Current practices find many hedgerows cut too often and at a uniform, low height. Ideally they should be cut no lower than 2m, and not when the hedges are in fruit (as the berries provide a vital source of food). However hedges should not be left unmanaged for too long, as otherwise they may become gappy. Hedges provide important corridors for many species, such as the dormouse and foxes.
Conservation headlands are areas of ground that runs between a hedgerow and the crop boundary. They perform the role of a buffer, where a mixed seed is sown. The width of the headland is required to be wide enough to prevent weed species from entering the crops, but not so wide as to severely reduce crop area. The mixed seed should contain a range of ruderal species, providing a food source for invertebrates and game. Careful management by cutting, should be undertaken, but not during nesting season.
Beetle banks are another important tool in organic farming. They are small strips of land planted with tussocky graminoids. They provide a food source for game as well as a refuge for important invertebrates. Both conservation headlands and beetlebanks are populated insectivorous invertebrates, which aid in pest control. beetle banks are also low cost, with a 400m long strip (Suitable for a field of 20ha) costing less than £80 to create, and <£30 a year in maintenance. Similarly to the CH, buffer areas of crops may be sown around the beetlebank to help prevent the spread of ruderal species into the crops.
Additional tools for replacing herbicides are undersowing and intersowing of crops. Intersowing combines two or more crop types. They may both be harvested, or the secondary crop can be used as a mulch. The objective is to either reduce the bare soil area to prevent the germination of weed species, or to use a crop as a preferential decoy for pest species, avoiding damage to the more valuable crop.
Undersowing uses a similar principal, where a low lying ruderal species is sown between crops. Often clover (trifolium spp.) is used, as it also provides soil nutrient fixing properties (N, P).
Farmland ponds are also important habitats for amphians such as the common frog and crested newt. They also provide a habitat wading birds.
Generally, organic farming practices increase alpha and beta diversity by reversing the homogenising impact of intensive farming. Increased heterogeniety in habitats, with bare patches of soil and uncropped areas, increase species richness. Vegetation is often first to recover, due to persistent seed banks. Fauna takes longer, and may require a larger proportion of farms to adopt organic practices before an increase in population numbers occurs (Due to fragmented habitats).
