For those who wish to avoid the complexities, direct drilling is an agricultural term used to describe a strategy of improving soil health by ‘directly drilling’ seeds into the ground (via the use of specialised machinery), as opposed to intense cultivation.
And now for the rest.
Soil is a valuable resource, essential to any ecosystem. Unfortunately, though, around 75 billion tonnes of topsoil is lost every year as 80% of all soils are considered to be highly vulnerable to erosive forces; this equates to the loss of 9 million hectares of agriculturally productive land. There are many reasons why this occurs and although these erosive forces are entirely natural in origin, they are severely exacerbated by human activity. General crop yield increases over the past 50 years have only been achieved to the detriment of soil fertility, as the overwhelming majority of tests conducted in most countries of the world demonstrated the fact that the organic material component of soil (the most vital for agricultural productivity and the basis of the food chain) has declined.
Agricultural mismanagement is the reason that the practice of direct drilling has come about. Where previously it has been common practice in European-style agriculture to intensely cultivate the soil before sowing, leave the soil fallow for long periods between crops and to totally remove stubble (whether manually or by burning), it is now realised that this makes a major contribution to soil erosion by loosening soil particles. These loosened particles are then eroded away, usually by wind or rain (especially with with lighter, sandier soils). In many cases, the soil is also damaged by the use of heavy machinery, meaning that the ground becomes susceptible to sheet erosion. The fact that fields are devoted to monocultural growth (i.e. a specific crop, usually with a shallow root system) is of no assistance either.
Under the practice of direct drilling, none of these detrimental activities are conducted (hence, it is described as a ‘minimum tillage’ method). Indeed, the nature of direct drilling is such that the land is simply tilled as little as possible and specialised machinery is used to plant seeds directly into the soil (as above). If the stubble is removed, it is only done after the heavy rain seasons. Many land managers who adopted the practice of direct drilling have found that it was necessary (albeit highly beneficial nonetheless) to place particular emphasis on crop rotation, particularly with regard to alternating high and low residue crops (and growing straw crops only sparingly, as direct drilling machinery encounters many difficulties otherwise). Unfortunately, some crop types cannot be grown using direct drilling methods (such as sugar beet, which grows poorly if farmed this way).
Measures of the strategy’s success include: Less soil loss.
An increase in general biodiversity, but particularly with regard to earthworms (which are an excellent indication of healthy soil).
Greater soil water holding capacity and infiltration rates (as sheet, gully or rill erosion tends to occur where water remains on the surface for extended periods of time, particularly in areas which have a sloping topography).
Solid plant root structures.
Heightened yields, a by-product of better soil structure and the retention of the nutrients contained in stubble or alternate (off-season) crops when they decay. Some tests indicated that initial crop production was lowered by direct drilling methods, although the long-term improvements in soil structure outweighed these initial problems.
Lowered incidence of weeds (and therefore pesticides; many weeds germinate more successfully when soil is highly disturbed).
Reduced need for fertilisers, as general soil fertility increases and deeply-rooted crops can access and efficiently extract more nutrients.
Reduction in labour, time and energy expenditure; specialist equipment initially require a high outlay, but long-term savings outweigh this.
SourcesAdoption of best management practices: Conservation Cropping (document - Dept. of Land and Water Management, Victoria, Australia).
http://www.regional.org.au/au/roc/1983/roc198377.htm (25 years of the Riverina Outlook Conference, Wagga Wagga 1973-1998)
http://www.agriseeds.co.nz/glossary.htm (Glossary of Agricultural Terms
http://www.ecifm.rdg.ac.uk/erosion.htm (The University of Reading: Soil Erosion).
http://www.nuffieldscholar.org.uk:8080/nfs/Members/International/Scoley/view (Direct drilling in a root crop rotation).