Biodiversity

Agriculture – Soil Erosion

What is soil erosion?

Soil erosion is one form of soil degradation along with soil compaction, low organic matter, loss of soil structure, poor internal drainage, salinisation, and soil acidity problems. These other forms of soil degradation, serious in themselves, usually contribute to accelerated soil erosion.

Soil erosion is a naturally occurring process on all land. The agents of soil erosion are water and wind, each contributing a significant amount of soil loss each year in Ontario.

Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks.

(source: Ontario Ministry of Agriculture and Fisheries)

This webpage also describes in detail the types of soil erosion in
considerable detail.

Causes of erosion:

Over intensive farming and inappropriate techniques
e.g. Dust Bowl in the Mid-West of America.
Mechanisation – soil compaction by large tractors.
Hedgerow removal – need for bigger fields for machinery and loss of protection from the wind.
Overgrazing (especially by goats – why?)
Over use of fertiliser – evidence that it will damage soil ‘crumb’ structure.
Pesticides can kill soil organisms leading to soil breakdown (especially fungicides)
Poor irrigation and drainage schemes e.g. soil is washed away.
Slash and burn policy used in deforestation.
Poor logging practices.
Climate change
Increase in population, urbanisation and industrialisation

Some important effects of erosion on biodiversity:

Photographic examples – visit the Seafriends webpage
(A New Zealand Conservation Organisation)
Loss of soil from food production systems
In India, 800.000 sq. km of land has a serious soil erosion problem.

1. There are a number of agricultural practices that can conserve soil and even increase topsoil levels.

Visit the ‘Farm Conservation Solutions’– (US Department of Agriculture)

Pick out a few which you think would have the greatest benefit to UK farmers.

The DEFRA website will help if you want to know more:
DEFRA Soil Code
DEFRA Codes of Good Practice

2. Plot the data in the table below on a graph.

Year	Max.daily rainfall	Total rainfall	Total soil eroded
Erosion and rainfall in an area of 36km2 of agricultural land on the South Downs
	20 sept - 1 March(mm)	Sept-Feb(incl) (mm)	(m³)
1982-83	42	724	1,816
1983-84	22	560	27
1984-85	30	580	182
1985-86	33	453	541
1986-87	38	503	211
1987-88	63	739	13,529
1988-89	39	324	2
1989-90	34	621	940
1990-91	51	469	1,527
1991-92	25	298	112

(Robinson, D. and Blackman, J. Water erosion of arable land on the South Downs)

Suggest reasons why there is not a perfect correlation between rainfall and the amount of soil that is eroded. Note that 1989-90 was very odd as there was a late winter rainfall peak in January and February. Most of the erosion was on land which was ploughed for plant spring cereals.
Which of the measures of rainfall seems most useful to predict erosion?

Drainage