Role of Grasses and Pastures, Wind breaks and Shelter belts in soil conservation.

1. Submitted by :
Abhilash Singh
Dept. of Agricultural Meteorology
CCSHAU, Hisar
Assignment
AGRON – 608
UNIT – II
Role of Grasses and Pastures,
Wind breaks and Shelter belts in soil conservation.
.

2. Pasture is Latin word originated from the word pastus which means "to feed“.
Pasture are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep
or swine.
The vegetation of tended pasture and forage, consists mainly of grasses, legumes and other non-grass
herbaceous.
Pasture in a wider sense additionally includes rangelands, other unenclosed pastoral systems, and land
types used by wild animals for grazing or browsing.
Pasture lands in the narrow sense are distinguished from rangelands by being managed through more
intensive agricultural practices of seeding, irrigation, and the use of fertilizers, while rangelands grow
primarily native vegetation, managed with extensive practices like controlled burning and regulated intensity
of grazing.
PASTURE

3. When there is no groundcover, soil is easily swept away by both the action of raindrops,
overland flow and wind, the two main causes of erosion.
Seedlings have difficulty establishing on the scalded, often sand-blasted surfaces.
Valuable rainfall which should be soaking into the soil is lost as runoff—also carrying away
topsoil.
Soil may be lost in sheet form, including the formation of scalds.
When runoff concentrates, either naturally or when influenced by roads, fences, stock pads or
firebreaks, both rill and gully erosion may occur.

4. Total groundcover includes pasture plants and their litter, tree leaf litter, twigs and woody
debris, organic crusts, rocks and gravel.
All of these components contribute to protecting the soil surface from erosion.
Roots of grasses and other plants hold the soil together, while their leaves block rain and stop it
breaking the soil apart.
Turf, ornamental grass, and low, spreading shrubs work best, since they cover the soil
completely.
If you have any bare ground, try to establish plant cover as soon as possible to limit erosion.
If the ground is mostly flat (slope of 3:1 or less), this might be enough to solve the problem.
Steep slopes erode faster, so they need more protection.

5. Maintenance of soil cover is the key to controlling erosion in grazing lands.
It prevents erosion by maintaining the soil in a condition that absorbs rainfall.
Any runoff that does result will be impeded by the cover and is less likely to concentrate into
an erosive force.
Erosion risk is significantly reduced when there is more than 30% soil cover.
Total cover is achievable for many grazing and cropping systems.

6. Treatment A B C
Per cent cover 87 69 6
Total runoff from
storm (mm)
1.5 14 38
Per cent of rainfall
that ran off
3 26 70
Soil loss (t/ha) 0.03 0.3 22
Depth of soil lost
(mm)
0.002 0.02 1.7
Sediment
concentration (g/L)
1.5 1.9 63
Nitrogen removed
(kg/ha)
0.14 1.9 15.3
Phosphorous removed
(kgha)
0.02 0.26 4.3
Table 1. Results from a 54mm storm at Mt Mort.

7. HOW PASTURES HELPS IN SOIL CONSERVATION ?
•The top few centimeters of soil contain most of the available nutrients and organic matter in the
soil profile.
•When this is lost, the soil becomes even less receptive to rainfall, resulting in a near constant
drought for the remaining pasture.
•For conserving soil and minimizing erosion losses from soil, management of pastures is of
utmost importance. It prevents erosion by maintaining the soil so it can absorb rainfall.
•Pastures are the main food source for ruminants and Grazing is one of the most effective and
economic means of maintaining and enriching the soil.
Well-maintained grazing land:
1. Protects soil with its vegetation cover against the beating action of rainwater drops
2. Reduces the speed of water flowing over the land thus holds back superficial water run-off .
A well-managed pasture with good cover will ensure that runoff spreads rather than
concentrating and causing erosion.
3. Minimize humus loss
4. Improves soil stability and structure
5. Improves soil permeability.
•Sheepwalk is an area of grassland where sheep can roam freely. The productivity of sheepwalk
is measured by the number of sheep per area.
•If the herd remains permanently on the pasture, the majority of the minerals in the forage are
returned directly to the soil.

8. The use of grazing as a part of soil conservation measures may be employed on
different classes of land.
(a) On land suitable for crops.
In this case, rotating grazing with crops is preferable to permanent grazing.
The length of time the land will be grazed depends on the soil erosion hazards.
For example, 2 out of 6 years will be given over to grazing for class I land (USDA
classification), 2 out of 4 for class II land, 3 years out of 5 for class III land.
(b) On land not suitable for crops.
It is advisable to make a distinction between land for grazing and land for forest
plantation.
Trees give a more effective cover than grazing pasture on poor soils.
Soils in class V are less susceptible to erosion and are more suitable for pasture than
soils in classes VI and VII.

9. But persistent, heavy grazing pressure can lead to woodland thickening.
A resultant lack of fire and reduced competition from the herbaceous layer allows
woody plants to proliferate. This can lead to:
 reduced grazing value
 reduced soil surface cover
 increased risk of erosion
 colonization by pest plants
 limited access for management purposes (e.g. mustering and weed control).
So land should be used in rotation between grazing pastures and crops, which
improves crop yield due to:
The provision of nutrients with the grass being ploughed in;
Maintenance of a more favourable level of soil humidity with structural improvement;
Smaller humus loss;
Reduction of plant disease and damage caused by harmful insects.

10. The following management options should be considered for keeping land in good condition with
a high proportion and density (and thus good ground cover) of preferred species:
 Manage total grazing pressure
 Implement appropriately timed spelling and herd management strategies
 Monitor pasture composition
 Use of hay, supplements, fodder trees and shrubs in a strategic manner
 Manage the tree/grass balance to avoid woodland thickening
 Implement forage budgeting strategies
 Use climate and seasonal forecasting resources
 Maintain native grassland free of encroachment from woody vegetation
Fence according to land types
Use appropriate fire management practices. Fire is useful for controlling woody weeds but it
needs to be managed carefully. Regular burning of pastures will further reduce ground cover and
promote runoff and erosion.

11. WINDBREAK AND SHELTERBELTS
Windbreaks are any structures which break the wind-flow and reduce wind
speed while
Shelterbelts are rows of trees or shrubs planted for protection of crop against
wind.

12. Introduction
The productivity of land for agriculture is dependent on the characteristics of soil.
Most soils within India have low levels of nutrients and top soils are very thin.
Indian soils are old, weathered and often depleted of valuable nutrients.
Top soils take a very long time to form. Over a one hundred year period only a couple of
millimeters of soil may be formed. This soil can then be quickly eroded by even modest winds.
Wind erosion is a serious problem in the arid west Rajasthan which forms a part of the Thar or
the Great Indian Sand Desert, along with the adjoining sandy arid areas of Punjab, Haryana and
Gujarat states .
The region is characterised by low and erratic monsoon rainfall, moderate to high wind
velocity during the dry summer months when temperature is also very high, and a dominantly
sandy soil in most of its area.
Additionally, the present vegetation cover is poor as compared with the situation in the other
climatic zones in the country.
According to the data compiled recently by the Ministry of Agriculture, Government of India,
10.46 million ha of land in India is affected by wind erosion.

13. Out of this total, Rajasthan accounts for 93.8% (9.81 million ha), followed by Haryana (5.1 %).
Wind degradation due to wind erosion has also been reported from Andhra Pradesh (0.4%),
Tamil Nadu (0.3%) and Punjab (0.3%).
Source : Wind Erosion Map of India–CAZRI

14. Clarence Helms, conservationist technician, observing a 31/2 foot bank of sand
deposited by wind erosion on a farm in South Carolina, USA ( Spring 2007).
Photographs courtesy B.W Anderson.

15. How Shelterbelts can reduce the impact of wind erosion
In the wind erosion areas, windbreaks and shelterbelts are to be planted.
1. It reduce the impact of accelerated soil erosion and in some cases prevent wind erosion by
intercepting wind and consequently reducing wind speed as wind passes through or over the belt.
2. It decrease wind speed within the sheltered zone to a level below the threshold for soil movement.
3. Even narrow or open belts can reduce wind speed for a distance many times the height of the belt
and therefore have a considerable impact on wind erosion.
4. Moderate wind speeds can begin the process of soil erosion.
5. Once soils are suspended the, soil carrying capacity increases in proportion to the wind velocity
cubed. Means reducing wind speed by half can reduce the rate of erosion to 1/8.
6. Therefore a modest reduction in wind speed can result in a significant reduction in soil erosion.
7. Even wind approaching belts on angles that are almost parallel to the belt can decrease wind speed.
Although the area over which shelter is provided will be reduced. This means that even sparse
shelterbelts can provide considerable reductions in soil erosion.
8. They provide suitable habitat for birds, wildlife and honeybees as well as produce cattle feed and
fuel wood.
9. They protect the agricultural crops and residential lands from being sandblasted by dust-storms.

16. One of the principal uses of shelterbelts from a universal aspect is the
control of wind erosion of the soil.

17. Shelterbelt design for reductions in wind erosion
1. The location, density, height and length of a shelterbelt will determine its effectiveness in reducing
wind erosion.
2. A grid of shelterbelts positioned at appropriate distances apart, provides the maximum level of
shelter for a property as shelter will be provided from all wind directions.
3. Shelterbelts provide the highest level of protection when they are located at right angles to erosive
winds.
4. It reduces the wind speed up to 60-80% on leeward side.
5. Good protection from wind erosion can be maintained for up to 30H of a shelterbelt if wind is
approaching the belt at right angles.
6. Therefore consideration should be given to the direction of winds when planning a shelterbelt
network.
7. Although maximum protection from erosive winds is achieved by placing belts at right angles to
the wind direction, but soil erosion can still be substantially reduced if wind is coming from other
directions.
8. However, the area protected by a belt will be reduced during events of higher wind speeds.

18. – Depending on the effectiveness of the barrier, reduction in
wind velocity can occur for a distance up to 20 times its
height.

19. Low porosity in shelterbelts (i.e., very dense) will generate maximum wind speed reduction but
over a reduced area when compared to less dense belts.
However, a moderately dense shelterbelt (~50% density) will provide a considerable reduction
in wind speed to a distance of at least 20H, where H is the height of the shelterbelt (Figure).

20. To control wind erosion over a large area the height of a belt
needs to be maximized.
Therefore it is wise to incorporate at least one row of tall
species within the belt.
If gaps occur within a belt wind will tunnel through the gaps at
an accelerated rate.
This can result in blowouts near the gaps and also be
detrimental to crops in leeward side.
Wind speed accelerates around the ends of shelterbelts.
By increasing the length of the belts or joining them to other
belts this impact is reduced. Belts can be joined where they can
form a right angle for protection from a range of wind directions
as illustrated in Figure.
Fig : Joining belts can
provide protection from a
range of wind directions
and reduce the impact of
accelerated wind speed
around the ends of belts.

21. • Generally, the distance of full protection from a windbreak or
shelterbelt is
• Where,
– d = distance of full protection (L),
– h = height of the barrier in the same units as d (L),
– Vm = minimum wind velocity at a height of 15 m required to move the
most erodible soil fraction (L/T), =9.6 m/s.
– v = Actual wind velocity at a height of 15 m (L/T),
– θ = the angle of deviation of prevailing wind direction from the
perpendicular to the windbreak.

22. How to plant a shelterbelt
An effective shelterbelt should contain a combination of shrubs, fast growing trees, and dense long
lived trees.
The outside row of a shelterbelt should generally be a dense shrub that will act to reduce wind near
the ground and act as a snow trap.
The next row should consist of a fast growing tree species that will allow the shelterbelt to quickly
gain height.
The next row should be made up of long lived trees that will allow shelterbelt to remain effective for
a long time.
The next rows that would be closest to the yard should be made up of tall dense crowned trees that
retain their foliage throughout the year.

23. Advantages of Windbreaks
Enhance crop yield
Protect soil from wind erosion
Shelter livestock and crops
Capture water runoff and nutrients
Improve irrigation efficiency
Filter and reduce dust
Help control odors
Screen unsightly areas
Provide wildlife travel corridors and habitat
Protect structures (homes, outbuildings, roads)
Reduce noise
Improve aesthetics