STRIP CROPPING FOR EROSION CONTROL
I. WIND STRIP CROPPING
M. N. MISHRA
AND RAM PRASAD
Central Arid Zone Research Institute, Jodhpur
Accelerated wind erasian in many parts af the warl d deve10ped after man
began ta interfere unduly with the natural equilibrium between climate; sail
and vegetative enviranment (Sears, 1935). Burning, avergrazing and avercu!tiv8,tian have been the chief means af disturbing their equilibrium.
Th-e prablem
af excessive wind erosian, therefare, is assaciatedprincipally
with the way the
farmer uses his land (Bennett, 1939 & Stallings, 1957). Beside, wind erasian is
generally assaciated with law rainfall, high wind velacity and scanty vegetatian
ta cover and protect the sail. Soil canservatianist recagnises several factors which
influence mechanics af wind erasian.
Chepil (1945, 1951) lists the follawing
factors affecting wind erasion.
HI
Il
GROUND
I
AIR
i)
ii)
iii)
iv)
v)
Velocity
ii) Density
a)
Temprature
b)
Pressure
c) Humidity
iii)
Viscosity
i)
Raughness
Caver
Obstructians
Temperature
Topagraphicfeatures
SOIL
i) Structure affected by
a) Organic matter
b) Lime and
c) Texture
ii) Maisture cantent
Crop strips function nat sa much as protective barriers but as sail traps
designed ta reduce soil avalanching.
Crap strips ar strip cropping are terms used
ta describe a method af farming, usually involving twa ar more strips, whereby
strips of erosian-resistant craps are planted between strips af erosian-susceptible
craps. The width afthe strips under different crops may vary or may be the same.
STRIP
CROPPING
The impartance
FOR WIND EROSION
af vegetative
CONTROL
cover an the land cannot be averstressed
as
it is one of the mast effective methad for permanant wind erosion contral. Zingg
et al.( 1952) stated that different amounts, type and arientatians af residues
STRIP
OROPPING
FOR
EROSION
OONTROL
239
reduced the direct wind force on the immediate soil surface from 5 to 99 percent.
Field strip cropping aligned at right angle to the direction of prevailing wind is
an effective and economic method of wind erosion control on farmer's field.
PLANNING OF WIND STRIP CROPPING
(a) Suitability of Crop8 - Strip-cropping as usually practiced does not
require any change in cropping practices, nor it envolves removal' of any land froni
cultivation unless fallowing: is practiced.
The field is sub-divided into alternate
strips of erosion-resistant crops and erosion-susceptible crops or fallow.
Erosion
resistant crops are small grains and other closely seeded crops as grasses and
legumes that cover the ground denselly and. rapidly.
Erosion-susceptible
crops'
are normally those grown in rows as cotton, tobacco, pearl millet, peas, potatoes
etc. Maize and sorghum are intermediate in their resistance to wind erosion
(Chepil and Woodruff, 1963). Ricinu8 communi8, LasiurU8 sindicus, Pka8eolu8
radwtu8 and P. aconitifoliu8 utilized in wind strip cropping at tbe farm of Central
Arid Zone' Research Institute, Jodhpur in rotations, gave promising result.
(Misra, 1963).
Erosion resisting and erosion-su!ceptible crops may be changed according
to the local climate, need and availability as the function of wind resisting strips
is to minimise soil drifting and deflecting ground air currents and for this purpose
a type of vegetation is needed that makes an erect growth, withstand air movements and resists deterioration for as long a time as possible (Bennett, 1939). In
the Southern Great Plains of the U.S.A. where cotton is grown, some special
form of wind strip-cropping
are followed wherein cotton in 2 to 4 rows is altered
with various numbers a.nd sequences of rows of Sorghum or of other high· residue
yielding crops (Chepil and Woodruff, 1963).
(b) Orientation of Strip8The planting of sorghum in rows running at
right angles to the direction of the prevailing winds has long been a recommended
practice for reducing the wind erosion hazard (Zingg et al 1952; Misra, 1963).
Chepi! (1960), suggested that since wind direction varies, the best that can be
done is to orient the field strips with broadside running as nearly as possible at
right angles to the prevailing or average wind direction.
If the prevailing dif(~ction is other than at right angles to the field strips, the width of strips has to be
reduced by the factor of Cosine A, where A is angle of deviation from perpendicularto the strips.
If A IS greater than 45 degrees and the sides of strips must
run north-sough and east-south then the strips must be turned 90° so tbat A will
be less than 45 degre~s.
PRASAD
L08s from
rows at f"ight angltfl to wind
pq.ralle~ to 'U,ind
1
- .3
STRlp CROI'PINQ FORF:R'6SioN'.c6NTIWL
241
ntuer. su'rface" barriers on the windward' side of eroding fields and. to 'some'
degree to a phenomenon caJled avalanching.
Soil avalanching is the increase in
rate of soil flow with distance downwind across an unsheltered
wind _ eroding
area.
The sheltering influence of standing wheat stubble
as fOund to extend
from 15 metres to 76 metres (Chepil. 1941).
<¢
The rate of soil avalanching
has, thus, an important
bearing on how
narrow erosion - susceptible field strips should be to prevent the rate of soil
,movement from .exceeding the tolerable miniIIlum.
Chepil (1957) carried out
an experiIIlent on measurement of soil flow to answer this question for different
soil textural classes and surface conditio~s.
Six soil catchers of 10.5 litre
capacity and 6 of 3.5 litre capacity were used for measuring soil flow at different.
locations across a block of-strips of eroding.land.
They were placed at interyals.
fully across the field on a line parallel with the direction of wind. Average wind
velocity at 1.5 m. above the ground was recorded with each set of measurements.
The rate of soil flow, as determined from 'the amount of soil caught in a given
time, was expressed in tons per rod width (1 rod = 4.8 metres) per hour'adjustedto a w.ind velocity of 48Km./hour at 1.1') metres Per second or an equiva,lent of
64 km. rer hour at 15 m. distance from the strip. The adjustment was bCl:~edon.
3
the relationship q IX v in which q is the ra.te of soil flow and v is the velocity
of the wind.
Measurements were taken on eroding fields or strips lying immediately to
the 'Lee' of non-eroding areas. The non-eroding' areaR usually were covered
with standing wheat or sorghum stubble.
'In accordance with the developed formula suitable width of erosionsusceptible strips rumiing at right angles to a 64 km. per hour wind and hiwing
a 30 em. high stubble on their windward side should be, on the average, 5.8,
7.8,24.4; 29.3, 44.0,64.2,73.9,
101.3 and 129.8 m. wide on sand, loamy sand,
clay, sandy loam, silty clay, loam, silt loam. clay loam, and silty clay loam,
respectively (Cheyil, 1957 ).
In another .experiment, Chepil (1960), studied the effectiveness of crop
strips in relation to soil texture and direction of erosive winds. The directional
deviation of erosive winds from the perpendicular
requires correspondingly
narrower strips, and the required width of strip increases' as soil texture becQmeli
finer except for clays and silty clays subject to granulation (Table 1). Mathews,
(1954) has recommended that strips should not be wider than 79.2 metres in order
to be suffiGiently effective, 01' narrower than 24.4 metres in order to make
economical use of farm machinery.
M. N. KISBBA
242
AND RAM PRASAD
.A:tleragewidth -oJ strips required to control wind erosion on different soiZ
classes and for different wind directions (Adapted from Chepil, 1960).
Width
Soil Clas8
Wind at right
angles to strips
of
Strips
metres
in
Wind deviating
20° from right
angles.
Wind deviating
45° from right
angles.
6.0
5.5
4.3
7.6
6.7
5.5
24.4
22.9
16.5
30.5
28.0
21.3
45.7
42.7
33.5
77.2
726
51.8
863
85.2
57.9
105.7
98.0
77.2
Bennett 0939} has suggested that wind resisting strips may be used in the
form of narrow buffer strips composed of 4 to 10 rows placed at 25 to 50 metres
intervals across the field or they may be used as wide rotation strips.
ffihe required
width of field strips for any prevailing
direction of wind
q}ay. be determined by Ghepil's alignment Chart (Chepil, 1950).
(d) Height of StubbleHeight of stubble is an important
factor
determinipg the loss of soil by wind erosion. These stubbles provide resista.nce
to high velocity wind and trap the soil material.
Zingg d al. (1952) hay;e
reported a. definite correlation between the height of stubble, orientation of
wind strips and soil texture to that of soil loss due to wind eroBion. 'The results
iir-epresentee. in Table 2. The data show that the soil loss is greatly affected by
the . ~I'iefrtation. As the texture
becomes finer, soil 'loss due 1'0 wind
erasion
iil\Creases.
As alread¥ discussed, it may further be seen that the rows aligned at
Figbt angles to the wind directions, are less subject to soil loss than the rows
aligned pa.rallel to the wind direction.
STRIP CROPPING FOR EROSION CONTROL
TABLE
243
2. Soil Material erodedfrom the leeward end of the wind tunnel in relation
to height above the ground surface (Adapted from Zingg et al. 1952).·
Height above
ground surface
Materials transported below given
heights in relation to total
removal from plants
Rows parallel
to wind
Om.
2.54
8.76
15.00
25.00
30 00 Esti- }
45.00 mated
Rows at right
angle to wind
%
%
22.2
48.9
68.2
87.3
89.6
99.2
8.9
26.9
42.2
60.3
68.0
85.0
Soil material finer than
0.44 mm.
Rows parallel
to wind
%
24.4
21.5
25.0
21).8
Rows at right
angle to wind.
%
27.7
26.3
31.8
38.9
Advantages of Wind Strip Oropping
(i) Soil loss Minimised Relatively
little wind erosion occurs on
grassland or wood-land and wind protected lanq either by means of wind breaks,
shelterbelts or by crop barriers, strip cropping or row crops. By strip cropping,
the surface becomes more rough.
A rough surface is generally less subject to
wind-erosion than a smooth one (Chepil and :Milne, 1941).
The greatest frequency and magnitude of wind erosion occurs on soils that
have been partly or completely denuded of vegetation or vegetative cover. Bare,
aggr~gated soils may exhibit resistance to erosion, but generally temporarily,
because aggregates exposed to the weather usually disintegrate to erodible
particles (Slater and Hopp, 1951, quoted by Chepil and Woodruff, 1963; Ohepil,
1954). A standing crop or stubble is more effective in controlling wind erosion
than is the fl~ttened vegetation because it has greater total roughness. A tall crop
or stubble is more effective than a short one for the same reason (Chepil, 1944).
In addition to above, wind strip cropping minimises soil temperature and
encourages better absorption of precipitation in soil and consequently minimises
the severity of wind erosion (Bennett, 1939; Zingg, 1950). It has been possible
to slow down the surface velocity and therefore, to reduce wind erosion by
roughning the surface and by establishing wind strips in the path of the wind
M. N. MISHRA
&.44
AND RAM PRASAD
1956; Woodruff
et q.,l., 1957, quote".d
(ii) Con§..ervatio1l:.
oj So~l 'Jloisture:- As alreaay aiscussed, a consiaeraBle
amount af organic matter is left as plant residue on the surface after harvest qf
the crops, which ultimately enhance granulation in soil and correspondingly
become more capable of storing soil moisture (Chepil,
1944).
Soil moisture stuGies at the Central A:rid Zone Research Institute Farm,
Jodhpur, at every 3.0 metre distance on the leeward sUe of the protp,cted strips
at 15.0 and 22.5 em. depth indicated 0.5 to 1.5 per cent more soil moisture
in protected cropland
as compared to unprotected
lands at these depths
resRectively,
(Misra,
1963).
(iii) Crop Yield:Average crop yields, due to the sheltering effect ohtrip
cropping, are usuall y more than control. Misra, (1963) reported higher yields of
crops due to strip cropping. Average crop yields of 186.6 kg.per hec. o['J'hasedlu.~
r.a ia ~ and 178.8 kg. Rer hectare of Phaseolus aconitiioli'us were obtained from
the protected plots. In addition to the grain yield in protected plots the yield of
Ricinus communis at the rate of 746.5 kg.fha. and 1650.0 kg·fha. dry matter of
hasiu1' s sindicus w.ere also obtained, which were used for the protective
strips.
(v) Improved Soil Structure.Sod crops grown in strips provitle mbre
organic matter wliicll in turn helps in iinproving the soil structure.
The size of
soil aggregate becomes so improved that they are only moderately eroded (Zingg
et al., '1952). An average of the dry sievings of G surface soil samples from tne
strip cropped fields eave clod size distribution as given in Table 3.
{} small amount of soil movement by atmospheric wind occurred during
the tests demonstrating that it was susceptible to drifting.
Therefore, a soil of
this structure is moderately erodible. Wind strip cropping increases moisture
conteP.1ton the leeward side of the strips than windward side (Misra, 1963).
STRIP OROPPING FOR EROSION
Therefore, particles
(Chepil, 1946).
TABLE
3.
CONTROL
become more or less damp and resistant to wind erosion
Clod Size distribution in, Strip Cropped fields
Clod size
Total
mm.
weight
per cent
<
0.42
283
0.42 -
0.84
13.7
0.84 -
2.0
9.8
6.4 - 12.8
15.6
12.8 - 38.0
18.3
>
38.3
1.6
Future line of Work:-Considerable
information is still lacking on air flow.
temperature, evapora tion, soil catching mechanism, and crop yields in the vicinity
of cropstrips and crop rows especially under Indian conditions. A large amount
of work on the wind stripwidths, their practicability and soil loss equation which
have been carried out by Chepil, et al. in the U.S.A. and other parts of the world
are of little value under our conditions in view of the different topo-climates
prevailing in agricultural fields of our country and the impoverished agricultural
machinery available with the Indian farmers. Knowledge of the commencement
of a particular wind stolm a few days earlier to its actual occurrance will help
farmers in planning suitable remedial measures to avoid substantial loss to soil
and crops. Tillage implements. chemicals required, value of soil surface roughness coefficient, role of legumes in arid zone strip-cropping etc. all are to be
determined to make the wind erosion control by strip. cropping effective.
ACKNOWLEDGEMENTS
Authors are thankful to Dr. P. C. Raheja, Director of the Institute and
Sri C. P. Bhimaya, Head of the Resources Utilization Studies Division for going
through the manuscript and valuable suggestions for improvement.
Assistance
of Dr. D. K. Misra, the then Agronomist in providing references and literature
on the subject is gratefully acknowledged.
24()
M. N.
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_----
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dry
sieving
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of
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_____
19
,
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STRIP
OROPPING
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247
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