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Essay on Strip Cropping
Essay # 1. Meaning of Strip Cropping:
Strip cropping is also a kind of agronomical practice, in which ordinary crops are planted/grown in the form of relatively narrow strips across the land slope. These strips are so arranged that the strips of close- growing crops are always separated to the erosion resistant crops.
Strip cropping as a technique for erosion control is a most effective measure in certain soils and topography. This method becomes more effective for erosion control, when it is followed with crop rotations in the area where terraces are not practically feasible due to division of slope into small segments. The strip crops check the surface runoff and force to infiltrate into the soil, and facilitating for conservation of rain water.
Strip cropping is more sensitive practice for conserving the rain water than contouring (i.e. about twice as effective as contouring) but it does not involve greater effect on soil erosion as terracing and bunding. Generally, the use of strip cropping practice for soil conservation is decided in those areas where length of slope is not too longer. Strip-cropping to control soil erosion against runoff, derives its effectiveness mainly from the following two reasons.
(a) Reducing the runoff flow through close-growing sod strips.
(b) Increasing the infiltration rate under cover condition.
The reduction in runoff velocity between the row strips is because of making obstruction in the flow path. The obstructions created by row crops are also responsible to dissipate the kinetic energy of flowing water, as a result the flow velocity at d/s section gets reduced, sufficiently, which causes deposition of soil particles over the soil surface.
The crops grown in strips not only reduce the flow velocity of water over the surface, but also encourage the water intake rate of the soil, which is might be due to following reasons:
i. The crops provide an obstruction in flow path of surface water, i.e. water gets additional time to stand between the rows. By this virtue, a large amount of water is infiltrated into the soil, as result the depth of water causing runoff generation is reduced significantly, and thereby the soil loss also get reduced, accordingly.
ii. The root system of the crops makes the soil more porous causing more amount of water is absorbed by the soil, and thus reduces the runoff and soil loss, both.
iii. The water also gets additional intake path along the roots of the plant, which creates a similar effect on runoff and soil loss, as in previous case.
When strips are laid with varying degree of divergence from the contour, then effectiveness of strip- cropping is influenced by the soil types, degree and length of land slopes, previous erosion etc.
The effect of soil type is imposed by all those soil properties, which are responsible to increase water-intake capacity. From field investigations, it has been found that 2 to 3 times greater soil loss is from the soils having moderately heavy to heavy sub-soil than the soils with light textured sub-soil for the same slope conditions.
The degree and length of land slope have pronounced effect on soil loss. The reason may be justified as: the erosive power of flowing surface water is increased due to increase in slope inclination, as a result the erosion from such soil surface is increased. The effect of slope length is concerned, as it increases up to a certain range, the erosion also increases, accordingly, but at greater length there starts sediment deposition due to reduction in runoff volume and its velocity.
Essay # 2. Types of Strip Cropping:
There are following four general types of strip cropping:
1. Contour Strip Cropping:
In contour strip cropping, the crops are planted in strips along the contour at right angles to the direction of natural land slope. The growing of crops in strips are in a definite rotational sequence. Although, it is not strictly essential that all the crops must be in the rotation in the same field and in the same year, but as far as possible it should be maintained to keep the soil in proper order.
Contour strip cropping is adopted on the level land across the slope instead of up and down hill, for checking the flow of surface water. From field studies, it has been observed that the strip cropping on the contour plays a key role in conserving the soil and water, when combined with terracing. The width of strips depends on the topographical features of the area.
2. Field Strip Cropping:
It is modified form of contour strip cropping, in which crop strips are laid parallel, across the land slope, but not always exactly on the contour; may be changed depending on the land situation.
This type of strip cropping is suitably used where the topography is either too irregular or undulating, as they make accurate layout of contour strip cropping, impractical. The depressed areas should be avoided for field strip cropping; they can be left for establishing the grassed waterways.
3. Buffer Strip Cropping:
In buffer strip cropping, the strips of grasses or legume crops are laid between contour strip crops in regular rotation. The width of these strips may or may not be uniform. The buffer strips are usually 2 to 4 m wide, and are placed at 10 to 20 m intervals. They can also be placed on critical slopes of the field. The main purpose of buffer strip cropping is to provide protection to the land from soil erosion.
4. Wind Strip Cropping:
In wind strip cropping system, the strip crops of uniform width are laid at right angles to the direction of prevailing winds, without regard of the contour. The main objective of this system is to control the wind erosion rather water erosion. This cropping is recommended for level or nearly level topography, where wind erosion is more effective. A guideline for deciding the width of wind strip-cropping can be have from the Table 11.3.
Layout of Contour Strip Cropping:
In layout of contour strip cropping the first step is to decide the width of strip at narrower points, let the minimum width is assumed to be 25 m. The next step is to establish a point for locating the contour line that will form the lower boundary of first strip. This point will be at 25 m apart from the top boundary of field, by measuring along the steepest part of the slope. A contour line is drawn by passing through this point up to the field boundary. This procedure is repeated until the entire field is laid out.
Width of Strips:
It varies with the degree and length of land slope, allowable soil loss, soil types, arrangement of crops grown in rotation and size of farm equipments, used. In terraced fields, the width of strip is adjusted according to the terrace interval, but in un-terraced fields narrow width than the standard terrace interval is normally used. In general, steeper the slope, narrower will be the strips of cultivated and dense growing crops, both. An approximate range of strip widths, based on the average land slope and soil types is given in Table 11.4.
The width of buffer strip in a permanent contour strip is normally kept between 3 to 5 m.
Crop rotations can be more effective for controlling the soil erosion when accompanied with strip-cropping system. It can be used on the same piece of land by growing tilled crops, small grain crops, hay crops or grasses either under a strip-cropping system or in a separate field system. In the areas, where perennial grasses and legumes are not feasible to grow, then the row crops of small grain and annual legume crops can be grown in the strips.
It is a general rule that, no two cultivated strips should have the same planting or harvesting dates. The sequence of crops should be in such a manner, that there could be formed a dense-fibrous root system to hold the soil and retard the erosion, until the roots are broken under tillage operations. All these activities under crop rotation add the organic matter in the soil, thereby the physical condition of the soil gets improved, ultimately the soil absorbs more water and also increases the capability to resist the erosion.
Under use of crop rotation practices for controlling soil erosion, the simplest way to combine different crops in row form and grow them in rotations. The frequency at which the row crops should be grown, depends on the severity of erosion taking place in the area.
For example – where erosion rate is very low, the row crops can be grown at every alternate year, but in high erodible areas or where rate of soil erosion is being more, the row cropping is practiced at intense scale. For erosion control by growing the crops in rotation system, probably the most suitable crops are legumes and grasses.
The main benefits credited by these crops are mentioned as under:
i. Reduction of soil erosion resulting from high degree of ground cover.
ii. Help to maintain or improve the status of organic content in the soil, thereby enriching the soil fertility and enabling to develop more stable aggregates in the soil.
iii. Increase in soil nitrogen, resulting from nitrogen fixation, associated to the legume crops.
Different crops and management practices used for growing them have different effects on the soil structure. The crops affect the soil structure by the activities of their root system and adding the organic residues/contents from the roots and top of the plants. The organic contents help in arranging and stabilizing the soil particles into granules or in aggregates form.
They develop bigger size pores in the soil mass, causing rapid water intake in the soil. Apart from above the soil aggregates are also developed by tillage operations, wetting and drying of soil, freezing and thawing of soil and activities of micro-organism and small animals like earth worms.
Inter-tilled crops including vegetables and grain crops usually do not have effective root system for improving the soil structure. However, most of the grain crops mix a considerable amount of organic matters in the soil, provided that the residues after grain removal has been covered into the soil by ploughing operations. The vegetable crops return very little organic matter to the soil. The dense root system of grass helps in binding the soil aggregates, together.
Essay # 3. Contour Buffer Strips:
These are the narrow strips of permanent herbaceous vegetative cover established across the land slope in alternate form. The array of strips is in parallel to each other.
The main objectives of this practice are outlined as under:
i. To reduce the sheet and rill erosions.
ii. To reduce the transport of eroded soil mass/sediments, and other soil contents, down the slope.
iii. To enhance infiltration rate; or in other words to enrich the water content in the soil.
The suitability of contour buffer strips is as below:
i. It is used in the croplands.
ii. It is very suitable on the soils having uniform slope ranging from 4 to 8% with the length less than the critical slope length. The critical slope length is the length of slope beyond which the contouring loses its effectiveness. The critical slope length for contour buffer strips is about 1.5 times of the critical slope length of contour farming.
iii. The contour buffer strips are also found suitable in the regions, where rainfall intensity varies from low to moderate.
Its unsuitabilities are pointed as under:
i. This practice is not suitable to the fields having extremely long slopes, i.e. slope length is more than the critical slope length for contouring (more than 1.5 times). However, the slope length can be reduced by using the conservation practices like terraces, bunds etc.
ii. Not suitable in undulating to rolling topography, because of difficulty in constructing parallel strip boundaries across the hill slope.
The criterion of contour strip cropping are related to reduce the sheet erosion and rill erosion, both; and also to check the transport of sediments and other soil contents.
However, they are also related to the following parameters:
i. Row grade
ii. Strip boundaries; and
iii. Base line
The grade of row cropped strips should be as close as to the contour of the field, to reduce the soil erosion by significant amount. The maximum row grade within the crop strips should not exceed one half of the up and down hill field slope or 2%, whichever is less.
For those crops, which are sensitive to the water stagnation for the periods less than 48 hours, the row grade not less than 0.5% from the ridge towards outlet should be provided. However, up to 3% row grade can be allowed for maximum 150 feet distance of outlet. The grade along up slope side of vegetated buffer strip should be the same to the cropped strip directly above it.
The cropped strips should be alternated with the buffer strips, down the slope. When it is followed in combination of terraces with underground outlets, diversions, or water and sediment control basins, then layout of buffer strips should be coordinated with the grade and terrace spacing, so that the strip boundaries would be parallel to the terraces, wherever possible.
The water flow from contoured crop rows should be drained to a stable outlet. The outlets may be the grassed waterways, underground outlets for terraces or diversions, water and sediment control basins, field borders, headlands or end rows, or similar stabilized areas.
The followings are mainly taken into consideration:
1. Width of Strip:
As for as possible the width of buffer strips should be uniform. It depends on the crops to be grown. If grass & legume mixtures are used, then width of buffer strips at their narrowest point should not be less than 15 feet. Similarly, when legumes are used alone, then it should not be less than 30 feet.
The crop strips should be of uniform width between the buffer strips; and should not exceed either (1) 50% of the slope length used for erosion computation, or (2) 50% of the critical slope length for contour buffer strips. Also, the strip width should be in the multiple of implement width, when tillage operations are to be done by using farm implements.
The purpose of contour buffer strips is to reduce the sheet and rill erosions. Therefore, the selection and growing of vegetations of suitable characteristics is very important. The vegetations should consist of grasses, legumes, or grass-legume mixtures recommended for the area, and have tolerance of anticipated sediment deposition depth.
3. Level of Erosion Control:
The level of erosion control required by the buffer strip crops is also very important. Design of buffer strip practice should strictly be based on it. The level of erosion control should either be equal to the desired level or in excess of soil erosion level specified under conservation plan.
4. Headlands or End Rows:
In the field if the row crops are grown in rotation, then the headlands or end rows should be kept under permanent sod, provided that their row grade is steeper than the designed grade of the crop strip.
Requisites to Reduce the Sediment Transport:
These are described as under:
One of the objectives of buffer strips is to reduce the sediment transport capacity of overland flow from the cultivated lands. This objective could be easily fulfilled by growing vegetations of suitable characteristics. In general, the permanent sod forming vegetations with stiff and upright stems are found most suitable for this purpose.
2. Strip Width:
It is normally suggested that if the slope of cropland is more than 3%, then width of buffer strip should be decided only on the basis of level of sheet and rill erosion reduction. And if slope is 3% or flatter, then width of buffer strip should be 15 feet or little more. However, the maximum width of crop strips between buffer strips should be one half of the field slope length but not to exceed 150 feet length.
The width of buffer strip should also be based on the width of farm machinery used for tillage operation, if there. Normally, for easy operation the strip width should be in the multiple of full width of machine, used.
3. Arrangement of Strips:
The buffer strips and crop strips should be arranged in alternate form, down the slope. The buffer strip should be established at the bottom of slope.
4. Headlands or End Rows:
The headlands or end rows should be vegetated; and their minimum width should be 15 feet between the end of tilled strip and the field’s edge.
Care and Maintenance:
The care and maintenance of contour buffer strips are carried out in following aspects:
i. All the tillage/farming operations should be done parallel to the strips at the boundaries, except at the headlands or end rows.
ii. The mowing of buffer strips should be done at proper time to maintain good vegetative cover of suitable height, so that the trapping of sediments from the upslope cropped strip could be effectively done during critical erosion period.
iii. For maintenance of proper vegetative stand, the application of fertilizers should be done at proper time, in proper dose.
iv. The mowing of sod strips and waterways should be done at least ones in a year.
v. If the vegetative cover has been destroyed due to any reason, then it should be reseeded or planted very soon, so that such patches should be covered with vegetation. Otherwise, there is possibility of occurrence of severe soil erosion from that portion.
vi. Normally, at the upstream of cropped strips there is deposition of sediments. This deposition requires to redistribute along the upslope edge of buffer strip interface to maintain a uniform sheet flow along the buffer/cropped strip boundary. If the deposition of sediment gets happen just below the upslope edge of the buffer strip to the depth of 6 inches, or the stem density becomes below the specified limit in the buffer strip, then relocation of buffer/cropped strip interface should be there.
vii. Cultivated strips and buffer strips should be in rotation form, so that a mature stand of protective cover could be developed in newly established buffer strips, immediately below or above the old buffer strips, before removing the old buffer strips.
viii. Alternate repositioning of buffer strips should be there to maintain their relative positions on the land segment.
ix. Renovation of vegetated headlands or end row area should be essentially done, to keep the ground cover more than 65%.
Effectiveness of Buffer Strip Crops:
Strip cropping is most effective when it is followed under a planned conservation system along with combination of the practices such as tillage, crop rotations etc. Its effectiveness also gets increase when strips are arranged as close as possible to the contour of the area. However, the primary factors affecting are the climatic conditions, land slope, cropping intensity, tillage practices and soil erodibility.
The strip cropping is extremely effective in reducing the soil erosion within the field, as well as chocking the transport of eroded soil particles from the field. The alternate strips of good cover either through more intense vegetation such as grasses and legumes or residue, reduce the soil particle detachment and their transport.
The effectiveness of buffer strips depends on the strip width, the mixed crops, and the rate of overland flow. The buffer strips are effective in light to medium rainfalls; and the soils likely to be under water logging at intense rainfall condition. The buffer strip crop strips act as filter and obstruction for flowing rainwater over the land surface. Because of these features the velocity of overland flow is slowed down, as result there is deposition of coarse sand particles and organic matters on the soil surface. Such depositions allow to increase the infiltration rate.
The filtering properties of strips is found more effective when they are formed in the mixture of pulses and grasses, and when there is large number of stalks or roots per unit area in the soil surface. The creeping plants with rhizomes and many scattered stalks are very effective in comparison to the large tufts grasses. For erosion control using tufts grasses, they should be grown in the form of light mulch. They can also be replaced by staggered live hedges in alternate rows over a strip 0.50 to 1.0 m width.
In an experiment it has been found that when strips of Andropogon gayanus are grown on the edges of plots or else at about 20m intervals, then there is a fair amount of sand deposition under wind erosion or water erosion. In aggressive climates and at the steep land there is generally less crop cover, as result there is more soil erosion; in this condition the strip width should be kept wide to ensure better effectiveness.
The leafy plants, particularly the natural fallow plants provide good cover for erosion control strips. The pulses with tap roots and large & deep-rooting perennial grasses are always beneficial to improve the soil infiltration. In tropical areas the Andropogon gayanus, Pennisetum purpureum, Paspalum notatum, Tripsacum laxum in the combinations of various Stilosanthes, sugar cane and various forage plants are very conducive to check the soil erosion.
The plants, whose seeds get spread very easily in the fields should always be avoided, unless the erosion control strips are mowed before flowering of the plants. The plants with sucker spreading, runners or stolons (Synodon dactylon) are found worse. While the plants with tightly packed roots and numerous stalks have better effect on slow-down of overland flow than the free-standing trees.
Advantages of Buffer Strip Cropping:
The buffer strips acts as sponge which allows partial absorbing of rainwater, and also as the screen (filter), due to which the overland flow gets slow down. In result there is deposition of soil particles, especially the coarser eroded sediments. The deposited soil mass involves very good soil porosity.
Also, the soil deposition at regular intervals towards u/s of the vegetative strips leads to the formation of small size terrace over the topsoil surface, which again acts a good source for soil erosion control.
Apart from above, the practice of buffer strip cropping also offers following advantages:
i. It is easy and inexpensive technique to control the soil erosion from medium sloped land, which can be very easily brought in practice by the farmers.
ii. Large areas can be easily treated with fast speed without investment of money or other inputs as normally required in mechanical erosion control measures.
iii. Forage produced from the strips can be used to feed the cattle or as the mulch materials.
iv. The live strips of vegetation along the contour lines can be used as reference point for orientation of crop geometry.
v. The lands used under buffer strips are not immobilized, because they are also productive.
Essay # 4. Advantages of Strip Cropping:
In addition to control the soil erosion/soil loss, the strip cropping is also very effective to maintain the soil fertility; and creating effects on several good farming practices including crop rotation, contour cultivation, proper tillage, stubble mulching, cover cropping, mainly.
For strip cropping to accomplish the erosion control, the selection of crops is normally done on the basis of following points:
i. Rainfall intensity and critical period of rainfall.
ii. Life of strip crop.
iii. Canopy and root characteristics of the crop.
iv. The growth of crop should be such that, maximum foliage can be developed by the crop within short duration to withstand against heavy rainfall. However, a good vegetative growth can be developed by applying fertilizers. Similarly, for developing a proper canopy cover to provide a good soil protection the seed rate can also be increased, especially when quality of seed is not good or soil condition is not very favorable for good germination.
v. The erosion-resisting crop should always be of locally available species. For example, the groundnut can form a good strip crop to check the soil erosion/soil loss, where it is in under cultivation.
vi. For long and narrow strips the erosion resisting crops such as Groundnut, Horse grams etc., are more suitable, while Jowar, Maize, Cotton etc., are good for the strips of erosion permitting crops.
vii. The leguminous crops are very suitable like natural vegetation for controlling the runoff and soil loss; and also for reducing the rate of surface flow to a considerable level, to protect the next strip, d/s.
The layout of strip cropping system is done based on the following considerations:
i. It should satisfy the farming pattern.
ii. It should provide an effective ground cover to control the soil erosion.
iii. It should satisfy the requirement of crop rotation.
iv. The strips should be rotated each year by shifting the erosion resisting crop strips upwards in a regular sequence.
v. Strips should be on contour of the field.
vi. The width of strips should be on the basis of soil, slope, rainfall and rate of soil erosion.