10 important Control Measures of Global Distribution

(i) Sand Dune Stabilization

About 58 per cent of arid Rajasthan is under different types of sand dunes. These are grouped under two systems, old and new. Barchans and shrub-coppice dunes are newly formed and are the most problematic.

The other dunes are of the old system and are under various stages of reactivation. CAZRI has now developed appropriate technologies for sand-dune stabilization.

These include: (i) protection of dunes from biotic interference, (ii) development of micro wind breaks from the crest to the base of the dunes in the form of parallel or chess board pattern and (iii) reseeding of grass and creeper seed in between the micro wind breaks and transplanting of nursery-raised tree seedlings at the spacing of 5 x 5 m in between the micro wind breaks. Most suitable tree and grass species for the purpose are Israeli babul (Prosopis juliflora), Phog (Calligonum polygonoides), Mopane (Colophospennum mopane), Gundi (Cordia myxa), Sewan (Lasiurus sindicus), Dhaman (Cenchrus setigerus) and Tumba (Citrullus colosynthis).

Nearly 80 per cent of the sand dune areas belong to farmers and are mostly under monsoon cultivation. To stabilize such dunes, the technique is the same, but the whole dune should not be brought under tree cover.

Trees should be brought under tree cover. Trees should be planted in the form of strips. In between the two tree strips, crop/grass can be cultivated. By adopting this model, a farmer can get foodgrains and can stabilise his dune plot.

(ii) Shelter Belt Plantation

Considerable soil erosion takes place from the flat cultivated areas due to sandy nature of the soil and high wind velocity, which during summer months is sometimes as high as 70-80 km/ hr.

The soil loss is sometimes as much as 5 tons per hectare. If shelterbelts with 3-5 rows of trees are planted across the wind direction, soil erosion can be minimized.

The shelterbelts reduce wind velocity by 20-46 per cent on the leeward side of the shelterbelt at 2H to 10H distance and the soil loss is only 184 kh/ha, as against 546 kg/ha form areas without shelterbelts. Moreover, soil moisture is 14 per cent higher in such areas as compared to the areas without shelterbelt and grain yield of pearl millet increases by 70 per cent. The fuel and fodder requirements can be met through lopping of trees, which will also maintain the desired porosity of the shelterbelts.

(iii) Aerial Seeding

Due to sandy nature of the soil, the water holding capacity is very low, with the result that sowing of seeds needs to be completed within two to three days to favour germination. Conventional methods of afforestation are inadequate for revegetation of such a large and inaccessible tract having low moisture, erratic rainfall and loose sandy soil. Therefore, aerial seeding could be practiced.

This technology has been used by different drought-prone states of India, like Gujarat, Rajasthan and Madhya Pradesh. The seeds of different trees and grasses are mixed and mass seeding is done from aerially in the pre-monsoon as well as post-monsoon period. The seeds are polluted using soil, polymer and farmyard manure.

The germination of grasses and tress is about 70-80 per cent. However, due to severe grazing pressure and high moisture stress, the seedling mortality could be of a very high order. A study revealed that under such conditions only one to two per cent trees could establish themselves in the successive years.

The grass population increased in the successive year, but again due to grazing pressure, the grasses were uprooted. The process should therefore, be repeated continually for four to five years, so that in a good rainfall year, there can be good establishment. The area should also be protected from biotic interferences.

(iv) Silvipasture Systems

Indiscriminate cutting of vegetation for meeting fuel and fodder requirements is accentuating desertification. In order to control it, there is the need to follow a systems approach.

This helps in reducing solarization and wind erosion and thus increases productivity on a long-term basis, besides conserving resources and also to provide economic stability. If trees alone (Acacia tortillas) provide 60q/ha of fuel wood and grasses provide 46 q/ha, then a combination was shown to yield 50 q/ha fuel wood and 55.8 q/ha of grass. Various trees and grass combinations provide opportunities to suit different ecosystems.

(v) Agronomic Manipulations Minimum Tillage

Tillage of agricultural land is necessary, particularly from the point of view of seedbed preparation, moisture conservation and weed control. Excessive tillage under dry conditions, however, breaks unstable clods and exposes the soil to wind action.

The common practice with the farmers of the region is to invert the soil after three to four years of cultivation, with an objective of capitalizing on the fertile sub-soil for crop production, particularly under non-fertilizer use production systems. This practice, however, seems to accelerate wind erosion.

The results of a study (Gupta, 1993) revealed that excessive tillage before monsoon lowers the percentage of clods of more than 5 mm size and also markedly increases the wind erosion, reduced tillage, on the contrary, provides better clod size distribution and significantly reduces wind erosion. In vulnerable areas therefore, summer tillage should be discouraged. Limited tillage after first showers and optimum soil moisture content help in clod formation, creation of a rough surface and thus minimize wind erosion.

(vi) Conservation Tillage/ Farming

Conservation tillage/farming for soil and moisture conservation and fuel economy are now practiced in the developed countries. Types of tillage, however, depend upon soils, climatic conditions and the crops to be grown. On a loamy sand soil under unirrigated conditions and with an average rainfall of about 300 mm, reduced tillage of one disking and sowing has been found to be adequate in increasing the production of pulse crop of mungbean, cluster bean and cowpea. For sandy soils (highly vulnerable to wind erosion), however, further reduced tillage may be adequate.

(vii) Stubble Mulch Farming

Crop residues protect the soil against wind erosion during the periods between cropping. It is an excellent control measure if managed properly.

The practice of using crop residues as stubble mulch began in North America as early as in 1910. Undisturbed residues in upright position are normally more effective than grazed or flattened ones. Crop residues of 2 to 5 tonnes/ha and pearl millet stubbles of 45 cm height were found very effective in preventing the blowing of sand from the sandy soils of Bikaner.

Crop residues like stubbles of 30-45 cm height should, therefore, be left over in agricultural land. Long stubbles of coarse cereals, however, have generally been found to be more effective than equal quantities of short stubbes. Crops with relatively more residues should be grown on vulnerable soils. In arid areas, however, the availability of crop residues for mulch purposes is generally low. In such situations, the perennial weeds could be killed and left over as organic mulch on the soil surface.

(viii) Strip Cropping

Strip cropping for wind erosion control is alternative plantation of erosion-susceptible and erosion-tolerant crop, perpendicular to the prevailing wind direction.

The main advantage of the systems is that the erosion-tolerant strips reduce the velocity of the prevailing wind, trapsaltating sand particles and thereby control soil avalanching. Therefore, narrow strips are more effective in reducing wind erosion in lighter soils. The width of the strip, however, depends upon the type of soil and the type of crops to be grown. It varies from 6 m in sand to 30 m in sandy loam.

Establishment of strips of perennial grasses of right angle to the prevailing wind direction in the CAZRI farm at Jodhpur reduced the impact and threshold velocity of wind to the minimum and checked the erosion. Consequently, crop grown in between the protective strips recorded increased production.

The grass vegetation, besides reducing wind velocity and erosion, helped in forming surface crust and in binding the sand particles. Agricultural lands can, therefore, be protected with strips and the marginal land can be put under complete grass cover.

(ix) Judicious use of irrigation Water

Irrigation plays a significant role in arresting desertification through its effect in promoting the establishment and growth of vegetation. In the highly sandy and dune covered areas, the sprinkler system of irrigation could be effectively used for raising crops and other vegetation.

This has been found to economies water and increase the production of Lasiurus sindicus in the extreme western part of Rajasthan. Excessive use of irrigation water, however, leads to rise of water table and reduces crop yield.

(x) Control of Mining Activities

Presently these mine spoils are either barren or have sparse vegetation cover (5-8 per cent), but need to be vegetated. Some of the xerophytic tree species like Prosopis juliflora, Acacia tortilis, Colophospernum and Dischrostachys have adopted well under arid conditions and could be used in revegetating the mined wastelands.