Wind Breaks and Shelter Belts
The success of dry crops depends upon the available moisture in the soil and the period of its availability.
Generally in the first row Agave, Sitaphal, Phalsa (Grewia species) and small flowering shrubs are planted at 0.5 to 1 m distance. Average height of the row is 1 to 2 m. In the second row tree of 5 to 8 m height such as Sesbenia, Glyricidia, Subabulare planted. The Last row and middle row of some tall trees of Eucalyptus, Casuarina, are planted at 1.5 m.to 2 m spacing, whose height may reach 10 to 15 in. The rows are spaced at a 3 m distance. In the coastal belts cashew also can be introduced in the second row, in which some branches need to be pruned. Other fruit bearing species like Guava, Pomegranate and Ber also raised for their economic value. If space is available and can be spared, a row of bamboo clumps at 5 m spacing is introduced in the fourth row, as bamboo is of high utility.
The Benefits Accruing as a Result of Planting of Shelter Belts / Wind Breaks are:
1) They reduce the wind velocity blowing over the crops and this reduces the evaporation losses, which reduces number of irrigations.
2) The reduction of wind velocity helps in large exposure of the stomata apertures, thus extending the period of photosynthesis on the leaf surface.
3) It is recorded that the dew formation in sheltered areas increases by 200 per cent. This is an important factor for the crops which thrive well in winter such as Sorghum, Horse gram etc.
4) The shelter belts provide a place for the snakes to live and multiply, which in turn prey on the rats, the major cause of damage to grain. 5) The birds nesting on the shelter belts are agencies to prey on the insect-pests, which damage the crops, and live on the seeds of weeds, thus reducing the weed population in the fields.
6) The birds nesting on the trees of the shelter belts, add good manure through their droppings.
7) There is perceptible movement of soil practice when the wind velocity is high. The shelter belts by reducing the wind velocity prevent such movement of the fine soil particles and effectively prevent wind erosion.
8) The species planted as shelter belts yield, fruit, fodder, fuel, small timber for the farmer and thus add to the agricultural income.
9) The belts regulate the weather by reducing high summer temperatures and increase the low temperatures of winter.
10) The continues and vast stretches of shelter belts add to the increased precipitation from cumulus clouds.
Biological methods to increase the yields will go a long way in improving the fertility of the land, creating a salubrious environment and make the country prosperous.
Planting of Wind Breaks:
Rows of trees along field margins, as far as possible perpendicular to the most high velocity wind of the locality constitute wind breaks. Roughly seven per cent of the total area should be planted for effective protection. The breaks are raised by planting two close rows of fast growing deciduous and one parallel rows of slow growing of longer living ever-greens (Tamarind). As far as possible dense crowned tree species are to be selected.
Species Suitable for Wind Breaks:
Dry and Arid Regions:
Casuariana. Pongamia, Azadirechta, Acacia planifrons, A. auriculiformis, Tamarin dus, Albizzia, Peltophorum, Dyal berja Melia azadirechta, Eugenia, Mangifera, Ailanthus, Sesbania, Morings, Eucalyptus sp., Artocarpus and Grevillea.
For Coastal Areas: Anacardium, Ailanthus, Acacia, Casuariana, Pongamia, Thespesia, Calophyllum, Mani, Gravillia, Cassia sp.
Shrubs and Grasses: Agave sp., Sesbania sp., Glyricidia, Cassia, Vitex, Dudonea, Euphorbia, Jatropha sp., Thevetia,
Saccharr species, Cynodon dectylon, Elusine coracana, Cenchrus ciliaris, Euleopsis binata
Suggested Pattern of Planting:
Shelter belts should be in three or more rows of trees, as the sheltered area is 15 to 20 times the height growth, the protection afforded will many a time cross the fields of the farmer. Therefore, rising of these belts should be on a co-operative basis, as holdings are small. The practices of raising shelter belts and wind breaks can be adopted before planning agriculture on treeless tracts or large farms. For this effort, the leadership has to be strong.
The belts are triangular in cross section. Tall trees are planted in the centre and shorter ones along the sides. A mixture of species is advisable, as far as possible species should be selected on the basis of their coppicing power. Spacing should be 1 metre for shrub, 1.5 m for trees in rows each row being 1.5 to 4 m apart and there should be five rows for proper protection.
Objections of Raising Shelter Belts / Winds Break:
1) They act as harbour for cattle, browsing animals, rodents, etc. The objection is more theoretical and can be overcome by keeping a watch for the period when there is a crop.
2) Roots of trees compete with agricultural crops. This can be overcome by removing the roots to a distance at half the tree height. Digging a small trench of 22 cm depth will serve the purpose.
3) Shade affects the crops. This is insignificant when compared to loss of yield by patchy cultivation in dry land. The shade effect will not be there for the first six to eight years by which time yield from the crops.