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Water harvesting system

Water harvesting is a technology of utilizing the collected and conserved water for the purpose of crop production. It includes tillage practices for an efficient use of moisture between and within the crop rows. Frequent stirring of the land by surface tilling provides mulch and prevents the evaporation loss of water from the soil.

Besides harvesting moisture from between and within the crop rows, run off losses are considerably reduced. The store water is used for providing life sowing irrigation to the crops grown in the surrounding areas. The water harvesting of this type can be done in areas situated near hill and on greatly undulated lands. In these cases, check dam tanks, and other reservoirs are constructed. The infiltration or percolation loss of water is prevented by spraying of asphalt compounds or by covering the bottom of the tanks or ponds through thin plastic sheets. The seepage loss may also be checked by providing a plastic lining. The evaporation loss of water is controlled by pouring some burnt crude oil over water surface.

On a highly eroded soil or soils having very high slopes, terraces are made for providing a gentle flow of run off water so that the soil is not further eroded and some crop may be grown on these terraces.

B. Physiological approaches

Hardly 1 % of the water absorbed by the plant roots is used for the growth and development of plants and remaining 99% is wasted through transpiration back to atmosphere. Thus one of the greatest causes of soil water wastage is loss of water through transpiration.

The extent of transpiration can be greatly influenced by using certain chemicals. These chemicals reduce transpiration, encourage root growth and protect the cytoplasmic proteins of the plants. These chemicals bring about more drought resistance in the plants. These compounds, according to their role, are classified as given below..

1. Anti-transpirants

Any chemical substance, which reduces rate of transpiration on its application to the plant surface, is called anti-transpirant. Any j substance which reduces the vapour pressure gradient in the stomatal cavity or increases stomatal resistance to water vapour diffusion, will act as anti-transpirant These substances have been used for arresting water loss from plant body with various degree of success. These are Phenylmercuric Acetate (PMA), Hydroxy Sulphonates (HS), Alkenyl Succinic Acid (ASA), Adol:-52 (a formulation of alcohol), and S-600 (a plastic transplanting spray).

2. Chemicals for improved cell membrane permeability of water

Dry fanning areas are characterized by scarce rainfall and usually the roots have lipid layers which lower the absorption of water from the roots. Some chemicals like Alkenyl Succinic Acid (ASA) and Decenyl Succinic Acid (DSA), when applied, penetrate into the root and increase its water absorption power 8 times. Therefore, these chemicals are applied in the root zone for increased water absorption along with some chemicals to retard the transpiration from foliage

3. Use of plant hormones and growth retardants

Some plant hormones like Indole acetic acid (IAA) and Abscissic acid (ABA) may be used for reducing the frequency and period of stomatal opening thereby minimizing the water loss from the plant body.

There are certain other chemicals known as growth retardants which either modify the plant structure or dwarf the plants by considerably reducing the total water requirement of the plants. The most important chemical of this group is cycocel or CCC (2- chlorocthyl trichloromethyl ammonium chloride). This chemical t\ also induces moisture stress tolerance in plants. Cycocel is presently used in cotton to encourage production of more fruiting branches (sympodial rather than monopodial or vegetative branches) and , Ii thereby even under drought condition it results in higher yield. In case of wheat, the use of Cycocel decreases the cell size and increases the density of the cytoplasm which ultimately results into a drought resistance into the plants.

4. Use of chemicals

There are certain chemicals which are used for seed treatment to bring about drought resistance in plants right from seedling stage. Soaking of seeds in calcium chloride solution (0.25%) for 20 hours soaking of seeds with frequent shaking results in better germination and drought resistance in the plants.Boron solution is also used for soaking seeds. Agrosan is a fungicide but also induces drought resistance in the plants when seeds are treated with this chemical.

C. Genetic approaches

Because of scanty and unreliable rains the farmers of dry farming areas are still practicing crop husbandry on the basis of traditional approaches like low intensity cropping, little or no use of fertilizers or manures, raising low value crops. Crop varieties grown till the recent past were generally of long duration and slow growing. It, They were poor yielders too.

As nearly 70% of our total agricultural land is rainfed and 45% -of rainfed area is dryland, there is no way out but to evolve suitable varieties as well as appropriate technology for getting the most from our rainfed or dryland areas. As such, the concerted efforts of our plant breeders have resulted in the cultivation of several new plant types which possess all the characters needed for rainfed areas or dry lands. In terms of modem technology, such plant materials are called "Ideo types". These are the suitable strains of dry land crops which are characterized by short growth duration, effective and extensive root system, drought tolerance, high yield potential having altered morphology of plants which are conducive to dry lands.

According to breeders, an ideal 'Ideo type" should have following qualities to give desired results in dry farming:
i. Early in growth duration and early vigour.
ii. Deeper root system with maximum branching at deeper zones.
iii. Dwarf plant types with lesser number of erect leaves.
iv. Moderate tillering; as profuse tillering causes competition.
v. Good expression of ear heads even at higher planting density.
vi. Resistance to diseases.
vii. Bolder grains with moderate dormancy in them.
viii. Effective photosynthetic behaviour with greater sink capacity.

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