As growth and development of plants is prevented due to scarcity of water, similarly excessive water also has an adverse effect on growth of plants.
Due to excess water in soil, voids are filled with water or water collects on the surface of soil. In such situation, balance of air and water is disturbed in pores and in the absence of air, plants are not able to breathe etc.
Hence, neither irrigation should be more nor less but it should be as per requirement because excessive irrigation is dangerous.
Excessive and irregular irrigation has the following effects:
1. Increase in Saline and Alkaline Elements in Soil or Increase in Salinity:
When irrigation is done regularly with excessive water, groundwater level comes up and quantity of solvent salts increases. Due to evaporation, salts from saline groundwater collect on the surface of the soil. Seepage of canal water also results in more salts in irrigation water. As observed in Rajasthan, concentration of soluble salts is so much in these soils that it has an adverse effect on the growth of crops and the production is lesser. When concentration of soluble salts in the soil is more than 0.1, growth of plants stops.
2. Problem of Water logging:
Excessive irrigation also causes problem of water logging as has happened in Indira Gandhi Canal area in Rajasthan. Soils and ground level of Indira Gandhi Canal area is very sensitive from the angle of irrigation as maximum soil there has bold granules and at a little depth below the surface, there are hard rocks of calcium carbonate which do not allow excess water to infiltrate underground but keeps it filled above.
Hence, the problem of waterlogging occurs there. Due to maximum dampness in Naurangdesar, Silvana, Lakhuwali and other areas near Indira Gandhi Main Canal, agriculture activity has almost completely stopped. Pilibanga and Badopal have also similar problem. Thus, 44,625 hectare land in the north of the canal has become waterlogged.
3. Hindrance in Air Communication:
Excessive water replaces air in pores of the soil. Hence, roots of plants and beneficial organisms do not get sufficient air for breathing and living. Hence, growth of plants is stopped and diseases destroy crops.
4. Reduction in Temperature of Soil:
Excess collected water becomes cold in the process of evaporation and it causes reduction in temperature of the soil. Seeds do not settle properly and growth of plants is affected. Activeness of organisms is also reduced.
5. Shallowness of Roots:
Due to excess water and shortage of air, roots do not go deep and they remain on the upper surface. Plants are not able to get nutritive elements in sufficient quantity and shallow roots, because of weakness, are neither able to develop nor are they able to bear swift winds. Due to this the plants fall on the ground.
6. Marshy Land:
Land becomes marshy due to stagnant water for a long duration and only forest grass can grow there. The land does not remain useful for agriculture.
7. More Nitrate Formation:
Due to absence of oxygen in waterlogged soil, process of de-nitrogenization starts. Organisms themselves start drawing available oxygen in nitrate, which convert nitrate into nitrus oxide, nitric oxide and nitrogen gases. Being in gas form, they are useless for plants. Such problems will not exist by balanced irrigation.
8. Shortage of Soil Nutritive Elements and Decrease in Productivity:
Due to excessive irrigation, nutritive elements of soil flow to sub-soil, resulting in decrease in soil productivity and deficiency in crops.
9. Acidity of Soil:
In excessively irrigated areas, H+ replaces positively charged Ca2, Mg2+, K+, Na+ stick to colloid granules of soil. These positively charged particles flow away to lower levels which cause decrease of basic positively charged particles and there is an excess of colloidal granules. This results in excess of H+ in soil water and soil becomes acidic.
10. Deformation comes in soil structure.
11. Attack of diseases and harmful insects.
12. It encourages the process of leaching.
13. Collection of other harmful salts and alkaline takes place on surface of the soil.
14. There is decrease in activities of living organisms.