Fodders grow vegetatively and hence require frequent irrigations for maximum growth. The optimum moisture range is from field capacity to about 75 per cent of the availability.
Berseem. It is well suited to the regions in the north and require about 20 irrigations during its growth at intervals of about 20 days during December to January, at those of 15 days November, February and March, and at 10 days during September, October and April. The water requirement of the crop is about 800 mm during eight months of its growth.
In the south, lucerne grows better and is perennial. It needs about 1,800 to 2,000 mm of water during the first year of growth. It is hardier than berseem.
If the soil moisture is allowed to fall below 75 per cent of availability, the yield reduction in berseem, lucerne, cowpeas, sorghum and cluster-bean (guara) will be 30, 15, 15, 10 and 5 per cent, respectively. Hence, depending upon the availability of water, suitable forage crops can be selected for a given locality.
Most of the vegetable crops are short duration and grow quickly and need frequent irrigation for their maximum growth. The soil moisture should range between 70 and 80 per cent of availability in the maximum root-zone.
Potato is grown on sandy-loam soil in the north and need water at intervals of 10 to 12 days. It can best be applied in furrows between the ridges. In Haryana and Rajasthan, the irrigation intervals varies from eight to ten days, as soil are sandy loam. The crop needs about 500 mm of water during its growth. Stolonization and tuber-formation stages during 20-60 days growth are critical in their demand for water. Adequate water-supply should be ensured during these stages.
Onion and garlic are shallow-rooted crops and need very frequent irrigation as compared with any other field crop. Bulbing is the most critical stage from the point of view of applying water. About three weeks before maturity, the irrigation are delayed to enhance the keeping quality of the bulbs.
Tomato is grown in India throughout the year. The crop should be grown on ridges and irrigated at intervals of 10 to 12 days during the summer and of those of 15 to 20 days during the winter. Excessive irrigation, during ripening results in fruit-cracking and, hence, it should be avoided.
Cabbage, cauliflower and knol-knol should be grown on ridges. The optimum moisture regime is from 100 to 50 per cent of availability in thesecrops.
Radish, turnip, beet-root and other leafy vegetables need frequent irrigation to maintain the range of 100 to 75 per cent of availability in the top 30 cm of the soil.
Water-melon and musk-melon are grown during the summer and need water at intervals of 8 to 10 days. These crops should be sown on the sides of ridges made 1.5 to 2 meters apart. Excessive irrigation should be avoided during the ripening stage, as it results in fruit-cracking. For the other crop of the cucubitaceae family, such as pumpkin, bottle-gourd, ridge-gourd, sponge-gourd, and cucumber irrigations should be applied at intervals of 10 to 12 days during the summer. The maximum root-zone of thesecrops lies between 40 and 60 cm in the soil profile.
Spices and condiments. Important crops in this group are tumeric, ginger, chillies, ajwan, cumin and coriander. Tumeric and ginger should be grown on broad ridges and irrigated to maintain 100 to 70 per cent of available moisture in the maximum root-zone, i.e. the top 50 cm of the soil. Chillies should be grown on ridges and irrigated to maintain 100 to 50 per cent of available soil moisture in the active root-zone extending to about 60 cm in the soil. Coriander, cumin and ajwan are winter crops and need irrigation at intervals of 10 to 12 days on light soils and 15 to 20 days on heavy soils. The water requirements during their period of growth are around 500 to 600 mm.
Fruit-trees. Fruit-trees may be evergreen or deciduous. The deciduous trees shed their leaves during the winter and remain dormant for 3 to 4 months. The typical example is the grape-vine. The evergreen trees include citrus, mango, banana, chikoo, pineapple, papaya, date-palm, etc.
All trees require adequate soil moisture during their establishment period of 3 to 4 years. Soil moisture should be maintained in the range of 100 to 75 per cent of availability. Later on the full development of the root-zone down to 75 to 90 cm, the crops maybe irrigated when two-thirds of the available moisture is depleted during blossoming, fruit-setting and fruit enlargement. At other periods and during dormancy in the case of deciduous trees, irrigations may be applied when soil moisture almost reaches the wilting point.
Papaya and banana are shallow-rooted and short-lived species. They need to be irrigated when the available moisture in the top 30 cm of the soil layer is depleted to 80 per cent of availability. This will necessitate irrigation at intervals of 8 to 10 days during the rainless period in the tropical climate. The date-palm can withstand high temperatures and low humidity but needs regular irrigation during flowering and fruiting to produce good yields. In case of grapes too much moisture during the ripening causes the splitting and rotting of the berries. A slight stress during this period results in increased sucrose content and better color.
Coffee. It is profitable to irrigate coffee after the cessation of the monsoon rains during flowering to avoid flower-shedding. Sprinkler irrigation has been successfully used to irrigate coffee during the post-monsoon period. This practice has doubled the crop yield.
Lawns and gardens. In lawns and gardens, the seasonal flowering plants need to irrigated very frequently to maintain the surface 30-cm layer moist. These plants should receive irrigation at intervals of 5 to 8 days, depending upon the severity of the climate. A lawn may be irrigated at intervals of 10 to 12 days in summer and at those of 15 to 20 days during the winter to maintain it fresh and green growth. In lawns, one has to resort to flood irrigation and, hence, proper consideration should be given at the time of planting to ensure that the site is perfectly level so that water will spread everywhere uniformly. The young shrubs and live fences should be irrigated along with the lawns. The fully developed trees may be able to tap water that has percolated deep. Hence, no special care is necessary for their growth though an occasional irrigation will be beneficial.