Application of Water at Critical Stages

Introduction :
Water is the life of plant and must be supplied in proper quantity. Most of the soils receive water through the rain and also supplemented by irrigation. The interval between two irrigation depends primarily on the rate of soil moisture depletion. Normally the crop should not allowed to extract more than 50% available water. The intervals are shorter in sandy soil than heavy soil. When the water supply is very limited, the crops are irrigated only at critical stages. Following are the important crops need to be irrigated at critical stages.

• Rice

When the water resources are limited, the land may be submerged at least during the critical stages of growth, viz. tillering and flowering, and maintained only saturated at other stages.

• Wheat :

The optimum soil-moisture range for tall wheat is from the field capacity to 50% of availability. The dwarf wheat need more wetness, the optimum moisture range is from 100-60% of availability. The active root-zone of the crop varies from 50-75 cm.according to soil type. The critical stages during the growth are crown-root initiation (three weeks after sowing) flowering and grain development.

• Barley

Barley is similar to wheat in its growth habit. The active root-zone of barley extends to 60-75 cm. on different soil types. The optimum soil moisture ranges from the field capacity to 40% of availability. About two irrigations are adequate on sandy-loam soils. The critical stages for water requirement are early tillering, boot stage, grain filling.

• Maize

The optimum soil-moisture range is from 100-60% of availability in the maximum root-zone which extends from 40-60cm.on different soil types. The critical stages of growth are the early vegetative period (30-40 days after sowing) and tasselling (45-50 days). In the northern parts, two or three irrigation is required to establish the crop before the on set of the monsoon.

• Sorghum and Other Millets

The optimum moisture range is from the field capacity to 40% of availability. The sorghum roots can extend down to 100-150 cm. but other millets have shallow root system extending to 30-45 cm. in the soil profile. Pre-flowering (boot stage) and grain development are the two critical stages in respect of moisture. The crop should be irrigated at least at the critical stages to maintain optimum moisture in the root-zone during the dry spell.

• Pluses or Grain Legumes

Important Kharif legumes are cowpeas, green-gram, black-gram, kidney-bean and pigeon-pea. When grown along, one or two irrigations would be beneficial to boost their yields. Critical periods in the legumes are the early vegetative growth, flowering and pod development.

• Oilseeds

The principal oilseeds are groundnut, sesamum and niger during Kharif and safflower, mustard, castor and linseeds during Rabi. Maintaining moisture in the range of 100-50% of availability by one or two supplementary irrigations increases their yield more than double. In case of groundnut 8-10 irrigation of about 50 mm each are applied at 10-15 days intervals during its growth period (critical stages-pegging to pod formation). Safflower, Mustard and Linseeds should receive 3-4 irrigation during their growth. Branching (30-40 days after sowing) and flowering (60-70 days from sowing) are the critical stages with respect of moisture stress.

• Cotton

The optimum range of soil moisture for the crop is from the capacities to 20% of availability in 0-75 cm. of the root-zone. On sandy-loam soils two pre-flowering, two in flowering and one post-flowering irrigation have been found tobe optimum. In the black soil of Gujarat 2-3 irrigation have been found to be adequate. Optimum soil moisture is necessary during the stages of flowering and boll formation. On heavier soil it is preferable to alternate furrows for maintaining better aeration.

• Jute

The optimum moisture regime is from the field capacity to 70% of availability in the maximum root-zone of the crop which extents to about 45 cm. of soil depth.

• Sugarcane

The optimum moisture for sugarcane is 100-50% range of availability in the maximum root-zone, extending upto 50-75 cm. in depth. Since only vegetative growth is of economic importance, a good crop should never suffer from moisture stress during its growth.

• Tobacco

The optimum moisture regimes are from the field capacity to 70, 60 and 50% of the availability in cigar, hookah and bidi respectively. Cigar tobacco needs light and frequent irrigation during 4 months. For hookah tobacco, 12-13 irrigation of 50mm. of water each are required. Water with high chloride content, is unsuitable for irrigating tobacco. In case tobacco topping is the critical stage for moisture requirement.

• Forage crops

Vegetative growth is important in case of fodders. The optimum moisture range is from field capacity to about 75% of availability. Berseem requires about 20 irrigations during its growth at intervals of 20 days during December and January and 10 days- September, October and April. The water requirement of the crop is about 800 mm during eight months of its growth. The Lucerne needs abut 1,800 to 2,000 mm of water during the first year of growth. Depending upon the availability of water, suitable forage crops can be selected for a given locality.

• Vegetables

The soil moisture should range between 70-80% of availability in the maximum root-zone. Potato is grown on sandy-loam soils in the north and needs water at intervals of 10-12 days. 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 insure during these stages. Onion and Garlic are required vary frequent irrigation. Bulbing is the most critical stage from the point of view applying water. Tomato should be irrigated at intervals of 10-12 days during summer and of those of 15-20 days during winter. Cabbage, Cauliflower and Knol-Khol are required the optimum moisture regime is from 100-50% of availability. Radish, Turnip, Beet-root and Leafy vegetables need frequent irrigation to maintain the range of 100-75% of the availability in the top 30 cm. of the soil. Pumpkin, Bottle-gourd, Ridge-gourd, Sponge-gourd and Cucumber irrigation should be applied at intervals of 10-12 days during summer. Water-melon and musk-melon need water at intervals of 8-10 days. Excessive irrigation should be avoided during the ripening stage, as it results in fruit-cracking.

• Spices and Condiments

Turmeric, Ginger, Chillis, Ajwan, Cumin and Coriander are they important crops. Turmeric and ginger should be irrigated to maintain 100-60% of the available moisture in the maximum root-zone. Chillies should be irrigated to maintain 100-50% of the available soil moisture in the active root-zone extending to about 60 cm in the soil. Coriander, Cumin and ajwan need irrigation at intervals of 10-12 days on light soils and 15-20 days on heavy soils.

• Fruit-trees

All fruit-trees required adequate soil moisture during their establishment period of 3-4 years. On the full development of the root-zone down to 75-90 cm, the crops may be irrigated when 2/3 of the available moisture is depleted during blossoming, fruit-setting and fruit-enlargement. In case of grapes too much moisture during ripening causes splitting and rotting of berries. A slight moisture stress during this period results in increased sucrose content and better colour.