Organic Farming: Water Management

Water Management For Different Crops

• Water Management For Paddy

Water requirement for paddy is high. Assured and timely irrigation influences the yield significantly. The critical periods are the seedling establishment period, tillering, and panicle initiation to flowering stage. Until the transplanted seedlings are well established, water should be allowed to stand in the field at a depth of two to five centimeters. Thereafter, about five centimeters of water may be maintained up to the dough stage of the crop. Water should be drained out from the field 7 to 15 days before harvest depending on the soil type to encourage quick and uniform maturity of grain.

Application of small quantities of water at frequent intervals to keep the soil under saturated conditions is more effective and economical than flooding at long intervals. However, flooding suppresses the weed growth.

The SRI technology advocates the following guidelines of water management for creating unsaturated soil conditions in the field.

• • During the vegetative growth period, water may be applied only to keep the soil moist and not for saturating the soil with standing water.
  • The field may be left dried out for several short periods of 2-6 days to the point of surface cracking; otherwise, flood and dry the field for alternate periods of 3-6 days each, throughout the period of vegetative growth.
  • After panicle initiation, only a thin film of water [1-2 cm] is to be kept in the field.
  • The field should be well-drained 10-15 days before harvest for uniform maturity.

In terms of field performance and yield, the SRI technology has attracted a lot of organic farmers who evince keen interest in large scale adoption.

• Water Management For Wheat

Adequate soil moisture is required for the normal development of the wheat crop at all stages of growth. In case of dwarf high yielding varieties, a pre-sowing irrigation should be given. At the crown root initiation stage [20-25 days after sowing], the first irrigation to the standing crop should be given to ensure good tillering, normal heads, sound root system and ultimately sufficient grain yield. The second irrigation should be given at tillering stage [within 40-45 days after sowing]. Irrigation is given at the late jointing stage [within 70-75 days after sowing]. Irrigation at the flowering stage [within 90-95 days] is important to ensure more grain number and better grain size. At dough stage [within 110-115 days after sowing], another irrigation is required. Of course, the number of irrigations required depends on soil type, rainfall, and amount of water applied per irrigation.

If only one irrigation is possible, it should be given at crown root initiation stage, i.e., 20-25 days after sowing. If two irrigations are available, first irrigation should be given at the crown root initiation stage and second at the flowering stage. If three irrigations are possible, first irrigation should be given at crown root initiation stage, second at jointing stage, and third at the milk stage.

• Water Management For Maize

Maize is sensitive to excess water as well as moisture stress. Water should not be allowed to stand in the maize field at any stage of its growth. Maize can tolerate heavy rains, provided excess water is drained away. A good crop requires about 460 to 600 mm of water during its life cycle. At Tasseling to silking stage water requirement is critical. At shortage may reduce maize yields considerably.

• Water Management For Barley

Barley is usually grown as rain fed crop because of its low water requirement. It may require two to three irrigations to give good yields. If supply of water is inadequate, irrigation may be given near the active tillering stage [30-35 days after sowing]. If two irrigations are possible, one should be applied at active tillering and the other at the flowering stage. An extra irrigation may be required on sandy soils. On saline and sodic soils, frequent light irrigations give better results.

• Water Management For Sorghum, Bajra, And Ragi

Sorghum is generally raised as a rain fed crop. The irrigation should be provided during flowering and grain filling stages if rains are not received. The plants should not be allowed to wilt. Proper drainage conditions should also be provided for the removal of excess rainwater from the field.

Bajra is a rainfed crop hence, irrigation is needed only if there are no rains. Two irrigations during the growing period of the crop are adequate. Ear head emergence is the most critical stage and the crop has to be irrigated to avoid yield loss. Bajra does not tolerate water logging. So, proper arrangement for draining the excess water must be made.

Ragi sown during Kharif does not require any irrigation. However, at tillering and flowering stages if there is no rain for a long spell, irrigation may be required to obtain a good yield. Ragi crop does not perform well under water logged condition; therefore, proper arrangements for draining of excess water is essential.

• Water Management For Pulses

Bengal gram is mostly sown as a rain-fed crop. However, if irrigation facilities are available, a pre-sowing irrigation may be given to ensure proper germination and crop growth. If winter rains fail, irrigation at pre-flowering and at pod development stage may be given. No irrigation should be given at the flowering time.

Garden pea is mostly grown in rainfed areas. It can tolerate drought conditions to some extent. With one or two irrigations, higher yield can be obtained. The irrigation for pea should be light and uniform. Water logging condition in pea field causes considerable loss in the yield.

Being a deep rooted crop, Red gram can tolerate drought. If planted in June, one or two pre-monsoon irrigations should be given. After the onset of the monsoon, there is no need for irrigation. If there is drought during the reproductive period of the crop, one or two irrigations may be required. The crop requires proper drainage.

If green gram or black gram is raised during rainy season, drainage is very important because both the crops are sensitive to water logging. For Rabi and summer crops, five to six irrigations may be given. The first irrigation should be given about 20 to 25 days after sowing. The subsequent irrigations should be given at an interval of 12 to 15 days.

During Kharif, soybean crop does not require any irrigation. If there is a drought at the time of pod filling, irrigation is required. During heavy rainfall, drainage is important. Spring crop may require five to six irrigations.

• Water Management For Oil Seed Crops

Groundnut does not require irrigation if raised as a rain fed crop. However, if there is a dry spell, irrigation may be necessary, irrigation should be given at the pod development stage. The field should be well-drained.

In South India, groundnut is grown in Rabi season. Then, three to four irrigations are necessary. The first irrigation may be given at the start of the flowering phase and the subsequent irrigations whenever required to encourage peg penetration and pod development. The last irrigation just before harvesting facilitates full recovery of pods from the soil.

The Sesame crop requires about 50 centimeters of water during the entire growth period. The first irrigation may be given after 25-40 days of sowing. Second and third irrigations may be given at flowering and pod development stages, i.e., 45 to 50 and 65-70 days after sowing. Light irrigation is recommended in the evening when there is no wind to avoid lodging. It is considered essential to irrigate. At maximum flowering phase, irrigation may be given to ensure the development of capsules fully.

Castor is usually a rain fed crop. However, it responds well to irrigation. Irrigations need to be heavy and less frequent to benefit this deep-rooted crop. Two to three heavy irrigations may get a good yield. Critical irrigation at flowering stage is essential. In heavy rainfall areas proper drainage is essential.

Generally, Rape Seed and Mustard are raised on the conserved moisture from monsoon rains. Adequate land preparation through ploughings and leveling, application of organic manures, and use of mulches may facilitate conservation of moisture resulting in high yield. These crops respond well to irrigation. Two irrigations at pre-bloom and pod filling stages are considered critical irrigation.

Sunflower is a crop of medium water requirement. No irrigation is needed for the Kharif crop. However, irrigation may be beneficial in the event of uneven distribution of rainfall. Pre-sowing irrigation is essential for Rabi and Zaid crops to get uniform germination and better stand. Rabi crop may be irrigated thrice at four to the five-leaf stage, flowering and grain filling stages of the crop [maybe after 40, 75, and 110 days of sowing]. Between flowering and grain filling stages of the crop, at least irrigation must be given. It requires four to eight irrigations at an interval of 10-15 days during Zaid season. Light irrigation at grain filling stage should be given, especially on a windless evening to avoid lodging.

• Water Management For Cotton And Jute

The first irrigation should be given 40-45 days after sowing the cotton crop. It helps in preventing excessive vegetative growth. The subsequent irrigations should be light. These should be given at an interval of two to three weeks. The crop must not be allowed to suffer from water stress during fruiting and flowering period; otherwise, it may cause excessive shedding of flower buds and young bolls resulting in loss of yield. During early growth period, Cotton is very sensitive to water stagnation for long periods. Hence, the excess water of rain or irrigation should be drained. The crop cannot tolerate water logging conditions at any stage of growth.

Jute is generally grown under rain fed conditions. The crop suffers if rains are not timely or abundant. During rainy season, excess water should be drained to avoid water logging. Jute yields better under irrigated conditions. An irrigation before sowing and three irrigations after sowing are considered optimum for increased fiber production of early sown Jute.

 

Water Harvesting

Water harvesting refers to collection of rainwater from the roofs of buildings and storing it underground for future use. It also denotes the rain water storage in low lying areas of a field or in the ponds during rainy season and their utilization for irrigation. Water harvesting facilitates recharging of the groundwater table and improves the quality of groundwater through the dilution of fluoride, nitrate, and salinity. Thus, water harvesting makes available more water for use.

Globally many methods of water harvesting have been used over centuries. In water-scarce areas, people have developed techniques of water harvesting suited to their situations. The people of arid and semi-arid areas have constructed tanks by excavating the ground and by providing bunds for the collection of rainwater. The people of Rajasthan developed reservoirs [Khadin], dams [Johads], tanks, and other methods to check water flow and to accumulate run-off. Water stored in these structures was available for irrigation. The people of other regions also developed similar systems; Jal Talais of Uttar Pradesh, the Haveli System of Madhya Pradesh, Ahar of Bihar, and Kanmai of Tamilnadu are a few examples. Farm ponds should be developed in organic farms to harvest and store rainwater in order to supply irrigation water during droughts and to enhance the water table.

 

Water Conveyance

Water conveyance is the process of water transportation from source to field to be irrigated.

Loss of water during conveyance in canals and other systems is mainly by seepage and evaporation. The seepage reduced by 30 percent by lining the canals with concrete. The loss due to evaporation from the canals can be reduced by providing water only on demand instead of keeping the canals continuously filled. Using underground conveyance system may altogether eliminate evaporation and deep percolation losses. These issues need policy intervention at the community and government levels.

 

Water Conservation

Water conservation implies the application of approaches to minimize water loss. Better management practices aim at increasing water-use efficiency. Determining the volume of water needed to maximize productivity is as important as minimizing the wastage of water. The techniques that are used to reduce the demand for water, deserve attention. Only a part of the rainfall or irrigation water is utilized by plants, the remaining water either percolates down into the groundwater or evaporates from the soil surface. By employing techniques that can help improve the water use efficiency and evaporation loss, water demand can be reduced.

Ploughing helps in holding more water and reduces evaporation. Adoption of contour farming in hilly areas and in low land paddy fields helps conserve water. Use of organic materials such as crop waste and compost for mulching slows down the surface run-off, improves the soil moisture, reduces evaporation losses, and ultimately improves soil fertility, cover crops also slow down run-off and minimize evaporation losses. Shelter belts of trees and bushes along the edge of agricultural fields slow down the wind speed and reduce evaporation and erosion. Similarly, planting of trees, grass and bushes reduces the velocity of rain and helps rainwater infiltration into the soil.

Conservation tillage helps preserve soil moisture by leaving at least 30 percent of the soil surface covered with crop stubble, thereby decreasing wind and water erosion. The crop stubble layer reduces evaporation in the soil profile by one-half compared to bare soil.

 

Availability Of Soil Water

Water availability to the crops depends on the crop variety, climatic, and management factors. Based on the availability of soil water to plants, some concepts are widely used in water management. These are saturation capacity, field capacity, available moisture readily available moisture, permanent wilting, temporary wilting, and ultimate wilting points. Let us have a closer look at each one of them.

• Saturation Capacity

This is also called as maximum moisture holding capacity of the soil. It refers to the amount of water required to fill all the pore spaces between soil particles. When the porosity of a soil is known, the saturation capacity can be expressed as equivalent cm of water per meter of soil depth.

• Field Capacity

The field capacity refers to the moisture content of the soil after the free flow water has moved due to gravity. The concept is useful in calculating the amount of water available in the soil for plant use. It is equivalent to 1/3rd atmosphere and depicted in percentage.

• Readily Available Moisture

The portion of the available moisture that is most easily extracted by plants is called Readily Available Moisture. It is approximately 75 percent of the available moisture.

• Available Moisture

The difference in the moisture content of the soil between field capacity and permanent wilting point is known as available water or available moisture regime.

• Temporary Wilting Or Incipient Wilting Point

Temporary wilting may sometimes takes place during hot windy days, but the plant may recover during the cooler part of the day. It does not require any addition of water. The temporary wilting may take place during the hot summer days, even when soil moisture is higher than the wilting coefficient. This happens due to higher transpiration.

• Permanent Wilting Point

Permanent wilting point or the wilting coefficient refers to the water content at which plants can no longer extract sufficient water from the soil for their growth. The permanent wilting point is at the lower end of the available moisture range. If the plant is permanently wilted, it will not regain its turgidity even after being placed in a saturated atmosphere.

At the permanent wilting point, the films of water around the soil particles are held so tightly that the plant roots can not extract enough moisture at a sufficient rate to satisfy the transpiration requirements of the plant, resulting in wilting of the plant. The permanent wilting depends upon the rate of water used by the plant, the depth of the root zone, and the water-holding capacity of the soil. Each crop or variety will have a different permanent wilting point.

• Ultimate Wilting

Ultimate wilting is slightly different from permanent wilting with respect to regaining turgidity. When ultimate wilting occurs, the plant will not regain its turgidity even after the addition of sufficient water to the soil. Consequently, the plant dies.

• Plant Appearance

Many farmers use plant appearance as an indication to decide when to irrigate the crop. The symptoms of water stress vary with the crops. The symptoms may differ from the stage of growth also. Leaves of crops become dark green as soil moisture stress becomes severe in crops such as beans, cotton, and groundnut. The leaves of maize and sorghum curl and change their orientation as moisture stress increases. In other crops, pronounced leaf wilting could be seen.

 

Critical Stages In Crop Development

In some stages of crop development irrigation is a must. Otherwise, there will be a definite reduction in yield. Such stages are called critical stages. When irrigation water is limited, there may be opportunities for irrigating the crop at least during the critical stages. Irrigation during certain periods indicated below seems to benefit the crops. Let us discuss the critical stages of some important crops.

• Cereals And Millets

The critical stages of wheat crops include early growth, booting, flowering, and grain formation. Early booting, tillering, and soft dough are the critical stages for Barley. The Oats require irrigation from the beginning of ear emergence to flowering. Flowering and early seed developments as well as grain filling period are recognized as critical stages for Maize crop. As far as millets are concerned, tillering, flowering booting, heading and grain development are the critical stages for sorghum, and heading and flowering are the stages for Pearl millet.

• Legumes And Oil Seed Crops

Among the legume crops, Alfalfa has to be irrigated immediately after cutting for hay. Flowering and seed/pod formation stages are the critical stages for other crops like Peas and Beans.

Oilseed crops like Groundnut and Sunflower require irrigation during the critical stages of flowering and pod setting/head formation.

• Vegetables And Fruit Crops

Flowering and periods of rapid fruit development are critical stages for crops like Tomatoes. Head formation and enlargement are the stages of critical irrigation for Broccoli and Cabbage. The fruit crops like Citrus and Mango require irrigation at critical stages like flowering and fruit setting.

 

Root Zone

Plants differ in their ability to withdraw water from the soil, water use rate, and ability to withstand soil water stress. About 40 percent of the water used by plants is taken from the top 25 percent of the root zone. So, any amount of water added to the soil beyond field capacity in the bottom 25 percent of the root zone will cause only deep percolation.

Crop rooting depth will be dependent on local conditions such as soil type, compaction, shallow water tables, soil salinity, and fertility. Different crops have different rooting depths. Plants have a shallow zone in clay soils and a deeper root zone in sandy soils. The rooting depths of some of the crops are presented below.

Rooting Depth Of Different Crops:

Wheat: 3-4 ft.
Corn: 2.5-4 ft.
Oats: 3-5 ft.
Sorghum: 2-3 ft.
Soybeans: 2-3 ft.
Groundnut: 2-2.5 ft.
Sugarcane: 4-6 ft.
Cotton: 3-4 ft.
Melons And Potatoes: 2-3 ft.
Onions: 1.5 ft.
Tomatoes: 2-4 ft.
Cabbage: 1.5-3 ft.