Water management in paddy cultivation

Dr Lydia Zimik
Water Requirement
Crop water demand is the amount of water required by plants for survival, growth, development, and the production of economic components. This requirement is met either naturally through rainfall or artificially through irrigation. Rice consumption varies from 6 to 10 mm per day, with total water use ranging from 1100 to 1250 mm depending on agro-climatic conditions, variety, duration, and soil characteristics. Since, the water requirement of rice is higher than that of any other crop of a similar duration, assured and timely supply of irrigation water has a great influence on the yield of the crop.
Water Management for Different Ecosystem
System of Rice Intensification (SRI)
Irrigation is limited to moistening the soil for the first ten days. After the appearance of hairline cracks in the soil, restore irrigation to a maximum depth of 2.5cm till panicle commencement and further increase irrigation depth to 5.0 cm.
Transplanted lowland rice
The use of water is reduced via ponding and levelling. Ploughing with a tractor-drawn cage wheel to reduce percolation losses and save up to 20% on water usage. Allow the green manure to decompose for a minimum of 7 days in the case of less fibrous plants like sun hemp and 15 days in the case of more fibrous green manure plants like Kolinchi (Tephrosia purpurea). A modest depth of 2 cm of water is sufficient for transplanting, as a deeper depth of water will result in deep planting, which will reduce tillering. Maintain a 2 cm water level for the first seven days after transplanting. The ideal practice for rice production after the establishment stage is periodic submergence of water. This 5 cm cyclic submergence must be maintained throughout the crop cycle. Moisture stress caused by insufficient water at the roots and tillering stages produces poor root growth, which results in reduced tillering, a poor stand, and low yield.
Drum Seeded Puddled Lowland Rice
Wet the soil with a thin film of water for the first week. Irrigation depth can be gradually increased to 2.5 cm as the crop matures. Provide appropriate drainage systems to drain excess water, or stick to a one-day irrigation plan after ponded water has vanished. It’s possible that the last irrigation will occur 15 days before harvest.
Common precautions for irrigation
Irrigation from field to field should be avoided. To prevent water leaking through the main bund cracks, a small bund can be created parallel to the field’s main bund at a distance of 30 to 45 cm within the field. The depth of stagnant water should be 5 cm or less to avoid percolation loss. Care should be taken not to allow development of cracks.
Critical Stages of Irrigation
The critical stage of water requirement refers to the point at which water stress produces substantial yield decrease. It’s also referred to as the moisture-sensitive phase. Rice requires a lot of water at different stages.
· Active tillering
· Panicle initiation
· Booting
· Heading and
· Flowering.
During these stages, the irrigation interval should not be longer than the specified period to avoid moisture depletion below the saturation threshold.
Continuous Submergence
Continuous land submergence for rice is commonly used due to the key benefits of increased nutrient availability and fewer weed management issues. Throughout the crop period, shallow submergence in water up to a depth of 5 cm is ideal for optimal production.
Components of Water Losses from Rice Field
The principal losses of water from lowland rice fields can be grouped into two: vapour losses and losses in liquid form.       
· Vapour losses are through transpiration from leaf surface and evaporation at water surface collectively referred to as evapotranspiration.
· The two types of liquid losses are deep percolation plus seepage and runoff of excess water over the field levees
Water Stress
Moisture stress refers to the effects of too much or too little water on plants. Moisture stress, on the other hand, is commonly used to describe water shortages. When transpiration exceeds absorption, the plant experiences a water shortage. The impact of water shortages on rice growth and output is determined by the stage of crop development at which the shortages occur.
Vegetative growth stage
To protect established seedlings from high winds and to allow for root development, appropriate ground submergence (5cm) is required immediately after transplantation. Following the early rooting stage, tiller formation and solid root attachment in the soil are aided by a shallow depth of land submergence (2cm). When moisture stress occurs during the active tillering phase, the yield is reduced by 30%.
Reproductive stage
From panicle primordial development to heading, the rice crop is particularly sensitive to water deficiency. Due to a high proportion of sterility, three days of moisture stress at 11 days and three days before heading causes the greatest yield loss. Moisture stress during the reproductive phase reduces production by 50% to 60%.
Maturity stage
This stage (milk to grain maturity) is the least susceptible to moisture stress in the soil. There is no need for standing water after the yellowish ripening stage. To make harvesting easier, water should be drained from the field 7-10 days before harvest.
Water stress management
Spray Cycocel @ 1000 ppm (1ml of commercial product in one litre of water) in water shortage circumstances to reduce moisture stress’s negative effects. The negative effects of soil moisture stress are alleviated by a split application of potassium (50% at basal and 25 % each at tillering and panicle initiation stages) combined with Azospirillum (seed inoculation, seedling dipping, or soil treatment). Seed hardening using 1% KCl for 16 hours (seed and KCl solution are mixed 1:1) and shade drying to achieve storable moisture. The crop will be able to survive early moisture stress as a result of this. To counteract moisture stress at different physiological stages of rice, a foliar spray of 3% kaolin or 1% KCl can be used.
Management of Excess Water
Excess water is removed from the ground via runoff when it is levelled. Excess water in the root zone is removed through drainage, which is damaging to plant growth. In poorly drained soils, late tillering is the optimal time for drainage. In a water-logged area, controlled irrigation reduces excessive water use. Flood-prevention strategies include: Bunds can be built to control the flow of water from rivers to arable land.
The writer is SMS (Agronomy), ICAR-KVK Imphal West, ICAR Research Complex for NEH Region, Manipur Centre