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Water Management
Introduction
- Of the agronomic factors known to augment crop production, water management stands second, next to fertilizers, contributing 27% in crop production.
- Groundnut is generally grown as kharif crop in rainfed area, but the productivity of kharif groundnut is lower than rabi/summer crop.
- Among the various constraints for low yield, the principal one is erratic, insufficient and unevenly distributed rainfall during kharif. The success will be assured in kharif season if irrigation is considered as a basic input and rain as a supplement.
- Since irrigated groundnut is not subjected to vagaries of monsoon and is less exposed to pest and disease complex, possibilities of increasing its productivity and stabilizing production are immense.
Principles
- Several stages in plant life cycle are sensitive to moisture stress but some have been found more sensitive than others. Peak flowering phase is considered as most sensitive period for moisture in groundnut. Very early growth has not been found to be sensitive to moisture stress as water absorbed during the first month after sowing is small. * At the peak flowering period, the root system is less efficient and the demand for water is high and so maximum sensitivity coincides with peak flowering. Pegs also can not enter the soil if the soil surface is hard due to prolonged dry spell.
- In general, water deficits during the vegetative period cause delayed flowering and maturity and reduce growth and yield. Water deficits during flowering cause flower drop or impaired pollination and during pod setting reduce pod weight. The early part of the pod setting is particularly sensitive to water deficit.
- For proper utilization of irrigation water, the following points should be considered.
Right amount of water should be applied at the right time.
Water should be of good quality.
Apply water by adopting proper method
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Critical Stages and Scheduling of Irrigation
Regulate irrigation based on physiological growth phases as given in the table.
Crop phase
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Days
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No. of
Irrigation
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From
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To
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| Pre-flowering
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0
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25
|
1
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| Sowing/ pre-sowing
|
|
|
1
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| Life irrigation (4-5 DAS)
|
|
|
1
|
Vegetative (20 DAS)
|
|
|
|
| |
| Flowering
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26
|
45
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1
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| Stray flowering (26-30 DAS)
|
|
|
1
|
Peak flowering (35-40 DAS)
|
|
|
|
| |
| Post-flowering
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45
|
105
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2
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| Pegging (46-65 DAS)
|
|
|
2-3
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Pod development (66-105 DAS)
|
|
|
|
| |
|
|
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Days of irrigation interval in different soil types.
Crop
phase
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Soil type
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Sandy/ lateritic
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Loamy
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| Pre-flowering |
6-8 days
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8-10 days
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| Flowering |
6-8 days
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8-10 days
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Post-flowering
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8-10 days
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10-12 days
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- The greatest sensitivity to drought occurs about 6-8 weeks after sowing, which coincides with the period of vigorous flowering. The peak flowering, being most susceptible to moisture stress, seems to cause delay in flowering and thereby the high reduction in formation of pods. The second most serious period for moisture stress is the pod-filling period. Stress in peg formation stage hardens soil and so the penetration resistance under stress is definitely very light. Moisture supply will be low and calcium supply inadequate, which would lead to, reduced pod formation and lower shelling percentage in pod produced.
- Irrigation scheduling based on IW/CPE, i.e., the ratio between fixed irrigation water (IW) and net cumulative pan evaporation (CPE) appears to be more practical. Scheduling irrigation by this approach indicated that irrigation at 0.4 and 1.0 IW/CPE ratio during vegetative and reproductive phases respectively is found optimum for getting higher yield.
- Scheduling irrigation by frequency and interval approach is very simple and can be used by the farmers without the help of any equipment. Irrigation is given in a fixed interval according to soils and climate. Total amount of water and number of irrigation required for groundnut varies in different places.
- Scheduling irrigation for summer groundnut have shown that about 11-12 irrigation are optimum. One irrigation at 0-10 days, one at 10-30 days, 2 at 30-50 days, 3 at 50-80 days, one at 80-90 days, 2 at 90-105 days and one at 105-120 days after sowing have been found most ideal.
- After the plant is established, irrigation may be withheld for 15-20 days. This will create stress and induce early flush of heavy flowering. Maintenance of soil moisture is very critical during 50-80 days (pegging and pod formation stages) of the crop.
- If irrigation is desired to supply based on climatic conditions, schedule irrigation at 0.40 and 0.60 IW/CPE ratio during vegetative and reproductive phases respectively. * Flowering, pegging and pod development phases are critical for irrigation, during which period adequate soil moisture is essential.
- The following irrigation schedule is followed. One irrigation at sowing or pre-sowing, one at 4-5 days after sowing as life irrigation, one at 20 days after sowing, two at flowering, two at pegging stage, 2-3 irrigation at pod development stage depending upon the soil type.
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Water Requirement
- Groundnut is relatively tolerant to drought as far as survival is concerned but its pod yield reduction is very high if proper soil moisture is not maintained especially during critical growth stages (flowering, pegging of pod development)
- The amount of water used by the crop is determined by the potential evapo-transpiration during the crop period and the degree of soil cover. The water requirement reaches a maximum during flowering and continues up to pod formation. * Groundnut requires on an average 400-500 mm of water but it varies with soil type, agro-climates and genotype.
- Total rainfall to a tune of 400-600 mm, well-distributed over the entire growth period during kharif results in good yield.
- During rabi/summer, the water use has been found to be 450-830 mm depending upon soil type and agroclimatic conditions.
Quality of Water
- Quality of irrigation water is the most important factor to decide the source of irrigation water. The water from different sources viz., rivers, canals, wells, lakes, tanks and drainage channels are being used for irrigating the crop.
- The river and canal water generally has low to medium salinity and low sodic hazard. The ground water is mostly saline or sodic or both. Rainwater is considered very good for irrigation because it contains very little of salts.
- The principal cations present in water are calcium, magnesium and sodium with small quantities of potassium. The main anions are carbonate, bicarbonate, chloride and sulphate with nitrate, fluride and boran occurring in low concentrations. The concentration and composition of dissolved salts in water determines its quality of irrigation water.
- Groundnut is very sensitive to saline water from germination to pod formation and only in later phases, it may tolerate somewhat higher salinity of irrigation water. The limits for saline water for groundnut are EC 4.00 mmhos/cm and residual sodium carbonate (RSC) 2 meq/lit.
- There are four important parameters, which determine the quality of irrigation water.
Total concentration of soluble salts
- Relative proportion of sodium to other cations viz., calcium and magnesium, i.e., Sodium Adsorption Ratio (SAR).
- Bicarbonate concentration as related to the concentration of calcium + magnesium.
- Concentration of boron and other elements (chloride, nitrate, lithium, fluoride, sulphate) may be toxic to other crops.
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Types of Irrigation and water management
- Generally border strip and check basin methods are being followed by farmers to irrigate groundnut. Besides, sprinklers are also used to some extent. Border strip method is the most suitable surface method of irrigation for groundnut.
- According to soil type and slope of the field, strips of 3-5 m width are formed and water from main channel is diverted into border strip. Labour cost for forming bund is less in this method than check basin. However, this method is not suitable if field is too sloppy or when field is not well leveled.
- In the check basin method, water is used more precisely. According to the slope of the field, water is diverted to sub-channel and then finally to sub-plot. More land area is wasted by bunds in this method.
- Sprinkler system of irrigation saves water to about 30-50 %. Although this system is more efficient and gives higher yield of groundnut, the initial investment on this is also high. This method is advantageous when water is a limiting factor as it is 50 % more efficient in use of water than the surface method.
Water Management in Kharif Groundnut
- About 84% of groundnut in India is grown in kharif in rainfed areas. Due to vagaries of monsoon, kharif groundnut shows great unstability in production and productivity. The timing and duration of moisture stress is responsible for reduction in yield.
- Moisture stress at an early stage delays reproductive development and at a later stage hastens attainment of maturity and causes heavy reduction in pod yield.
- Pre-monsoon sowing and life saving irrigation during critical growth period are the two important aspects considered for getting higher yield in kharif groundnut.
- If one irrigation is made available for pre-monsoon sowing followed by a life- saving irrigation at the time of prolonged dry spell during critical growth stage, yield level of groundnut may be increased significantly.
- The following points may be taken into consideration for conserving the available soil moisture or to mitigate the ill effects of water stress in kharif groundnut.
- Spraying of potassium chloride (5 g/lit of water) during flowering and pod development stages.
- Kaolin (30 g/ lit of water) as foliar antitranspirants applied at 30 DAS and at 60 DAS reduced the leaf temperature and increased the pod yield by 15.6 per cent over control.
- Soil incorporation of decomposed coconut coirpith @12.5 t/ha.
- Soil mulches
- Broad bed and furrow system of planting, scooping of soil at random and ridge tieing.
- Border strip irrigation is recommended in command areas in light textured soils.
Water Management in Rabi/Summer Groundnut
- Rabi/summer groundnut is grown in irrigated areas. Since irrigated groundnut is less dependent on weather unlike rainfed crop, possibilities for increasing production are immense. Depending upon soil temperature, irrigated groundnut is sown at different times.
- Rabi groundnut is grown on a limited scale in areas where winter is not severe and night temperatures do not fall below 15°C. Rabi crops are sown from September up to December. It is grown under residual soil moisture after the harvest of rice mainly in the coastal regions.
- The moisture, which is enough or sometimes more at the time of sowing, starts depleting faster with the advancement of summer. Irrigation, if provided during this period, can increase pod yield substantially. Normally 5 to 9 irrigation are required for rabi groundnut.
- Sowing of summer groundnut is done from second fortnight of December to February. On an average summer crop requires 9 to12 irrigation depending upon soil type and atmospheric temperature.
Drainage
- Drainage is a very important aspect of crop production. Plants of groundnut under saturated soil become yellow and degree of yellowing increases with increased period of saturation. Its overall effect leads to poor yield. Poor drainage causes chlorosis in groundnut. Chlorotic symptoms of the foliage clearly manifest 60 days after sowing. Soil with excess quantities of water contains inadequate oxygen which affects respiration. It has also been indicated that oxygen in the pegging area is necessary for fruit production.
Summary
- The average total water consumption varies from 450-500 mm.
- The crop has to be irrigated immediately after sowing and subsequently no irrigation given till 21 days. This stress enables the plant for better germination, growth and enables the root to go deeper for a better anchorage.
- Any irrigation given within 21 days given reduces the yield by affecting the growth of the plant.
- The crop in given second irrigation on 21 st day followed by normal irrigation once in 10 days.
- The critical stage when water is needed for this crop are flowering, peg penetration and pod development.
- The water requirement for groundnut reaches a maximum during flowering stage and continues up to peg penetration and pod formation stage since most dry matter is accumulated at this stage.
- Moisture stress during this period causes greatest reduction up to 30-35 per cent in pod yield.
- Moisture stress from sowing to active pegging do not appreciably influence the pod yield, was found to be favoured by the crop in reducing its internodal length and induces synchronized flowering
.
- The evapo-transpiration is less during the first 35 DAS and reaches peak during flowering and peg penetration stages. Hence, the crop can be irrigated once in 17 to 18 days in the early phase and once in 8 to 9 days during pegging and pod formation and once in 17 to 18 days at maturity phase.
- In heavy soils of Periyar - Vaigai command area, application of 20 t of coconut coir waste/ha improves the physical soil characters there by increases the pod yield.
- Under limited water supply conditions one irrigation during vegetative and maturity phases can be skipped, which will save 100 mm of irrigation water and there is no deleterious yield reductions.
- Application of organic mulches to a depth of 2.5 cm 30 DAS was found to save two irrigation to the tune of 100 mm and an yield increase of 10 per cent was observed.
- Application of mulches also has an added advantage of reducing the weed growth and lower the incidence of pests and diseases.
- Spraying of potassium chloride (5 g/lit of water) during the critical stages of flowering , pod development and pod maturation will aid to mitigate the ill effects of moisture stress at these crop growth stages and minimises the yield reductions from 18 (unsprayed control) to 7 (KCl sprayed) per cent.
- Sprinkler irrigation not only saves irrigation water (18-24%) but also increases the pod yield due to better soil aeration and basal pod setting.
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