Water management in groundnut

THE RAINFED groundnut is usually exposed to mid or late season drought. If there is failure of rains during the critical stages, yield is reduced to more than 50 per cent. Hence there is a great scope for increasing the productivity of rabi groundnut which is usually grown under assured supply of water.

Water required by groundnut varies from 400-600 mm depending upon the soil and groundnut grown. Water status invariably affects growth and development since about 80 per cent of plant fresh weight is water. Reduction of plant water status much below this level causes visible wilting. Moisture stress in groundnut crop results in.

- Reduction of leaf area and thereby reduced photosynthetic area and crop growth rate.

- Reduced plant height, fewer branches and flowers.

- Reduction of yield upto 46 per cent if the moisture stress is from 50 to 80 DAS.

- More number of infilled pods and reduction proportionately of sound matured kernels.

Critical stages of irrigation in groundnut are flowering, pegging and pod development. Moisture requirement was lowest. Withholding irrigation immediately after establishment of plant stand till flower initiation results in good root growth, profused basal flowering and ultimately higher yields. Gynophore production seems relatively insensitive to early drought. Hence for fruiting to occur the gynophores must enter the soil for which physical condition is important. The gynophores can exert a force equivalent to 3-4 grams only on the soil and mechanical resistance expressed in a dry soil during pegging stage is a problem. Hence during the pegging period enough care should be taken to optimum soil moisture for easy peg penetration. Similarly during pod development, irrigation should be given as the moisture stress during this period results in more number of illfilled pods which drastically reduces the kernel yield of groundnut.

Groundnut may require a minimum of 7-10 days of irrigation depending upon on the soil type. As compared to heavy soils, light textured soils require more frequent irrigation. The irrigation schedule for bunch type groundnut with a duration of 105 days is as follows: I irrigation - Immediately after sowing (Not necessary of optimum soil moisture in the soil at the time of sowing), II irrigation - 5-7 DAS, if needs (Early growth stage), III irrigation - 25 DAS (Flower initiation), IV irrigation - 32 DAS (Flowering stage), V irrigation - 39 DAS, VI irrigation - 46 DAS (Pegging), VII irrigation - 56 DAS, VIII irrigation - 66 DAS (Pod filling), IX irrigation - 78 DAS (Pod maturity stage) and X irrigation ) 88 DAS. The crop should not be irrigated thereafter till harvest.

K. Subrahmaniyam, P. Kalaiselvan & N. Arulmozhi TNAU, Vridhachalam 60 6001

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