Groundnut

Water Management

• By about 50% at 4.9 and 100% at 6.5 mmhos /cm.
• The following limits for use of irrigation water for groundnut EC less than 4.0 mmhos/cm and RSC less than 2 meq/litre.
• Vigorous flowering was the period of greatest sensitivity to moisture stress which is 6-8 weeks after seeding.
• The water absorbed by the groundnut during the first month after sowing is relatively small, hence the very early growth phase is not highly sensitive to moisture stress.
• At the peak of flowering, the root system is less efficient and the demand for water is high, coinciding with the highest sensitivity.
• The pegs cannot enter the soil if the soil surface is hard due to prolonged dry-spell.
• Flowering, peg penetration and early pod formation are the moisture sensitive phases of groundnut growth, since most of the dry matter is accumulated during these periods.
• Water deficits during the vegetative phases generally delay flowering and maturity, reducing the crop growth and yield, and moisture stress during flowering causes flower drop, impairs pollination and during pod setting, it decreases pod weight.
• The early phase of pod setting is especially sensitive to water deficit.

• Irrigation is aimed at supplying sufficient water to the crop rooting zone at appropriate times to prevent soil water deficit and crop stress.
• This goal may be achieved by : (a) measuring soil water status to schedule irrigation at a soil water potential above which the crop will not be stressed. (b) estimating crop water use (Et) from calibrated data or as a fraction of cumulative pan evaporation (CPE) and irrigate to replenish water lost by Et.
• The estimates to effective rooting zone, soil water holding capacity, rainfall, irrigation amounts and daily crop Et are required to monitor the depletion of available soil water enough to cause crop stress.
• In practice both the above approaches are often combined.
• These approaches need estimates of soil water holding capacity and effective rooting depth to calculate the amount of water to be applied without causing deep percolation.
• Irrigations are generally scheduled on the basis of following three approaches :
  1. Measurement of water potential (vs) or soil water depletion (SWD)
  2. Use of published evapotranspirational values or cumulative pan evaporation (CPE) data
  3. High frequency in irrigations (in arid zones).

• The amount of water needed by groundnut crop can be determined by measuring evapotranspiration potential during the crop growth and the degree of soil cover.
• The groundnut crop required maximum amount of water during flowering and it continues up to pod formation period.
• The total requirement of water by the groundnut crop grown on different types of soil as reported by various workers is shown.