Water Management in Horticultural Crops

Kc values of crops

• Crop coefficient is the ratio between crop ET and potential ET. Crop coefficient depends on soil cover, soil moisture and crop height. At early stage crop covers only a fraction of soil and covers as it matures. The rate at which plants grow and cover the soil depends on the crop. In the early stage main component of ET is evaporation, while under fully covered condition transpiration is the main component. ET of a crop depends on plant height and leaf area index. Tall plants with high LAI transpire more water than short plants with low LAI. The relationship between ETo and ETc is expressed as


• ETc is also known as maximum evapotranspiration ET(max). Kc value is inbuilt with crop and soil characteristics and management practices and varies with in the crop duration.
  
• For a precise estimate, duration of (annual) crop is divided into four stages:
  
(i) seedling stage which represents germination and early growth when the soil surface is hardly covered by the crop.The
ground cover is less than 10 per cent
(ii) active vegetation stage form the end of initial stage to attainment of effective full ground cover which is less than 80
percent coverage,
(iii)reproductive stage from attainment of full ground cover to first sign of maturity as indicated by discolouration of leaves
,leaf falling etc.,and
(iv)maturity stage from reproductive stage to full maturity.
• Crop coefficients vary with relative humidity and wind velocity. Strong winds and low RH cause more transpiration. In brief, Kc values vary with crop development stage of the crop and to some extent with wind speed and RH. For most of the crops, Kc value increases from a low value at the time of emergence to a maximum value during the period when the crop reaches flowering and declines as the crop approaches maturity.