Sugarcane Crop Water Requirement and Annual Irrigation Requrement in Sri Lanka

Sugarcane Irrigation Water Requirement in Sevanagala and Udawalawe, Sri Lanka 
උක් වගාව සඳහා  ජල අවශ්‍යතාවය 

The irrigation water requirement in Sevanagala and Udawalawe sugarcane growing areas have a bimodal pattern ,opposite to the pattern of rainfall distribution. The grand growth period which has a maximum daily crop evapo transpiration starts at 95 days after planting. If planting is done in January, maximum amount of rainwater can be utilised by the crop during this grand growth period, which starts on April.  At this time, Yala rainy season is well established. If planting is done in June, the grand growth period starts in October. Usually, 2^nd inter monsoonal rainfall for Sevanagala and Udawalawe area starts in late September. The Maha rainfall continues till end of December for a period of 3 and half month.  Hence, maximum amount of rainwater can be utilised by the crop during this period, coinciding with grand growth period of sugarcane crop.  Considering the use of rain water, month of January and (1^st planting season) and from June to July (for 2^nd planting season) are more suitable for planting sugarcane. The annual irrigation water requirement  for Seavanagala sugarcane is varied from 649-794 mm and 697-783 mm for Udawalawe respectively. 

For more details, read flowing research paper 

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Estimation of reference evapo-transpiration (ET0)

Gidelines for estimating Evapo-Transpiration ina perticuler crop is given by ,

ET^O = C [W.Rn + (1-w). f (U). (ea – ed)]  

where, 
Rn = net radiation in equivalent evaporation expressed as mm/day, W=temperature of altitude related factor, f(U) = wind related function, Ea–ed= vapor pressure deficit (mili bar),   C=the adjustment factor (ratio of U day to U night), Rn (0.75-Rns), Ea=Saturated vapor pressure (m.bar), Ed=mean actual vapor pressure of the air (mili bar). In this method, radiation, air temperature, relative humidity and wind speed are incorporated into the ETo estimate. 

annual crop water requirement (CWR) of sugarcane in Sri Lanka

In Sri Lanka, sugarcane is commercially cultivated in dry and intermediate zones where annual rainfall exhibits peculiar bimodal pattern of distribution. The total annual rainfall receives in the intermediate zone varies from 1750 to 2500 while in sugarcane growing areas of dry zone, it varies from 1500 to 1700 mm. The annual crop water requirement (CWR) of sugarcane varies from 1200-1500 mm per annum and it depends on the local climatic conditions, variety and crop growth. Generally, the rainfall receives in these areas sufficient to meet the considerable fraction of crop water requirement of sugarcane but balance has to be supplied externally by irrigation to obtain higher crop growth. The normal crop cycle of sugarcane is 12 months. Thus, commercial planting under irrigation is carried out usually in every month, available rain-water could be utilised to the maximum efficiency while reducing irrigation water demand by planting sugarcane to coincide higher water demanding stages of crop growth to rainy periods and manipulation of other agronomic practices accordingly.