Irrigation and drainage needs of transplanted rice in diked rice fields of rainfed medium lands

An experiment was conducted in diked rice fields with various weir heights (6 cm to 30 cm at an interval of 4 cm) for three consecutive years in the sub-humid climate of eastern India. The results reveal that about 56.75% and 99.5% of the seasonal rainfall can be stored in 6 cm and 30 cm weir height plots, respectively. Sediment losses of 347.8 kg/ha and 3.3 kg/ha have been recorded in runoff water coming out of 6 cm and 30 cm weir height plots, respectively in a cropping season. Similarly, total Kjeldahl nitrogen loss in runoff water from rice fields ranged from 4.23 kg/ha (6 cm weir height plots) to 0.17 kg/ha (26 cm weir height plots). The available K loss ranged from 2.20 kg/ha (6 cm weir height plots) to 0.04 kg/ha (30 cm weir height plots). Keeping in mind the aspects of conserving rainwater, sediment and nutrient and minimizing irrigation requirement, 22–26 cm of dike height is considered to be suitable for rice fields of the Bhubaneswar region during the Kharif (rainy) season. A lumped water balance model for diked rice field was developed and used for the present investigation. The computed values of runoff obtained from the simulation model are in close agreement with the observed values obtained in an experiment using higher weir heights (22 cm and above). The temporal distribution of runoff and irrigation requirement at fortnight intervals reveal that highest irrigation requirement is found during the first half of November followed by the second half of October and the first half of October. Rice fields up to a weir height of 18 cm produced about 20% of the total runoff in each of the first three fortnights. A gradual reduction in runoff was observed in the remaining fortnights. The least runoff was noticed in the month of November (during the first fortnight).