Developing soil matric potential based irrigation strategies of direct seeded rice for improving yield and water productivity

Water and labour scarcity besides increasing cost of cultivation in transplanted puddle rice (TPR) warrants to develop and adopt input use efficient and cost effective direct seeded rice (DSR) method of cultivation. Though DSR saves substantial amount of irrigation but there are contradictory observations on yield realization. Therefore, a two year field study was undertaken with the aim to develop efficient irrigation strategy for maximizing tilled DSR yield with minimum irrigation input. Total 08 irrigation strategies, based on 03 soil matric potential (SMP) levels (-15, -30 and -45 kPa) and their combinations based on crop growth stages, were evaluated for fine grain aromatic (Basmati) rice variety 'CSR30'. Responses of respective irrigation strategies were evaluated on crop water use and its components, biometric parameters and yield attributes and yield of DSR. Performance of DSR was also compared with standard TPR practice. Soil profile moisture content ranged from 32 to 39, 27-39 and 22-39% in -15, -30 and -45 kPa irrigation regimes, respectively. Irrigation input in DSR method of cultivation varied between 709-1541 mm as compared to 1807 mm of TPR. With different irrigation strategies, DSR grain yield and irrigation water productivity (IWP) varied from 1.72 to 2.89 Mg/ha and 0.19-0.24 kg/m(3), respectively. Irrigation threshold -15 kPa at all stages in DSR produced the highest yield and crop water productivity (CWP; 0.48 kg/m(3)), but with lowest IWP. Irrigations at or below -30 kPa during initial phase (< 90 DAS) and at -15 kPa during remaining period produced comparable yield with significantly higher IWP. Though TPR registered lower IWP (0.18 kg/m(3)) as compared to the best DSR treatment but recorded about 11% higher grain yield with significantly higher crop water productivity (0.58 kg/m(3)) than DSR. Water balance studies revealed better utilization of precipitation in DSR due to irrigations at more negative SMP. Overall, study suggests irrigation scheduling at <= -30 kPa during initial phase and -15 kPa during the remaining crop season proved to be the optimum irrigation threshold for maximizing DSR yield with limited irrigation input.