Abstract:

Risk bearing, low productive, rainfed lowland rice ecosystem is the dominant food grain production chain of the Northeastern Hilly states of Meghalaya. Despite being home to the highest annual rainfall receiving zones of the world, rainfed rice production systems in Meghalaya often suffers from water stress during peak growing seasons, mostly due to the erratic distribution of rainfall in space and time dimensions and the absence of any alternative life saving water supply systems. Impact of regional climate change on any abrupt change in rainfall pattern may further pose a serious threat to the water availability and rice production vis-a-vis food and environmental security of the region. Under such circumstances, foremost requirement for devising efficient water management practices (including irrigation expansion & scheduling) are quantification of consumptive use of water or actual evapotranspiration (AET), major sources of losses of water from the paddy field, crop water productivity and finally, stage wise estimation of crop co-efficient (Kc) factor considering local climatic condition. Keeping this in view, present investigation was conducted at mid altitude of Meghalaya (250 41/ N latitude, 910 55/ E longitude, altitude of 1084 m from msl) involving four lowland rice genotypes grown under natural fertility (farmers practice) and fertilized condition: without phosphorus (N & K alone @ 90-0-40 kg ha-1) and with phosphorus (NPK: 90-60-40 kg ha-1). Results revealed that out of the total water (rainfall) received during crop growth periods (1261-1275 mm), only 27-29% were used to meet AET losses while more than 70% of the rainfall was Llsed to meet unproductive losses (in the form of deep percolation and under bund seepage). Reference ET (Penman-Monteith) loss during the same period was 375 mm. The estimated values of average crop coefficient factors across all treatment combinations at five crop growth stages (initial, panicle initiation, flowering, physiological maturity and maturity) were (Kc.ini: 0.81-0.93), at mid season (Kc.mid10: .98-1.07, Kc.mid21: .05-1.17, Kc.mid3:1.04-1.11) and at the end of late season, (Kc-end:0.81 to 0.93). Average grain yield production varied from 3.82 t ha-1 (farmers practice) to 5.66 t ha-1 (NPK: 90-60-40 kg ha'\ Local genotype Ngoba produced higher grain yield (4.2 t ha'1) under farmers practice while Sahsarang and RCPL-1- 160 produced higher grain yield (5.48-5.66 t ha-1) in fertilized condition. Real water productivity (WPET) ranged from 0.95 to 1.55 g grain kg-1 water while apparent water productivity including land preparation (WPPIFT) was very low (0.25-0.33 g grain Kg-1 water). To produce 1 kg rice grain, nearly 2700-4000 liters of water (rainfall) was supplied to the field of which, crop used (consumptive) only 645-1050 litres. Thus, it is imperative to implement water management practices to reduce the unproductive losses while narrowing down the wide gap between actual and potential crop and water productivity for the resource poor farmers of hilly states of Meghalaya.