RAINWATER HARVESTING FOR SUPPLEMENTARY IRIGATION TO RAINFED CROPS

摘要

Parallel open ditches across the contours were constructed over a 5,000m2 flat area so thatrnthe runoff could move down and flow longitudinally towards an end collecting channel. Inrnorder to achieve maximum runoff efficiency, the whole catchment was covered by plasticrnsheets. Runoff collected by the end channel was then discharged into the downstreamrn500m3 ground storage. A recording data logger was installed at the end of collecting channelrnfor runoff and rainfall measurements. The experimental farmland located next to the runoffrncatchment was divided into 8 plots from which four plots were irrigated using water fromrnthe rainwater harvesting (RWH) system and the rest four replications were treated as controlrnwithout irrigation.rnExperimental farming started in 2005 with planting a commercial wheat variety after first rainfallrnin November. Rainwater collected during wet season was conducted to the farm land (via anrninstalled pressurized irrigation system) during critical stages of wheat growth. During the firstrnyear of study a total of 105mm rainwater were applied during two critical growing periods (35%rnof required water in addition to the natural rainfall). Compared to the conventional drylandrnfarming, grain yield under the experiment increased by 70%. The second trial of supplementaryrnirrigation was conducted during the next year (2006–2007). It was observed that an equivalentrnof 150 mm runoff water (58% of required water in addition to natural rainfall) was producedrnfrom RWH system and fed to crop during 3 critical growth stages. Compared to the controlrndryland farming, wheat grain yield increased in the second year by 87%.rnSuch a production growth is considered very satisfactory since it is far beyond the normalrnproduction rate in the neighboring areas and it is also very encouraging because drylandrnwheat cultivation is a very competitive business in arid and semi arid region of the country.