Evaluation of improving Water Productivity Using Rain Water Harvesting System and Supplemental Irrigation on Barley

Due to water shortage, increasing production by increasing cultivation area is limited in arid and semi-arid regions and approach to optimize the use of rainfall and limited irrigation to be considered, in order to increase water productivity. Development of rainwater harvesting systems and supplemental irrigation can be effective in increasing semi-irrigated cultivation area and decreasing water shortages. Rainwater harvesting is defined as a method for inducing, collecting, storing and conserving local surface runoff for agriculture in arid and semi-arid regions. The supplemental irrigation in condition which rainfall alone cannot have a good performance can be effective to improve the yield. The objective of this study was to investigate the effects of rainwater harvesting system and supplemental irrigation on water productivity index in winter barley (Hordeum vulgare L. Var. Abidar). A field experiment was conducted in a semi-arid region at Research Field of Tarbiat Modares University, located 16 kilometers of west of Tehran, Iran during the 2011-12 growing season. The land was located at 5110  E. longitude and 3535  N. latitude, at a height of 1269 m above the sea level. In order to cultivation, first it was attempted to plow to a depth of 30 cm, formed lumps were compacted using disc ,then seeds with a density of 130 kg per hectare were planted in furrows at 20 cm intra-row space and finally seeds were covered by soil using trowel so that the depth of cultivation was 4-5 cm. The size of each plot was 3×6 m considering the catchment and cultivate area ratio was 1:1. The experimental plots spacing were 1 m apart to avoid side effects. The maintenance of barley plants during the growth season was made by removing the weeds and applying fertilizer urea at a rate of 85 kg/h (half at the seeding and half in the spring). During the planting season, it was attempted to remove the weeds over the rain water harvesting catchment. The supplemental irrigation was applied during the grain filling stage. The volume of applied water was calculated based on the soil moisture deficit up to a depth of 45 cm. The amount of applied water in each plot was measured using the flow meter. The experiment was a split plot in a randomized complete block design with three replications. Irrigation treatments at five levels (twice with water, twice with treated municipal wastewater, once with water, once with treated municipal wastewater and without irrigation) as main plot and rainwater harvesting surface treatments at three levels (compacted, incompacted and natural surface soil) is defined as sub-plots and rainfed was defined as control. The analysis of variance was carried out using the generalized linear model (GLM) and after ensuring, normal distribution of residuals was tested using the SAS software. The comparison of treatment means was made using the least significant difference (LSD) at the level of 0.05. The results indicated that the use of rainwater harvesting system had increased the yield and the total water productivity in comparesion with the rainfed condition. The supplemental irrigation maximized the total water productivity (in grain and biomass yield) and increased significantly (by 6.3% and 13.2%) compared with non-irrigated plots respectively. The compacted surface plots had significantly higher values of the total water productivity in grain and biological yield (15.8% and 14.9% respectively) in comparesion with natural surface treatment. There was no significant effect of supplemental irrigation with treated municipal wastewater on the yield and yield components. The use of compacted catchment in the rainwater harvesting system caused an increase in the number of spikes m - 2 and the application of the supplemental irrigation during grain filling stage could increase the thousand grain weight by increasing the grain filling period, resulting in the desired yield. Applying the supplemental irrigation by treated municipal wastewater made the renewed pressure not exert on the surface and groundwater resources for the production of crops. Using this project can be helpful for the lands beside the smaller cities and rural areas, where there is not possibility of sustainable rainfed farming, to be planted using rainwater harvesting system and to be irrigated supplementary by the treated municipal wastewater