Subtantial immmprovements in the application efficiency of furrow irrigation systems are possible when tailwater is no longer a wast.But there must be reuse.Therefore it was attempted to make such an evaluation at cotton farms under study in the Gorgan and Gonbad regions which are the cotton producing regions in the country.during this research four treatments continuous inflow with rates of 1.7,1.4,1.1, and 0.8 liters per second,in gradient furrow 120 meters long with open end ,were investigated in complete randomized block design with 4 replications per treatment.the range of discharge from erosive flow to none erosive flow was different.A1l planting ,and harvesting operations were done in the conventional fashion of cotton farming and irrigation was done according to requirement by gated pipe.During each irrigation the quantity of runoff water was measured with I inch parshal flume and samples of the runoff water was sent to the water precisely evaluated.The results show that the quantity of runoff water the requires the construct of reservoir suitable with the volum of runoff water in each area in order to enable its reuse,thus some of the farm land must be allocated to reserviors must be designed to occupy the minimum amount of land .Also since there was no statistically significant difference between the runoff water of 1.1 and 0.8 liters per second discharge and since these were the smallest capacities under study,hence the use of about 1.1 liters per second discharge or less is recomended for reuse of irrigation ,higher rates of discharge are erosive and produce a larger volum of runoff water and hence need larger reservoir whilst they do not increase yields per unit area.Also,qualitatively ,the results show that the reuse of runoff water for irrigation from the stand point of salinity,acidity,SAR,SSP and the quantity of nutrients contained in it is quite desirable ,and that water together with irrigation water can be classified as C2-S1.But since a pump and pips are necessary to transport and reuse runoff water from down ground in up grounds, in order to prevent settling down of precipitates,which are commonly particles of silt and clay ,within the return pipes,it is necessary to construct precipitation pools.
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