the effect of water stress on yield of new cotton variety-sepid (gossipiumhirsutum l.) in drip irrigation

introduction: iran is a vast country with limited water resources. iran is located in arid areas and average precipitation is estimated to be 250 mm. in recent years, water shortage has created many problems for iranian farmers. in these conditions, surface and ground water use is excessive. high consumption, low irrigation efficiency, bad time and geographical distribution of precipitation, population growth and increasing agricultural land are one of the main reasons for the irrigation water crisis. therefore, the main problem of drought and water shortages still remains. the area of agricultural land in golestan province is high, but most of them are rain-fed cultivation or left fallow. due to the loss of irrigation water in traditional agriculture, development of pressurized irrigation as a solution to increase productivity and reduction of strain on water resources was raised. with government support, the use of pressurized irrigation systems is increasing. materials and methods: to evaluate the effect of different amounts of water on new variety of cotton-sepid, a two-year study was conducted using drip irrigation at hashemabad cotton research station, gorgan, iran.the hashemabad cotton research station is located in north of iran at 36° 51' n latitude and 54° 16' e longitude at the south-east corner of caspian sea and its height from sea level is 13.3 meters. that station has a mediterranean climate with relatively mild winters and relatively dry summers. the station's annual evaporation, precipitation and relative humidity are 1311mm, 525 mm and 71%, respectively. soil texture of hashem abad station is silty clay loam. in this study, four levels of irrigation water: 0%, 40%, 70% and 100% evaporation of class a pan were studied in a randomized complete block design. land was plowed in autumn last year and was ready for planting in april with the disc. during tillage, manure fertilizer on the soil surface was sprayed based on the soil test recommendations. at this stage, for combating weeds, herbicide trifluralin (2.5 liters per hectare) was used. planting new varieties of cotton - sepid was in the first decade of may. each plot consists of 8 lines which was ten meters. after evaporation of 50 mm from class a evaporation pan, irrigation is done. irrigation tapes were placed just alternate between planting rows. water consumption was measured using a volumetric water meter. to measure the product, cotton-seed of four rows of each plot were harvested. yield components were measured in the same four rows. product wastaken in october and early november during two harvesting. results and discussion: cotton as thermophilic plants, especially in humid areas, is strongly influenced by farm management. among the controllable factors, irrigation management had very effective role in the balance between vegetative and reproductive growth. in other words, water stress control in cotton fields is essential for economic output. through advanced techniques, drip irrigation despite high initial cost, will be the first choice. because in addition to irrigation efficiency, with earliness management, mechanization harvesting is done better. according to the analysis of variance, the effect of different amounts of water on the total yield was significant at the level of one percent. the lack of statistical significant differences between treatments in terms of total yield of i100 and i70, the second treatment due to a 30% saving in water consumption and earliness as the best in the normal condition. one of the parameters that are usually affected by irrigation management is earliness. average comparison shows in term of earliness, three treatments of i70، i40 and i0 in group a and treatment i100 are in the latter group. thus, from this aspect i70 can be recommended. in terms of water use efficiency i40 and i70 with 1.44 and 1.17 kg per cubic meter had the highest wue, respectively. conclusions: the results shown that irrigation water had significantly effects on first pic, second pic and total yield. but irrigation water treatments had no significant effect on earliness and boll weight. according to the combined analysis table (two years data), as much as % 70 of cumulative evaporation from class a pan, will be recommended for cotton farming in north of iran in normal weather. in dry years, % 100 of cumulative evaporation from class apan is suggested.