اثر مقادير كربن آلي و ازت كل خاك بر واكنش گندم ديم (سرداري ) به مصرف كود نيتروژن و تعيين حد بحراني آن ها در استان كرمانشاه

Effects of organic carbon and total nitrogen in the soil on the response of dryland wheat(Sardari c.v.) to application of nitrogen fertilizer in Kermanshah province

In the past, fertilizer trials conducted on nitrogen rate have not considered OC and TN in soil. Thus, in many trials, fertilizer could not increase wheat yield under rainfed condition even with supplementary irrigation or high rainfall. In this investigation, those factors especially OC & TN that cause non-response to N application on Sardari variety were studied. Statistical results for five out of 12 experiments conducted for nine years showed that nitrogen fertilizer up to 30 kg/ha significantly increased grain yield in comparison with control. Mean of grain yield was enhanced up to 393 kg/ha in Kermanshah province. Increased application of nitrogen (N45) caused an increase in grain yield but wasnʹt significant. More than this rate (N45) not only didnʹt increase grain yield but also decreased grain yield in some years with low rainfall. In the remaining experiments, due to high amount of OC and NT in sites of the experiment, nitrogen fertilizer not only did not increase grain yield, but in two experiments, grain yield decreased. Therefore, critical level of OC and TN in soil with the Cate-Nelson procedure for 95% percent of maximum yield is equal to 1 percent and also critical level of mineral-N in soil is equal to 0.12 percent. In general, based on conducted field trials application of 30 kg/ha of net nitrogen in soil of containing less than 1 and 0.12 percent of OC and TN, respectively, for dryland wheat (Sardari cv) in Kermanshah province are recommended.