Effect of Different Nitrogen Top Dressing Strategies on Rain-fed Wheat Yields Grown in a Soil Dominant with Expanding Clay Minerals

In this study, it was proposed that nitrogen demands of rainfed wheat plants may be met by the release of ammonium fixed in 2:1 clay minerals. In order to do that single top dressing of nitrogen given in the forms of urea or ammonium in the early stage of plant growth and two split applications of N as ammonium-nitrate were compared in rain-fed wheat plants. As a result of the study, grain yields obtained from single applications of urea and ammonium were found to be higher than two split applications of ammonium nitrate. Thousand-grain weight was found to be the highest with the ammonium sulfate application and the lowest with the ammonium nitrate application. It was seen that applying nitrogen fertilizers to the soil which is dominant with expanding smectite and vermiculate clay minerals in the forms of urea and ammonium at once in the early stage is more effective than two split applications as ammonium nitrate.