Variation of Organic carbon, Nitrogen, Phosphorous, Potassium, Iron, Zinc, Copper and Manganese in Soil in several Wheat Based Rotations.

In order to ‍ study the variations of organic carbon, nitrogen, phosphorous, potassium, iron, zinc, copper and manganese residual in soil under different crop rotations, an experiment was designed in randomized complete block manner, with eight treatment and three replications, from 2007 for five years at Jolgeh Rokh Agricultural and Natural Resources Research Station. Treatments were consisted of eight crop rotations: T1- continuous wheat culture. T2- wheat, wheat, wheat, canola, wheat. T3- wheat, sugar beet, wheat, sugar beet, wheat.T4- wheat, potato, wheat, potato, wheat. T5- wheat, potato, wheat, canola, wheat. T6- wheat, sugar beet,wheat, potato, wheat. T7- wheat, corn, wheat, potato, wheat. T8- wheat, corn, wheat, sugar beet, wheat. Results showed that the amounts of organic carbon and residual nutrients were affected significantly with changes in crop rotation. The amount of organic carbon was increased after two years and then reduced. The amount of residual nitrogen increased, the amount of residual phosphorus fixed and the amount of residual potassium reduced during five years. Different crop rotations had significant effects on soil organic carbon and residual phosphorus, potassium and zinc, but had no significant effects on residual soil nitrogen, iron, manganese and copper. In continuous wheat manner culture and wheat- canola rotations the level of organic carbon and the amount of residual nitrogen were in highest rates compared to the other rotations, and the lowest ones was attributed to wheat rotations in corporation to corn and potato. Meanwhile, continuous wheat culture and wheat- canola rotations had the lowest levels of residual P. The highest level of residual K was observed in wheat- potato- canola rotation. In rotations with wheat and canola the amounts of organic carbon, residual nitrogen, potassium and copper were increased. When potato was added to the rotation, rate of residual manganese in soil increased too. Therefore, it seems these crops could increase the soil nutrients and could be recommended in such agroecological areas. Keywords: Residual nutrients, Macro-nutrientd, Micro-nutrients, Organic carbon, Cropping system