The invention relates to a system to control the power of a tractor&rsquo；s engine comprising: a movable element of an agricultural cultivation machine, made for cyclic interaction with a certain amount of material of a cereal crop； the tractor&rsquo；s engine, delivering energy on said movable element, said tractor is connected to said agricultural cultivation machine； an element, generating signals, connected to said agricultural cultivation machine and made for providing a signal, relating to the expected amount of material of the cereal crop, prior to interaction of said movable element with said amount of the cereal crop； and a unit for changing a rotational moment, connected to said tractor and made for changing the amount of the rotational moment, delivered to said movable element depending on said signal by said engine； in doing so said element, generating signals, is a forecasting unit, made for generating said signal, depending on the previous impingements of said movable element with previous amounts of said material of the cereal crop by means of comparing the amount of material of cereal crop, with which said movable element had interacted, with the current amount of material of the cereal crop being measured and developing the necessary rotational moment on the basis of the previous observations. In the invention a method for changing the rotational moment, delivered onto the agricultural cultivation machine, is also characterized. Said method comprises the stages, at which a cyclic amount of material of cereal crops, which is introduced into a cultivating element of the cultivation machine, is forecasted with the aid of a forecasting unit. The mentioned amount requires the forecasted rotational moment； a signal is sent depending on said forecasted rotational moment, and the output of the rotational moment from the engine is changed depending on said signal. Said output of the rotational moment is increased in such a manner that said forecasted rotation
