and his colleagues use mechanical methods to deal with weeds not chemicals the equipment can only be used between the rows of crops any weeds right up against the wheat remain. the crop rotation is carefully planned six different crops over a six year cycle and then it starts all over again. each crop takes a different mix of nutrients from the soil depletion is slower and more balanced. the insects thrive in the good soil. there's no need for synthetic nitrogen fertilizer its job is done by the legumes such as clover and beans that make up part of the rotation cycle their roots bind nitrogen from the air and make it available to the soil. crop rotation is