1. A method of guiding an agricultural vehicle having at least one steerable wheel in an agricultural field having a plurality of rows of crops, the method comprising: taking a picture of the rows of crops with an electronic camera; successively processing a plurality of lines of the picture; extracting from the plurality of processed lines at least one value indicative of a crop line; extracting another value from the at least one value that is indicative of the lateral displacement of the crop line with respect to the vehicle; processing the another value in a fuzzy logic input membership function, then a fuzzy logic inference engine and then a fuzzy logic output membership function to develop a signal indicative of the degree the at least one steerable wheel should be turned; providing the signal indicative of the degree to which the steerable wheel should be turned to a feedback control circuit configured to steer the at least one steerable wheel in a direction that minimizes a difference between the signal indicative of the degree the at least one steerable wheel should be turned and another signal indicative of the degree to which the at least one steerable wheel is actually turned; generating a valve control signal calculated to reduce the difference; applying the valve control signal to an electro-hydraulic control valve configured to steer the at least one steerable wheel; and steering the wheel accordingly.