A very accurate vehicle guidance is required in numerous agricultural applications, as seed-ing, spraying, row cropping,. .. Accuracy in vehicle localization can be obtained in realtime from a RTK GPS sensor. Several control laws, relying on this sensor , have been previously designed and provide satisfactory results as long as vehicles do not slide. However , sliding has to occur in agricultural tasks (slop-ing fields, curves on a wet land,. . .). The challenge addressed in this paper is to preserve vehicle guidance accuracy in such situations. A nonlinear adap-tive control law is here designed. Simulation results and field experiments, demonstrating the capabilities of that control scheme, are reported and discussed.