  We report on the valley blockade and the multielectron Kondo effect generated
by an impurity atom in a silicon nano field effect device. According to the
spin-valley nature of tunnelling processes, and consistently with those allowed
by the valley blockade regime, the manifestation of Kondo effect obeys to the
periodicity 4 of the electron filling sequence typical of silicon emerging at
occupation N=1, 2, 3. The spin-valley Kondo effect emerges under different
kinds of screening depending on the electron filling. By exploiting the valley
blockade regime, valley index conservation in the Kondo SU(4) is deduced
without the employment of an external magnetic field. Microwave irradiation
suppresses the Kondo effect at occupancies up to three electrons.
