It is very hard to applying your treatments with 4 levels of N, 4 levels P, 4 levels of K and 2 levels of S in a farm. Because min. 128 plots are need for a replication. it is suggested reduce your treatments in accord with previous available researches.

I know that a factorial fractional design allows to reduce the number of treaments by neglecting high order interactions

I agree with Ablfazi. You need to establish an hypothesis based on existing knowledge, and if that is not possible to use an approach such as: control, N alone, P alone, K alone and the combination N + P + K + trace elements. Then all you need do is choose one level of each treatment.

PUEDES SABER CUAL ES EL NIVEL ADECUADO DE FERTILIZANTES n,p,k,... APLICAR SI TU SABES CUAL ES LA EXPORTACION DE NUTRIENTES DEL CULTIVO Y LA CANTIDAD DE NUTRIENTES QUE TIENE EL SUELO DISPONIBLE PARA LA PLANTA, LUEGO APLICAS LA SIGUIENTE ECUACION

RF=(Q.ABSORVIDA-Q.SUELO)/ EFICIENCIAFERTILIZACION