A village was selected in a basin within the karst mountain area in south-western China, with the aim of increasing the productivity of maize and highlighting the problem(s) of the farming system. The rock of the Karst Mountains surrounding the village is composed of dolomite, and thus, the soil contains a large amount of Ca and Mg and a relatively small amount of K The cropping land was separated into flat and sloping areas and slopes up to 25° were utilized (or the production of maize, because of population pressure. In the sloping areas, the available P content was very poor compared with the flat area where a large amount of available P was observed from the top layer to a depth of 70 cm. Although the soil was poor in P and (or) K, farmers only applied manure and N in the form of ammonium carbonate [(NH4)2CO3]. The amount of N applied by the farmers as manure was normally 100-200 kg N ha-1 and (NH4)2CO3 was applied at the rate of 60.5 kg N ha-1 twice during the growing season (150 days). This caused about 50-70% of the applied N to be left in the field. An increase in productivity and N use efficiency was achieved by using a chemical K fertilizer in the flat areas. It is proposed that there is a need to reduce the amount of manure and (NH4)2CO3 used in this area and that the proper application of K in flat areas and P and K in sloping areas could improve the productivity of maize and N use efficiency of applied manure.