Simplified balance of nutrients and crop yield in nine years of superficial pig slurry application on an Oxisol in southern Brazil

The application of pig slurry in doses greater than the recommended nutrients supply for the crops results in the excess of these nutrients in the soil system. In order to estimate this exceeding amount in a crop system for grain production, we calculated the simplified balance of N, P and K with the application of three doses of pig slurry (50, 100
and 200m3/ha/year), 50% in the autumn and 50% in the spring, and one treatment with reposition of the P and K exported throughout the grains harvested, applied in the form of soluble fertilizer in an only parcel in the spring. At the end of the ninth year extractable P and exchangeable K content in the soil were determined in samples collected in six
layers (0 to 2.5; 2.5 to 5; 5 to 10; 10 to 20; 20 to 40; and 40 to 60cm deep). The simplified balance of N, P and K varied basically in function of the amount applied, since the grain yield, and consequently the amount of these nutrients exported, showed low magnitude of variation among treatments. The application of increasing doses of pig slurry determined
linear increasing of extractable P in the soil layers sampled between 0 and 5cm and exchangeable K between 5 and 60cm deep.