N-P-K balance in a milk production system on a C. nlemfuensis grassland and a biomass bank of the P. purpureum CT-115 clone

The N, P and K balance was studied in a 52.4 ha dairy farm on a brown soil with carbonates having a steady drainage in a sward of C. nlemfuensis (60%), P. purpureum CT-115 clone (40%)., L. leucocephala and C. cajans were intercropped in 28% of the grass area. The herd had 114 cows, 35 heifers and 24 calves, with a total yearly milk production of 100 000 litres. In general, the system showed a negative balance in the three elements (-28, -11 and -39 kg/ha/year of N, P and K, respectively), since 40% of excretions were left in the shade pens and milking parlour and were not recycled in the grassland. On the other hand, there was also a negative balance of these nutrients in the soil component with values of -103, -22 and -76, kg/ha of N, P and K, respectively, mainly due to high extraction of these elements by the pasture. Values found in the different recycling rates are discussed. These are: litter, pasture remobilization, excretion, volatization and others. The return of all the excretion to the grassland ecosystem is recommended as well as increasing the area with legumes to attain a satisfactory balance in these nutrients. Further studies must consider maintenance fertilization, nutrient losses due to leaching and denitrification, as well as the variation of the stable OM in the soil and the influence of hydrophysical properties in the recycling process.