NITROGEN AND PHOSPHORUS IN RUNOFF FROM GRASSLAND WITH BUFFER STRIPS FOLLOWING APPLICATION OF FERTILIZERS AND MANURES

We examined whether nitrogen(N) and phosphorus(P) export was enhanced from grassland receiving inorganic fertilizer and manures typical of i ntensive livestock production. Buffer strips were included in the stud y to determine if they could reduce nutrient export. Hillslope plots r eceiving granular inorganic fertilizer, liquid cattle slurry and solid cattle manure (FYM) were compared using rainfall simulation for 4 sto rms on consecutive days at 22 mm h(-1) and 35 minutes duration. The pl ots were hydrologically isolated in a randomized block layout of 4 tre atments x 3 replicates and measured 30 x 5 m; the upper 20 m received either fertilizer, slurry or FYM, while the lower 10 m acted as an unf ertilized grass buffer strip. Nitrogen and P export in surface runoff from grassland receiving inorganic fertilizer exceeded that from FYM o r slurry treatments; concentrations up to 46 mg N l(-1) and 15 mg P l( -1) were recorded. Sixty eight % and 62% of the N from FYM and slurry respectively was exported in organic form. Seventy four % (FYM) and 39 % (slurry) of the P was in particulate or dissolved organic form. The buffer strip reduced N export in surface runoff by 94% and P export by 98% from inorganic fertilizer plots. A 75% reduction in N export was recorded from the buffer zone below slurry plots but only a 10% reduct ion in P, with most P remaining in the particulate or dissolved organi c fraction. There was no significant difference in N export from the b uffer zone between the inorganic fertilizer treatment and the untreate d control.