Sp. Cuttle et al., A 6-YEAR COMPARISON OF NITRATE LEACHING FROM GRASS CLOVER AND N-FERTILIZED GRASS PASTURES GRAZED BY SHEEP/, Journal of Agricultural Science, 131, 1998, pp. 39-50
Nitrate leaching was measured over a 3-year period from rotationally g
razed perennial ryegrass (Lolium perenne L.) pasture receiving 200 kg
fertilizer-N/ha and from similarly grazed ryegrass/white clover (Trifo
lium repens L.) pasture that received no N fertilizer. The results are
discussed together with those from the same plots in the preceding 3
years when they were stocked continuously. Under both managements, the
numbers of grazing sheep were adjusted on the basis of the quantity o
f herbage available on the plots. During the whole 6 years, mean nitra
te concentrations in soil water collected by porous cup samplers remai
ned below the European Union limit of 11.3 mg N/1 except for the ferti
lized grass plots in year 5 of the study. Quantities of nitrate leache
d ranged from 6 to 34 kg/ha per year from the grass/clover plots and 2
-46 kg/ha from the fertilized plots. Leaching losses from both types o
f pasture were positively correlated with the numbers of lamb grazing
days in the later part of the grazing season. This relationship and th
e high spatial variability associated with the measurements indicated
that N derived from excreta was the main source of leached nitrate. It
was concluded that, where pastures of equal productivity are compared
, similar quantities of N are likely to be leached from grass/clover s
wards as from grass swards receiving N fertilizer.