Vegetated buffer zones for agricultural non-point source pollution control

The effects of 10-metre wide annually cut grass buffer zones (GBZ) and vegetated buffer zones under natural vegetation (VBZ) on losses of total solids (TS), total phosphorus (TP), particle-bound P (PP), orthophosphate phosphorus PO4-P), total nitrogen (TN), nitrate nitrogen (NO3-N) and ammonium nitrogen (NH4-N) in surface run-off from experimental field plots have been studied for 15 years at MTT Agrifood Research Finland, Jokioinen, SW Finland. The results have been compared with those from 70-m-long and 18-m-wide plots without a buffer (NBZ). Spring barley or oats were grown in the period 1991-2002 and there was a pasture grazed by cows 2003-2005 both on the whole field area and the buffer area of NBZ. Both GBZ and V13Z mitigated significantly the losses of TS, TP and PP from surface run-off on cereal field plots. The retention of TS, TP and PP was > 50, 40 and > 45%, respectively. However, the cumulative loss of PO4-P over the I I-year experiment was the largest (2.4 kg ha(-1)) from the VBZ where the plants on the buffer zone were not harvested. Over 3 grazing years, the losses of TS, TP, PP, PO4-P, TN and NO3-N were around 700, 2.3, 0.8, 1.5, 4.2 and 0.8 kg ha(-1) from all treatments. The mean annual losses were smaller from the pasture than from the field with spring cereals. There was, however, one exception - during grazing the mean annual PO4-P loss (0.5 kg ha(-1) yr(-1)) was twice or even threefold compared to the load during spring cereal years. The buffer zones are excellent for retention of TS, TP and PP from surface run-off in annually ploughed cereal fields, whereas they are not so important for perennial grass fields.