NATURAL regeneration is just as good at preventing nitrate leaching on set-aside as cover crops – at least on heavy clay loams.
That is the tentative finding from one years trials by farming company CWS, outlined by research manager Alistair Leake. He told last weeks Fertiliser Manufacturers Association conference that establishing cover crops could be difficult in dry years, involved extra expense and only rarely benefited following crops.
The CWS work compared natural regeneration without cultivation, a "one-pass" cultivation without sowing, a "low cost" rape/grass and vetch mix, a more expensive but potentially longer acting mustard/rye/clover mix, and undersowing a grass/clover mix in the spring.
"Natural regeneration performed as well as anything except the undersown system," Dr Leake said. "But unfortunately it is not practical for conventional systems because crops tend to be too thick and you cannot use herbicides because of the clover."
The mere act of cultivating to establish covers tends to release more potentially leachable N, he noted. Cover crops may be more useful on lighter land, he conceded. "But there they are often more difficult to establish in dry weather."