Winter Green Manure
Any ground which is to be left fallow over the winter can be sown with a winter hardy green manure. These green manures normally precede a spring sown cash crop.

Winter green manures (nitrogen lifters) scavenge excess nitrogen from previous crops and they are an excellent tool to prevent nitrogen leaching which would otherwise occur with winter rainfall. Some species can pick up 90% of nitrate within the soil. The nitrogen held within the green manure crop is released once the green manure is incorporated. Some leguminous crops (nitrogen fixers) can be used for winter cover and provided that these are sown by mid September they can fix up to 200 kg/hectare of free nitrogen for use by the following spring sown crop.

These green manures protect the soil from erosion. The canopy they produce stops rain pelting the soil and enables water to drain effectively into the soil. Winter green manures can also be selected to suppress weeds. For details of suitable winter crops see our winter green manures section.

Lifting Nitrogen
Most nitrate leaching occurs during the autumn and winter months when fertiliser applications have exceeded a previous cash crops requirement. Leaching can be minimised by growing a winter hardy green manure to mop up remaining free nitrogen. Crops such as rye and westerwolds are ‘hungry’ for nitrogen during their early growth stages. Research shows that these green manures can absorb nearly all surplus nitrogen, holding it during the winter, before releasing it to the following cash crop.

Winter green manures also protect wind and water erosion prone soils by providing a canopy at times when soils would be vulnerable to the extreme weather.