Livestock manure is an important resource
for agriculture, because it contains a high level of
nutrients and organic matter. In Japan, the quantity
of livestock manure has been increasing as farms
have become larger and the number of livestock
have grown. The total amount of livestock manure
produced each year has now reached 97 million mt.
The nitrogen content of this manure has been
estimated at 7.6 million mt. If these animal wastes
were to be recycled evenly over all Japan’s cropland,
the load of nitrogen would be 140 kg/ha. However,
actual recycling is uneven, and there are some
regions where the nitrogen produced (250 kg/ha or
more) exceeds the capacity of the soil to absorb it
safely (Fig. 1).