September 30, 2008 by greengard
Soil
organic matter is valuable, that is an old truth. Is it still valid?
The issue
is not simple and straightforward. It seems to be so that our most productive
soils in Sweden have fairly low content of organic matter, but also that the
yields on those soils increase further if organic matter is increasing.
We have in
Sweden 11 soil fertility experiments about 50 years old with two rotations
(with leys and without) and four fertilizer intensities. The four experiments
with highest yields now give about 10% higher yields in the ley rotation and
the difference has an increasing trend. The difference is no nitrogen effect.
The organic matter content is now higher in the ley rotation.
There
should be some environmental advantages in addition:
Less carbon
dioxide emissions.
Less
erosion.
Less soil
dispersion causing phosphorus losses.
We have a
Win-Win situation, providing the costs are not too high. Is is worth looking at
the whole picture.
But there
are no yield effects on the sites with lower yield capacities (and higher
organic carbon). There seems to be a limit at about 2% organic carbon.