Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 138

Fig. 3.5.2. The effects of the main treatment on nitrate leaching, assessed from the nitrate
concentration in dipwells.
grass-clover plots in 1996/97, the first winter after ploughing. Winter crop
cover also affected nitrate leaching significantly in both years. More nitrate
leached from the plots left as undisturbed spring barley stubble than from
those planted with winter barley in 1996/97, but there was little difference
between the crops in 1997/98.
We estimated the total amount of nitrate leached from each treatment
in each year by multiplying mean nitrate concentration by the pipe drainage
measured on a nearby experiment. Annual leaching loads were relatively
low (6.4-19.6 kg N ha −1 ), compared with swards that were ploughed out in
the late summer of 1993 (Davies, 1996).
Gaseous losses of nitrogen and carbon
In the first year, nitrous oxide emissions shortly after drilling spring barley
were high, reaching a peak of 510 g N ha −1 day −1 . Surface conditions were
important for nitrous oxide emission. Emissions from the areas around drill
slits in the no-tillage treatment were more than double those in the area
between drill slits. This indicates the importance of macropore volume and
continuity near the surface in regulating gas emissions.
In the following year, nitrous oxide emissions from no-tillage were
even higher, reaching a peak of 2000 g N ha −1 day −1 after heavy rainfall.
Soil measurements showed that much of this nitrous oxide was produced
or accumulated near the soil surface. Nitrous oxide emissions on the other
treatments were typically lower, giving peaks of ~200 g N ha −1 day −1 under
conventional ploughing and ~120 g N ha −1 day −1 under deep ploughing. In
the first two seasons, N 2 O fluxes showed a marked and rapid response to