Disproportionately high N-mineralisation rates from green manures at low temperatures - implications for modeling and management in cool temperate agro-ecosystems
J. Magid et al., Disproportionately high N-mineralisation rates from green manures at low temperatures - implications for modeling and management in cool temperate agro-ecosystems, PLANT SOIL, 228(1), 2001, pp. 73-82
We examined the decomposition of Medicago lupulina, Melilotus alba and Poa
pratensis at 3, 9, and 25 degreesC during 4 weeks. There was a strong tempe
rature effect on the rate of CO2 evolution, and thus the extent of energy e
xhaustion from the added substrates. However, there was no concomitant reta
rdation of N mineralisation at low temperatures. In the analysis of varianc
e of mineralized N the residue type gave a 10 times larger contribution to
the regression than the temperature (T), whereas for CO2 evolution residue
type and temperature were equally important contributors. This indicates th
at although the temperature has a statistically significant effect on N-min
eralisation it is substantially less than compared with the effect on carbo
n mineralisation in the materials examined. The retardation of carbon miner
alisation was least strong in Melilotus alba that had a relatively low cell
ulose content, and a higher content of low molecular compounds. Though more
research will be necessary to consolidate and explain this phenomena, it i
s likely that an important factor is a decrease in the bioavailability of C
-rich polymers at low temperatures, and thus a preferential utilization of
N-rich low molecular substances. Nitrification was not effectively deterred
at 3 degreesC. Thus, in terms of management, it is pertinent to reconsider
the timing of green manure and catch crop incorporation in cool temperate
climate regions, since the rapid release of nitrogen, coupled with the rela
tively undeterred nitrification may result in a high N leaching risk by ear
ly incorporation, but a low risk for N immobilization at late incorporation
, if N rich residues are used.