Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 210

aggregation. The differences in organic matter stabilization can be
explained by the association of humified organic substances with clay
particles and by the occlusion of the organic matter within aggregates.
However, because of the low amount of clay particles in this soil, the
stabilization of organic substances from perennial grass-clover mixture was
insufficiently strong to protect this organic matter against decomposition
and the water-stable aggregates against breakdown during the further
period of the crop rotation. As a consequence of this weak stabilization
of organic matter, a decrease in the amount of water-stable aggregate size
fractions was observed 5 years after growing of the perennial grass-clover
mixture of second year use.
Conclusions
The growing of a perennial grass-clover mixture for 1 and especially 2 years
resulted in increases in organic matter content of both whole soil and
aggregates and in water-stable aggregation of podzolic loamy sand soil.
Compared with conventional tillage, the use of minimum tillage resulted in
(i) increasing total organic carbon content and (ii) decreasing water-stable
aggregate organic matter content. Nevertheless, there were no significant
differences in the effects of the conventional and minimum tillage on
water-stable aggregation. There was an accumulation of total organic
carbon in the whole soil and in the water-stable aggregates, and in amount
of 0.5-7.0 mm water-stable aggregates from May to September for both
types of soil tillage. During the further 5-year period of crop rotation with
potato, spring barley, spring wheat, winter rye together with downy vetch
and spring wheat, decreases in total and water-stable aggregate organic
matter content and amount of water-stable aggregates were observed.
Acknowledgments
We are pleased to acknowledge the assistance given by Drs Brennan
D. Soane and Robert Rees in the sponsorship of the visit of Dr Natalya
P. Buchkina to the BSSS Conference. We extend the warmest of thanks to
Dr Brennan D. Soane for the editorship of early drafts of this paper without
which publication would not have been possible.
References
Broersma, K., Robertson, J.A. and Chanasyk, D.S. (1997) The effects of diverse
cropping systems on aggregation of a luvisolic soil in the Peace River region.
Canadian Journal of Soil Science 77, 323-329.