Carbon cycling in cultivated land and its global significance.
Buyanovsky, G. A.; Wagner, G. H.;
Global Change Biology Year: 1998 Vol: 4 Issue: 2 Pages: 131-141 Ref: 40 ref.
1998
บทคัดย่อ
Long-term data from one of the oldest experimental fields in the USA, were used to determine the direction of soil organic carbon (SOC) dynamics in cultivated land. Changes in agriculture in the last 50 years including introduction of more productive varieties, wide scale use of mineral fertilizers and reduced tillage caused increases in total net annual production (TNAP), yields and SOC content. TNAP of winter wheat more than doubled during the last century, rising from 2.0-2.5 to 5-6 Mg/ha of carbon, TNAP of maize rose from 3-4 to 9.5-11.0 Mg/ha of carbon. Amounts of carbon returned annually with crop residues increased even more drastically, from less than 1 Mg/ha in the beginning of the century to 3-3.5 Mg/ha for wheat and 5-6 Mg/ha for maize in the 90s. These amounts increased in a higher proportion because in the early 50s removal of postharvest residues from the field was discontinued. SOC during the first half of the century, when carbon input was low, was mineralized at a high rate: 89
and 114 g/m2 per y under untreated wheat and maize, respectively. Application of manure decreased losses by half, but still the SOC balance remained negative. Since 1950, the direction of the carbon dynamics has reversed: soil under wheat monocrop (with mineral fertilizer) accumulated carbon at a rate approx equal to 50 g/m2 per y, three year rotation (maize/wheat/clover) with manure and nitrogen applications sequestered 150 g/m2 per y of carbon. Applying conservative estimates of carbon sequestration documented on here to the wheat and maize production area in the USA, suggests that carbon losses to the atmosphere from these soils were decreased by at least 32 Tg annually during the last 40-50 years.