Environmental Engineering Reference
In-Depth Information
digging,. the. original. ancient. buried. layers. of. soil. were. gradually. exposed.
as.the.surface.layer.of.this.polder.land.and.have.been.continuously.used.for.
irrigated.rice.cultivation.even.today,.a.practice.in.existence.since.at.least.3000.
years.ago..There.were.plenty.of.these.types.of.box.paddy.ields.in.the.Jiaxing.
region.up.until.20.years.ago;.however,.most.of.them.have.since.been.leveled.
out.during.the.urbanization.period..The.Luojiajiao.site.is.now.the.only.place.
protected.by.law.(as.a.national.cultural.relic.site);.thus,.it.remains.a.region.
of.vibrantly.productive.paddy.ields,.with.rice.grain.yields.of.9.t/hm
2
.today..
Therefore,.it.may.well.be.the.world's.oldest.paddy.ields.of.continuous.rice.
cultivation.at.present,.which.also.provides.the.most.convincing.evidence.in.
supporting.the.eficiency.of.paddy.soils.as.a.means.for.sustaining.the.land.
(Dong.et.al..2006,.Lu.et.al..2009).
Productivity Increased as Rice Cultivation Was Prolonged
within the Paddy Soil Chronosequence
At. the. South. bank. of. Hangzhou. Bay. in. the. Yuyao. and. Cixi. counties.
(N30°-30.50°,.E121°-122°).(Figure.18.5),.a.total.of.11.sea.dikes.were.contin-
uously. constructed. between. 1074. and. 1980,. and. the. marshland. that. was.
created.in.this.process.was.reclaimed.for.rice.cultivation..For.this.reason,.
a. unique. paddy. soil. chronosequence. with. different. rice. cultivation. years.
from. 50. to. 2000. years. old. (recorded. by. local. chorography). were. identi-
ied..This.chronosequence.was.developed.from.the.same.parent.materials,.
under.the.same.ecological.conditions.with.similar.cropping.systems.(Cao.
2007,. Cao. et. al.. 2007,. 2010,. Cheng. et. al.. 2009,. Kögel-Knabner. et. al.. 2010),.
where.the.natural.fertility.of.surface.soils.increased.as.cultivation.time.was.
prolonged.(Figure.18.6).
FIGURE 18.5
Coast.sediments.and.dikes.on.South.bank.of.Hangzhou.Bay.
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