Man-made Salinization
Kane
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Desert and
semi-arid soils are generally saline, rich in sodium, magnesium and calcium. We
know, when there is extremely high evaporation rate that it excess the actual
precipitation amount, excess compounds like sodium chloride, magnesium and
calcium carbonate and sulphate will be deposited in
the soil pores and on the soil surface through the capillary action. The
process will naturally happen and cause a salinization.
However, some man-made salinization also occurs.
沙漠及半乾旱地區的土壤普遍為鹽土，含鈉、鎂及鈣量豐富。我們都知道，當蒸發率遠遠高於其實際降水量時，多餘的化合物如氯化鈉、鎂及碳酸鈣及硫酸鹽等都會經毛細管作用在土壤中的空隙中或表面上累積。這個過程是自然發生在乾旱地的並引致了鹽化過程。然而，有些鹽化的情況是人為因素造成的。
When
people would like to practice farming on aridisol,
they should first overcome the problem of drought and high salinity of soil.
And the most efficient way seems to be irrigation. When they continually
irrigate the land without adequate drainage, there is a gradual rise in the local
water table. As a result causes waterlogging of the
subsoil. Water can be carried up by capillary action even more easily. So what
happens then? The upper soil horizons will suffer from an increasing rate of salinization. The case can be found in the
當人們想在旱成土上耕作，他們首要的是解決土壤的乾旱及高鹽份問題。而最有效率的方法似乎是灌溉。當他們持續地進行灌溉又沒有足夠的排水設施時，最終的結果是令該處的水位或潛水面升高。最後表土之下出現了水浸的情況。在此情況下，水份更容易經由毛細管作用流失至大氣中。然後呢？較高的土層便愈來愈受鹽化的情況影響了。這樣的情況可以在美國西南的科羅拉多河附近發現，那裏有著一個水塘及九個主堤壩構成的灌溉系統。可是河水中仍有著礦物鹽，而當這些水用作灌溉時，水份很快被蒸發而大量的礦物鹽會留在地表上！這造成了一層鹽殼的出現，而其餘的可能會下沉至地下水中。地下水也變得更富鹽份，當植物透過根部吸取地下水時，這時鹽份便開始集中在植物根部附近並對之造成不良影響。
More cases
of man-made salinization can be found in the Middle
East, the USSR, India and Pakistan, the western US, Egypt, China and Australia.
Actually, more than 10% of the world’s irrigated lands are seriously affected
by man-made salinization. Although most irrigated
crops are relative salt-tolerant, (as well as drought-tolerant) like alfalfa,
increasing accumulation of salts above optimum level can be harmful. It will
slow down water absorption and nutrient flow. Excess sodium and calcium is an
imbalance of nutrients, making unavailable conditions of other nutrients such
as iron, phosphorous and copper. Gradually it may cause harmful effect in crop
yield which may fall below economic level. Irrigation scheme in LDCs have been poorly designed and managed, they may easily
cause salinization which result in crop failure, in
turn may bring famine to the countries.
更多的人造鹽化可在中東、俄羅斯、印度及巴基斯坦、英國、埃及、中國及澳洲。事實上，全球有超過10%的灌溉土地正面臨著嚴重的人造鹽化過程影響。雖然大多數灌溉作物都是較為耐鹽的（同時亦為耐旱植物），如苜蓿花，但過度的鹽份集中量若超出於最適合的鹽度範圍對它們仍是有害的。這會減慢了水的吸收及養份的流動。過量的鈉及鈣是屬於養份不平衡，只會使其他養份如鐵、鏻及銅變得難以應用。最後只會損害了穀物的產量，其產量甚至可能低於經濟水平。許多發展中國家的灌溉計劃的設計及管理都是不完善的，這只會造成更嚴重的鹽化現象及帶來失收，最後換來的是全國飢荒。
There are
ways to reduce the effect of salinization, however,
with insufficient resources (e.g. lack of capital),
such measures have not been widely attempted in salinized
region. Ways include flushing, drainage and trickle irrigation.
其實是有方法將鹽化的影響減低的，但在缺乏足夠資源（尤其是金錢）的情況下，這些措施普遍都不被鹽化地區所採用。這些方法包括洗土、排水及根部灌溉。洗土是最容易的，但如缺乏正確的管理，卻會形成鹼化情況。即是土中的氯化鈉集中量過高。這會使泥土更堅實、滲透度更低。此外，有機物質的分佈更分散，更容易被沖往地下水層中。這只會愈使土壤的貧瘠情況惡化。若要建造能將鹽份自排出的水中分隔的排水系統，卻又會牽涉巨大的投資額，這對多數發展中國家是不符合實際的。根部灌溉意指以導管將水直接灌入根部層，耗水量是最低的，這是最有效率但又最昂貴的方法。
When more
and more poor drought-countries practice farming to
earn a living, with low level of knowledge and technology, the land is just
degraded as a result of improper farming. As they found that the land cannot
produce enough food for them, they simply enlarge the scale with the same poor
skills. Finally, they all fell into the vicious cycle.
當愈來愈多窮困的乾旱國家以農耕換取生活，但以其低知識及科技水平，只會使土地質素愈下降。他們發現土地不能供應足夠的糧食時便更擴大農作規模。最後跌入惡性循環之中。
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~