2 questions of Biology
- 莫愁Lv 61 decade agoFavorite Answer
Soil has different sizes from large one to small one. Soil includes
coarse sand, fine sand, slit, clay and humus and the composition of
sand is called soil texture. For coarse sand, it is loosely packed so
that its aeration is good and its drainage rate is fast,so its retentivity is
however low (retentivity: is the ability to hold water). For clay soil,
it is closely packed so that its aeration is poor and its drainage rate is
slow,so its retentivity is however great.
Humus acts as a glue to make coarse sand to pack more closely.
Hence its aeration become poor and its drainage rate is slower,so its
Retentivity is however great. For clay soil, humus turns their small size
to large size, so that its aeration becomes good and its drainage rate is fast.
Thus its retentivity becomes low (retentivity: is the ability to hold water).
The soil texture is thus change when humus is presence.
A proper ratio of coarse sand to clay soil should improve the aeration,
drainage rate and retentivity. The improved soil texture has several
(1)Soil can hold more water and will not be dried by direct sunlight.
(2)Good aeration enhances the decomposition rate of dead organic
matters and excretory products ,leading to more fertile soil.
(3)If aeration is poor, the growth of denitrifying bacteria will be
enhanced, leading to infertile soil.
(4)Proper drainage rate prevents water-logging during raining season.
(5)Humus acts as a sponge(海綿) to hold more water. Its function is the
same as clay soil so that the soil will not be blown away by wind.
(6)With water held by soil, the temperature fluctuation between dawn
and evening will not be so large. This can ensure a good working
condition for enzymes secreted in plants.
2008-04-25 15:34:32 補充：
(7)Humus provides food and shelter for micro-organism to live and
grow so that the rate of decomposition of dead organic matter and
excretory products will be faster.
2008-04-25 15:34:53 補充：
(8)Humus is basically a kind of ammonium compound which makes
the soil fertile. Due to humus, the soil texture is improved. The faster
rate of organic matter decomposition will be carried out. The soil
becomes more fertile.