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为什么说团聚体是肥沃土壤的标志之一?

答案

参考答案:

(1)团粒结构土壤的大、小孔隙度协调:团粒结构是经过多次复合,每一次复合或团聚,都产生相应直径的孔隙,初级复合的孔径小,多次复合的孔径大。因此,团粒结构土壤不仅总孔隙度大,而且具有3~5个直径级别的孔隙,即大小孔隙比例协调。团粒结构土壤的多孔性和多级孔性使土壤具有良好的物理耕作性质,以及对水、肥、气、热的良好协调性。

(2)团粒结构土壤中的水汽协调:在团粒结构土壤中,团粒之间主要是非毛管孔隙,可以透水通气,团粒内部主要是毛管孔隙,可以蓄水,大小孔隙的共存使土壤水分和空气协调的兼蓄并存。

(3)团粒结构土壤的供肥与保肥相协调:由于团粒结构土壤的大、小孔隙协调兼备、水汽协调兼容,因而好气性空间和厌气性空间也协调存在,好气性微生物和厌气性微生物能共存,使土壤养分的分解与合成共存,即供肥与保肥相协调。

(4)团粒结构土壤具有良好的耕性:团粒体的比表面积小,团粒之间的接触面也小,土壤的粘结性、粘着性和塑性等都小,因而耕作阻力小,宜耕期长,耕作质量好。

(5)团粒结构土壤具有上松下实的土层构造:团粒体主要存在于土壤的耕层,下层由其他结构体组成,土壤孔隙呈上层大、下层小的特点,这种上松下实的土层构造有利于接纳和保蓄水分,有利于早春土温升高、养分释放和根系发育、伸展,也易于耕作。

阅读理解

Thomas Edison was born in America. He invented plenty of electric appliances(电器) and people from all over the world know him. At that time, there was no electric lamp in the world. And it brought people much trouble. Young Edison decided to invent it. He didn’t know which material was suited to be a lamp filament(灯丝). He failed and failed and he spent a lot of time on it. Some of his friends asked him to stop the experiments, but he didn’t listen to them and tried his best to find the material.

One afternoon, one of his friends came to visit him, he was doing his experiments in the lab when the man came in. But he only asked his friend to sit down and didn’t stop to talk with him. The man sat for a long time and Edison said nothing to him. His friend was angry with him and said, “You’ve done the experiments 1,200 times but you failed 1,200 times too!”

“You’re right, my friend,” Edison went on doing his experiments and said. “But I’ve known 1,200 materials are not suited to be a lamp filament!”

小题1:Why do many people know Edison?

A.Because he was very clever.

B.Because he worked hard.

C.Because he spent much time on his work.

D.Because he invented many electric appliances.小题2:He tried to find a kind of material which was suited to be ______.

A.a lamp

B.a lamp filament

C.a telephone

D.a light小题3: Edison was busy with his work, so ____________.

A.he asked his friend to help him

B.he asked his friend to go back first

C.he didn’t stop to talk with his friend

D.he asked his friend to watch him working小题4:His friend was angry because ____________.

A.he couldn’t persuade Edison to give up

B.Edison didn’t say hello to him

C.Edison failed 1,200 times

D.he didn’t think Edison was polite to him小题5:From the passage, we learn that ___________.

A.Edison was a hard-working person

B.Edison never gave up

C.Edison was rude to friends.

D.Both A and B

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