Question

Which of the following plants are used as green manure in crop fields and in sandy soil?
(A) Dicanthium annulatum and Azolla pinnata
(B) Crotalaria juncea and Alhagi camelorum
(C) Calotropis procera and Pitylanthus niruri
(D) Saccharum munja and Lantana camara

Answer 1

In the field of agriculture, green manure is made by leaving sown or uprooted crop parts to wither on a field so that they serve as a mulch and soil amendment. It is commonly associated with organic farming and can play an important role in sustainable annual cropping systems.

Complete answer:
Green manures are fast growing herbaceous crops which are ploughed down and mixed with the soil.
These provide both nitrogen and organic matter, in which Indian soil is generally poor. The green manures help the soil through increasement of area, water holding capacities and fertility. Some important green manure crops are mainly members of family Leguminosae are Alhagi and crotalaria juncea(sunn hemp). Lignified fibre is obtained from the stem of crotalaria juncea.
Green manure acts soil-acidifying matter to reduce the pH/alkalinity of alkali soil by generating humic acid and acetic acid.
Leguminous green manure such as clover and vetch contain nitrogen-fixing symbiotic bacteria that fixes atmospheric nitrogen in the root nodules in the form that plants can use.

Hence, the correct answer is option (B). Crotalaria and Juncea and Alhagi camelorum.

Note:
The best way is to sow green manures. Green manures are the plants such as clovers, mustards, annual ryegrass, field beans, buckwheat, phacelia sown fairly thickly to produce a dense mat of green growth that is dug in before the plant flowers to increase soil fertility.