Question

Which of the following plants are used as green manure in crop fields and in sandy soils
A. Crotalaria juncea and Alhagi camelorum
B. Calotropis procera and Phyllanthus niruri
C. Saccharum munja and Lantana camara
D. Dichanthium annulatum and Azolla nilotica

Answer 1

Hint: Green manure are plants which are grown and turned into soil to improve the soil quality. They are uprooted and plowed into the soil or just kept there for an extended time period prior to tiling that land.

Complete Answer:
- Green manure provides nutrition to the soil, decreases the soil porosity, makes it drought resistant and lessens the chances of soil erosion. It also decreases the alkalinity of alkali soil by generating humic and acetic acid. Some cover crops also rescue from insect pests and diseases.
- Green manures reduces the use of fertilizers and pesticides. If allowed to bloom, they act as food for pollinating insects.
- Generally, leguminous plants are used as green manure because of their symbiotic association with rhizobium species. Rhizobium can fix nitrogen from air to nitrate which is taken up by the leguminous plant. Thus the concentration of nitrogen in leguminous plants is more than the non-leguminous.
- The carbon-nitrogen ratio in the soil is an important factor and the selection of an incorrect plant may affect the nutrient contents of the soil. Hence, leguminous plants are preferred for green manure. Non-leguminous plants are used to increase the biomass which improves the water retention capacity, aeration etc.
- Crotalaria juncea and Alhagi camel families Fabaceae and Papilionaceae are used as green manures in crop fields and in sandy soils. These plants are fast growing, and have high nutrient accumulation capability. They protect from flood, make drought resistant and increase the inoculation capacity.

Hence, the correct option is option A, ‘Crotalaria juncea and Alhagi camelorum’.

Note: Crotalaria juncea, also known as sunn hemp, is a strong nitrogen fixer and provides resistance to root knot nematodes.