Your Answer : (Not Answered)

Correct Answer : C

The leaching requirement is \(LR = EC_{w}/(5\,EC_{e} - EC_{w})\).

For surface irrigation, the FAO (Rhoades) relation gives the fraction of applied water that must drain below the root zone to keep salts at a level the crop tolerates:

\[ LR = \frac{EC_{w}}{5\,EC_{e} - EC_{w}} \]

For example, with \(EC_{w} = 1.2\) dS/m and a crop tolerating \(EC_{e} = 2.0\) dS/m, \(LR = 1.2/(10 - 1.2) \approx 0.14\), so about 14 per cent extra water is needed. The other options rearrange the same terms wrongly; \(5\,EC_{e} - EC_{w}\) alone is not even a fraction.

Your Answer : (Not Answered)

Correct Answer : A

The process is denitrification.

In denitrification, anaerobic bacteria such as Pseudomonas and Thiobacillus denitrificans use nitrate in place of oxygen and reduce it, through nitrite, to gaseous nitrous oxide (N₂O) and nitrogen (N₂), which escape to the atmosphere. It is the step that returns fixed nitrogen to the air, and it is common in waterlogged soils.

Ammonification is the release of ammonia from decaying organic matter, and nitrification is the oxidation of ammonia to nitrite and nitrate by bacteria such as Nitrosomonas and Nitrobacter, the opposite direction.

Your Answer : (Not Answered)

Correct Answer : B

The most effective, easy and economical method is re-vegetation.

Plant cover breaks the impact of raindrops, slows runoff, increases infiltration and binds the soil with roots, so re-vegetating bare slopes and gullies controls water erosion at its source at low cost and lasts on its own.

Fencing only keeps out grazing animals. Check dams are costly engineering structures that control gully erosion locally. Soil filling replaces lost soil without stopping the erosion.

Your Answer : (Not Answered)

Correct Answer : C

The nutrient is potassium.

Potassium is needed for the formation and movement of carbohydrates, so it matters especially for starch and sugar crops such as potato, sugarcane and fruit. It strengthens cell walls and regulates stomata, which improves resistance to disease and drought, and it improves the size, colour and quality of flowers, fruits, vegetables and grain.

Nitrogen mainly drives leafy growth, phosphorus root growth and energy transfer, and sulphur protein and oil formation.

Your Answer : (Not Answered)

Correct Answer : C

Plants take up nitrogen mainly as Nitrate.

Roots absorb nitrogen from the soil water chiefly as nitrate ions (\(NO_{3}^{-}\)), and to a lesser extent as ammonium ions. Nitrifying bacteria in the soil convert ammonium into nitrate, and inside the plant nitrate is reduced again and built into amino acids and proteins.

Chloride is a chlorine ion and carries no nitrogen. Plants cannot use nitrogen oxides from the soil, and nitric acid is not absorbed as such; it would simply dissociate into nitrate in the soil water.