Question

Urea is preferred to ammonium sulphate soluble in water as a nitrogenous fertilizer because:
A. It is more soluble in water
B. It is cheaper than ammonium sulphate
C. It is quite stable
D. It does not cause acidity in the soil

Answer 1

We must know that the ammonium Sulphate is inorganic in nature whereas urea is organic in nature. Also the ammonium sulphate is used mainly for alkaline soil. The ammonium sulphate is salt of strong acid and weak base which is formed by the reaction of sulphuric acid (strong acid) and ammonium hydroxide (weak base). Therefore, ammonium sulphate is acidic.

Complete step by step answer:
Let’s discuss the properties of ammonium sulphate and urea so that we can get the answer.
Ammonium Sulphate having chemical formula ${\left( {N{H_4}} \right)_2}S{O_4}$ is an inorganic salt, one of the most common use is soil fertilizer for alkaline soil. It is mainly used for alkaline soil because it forms a small amount of acid which lowers the $pH$of soil. It fixes the nitrogen imbalance in soil and provides essential nitrogen for plants to grow. We can write the chemical equation for the reaction of ammonium sulphate with water as,
${\left( {N{H_4}} \right)_2}S{O_4}\xrightarrow{{{H_2}O}}2NH_4^ + OH + SO_4^{2 - }$
Urea having chemical formula $CH{\left( {NH_2^ - } \right)_2}$ is an organic compound and is also used as a fertilizer and moreover is preferred over ammonium sulphate as a nitrogenous fertilizer. The reason being it does not produce acid like Ammonium sulphate does when added to water and hence does not lower the pH of the soil. Hence, the answer to this question is D.

Note: Due to overconsumption of nutrients from soil, soil becomes deficient of nutrients hence one of the solutions majorly used is use of fertilizers to replace these nutrients in soil. This increases the total yield of the product. But overuse of these fertilizer results in degradation of soil. We need to remember that the ammonium sulphate is acidic in nature.