Concept:Sub-surface irrigation is a method of applying water below the soil surface, and the question asks which statement is a disadvantage rather than an advantage.
Explanation:Sub-surface irrigation delivers water directly to the root zone, which greatly reduces loss of water by evaporation.
Hence, option C, stating that the rate of evaporation is greatly reduced, is a genuine advantage.
Since the soil surface remains dry, the method also reduces the incidence of pests, making option D an advantage as well.
It can be used effectively even in soils with low water holding capacity because water is supplied near the roots without waiting for surface infiltration, so option A is also an advantage.
However, the fact that sub-surface irrigation can be used only for specific types of crops is a limitation or restriction of the method.
Therefore, this statement is not an advantage among the given options.
Answer:B. it can be used only for specific types of crops