Correct option is C
·
DAP (46% P₂O₅) is highly
water-soluble, directly available to plants.
· FAO lists DAP as a
completely water-soluble P fertilizer.
Why other options are wrong
· (a) Rock phosphate →
not water soluble; citrate soluble only in acid soils.
· (b) SSP → contains monocalcium phosphate + gypsum;
partly water-soluble, not fully.
· (d) Basic slag → low solubility P; used in acidic soils.