Fertigation is applying nutrients through an irrigation system. In a mango orchard it can deliver small, scheduled applications to the wetted root zone, but it requires suitable equipment, compatible materials, and safeguards against contamination of the water supply. Uneven irrigation produces uneven nutrient delivery, and blocked emitters can leave trees underfed or dry. Check the system and follow applicable instructions rather than treating fertigation as simply pouring any fertilizer into a water tank.
Field capacity describes the soil moisture remaining after substantial gravitational drainage has slowed. It is a useful reference for irrigation planning, not a fixed moisture percentage shared by every soil. A mango root zone can hold very different amounts of plant-available water depending on texture, structure, and rooting depth. A sensor reading is most useful when interpreted for the actual soil and placement. Do not equate field capacity with continuous saturation, which leaves much less air available to roots.
Fruit retention is the continued holding of developing fruit after initial set. A mango tree normally sheds many flowers and small fruitlets, so retention should be considered relative to stage, tree size, and normal behavior. Unusual losses can follow stress, disease, injury, or competing demands within the tree. Maintain suitable root-zone conditions and investigate the pattern rather than treating every fallen fruitlet as a nutrient deficiency or assuming a spray can preserve every fruit that initially sets.