Many factors influence post-harvest losses, from the soil in which the crop is grown to the handling of the produce at retail. Pre-harvest production practices can seriously affect post-harvest yields.
Plants need a continuous supply of water for photosynthesis and transpiration. Damage can be caused by excess rainfall or poorly conducted irrigation, which can lead to rotting; by lack of water; or by an irregular water supply, which can, for example, lead to growth cracks. Lack of plant food can affect the quality of fresh produce, which can lead to stunted growth or leaf discoloration, abnormal ripening and various other effects.
Too much fertilizer can affect the development and condition of the harvested produce. Good plant maintenance is important to reduce losses. Weeds compete with crop plants for nutrients and soil moisture. Decaying plant residues in the field are also a major factor in losses.
Source: Wikipedia.org