Effect of phosphorus application on substrate and use of saline water in sugar-apple seedlings

The irrigation with saline water affects the growth of sugar-apple plants. Some reports indicate that phosphorus affects the plants growth, with positive effects on the salts attenuation. This study aimed to assess the effects of the irrigation water electrical conductivity (iwEC) levels and triple superphosphate (TSP) doses in the growth and leaf levels of sugar-apple seedlings (Annona squamosa L.). The experiment was conducted in a protected environment, in an experimental design of randomized block, with nine treatments that combined phosphorus doses (0.00 g dm-1, 1.10 g dm-1, 3.00 g dm-1, 5.13 g dm-1 and 6.00 g dm-1 of TSP) with irrigation water electrical conductivity (0.50 dS m-1, 1.10 dS m-1, 2.50 dS m-1, 3.91 dS m-1 and 4.50 dS m-1), to evaluate the growth and leaf levels of Na+, K+, Ca+2 and P of sugar-apple seedlings. The increased curve for stem diameter presented by plants was proportional to the amount of TSP. Nevertheless, the iwEC levels were inversely proportional to this variable. The use of TSP directly affected the plant height (2.02 g dm-2/14.50 cm), dry mass (1.25 g dm-2/0.90 g) and total dry mass (2.32 g dm-2/2.00 g). The increase in the iwEC levels was directly proportional to the Na+ values (16.20 mg g-1), as well as to the Na+/K+ ratio (1.48 mg g-1), which cause metabolic disorders in the cellular environment. The TSP doses improve the seedlings growth, proving to be not phytotoxic; however, in combination with the iwEC, they reduce the amount of K+ in sugar-apple seedlings