Residual Level of Phosphorus and Potassium Nutrients in Hydroponically Grown Cotton (Gossypium hirsutum)

Sustainable agriculture requires economical and judicious use of mineral fertilizers and other farm inputs such as synthetic plant hormones so as to benefit crop growth, development and yield. The present study investigated residual levels of phosphorus (P), potassium (K) nutrients and nutrient solution level in the hydroponics by application of low P, low K and high PK nutrients to hydroponics pots in the first experiment, and by spraying cotton plants with indole -3- acetic acid (IAA), gibberellic acid (GA3), zeatin (Z) and their combinations at high level of PK nutrient in the second experiment. In the first experiment, nutrient solution level in the hydroponics irrespective of varieties of cotton planted in them and those with specific cotton varieties were significantly affected by the treatments. However, low P, low K and high PK treatments irrespective of the two cotton varieties planted in the hydroponics pots significantly influenced residual level of P and K nutrients. During the second experiment, the exogenous hormones applied irrespective of two cotton varieties planted in the hydroponics pots did not affect nutrient solution level in the hydroponics except at 43 and 80 days after transplanting (DAT). Nevertheless, taken the two cotton varieties into consideration, Zhong cotton variety had higher nutrients solution level than Xin cotton variety. In general, hormones applied did not affect residual P and K in the nutrients solution after every nutrients change except at 43 DAT. However, varietal differences were observed for high residual P and K nutrients at 80 and 90 DAT for P and 74 and 90 DAT for K in the nutrient solution grown with Xin cotton variety. It is clear from these results that wise usage of mineral fertilizers and synthetic plant hormones should be taken into consideration in order to avoid wastage.