IMPROVING COTTON PRODUCTIVITY BY PLANT GROWTH RETARDANT AND BORON APPLICATION

Abstract

Studies on plant growth regulation and boron (B) nutrition for improving earliness, productivity, quality and nutrient dynamics of cotton were conducted in two field experiment at Agronomic Research Area, Department of Agronomy, University of Agriculture, Faisalabad during 2014 and 2015, and two pot experiments at Agro-Biology Lab Department of Agronomy, University of Agriculture, Faisalabad, Pakistan during 2015 and 2016. In first field experiment the treatments were two planting densities (55333 and 88888 plants ha-1 maintained by varying the plant spacing i.e. 25 and 15 cm, respectively), foliar application of mepiquat chloride solution (0 and 70 ppm at squarin=-g and flowering stage) and foliar application of B solution (0, 600 and 1200 ppm). In second field experiment treatments were foliar application of mepiquat chloride solution (0 and 70 ppm at squaring and flowering stage) and soil application of B (0, 1, 1.5, 2 and 2.5 kg ha-1). Water was sprayed as control in both experiments. In pot experiments seed obtained from both field experiments was used for a soil bioassay to determine the effect of maternal B nutrition, growth regulation and planting density induced changes on progeny performance in terms of emergence and seedling growth. The results revealed that plant growth and development was improved by B nutrition through foliar and/or soil application while decreased by mepiquat chloride. However, taller plants with lesser monopodial and sympodial branches were produced at higher planting density. Application of B, mepiquat chloride and increasing planting density enhanced the earliness and production rate index. Moreover, dry matter partitioning to reproductive structures was increased by foliar and/or soil application of B and foliar application of mepiquat chloride. Total dry matter production as well as dry matter partitioning to reproductive structures was enhanced at higher planting density. Seed cotton, lint and cotton seed yield was improved interactively by foliar and/or soil applied B and mepiquat chloride application by improving the number of bolls and boll weight. Likewise, increasing the planting density produced higher yield by increasing the boll density; while, foliar applied B significantly interacted with planting density in this regard. Some of the fiber quality attributes were improved by B, decreased by higher planting density while did not affect by mepiquat chloride application. However, the biosynthesis of chlorophyll and carotenoids was improved synergistically by foliar and /or soil applied B and foliar applied mepiquat chloride but decreased by increasing the planting density. Oil and protein yield was increased by application of B and mepiquat chloride, as well as increasing the planting density. Moreover, uptake and translocation of nutrients (N, P, K, B, Zn and Fe except Mn), nutrient use efficiency (NUE) and critical value of B was improved by B and mepiquat chloride. Mepiquat chloride application significantly interacted with B in improving the leaf and seed B contents. However, increasing the planting density decreased the leaf and seed nutrient contents, and critical value of B, while, increased the NUE. It was observed that earliness, yield, photosynthetic pigments, nutritional quality as well as nutrient uptake and translocation was enhanced by increasing the B dosage (both foliar and soil application) and mepiquat chloride application at squaring stage. Furthermore, economic analysis also revealed that higher profits and benefit cost ratio was obtained by foliar application 1200 ppm B solution in combination with mepiquat chloride (squaring stage) at higher planting density as well as application of 2.5 kg B ha-1 in combination with mepiquat chloride (squaring stage). The soil bioassays showed that the application of both foliar as well as soil fed B and mepiquat chloride application on maternal cotton plants improved the emergence, seedling vigour and biomass accumulation in offspring; while, sowing of maternal plants at higher planting density imposed a negative effect on these traits.