Effects of different rates, sources and time application of potassium fertilizer on quantitative and qualitative parameters of cotton (Gossipium hirstum)

To determine the effects of sources and rates of potassium on quantitative and qualitative properties of cotton an experiment was conducted in a clay loam soil، with 220 mg. kg-1 available potassium (K). The experiment design was randomized complete block design (RCBD) with three replications and eight treatments as follow: 1-Control (N. P) 2-N. P. K (50 kg. ha-1 K2O before planting as MOP) 3- N. P. K (50 kg. ha-1 K2O before planting as SOP) 4 N. P. K (100 kg. ha-1 K2O before planting as MOP) 5-N. P. K (100kg. ha-1 K2O before planting as SOP) 6- N. P. K (50 kg. ha-1 K2O top dressing as MOP) 7- N. P. K (100 kg. ha-1 K2O top dressing as MOP). Data showed that there was a significant difference in yield among treatments. The highest yield (4091 Kg. ha-1) was obtained by using K as topdressing in flowering stage (treatments no: 6 and 7). Duncan multiple range test showed that there was not a significant effects on yield among treatments No: 1 to No: 5. This means that use of potassium before planting (different amounts and different sources) did not significant effects on yield. Data showed that use of MOP as topdressing increased yield significantly. Use of MOP as topdressing improved cotton fiber quality. Use of 50 Kg. ha-1 K2O produced maximum fiber length (32. 1 mm)، fiber percentage (46%)، fiber strength (4. 29g. tex-1) among treatments. Data also showed that potassium concentration in petiole in this treatment was highest. There were significant correlations between potassium concentration in petiole with yield and with fiber strength. Fertilizer use efficiency was increased due to use of potassium as MOP as top dressing.