Doses of controlled-release fertilizer for production of rubber tree rootstocks

this experimental study aimed to evaluate the effects of doses of controlled-release fertilizer (all) on the development of rubber tree rootstocks. the fertilizer used was osmocote？, scheduled to be released for 8-9 months and with the following composition: n (15%), p2o5 (9%), k2o (12%), mg (1%), s (2.3%), b (0.02%), cu (0.05%), fe (1%), mn (0.06%), mo (0.02%) and zn (0.05%). a randomized block design was used, with four treatments and eight replicates of 20 plants per plot. the controlled-release fertilizer was added to rendimax floreira？ substrate at doses of 0, 3, 6 and 9 g per liter, and rootstocks were produced in plastic containers with a capacity of two liters of substrate. three seeds of clone gt 1 were scattered in each container and thinning was performed on day 60, leaving the most vigorous plant only. after the fourth leaf shot from each rootstock, the containers of each treatment were topped, due to compaction, with 300 ml of the relevant fertilizer and substrate mixture. the rootstocks were evaluated at eight months of age as to height, stem diameter (dc) 5 cm above root collar, total dry matter, shoot and root dry matter, leaf nutrient levels and percentage of plants suitable for grafting (dc>1.0 cm). results revealed that adequate development and nutrition of rootstocks was achieved by using 6 g of controlled-release fertilizer per liter of substrate.