Combination of exploitation systems to optimize yield of GT1 clone in smallholder rubber (Hevea brasiliensis) plantation in Sumatera Utara, Indonesia

Clone GT1 is one of the low metabolism clones and is recommended for smallholder and large plantations. These clones are responsive to stimulants and reach production peak at the mid-economic cycle period. Its production can reach 2200-3000 kg-1ha-1year-1 and is relatively more resistant to high exploitation pressures if the agroecosystem conditions are suitable. This study aimed to determine the effect of the combined application of liquid stimulant concentration and tapping interval on the physiology and productivity of latex in rubber clone GT1. This research was conducted at Naga Rejo Village, Galang District, Regency of Deli Serdang, Province of Sumatera Utara, located at an altitude of 49 masl with Ultisol soil type. The research design is factorial randomized completed block design (RCBD) consisting of 9 levels, namely S2d4 without a stimulant, S2d4 ET 3.5%, S2d4 ET 4.5%, S2d5 without a stimulant, S2d5 ET 3.5%, S2d5 ET 4.5%, S2d6 without a stimulant, S2d6 ET 3.5%, S2d6 ET 4.5 % with three replicas of each treatment. The results showed that the tapping system on clone GT1 obtained the highest annual production with tapping system S2d4 ET 4.5% (DS3) of 214.51 g/t/y. The lowest production is obtained in January-March when the leaves fall. High sucrose levels in the non-stimulant treatment (8.54 -12.98 mM) indicated that at least sucrose was converted into latex. The pH of latex is directly proportional to the stimulant, so an increase in the concentration of the stimulant raises the pH and metabolism of latex formation