Cations-Base Application in Rubber Plantation: The Change of Calcium, Magnesium, and Potassium Status in the Soil and Leaves and Its Relation to Latex Yield

Nutrient balance in the soil support plant growth and yield. The objective of this study was aimed to obtain doses of calcium, magnesium, and potassium fertilizers in relation to the ratio of cations-base (Ca2+, Mg2+, K+) to increase latex yield in rubber plants. The study was conducted on a rubber plantation in Dolok Masihul Sub-district, Serdang Bedagai District, North Sumatra, Indonesia, from January to August 2019. The treatment was used with three factors, including the first factor was CaCO3 (0; 1 500 g/tree/year), the second factor of MgSO4.H2O (0; 1 500; 3 000; 4 500 g/tree/year), and the third factor by KCl (0; 500; 1 000; 1 500 g/tree/year) in a Randomized Block Design (RBD) within three replicates. Results showed that the calcium of 1 500 g/tree/year increased the Mg-latex and latex yield by 160.70 g/tree/tapping. An increase in the three cations-base in soil, leaves, latex, and latex yield was also observed after the application of magnesium ranged by 1 500 to 4 500 g/tree/year. The potassium 500 - 1 500 g/tree/year increased the cations-base in soil, latex, and Ca-leaves. The interaction of calcium 1 500 + magnesium 1 500 - 4 500 and potassium 0-1 500 g/tree/year increased the exchange-K, Mg-latex, and also Mg- and K-leaves. The ratio of Ca:Mg:K in soil, leaves, and latex were 2: 1: 2 (optimum), 5: 1: 11 (high), and 1: 11: 32. The Ca, Mg, K in leaves and K-latex positively correlates and increases latex yield due to the three fertilizations.