Influence of Rainfall and Rainy Day on Oil Palm Production 8, 16, and 19 Years Aged In Bah Jambi Plantation PT. Perkebunan Nusantara IV Persero - Barus, Yolan Surya (Program studi Agroekoteknologi, Fakultas Pertanian, Universitas Sumatera Utara-Medan, 2016)