Optimizing Nitrogen Fertilizer Application for a High Density Planting of Satsuma Mandarin

Abstract

A differencial nitrogen fertilization trial for a high density planting of satsuma mandarin was conducted for 11 years. Starting in 1981, 12-year-old satsuma 'Sugiyama Unshiu' trees, which had been grown in a 0.4 ha field with little or no fertilizer were administered a combination of 2 levels of organic matter application and 3 levels of N replicated 3 times as a factorial design. Levels of organic matter were-OM (no organic matter application) and +OM (rice straw application of 20 t•ha-1•year-1).Levels of nitrogen fertilization were N-1 : 100, N-2 : 200, and N-3 : 300 kg-ha-lyear-1.The trees were spaced 2.2 m × 2.2 m, a quarter of the trees being designated as the permanent, another quarter of trees as the semipermanent, and the rest as fillers.1. The yield per hectare in all treatments increased significantly in the second year but then decreased slightly on account for bacterial canker attack ; the trees recovered and the yield increased rapidly but eventually leveled off with some yearly fluctuations.2. In the + OM treatment, the yield per hectare in the N-1 treatment was less than 10% of the N-2 and N-3 treatments, whereas in the OM treatment, the N-2 and N-3 treatments, the yields were 8% and 14% larger, respectively, than in the N-1 treatment. These results led to the conclusion that the amount of nitrogen fertilizer in a high density planting of satsuma mandarin can be reduced to 100 kg•ha-1•year-1 when 20 t•-1•year-1 of rice straw was annually applied or 200 kg•ha-1•year-1 when no organic matter was applied, without substantial crop reduction.