Influence of lime and phosphorus fertilizer on shallot growth and bulb yield in strongly acid soils in West Java, Indonesia

Shallot yield is lower in acidic soils and under low soil P status. Increasing shallot bulb yield can be achieved by improving the soil fertility of acidic soils. This study investigated the effect of lime and phosphorus (P) fertilizer on shallot growth and yield. Three field trials were set up in the early rainy season (2018-2019) in Kabupaten Bandung, West Java, Indonesia. They were: 1) Field 1, extremely acidic - low soil available-P (initial soil pH=4.23, Bray-P = 14 mg P kg^‑1); 2) Field 2, very strongly acidic - medium soil available-P (initial soil pH=4.98, Bray-P = 27 mg P kg^‑1 and 3) Field 3, strongly acidic - low soil available-P (initial soil pH=5.15, Bray-P = 8 mg P kg^‑1). Each trial site had 12 treatments; each replicated four times. The treatments were combinations of lime (0, 0.5 and 1.0 t ha^‑1) and phosphorus fertilizer (0, 50, 100, 150 P kg ha^‑1). Lime significantly increased soil pH, reduced Al³⁺ in all fields, but only increased dry weight at eight weeks after planting and shallot bulb yield in Field 2 (from 7.7 to 10.6 t ha^‑1). Phosphorus fertilization increased soil available P in Field 1 and 3 but only improved dry weight at eight weeks after planting and shallot bulb yield in Field 3 (from 8.4 to 10.0 t ha^‑1). However, neither lime nor phosphorus fertilizer improved shallot biomass nor bulb yield for Field 1. In conclusion, application of lime improved the shallot bulb yield in the strongly acidic soil by increasing soil pH, Ca²⁺ content and by reducing the exchangeable Al³⁺. Phosphorus fertilization improved P-availability and improved the bulb yield in soil with low available-P status. A higher rate of lime (>1.0 t ha^‑1) in extremely acid soil is required to increased soil pH, to adequately lower exchangeable Al³⁺ and to achieve a yield response. Bulb yield is a fresh bulb yield of shallot without leaves.