Lime and phosphorus fertiliser application to improve shallot bulb yield in extremely acid soil conditions

Shallots are important vegetable crop in Indonesia, but increasing demand has increased the growing of shallots on marginal land with extremely acidic soils. Shallots are susceptible to low soil pH, which can result in low yields due to induced nutrient deficiency and aluminium (Al³⁺) toxicity of microelements. High is often the most limiting factor in many acidic soils. Therefore, correcting the Al³⁺ toxicity is essential to support plant growth and achieve high bulb yields. The objective of the trial was to assess the effect of lime and P fertiliser application on soil properties of extremely acidic soil (soil pH 4.1, Al³⁺=1.93 cmol (+) kg^‑1, Bray1-P=9.8 mg P kg^‑1) and on shallot bulb yield. An application of 4 t lime + 120 kg P ha^‑1 increased soil pH from 4.1 to 4.7, reduced exchangeable Al³⁺ from 1.93 to 0.44 cmol (+) kg^‑1 and increased Bray1-P from 10 to 25 mg P kg^‑1. The bulb yield in the control (0L+0P) treatment was only 3.10 t ha^‑1, and the application 4 t lime + 120 kg P ha^‑1 doubled yield. However, yields in this trial were low (<7 t ha^‑1), and there was a relatively flat response to Bray1-P. It seems there were other factors that potentially limited the shallot growth more.