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Neutralize acidic soil with ash.
Literal
Acidic-soil [object-を] ash [with-で] neutralize.
Gardening/chemistry instruction. 酸性 ('acidic') uses the ~性 suffix for '-ity/-ness,' forming a noun-attribute. 中和する ('to neutralize') is a chemistry term for acid-base neutralization — here applied to gardening practice of adding lime or wood ash to lower soil acidity. で marks the instrument/means ('with ash').