The availability of iron in soil is highly correlated with pH value, which is the core reason many farmers apply iron fertilizer but see no effect. EDTA chelated iron has a clear stable range, and precise matching of soil pH is required to achieve the best fertilizer efficiency.

EDTA chelated iron has a stable pH range of 4.0-7.0. In acidic to neutral soils, the chelate structure is complete and stable, iron ions will not be fixed by soil colloids, and crop absorption efficiency can reach more than 80%. When the soil pH is between 6.5 and 7.0, EDTA iron can still maintain most of its activity, making it suitable for most neutral cultivated land in China.

When the soil pH exceeds 7.0 and enters the alkaline range, the EDTA chelate structure will gradually dissociate, and the released iron ions will quickly form iron hydroxide precipitate and fail. It is not recommended to blindly increase the dosage of EDTA iron. Instead, it can be applied together with acidic organic fertilizers such as humic acid and fulvic acid to improve iron availability by locally reducing rhizosphere pH. For severely alkaline soils, products with stronger alkali resistance such as EDDHA chelated iron are more recommended.

In strongly acidic soils (pH < 4.0), although iron availability is high, it is prone to iron overdose toxicity, and will aggravate the toxicity of manganese, aluminum and other elements. It is necessary to appropriately reduce the dosage of EDTA iron and adjust the acidity to a reasonable range with lime.