Critical values of soil solution Al³⁺ activity and pH for canola and maize cultivation in two acidic soils

Aluminum (Al) toxicity caused by soil acidification is the main constraint for crop growth in tropical and subtropical areas of southern China. The critical values of soil solution Al³⁺ activity and pH for crops in acidic soils can provide a useful reference for soil acidity amelioration.

A pot experiment in a greenhouse was conducted to investigate the critical values of soil solution Al³⁺ activity and pH for canola and maize in an Ultisol and an Alfisol. The critical values of soil solution Al³⁺ activity in Ultisol and Alfisol for canola were 1.5 and 10.0 μmol L^-1 , and 13.9 and 30.4 μmol L^-1 for maize, respectively. The Al tolerance varied with soil type for the same variety of crop. There was more biomass of roots and shoots and higher plant height under the same Al³⁺ activity, and thus greater critical values of soil solution Al³⁺ activity for both crops in Alfisol than those in Ultisol, owing to higher Ca²⁺ /Al³⁺ , Mg²⁺ /Al³⁺ and K⁺ /Al³⁺ ratios in soil solution caused by higher cation exchange capacity and exchangeable base cations in Alfisol, when compared with those in Ultisol. The critical values of soil solution pH for canola and maize in Ultisol were 5.09 and 4.72, respectively; while those in Alfisol were 4.87 and 4.54, respectively.

The critical values of Al³⁺ activity were higher for maize than for canola and the critical values for both crops were higher in Alfisol than in Ultisol. The critical soil pH for both crops showed opposite trends to soil Al³⁺ activity. © 2022 Society of Chemical Industry.