Inexpensive biological tests for soil calcium deficiency and aluminum toxicity

Two relatively simple procedures based on 4-day seedling growth were developed for identifying soil calcium (Ca) deficiency and/or aluminum (Al) toxicity. Test A uses any large-seeded cultivar that a farmer might consider planting and reveals whether the cultivar will suffer from Ca deficiency by comparing root growth in untreated soil to that in soil receiving a minimal Ca addition (0.1 meq. 100 mL⁻¹ soil), sufficient to eliminate possible deficiency. Al toxicity is detected by comparing root growth in a sample receiving the minimal Ca treatment with growth in the soil treated with enough lime to neutralize exchangeable Al. In test B, potential Al toxicity problems are detected for any widely-grown standard crop by comparing its growth with that of a different, Al-tolerant variety on soil samples receiving 0.1 meq. 100 mL⁻¹ Ca. With this test Ca deficiency in the untreated sample is detected by an increase in root growth of the Al-tolerant variety resulting from a small addition of Ca. The tests agreed with diagnoses made by standard chemical methods in about 84% of the cases examined. The proposed tests can be carried out using simple, easily-available materials without the necessity of sending soils to an analytical laboratory.