Alfalfa,Medicago sativa L., in highly weathered, acid soils
SummaryRooting into acid subsoils would be a desirable trait for alfalfa which should result in better water extraction and yield. In this study, the rooting depth into acid subsoils and top yield of alfalfa plants selected for acid tolerance were investigated in a repacked profile with a limed, fertile topsoil, but unamended, acid subsoil. The effects of subsoil modification by CaCO3 and CaSO4·2H2O addition on alfalfa rooting, top growth, and water extraction were also studied.Plants from acid selections rooted deeper into acid subsoil when compared to control plants (selected under limed conditions). However, the reverse response was found in the CaSO4·2H2O treated subsoil. There were no differences among selections for total top yield for any subsoil treatment. Water extraction from the lower subsoil and top growth yield (data pooled by selections) were improved mainly in the subsoil treatment containing the highest addition of CaCO3.
Response to soil aluminium of two white clover (Trifolium repens L.) genotypes
An aluminium (Al) tolerant genotype of white clover was compared with an Al susceptible genotype in artificial soil profiles in which exchangeable Al increased with depth. The tolerant genotype had a greater proportion of its root mass deeper in the soil than the susceptible genotype. Nitrogenase activity showed a similar pattern. Shoot Al concentration did not vary between the genotypes but root Al in the susceptible line was twice that in the tolerant genotype. Plant potassium content in the susceptible line was relatively less, probably in response to higher aluminium content.
Aluminum toxicity in corn at near neutral soil pH levels
Abstract Aluminum toxicity to plants is often responsible for yield reductions under acid soil conditions. Despite the fact that Al becomes insoluble in the slightly acid to neutral pH range, there are indications that it can still be taken up and become toxic to plants. Corn plants were grown in the greenhouse on three highly weathered soils (Oxisol and Ultisols) containing substantial quantities of exchangeable Al. The soils were limed at various rates up to pH values near or above neutrality. On all soils a positive yield response to lime occurred at low pH values while on two of the soils, yields decreased significantly as the pH approached neutrality. Yield and Al content of the tissue were exponentially related irrespective of the level of phosphate applied (r2 = 0.34 and 0.71). The mechanism by which Al becomes increasingly available to the plant as the pH approaches neutrality is not clear and needs further investigation. Strong Al‐Mg and Al‐P antagonisms occur at the high and low pH values. The e...