DIFFERENTIAL RESPONSE OF WHEAT GENOTYPES TO PHOSPHORUS IN ACID SOILS

A substantial acreage of soils in northwestern Canada is acidic and P-deficient. In this study wheat (Triticum aestivum L.) genotypes with different tolerance to acid soils were evaluated for their response to P fertility levels in greenhouse experiments. In Experiment 1, six wheat genotypes were grown on an acid soil (pH 4.8) with toxic level of Al. The Al-tolerant genotypes included the Brazilian BH1146 and three experimental lines developed in Alberta. The soil was amended with CaCO3 to three pH levels (4.8 (untreated), 6.3, and 7.1) and with 0, 1, or 2 mmoles P/kg soil. Liming to pH 7.1 increased dry matter yields and P uptake but not liming to pH 6.3, most probably because of decreased P solubility at the lower lime rate. Consequently, yields were not correlated with soil pH. Phosphate addition increased both dry matter yield and P uptake. Shoot and root dry matter yields were positively correlated with the interaction factor P x pH but not with P alone. Differential response in this regard appeared to be related to acid-soil tolerance. Some Al-tolerant genotypes, such as the Alberta lines, were P efficient as measured by P uptake per g of root biomass, whereas BH1146 appeared to have a low internal P requirement combined with a relatively low shoot/root ratio. A second experiment was conducted with four acid soils (pH 5.0 to 5.8) with non-toxic concentrations of Al and two cultivars of wheat: Laura cultivar has some tolerance to acid soil and Wildcat little. The soil treatments were combinations of unlimed or limed (pH 6.1) soil and 0, 1, or 2 mmole P/Kg soil. A major objective of this experiment was to determine whether genotypes with different acid soil tolerance had different effects on soil pH and soil solution composition. Soils analyzed after crop harvest showed that Laura cultivar increased soil pH relative to Wildcat, even though plant growth was not limited by the acidic soil pH. Phosphate was effective in increasing biomass, however, and there was a genotype x P interaction. Wildcat wheat had a higher P requirement than Laura and appeared to increase its P acquisition without increasing its root growth but by lowering soil pH, thereby increasing P solubility. This relatively high P requirement and the adaptive mechanism rendered it acid soil sensitive.