THE EFFECTS OF ALUMINUM AND PHOSPHATE ON THE GROWTH OF ANNUAL BLUEGRASS AND BENTGRASS IN SOME ACIDIC WESTERN WASHINGTON SOILS

Abstract

Twenty-one diverse soils were used to determine the differential growth response of bentgrass and annual bluegrass to pH, aluminum (Al), and phosphate (P) under glasshouse conditions. Nutrient solution containing no P was added to the soils which were maintained at a moisture tension of 33 kPa with an automatic, overhead sprinkler system throughout the experiment. The clipping yields for both grasses were highly correlated with the exchangeable Al content or the molar ratio of the NaHCO3-P to exchangeable Al. The same correlation using water-soluble P and the monomeric Al estimated by the 8-hydroxyquinoline method with 15-s reaction was poor, and the inclusion with pH in a multiple regression was necessary to better account for the yield variabilities among the soils. The parallel response of clipping yields of both grasses to NaHCO3-P, exchangeable Al, or the molar ratio of the NaHCO3-P to exchangeable Al indicates that the two grasses could not be differentiated in terms of the requirement for P and tolerance to Al based on clipping yields. Unlike the top growth, the root growth of annual bluegrass and bentgrass showed differential responses to the molar ratio of NaHCO3-P to exchangeable Al. Both the root length and root yields for bentgrass were substantially higher than those of annual bluegrass at the low molar ratios (<0.2) but lower at high ratios. The result suggests that the quantity of exchangeable Al should be considered in the selection of proper P and pH levels to improve the bentgrass root activity and reduce competitiveness of annual bluegrass, particularly for the diverse soils.