EFFECT OF LIME AND PHOSPHATE ON THE GROWTH OF ANNUAL BLUEGRASS AND CREEPING BENTGRASS IN 2 ACID SOILS

Characterization of the growth of annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis palustris Huds.) over a broad range of pH and phosphate levels was needed to better investigate potential effec ts of soil acidity and P on annual blue-grass infestation in creeping bentgrass stands. Two acid soils were treated with varying rates of li me and P fertilizer. Clipping yields and P uptake of both grasses, as well as the levels of soil NaHCO3-extractable P and exchangeable Al, w ere all significantly related to lime and P treatments. High lime and high P treatments benefited annual bluegrass more than creeping bentgr ass as revealed by clipping yields and P uptake. Lime invariably reduc ed the exchangeable soil Al with a small effect on NaHCO3-P levels in the lime rates used. The increased responses of clipping yields and P uptake to NaHCO3-P by liming could be attributed to the reduction of p hytotoxic Al. The molar ratio of NaHCO3-P to exchangeable Al was a sui table parameter to describe the overall lime and P effects on the grow th of either grass. High lime and high P applications which lead to hi gh molar ratios of NaHCO3-P to exchangeable Al should be avoided in or der to reduce the competition of annual bluegrass, particularly for so ils that contain high organic matter and organic N. Further study is n eeded to elucidate the contribution of organic N mineralization to the differential growth behavior between the two grasses in the turf syst em.