FACTORS ASSOCIATED WITH ANNUAL RYEGRASS YIELD RESPONSE TO LIMESTONE

Quantifying the effects of soil acidity on plant growth remains a chal lenging research topic as numerous soil and plant growth factors are i nfluenced by pH and lime. In the field, annual ryegrass (Lolium multif lorum Lam. 'Marshall') responded positively to the application of 3.8 Mg lime/ha on a strongly acid (pH 4.7) Lilbert loamy fine sand (loamy, siliceous, thermic, arenic Plinthic Paleudult) over three growing sea sons. Dry matter yield in some cuttings, however, was better correlate d with soil Al, P, Ca, Mg, and K than with pH. A greenhouse study was undertaken to quantitatively determine the effects of these five miner als plus Mo on ryegrass yield in limed and unlimed Lilbert soil materi al. Three ryegrass cuttings were obtained from unlimed (pH 4.8) or lim ed (1000 mg CaCO3/kg) Lilbert soil which was also amended with five ra tes of Ca, K, Mg, Al, P, and Mo in combinations stipulated by central composite design methodology. Response surface models that fit yield t o the applied treatments and soil test data were complex because all f actors and many interactions were significant. Furthermore, the models were transformed as the plants matured and element availability chang ed due to mineral uptake. Most yield improvement derived from liming o ccurred as a result of the elimination of exchangeable Al with a conco mitant increase in P efficiency. Applied Ca did not alleviate Al toxic ity in unlimed soil. Chlorotic plants developed in all pots where Mg w as excluded. Yield was increased by applied Mg and Mo in unlimed soil, but not in limed soil. Applied K improved yield only in limed soil. A lthough regression accounted for a large portion of the yield variabil ity (R2 values ranged from 0.75 to 0.95), these models were unable to accurately predict yield in control treatments.