Phosphorus requirements for the early growth of red clover, trefoil and flatpea

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Abstract
A greenhouse experiment was conducted to compare the P requirements for early growth of red clover, birdsfoot trefoil and flatpea. P sorption isotherms were used to predict P fertilizer additions required to adjust 2 Appalachian soils to 8 equilibrium solution P levels (0.005-0.50 .mu.g P/ml). Flatpea dry matter production was equal to or greater than that of red clover and trefoil at low adjusted P levels. With increasing P level, flatpea dry matter yield peaked at a lower production level and at a lower adjusted P in soil solution than the other 2 legumes. The approximate P level in soil solution for 90% of maximum yield was as follows: flatpea, 0.074 .mu.g P/ml; red clover, 0.104 .mu.g P/ml; and trefoil, 0.141 .mu.g P/ml. Flatpea apparently has a lower internal P requirement than either trefoil or red clover. P concentrations in top growth for 90% of maximum yield were as follows: flatpea, 0.21%; trefoil, 0.24%, and red clover, 0.27%. The low internal P requirement and the ability of flatpea to achieve maximum yields at low adjusted P levels would suggest advantages for this legume in low fertility soil environments.