Liming Double‐Cropped Ryegrass and Sorghum

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Abstract
The grower must apply lime to maintain crop yields when double‐cropping forage sorghum [Sorghum bicolor (L.) Moench] in summer and ryegrass (Lolium multiflorun Lam.) in winter on Coastal Plain soils of the U.S. Southeast. The purpose of this research was to determine the frequency and rate of liming needed for optimal growth of these crops and to identify soil properties having greatest effect on yield. The experiment was conducted on a Tangi silt loam (fine‐silty, siliceous, thermic Typic Fragiudult) during a 12‐y period. Dolomitic lime treatments were: 0 lime, 2.2 and 4.4 Mg lime ha‐1 applied every 2yr, and 2.2 and 4.4 Mg lime ha‐1 applied every 4 yr. Soil samples were taken annually and analyzed for pH, exchangeable Al, Ca, Mg, and K, and extractable P. Surface soil pH was maintained at 5.8 and 6.0 when lime was applied at 2.2 and 4.4 Mg ha‐1 every 2 yr. Soil pH declined when lime was applied every 4 yr. In unlimed soil, the pH declined from 5.6 to 4.7 during the 12 yr. Significant differences in forage yields between unlimed and limed treatments did not occur until the sixth year (for sorghum) and the 11th year (for ryegrass). Reduced yields of ryegrass first occurred when soil pH decreased to 4.8 ± 0.11; for sorghum, yields declined at pH 5.2 ± 0.078. Crop yields of limed treatments were not affected by liming frequency. It may take longer than 12 yr for soil property differences among lime treatments to be large enough to alter plant yields. Ryegrass yield was not correlated with any surface soil parameters; Sorghum yield was positively correlated with surface soil extractable Ca. Exchangeable Al tended to decline and extractable Ca and Mg tended to increase with lime applications. Neither extractable P nor K was signigicantly altered by lime treatment. In a double‐cropped system of ryegrass and sorghum, liming would be of more benefit to sorghum.

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