Influence of Organic Amendments on Solution Phosphorus Requirements for Vegetables in Minesoil

Green-manure systems of a tall fescue ( Festuca arundinacea L.) sod and a rye ( Secale cereale L.)-soybean ( Glycine max. L.)-rye rotation were grown for 2 years to provide organic amendments to minesoil. One year after incorporating the green-manure crops, tomato ( Lycopersicon esculentum Mill.), pepper ( Capsicum annuum L.), and eggplant ( Solanum melongena L.) were grown on the amended minesoil and on adjacent, unamended minesoil. Six levels (0.05 to 2.4 ppm) of solution P were established within each plot, based on phosphate sorption isotherms. P sorption decreased in the organic-amended minesoils, thereby reducing the inorganic P fertilizer needed to establish each P solution level. Levels of amorphous Al oxides decreased while exchangeable Al remained relatively constant in the amended minesoil. Moisture relationships and other physical properties were improved in each green-manure regime. Organic amendments had no effect on optimum solution P requirements as tomato and pepper produced highest yields at 0.20 and 0.40 ppm solution P while eggplant produced highest yields at 1.60 and 2.40 ppm solution P in all minesoils. Yields of vegetables were higher in the amended minesoils for most solution P levels, while tissue P and other nutrient concentrations remained unchanged. Yield increases at each P solution level were attributable to improvements in minesoil moisture properties, not to nutritional factors. No differences between the 2 green-manure systems were apparent in their effect on external (solution P) or internal (tissue P) P requirements of the vegetable crop.