AbstractDifferent levels of a leguminous green manure from velvetbeans, either left as a mulch or turned under, were added to two acid soils in Río Piedras and Mayagüez, Puerto Rico, that received 4 tons of ground limestone and 100 pounds P2O5per acre. The objective was to study the effect of the manure upon the yield of corn fertilized with 240 pounds of K2O per acre. Five tons of the green manure increased the corn yields in Catalina clay at Mayagüez whether left as a mulch or turned under. However, 10 tons increased the yields when turned under but not when left as a mulch. There was no significant difference in corn yields in acid Fajardo clay at Río Piedras whether 5, 10, and 25 tons of green manure were used. But significant yield responses of sweetpotatoes and corn were obtained before (2) in two other fields of this soil. The difference in behavior is explained on the basis of the higher nitrogen and organic-content of the soil in the field where responses were not obtained. The residual effect of the green manure did not raise the yields of a second corn crop at Río Piedras.
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