Effect of lime-phosphorus and green manure on sweet potatoes and corn grown in acid soils

Abstract

Data are presented here on the efflect that four types of green manure had, on the yields of one sweet potatoes and two corn crops planted in two acid soils of Puerto Rico, in the absence or presence of lime and phosphorus. Comparison is also made as to what effect the green manure had on the crop yields when it was applied as a mulch or when it was plowed under the soil. In the last corn crop, the effect of fertilizing with potash was also studied as well as the effect of adding inorganic nitrogen and potash to the check plots, in the absence or presence of lime and phosphorus. The field experiments were established in Fajardo clay at Río Piedras and in Catalina clay level phase at Mayagüez, located about 75 miles apart. The green manure sources were from four leguminosae: velvet beans Stizolobium deeringianum; crotalaria Crotalaria striata; cowpeas Vigna sinensis; and soybeans Soja max Otootan variety. The sweet potato used was the Don Juan variety and the corn was the Mayorbela variety, a flinty type. In general, the leguminosae and the crops responded significantly to lime and phosphorus. Velvet beans gave the highest significant yields of green manure. In general, the velvet beans with lime and phosphorus gave the highest significant yields of sweet potatoes and corn. Cowpeas showed a highly significant detrimental effect in the yield of sweet potatoes. When the green manure was either mulched or plowed under the soil there was no significant difference between the yields of sweet potatoes and corn. The last corn crop at Mayagüez responded significantly to the application of potash and to the application of potash and inorganic nitrogen specially when lime and phosphorus were added to the checks, but no response was obtained with the green manures. No response to potash in the check and green manure plots were obtained at Río Piedras.