Vegetables in multiple cropping with corn: allelopathy; effects on soil properties, crop performance and yield

Caffeic and coumaric acids were identified as the allelopathic substances in cowpea and bush sitao. Ferrelic and salicylic acids were detected on corn, cowpea and pole sitao extracts. Cowpea and bush sitao extracts were consistently found allelopathic to corn in terms of seed germination and length of shoots and roots of seedlings under laboratory conditio2048ns. None of the sequential crops tested had detrimental residual effects on the succeeding corn crop under field conditions. N applied either as ammonium sulfate or ipil-ipil leaves as well as crop sequential planting regardless of the crop sequence, increased N, P and K uptake of all the crops in the sequence. Gross or net returns in all cropping scheme were increased significantly by the sequential crop yields rather than by the base crop yields. Intercropping did not alter most of the soil properties measured such as pH, OM and soil N, P and K contents. Likewise LAI (leaf area index) was not significantly altered. Light transmission or penetration increased with wider spatial row arrangement and was accompanied by a decrease in light interception of the base crop. All of the intercrops used provided greater net returns and land equivalent ratio (LER) values over the sole corn crop. The significant effects on LER values indicate that the combination of base crop and intercrops must have exploited the environmental resources more effectively than the pure stand. Corn as base crop was a better competitor than the vegetable intercrops although competition between them was minimal. Trellising of pole sitao, transplanting of tomato and chinese cabbage and the use of cuttings for sweet potato improved their competitiveness, as measured by beta values, which enable them to compete with corn for the environmental resources avail