GRAIN YIELD AND MICROBIOLOGICAL QUALITY OF COWPEA PLANTS GROWN UNDER RESIDUAL EFFECT OF SEWAGE SLUDGE FERTILIZATION1
ABSTRACT Cowpea plants produce protein-rich grains and present high yield potential when grown under irrigation and organic fertilization, enabling to substitute part of the mineral fertilizer with sewage sludge, reducing costs and generating environmental benefits. Thus, a field study about residual effect of sewage sludge fertilization on cowpea was developed to evaluate this substitution. The experiment was conducted using a randomized block design with four replications, in a 2×5 factorial arrangement consisted of two fertilization types (residual effect of sewage sludge fertilization, and mineral fertilizers) and five cowpea cultivars (BRS-Pajeu, BRS-Xiquexique, BRS-Marataoa, BRS-Pujante, and BRS-Cauame). The residual fertilizations were from applications of sewage sludge and NPK mineral fertilizers for pineapple crops grown in the area before the cowpea crop. The experiment was conducted using 80,000 plants ha-1 and micro-sprinkler irrigation. Vegetative and yield components, grain yield, and microbiological quality were analyzed. BRS-Pujante had the highest cowpea grain yield (4,124 kg ha-1) and the highest means for vegetative and yield components. The soil with residual sewage sludge fertilization improved the cowpea root growth and grain yield (3,854 kg ha-1); the latter was 19% higher than that of treatments with mineral fertilization. These results were related to the great soil organic matter content provided by the sludge fertilization, which promotes nutrient mineralization, increasing grain yield. Fresh and dry grains of cowpea plants grown under residual effect of sewage sludge fertilization have similar microbiological quality to those of plants grown under mineral fertilization.