Organic fertilizers, green manures and mixtures of the two revealed their potential as substitutes for inorganic fertilizers used in pineapple cropping

Pineapple crops require large amounts of inorganic fertilizers applied in fractions from planting until flowering induction. Organic fertilization is rarely used and little documented. Our aim was to investigate the feasibility of replacing inorganic fertilizer with organic fertilizer. We screened a wide range of green manures and organic fertilizers, alone and in mixtures, using laboratory biochemical analyses, incubation experiments, and by computing nitrogen mineralization indicators and humus potential. We conducted field trials to test a smaller number of fertilizers. A Mucuna pruriens green manure fallow and two organic fertilizers (poultry feathers and blood meal, and composted manures) only applied at planting were compared to a mineral fertilizer applied at regular intervals as control. Our results showed that organic fertilization is possible, even only applied at planting, and that average fruit weight was similar to that with conventional fertilization. The laboratory tests enabled us to classify the green manures and organic fertilizer candidates and to recommend use vs rejection based on mineralization. We also showed that synergetic nitrogen mineralization (+18.4%) occurred when poultry feathers and blood meal were mixed with Lablab purpureus. This result is in line with the results of the field trial in which the combination of green manure and organic material provided sufficient nitrogen for pineapple nutrition. As field trials are costly and difficult to manage, we recommend screening of potential candidates for pineapple organic fertilization using a combination of biochemical analyses, incubation experiments in the laboratory, and computing the nitrogen mineralization indicator and humus potential.