Validation of Compost-Derived Biofertilizers from Cattle Manure in Lettuce Cultivation Using Multispectral Imaging and Vegetation Indices

The transition towards circular agriculture requires sustainable fertilization strategies that maintain crop productivity, reducing environmental impacts associated with synthetic inputs. In this study, compost-derived biofertilizers produced from cattle manure, with and without structuring agents (wheat straw and almond pruning), were evaluated as alternatives to mineral fertilization for lettuce (Lactuca sativa L.) grown under controlled greenhouse conditions. A two-cycle pot experiment was conducted to increase total nitrogen, extractable phosphorus and exchangeable potassium, while slightly decreasing soil pH. Mineral fertilization produced the highest biomass in the first growing cycle, whereas compost treatments achieved comparable yields and showed clear residual effects in the second cycle. Multispectral sensing shows to be a useful non-destructive tool for monitoring crop development. Red-edge-based indices (NDRE) showed high sensitivity to variations in nutrient content dynamics. Generalized additive models (GAMs) enabled nutrient prediction, with strong performance for phosphorus (R2 = 0.79) and selected micronutrients and moderate performance for nitrogen (R2 = 0.62) and weaker performance for potassium (R2 = 0.45). These results indicate that combining compost-based fertilization with multispectral sensing can improve nutrient use efficiency and support precision horticulture under circular agricultural frameworks.