Enhancing Ultisol fertility index, nutrient uptake and agronomic yield of cucumber (Cucumis sativus) through biochar types and incubation periods

Ultisol, characterized by acidic pH and low fertility index, present significant challenges for crop productivity. This study investigated the efficacy of three biochar types, oil palm empty fruit bunches (OPEFB-B), rice husk and maize cob (MC-B) applied at 10 t·ha–1, with varying incubation periods (0, 10, 20 and 30-d) with three replicates, to enhance Ultisol fertility index and cucumber performance. A factorial randomized complete block design was used, which was conducted in farmer fields in Medan, Indonesia from June to October 2023. This investigation used the cucumber hybrid Metavy F1, cultivated in a composite sample of randomly collected Ultisol. Following analysis of variance, significant means were separated by Duncan’s multiple range test at a 5% level, and correlations among the variables were evaluated. Soil fertility index (SFI) of Ultisol was established and classified. Results demonstrated that MC-B was superior in boosting cucumber yield to 47.4 t·ha−1. This increase is attributed to a significant elevated in the uptake of nitrogen, phosphorus and potassium by about 125%. In contrast, OPEFB-B was most effective at improving Ultisol SFI by 0.447 (a 38.8% increase). An incubation period of 20-d was identified as optimal for maximizing yield and nutrient uptake. The interaction between biochar type and incubation periods were significant effect on plant height and leaf area. Specifically, the combination of OPEFB-B with 10- or 20-d incubation enhanced soil fertility and increased the N and K content in plant shoots. Correlation analysis revealed significant positive associations between cucumber productivity and key soil properties: organic C, cation exchange capacity, base saturation, and exchangeable Ca and K with values of 0.321, 0.342, 0.420, 0.392 and 0.487, respectively. Synergistic improvements in soil fertility and crop yield require the extended incubation period of MC-B and OPEFB-B, applied separately or in combination.