Dryland soils vary widely in texture, salinity, carbonate content, and phosphorus availability, and this variation shapes how crops respond to biochar. We tested fenugreek (Trigonella foenum-graecum L.) response to acidified biochars made from neem (Azadirachta indica) and mesquite (Neltuma juliflora) pruning residues in three contrasting Sudanese dryland soil materials, classified as Vertisol, Entisol, and Aridisol, all of them calcareous (2.3% - 3.5% CaCO3). The residues were carbonized under traditional limited-oxygen conditions and then saturated with dilute phosphoric acid. Final biochar pH was 4.0 for neem and 3.5 for mesquite, with Olsen-extractable phosphorus of 1500 and 1800 mg？kg？1, respectively. A 60-day completely randomized pot experiment compared the two feedstocks at 2.5% and 5% w/w against unamended controls, with three replicates per treatment and 45 pots in total. Plant height and leaf number were recorded during growth; shoot and root biomass and post-harvest available phosphorus were measured at harvest. Post-harvest pH and ECe were recorded at the treatment level. Responses differed by soil material, feedstock, rate, and trait. In the Entisol material, neem 5%, neem 2.5%, and mesquite 2.5% gave the tallest plants, neem 5% the highest shoot fresh and dry biomass, and mesquite 2.5% the highest leaf number and root fresh weight. In the Vertisol material, neem 5% produced the strongest shoot response and the highest post-harvest available phosphorus, while mesquite 2.5% again gave the highest root fresh weight. The Aridisol material responded less consistently: mesquite 5% raised shoot fresh and dry weight, but root traits did not improve significantly. Post-harvest pH stayed slightly alkaline throughout, between 7.45 and 7.72, and ECe rose only marginally under all treatments. Available phosphorus increased sharply at the 5% rate, yet higher phosphorus did not reliably produce balanced shoot and root growth. Under these pot conditions, the performance of acidified neem and mesquite biochars was both soil-specific and trait-specific. Texture, carbonate content, initial salinity, feedstock, and application rate all warrant consideration before these amendments are recommended for dryland soils.
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