Effects of biogas-derived liquid digestates on wheat yield, kernel quality and economic performance under semi-arid conditions

This study evaluated the effects of biogas-derived liquid digestates on wheat yield, yield components, kernel quality, nutrient contents, and economic performance under semi-arid Central Anatolian conditions. Field experiments were conducted using three digestate types—poultry manure + poppy residue (PP), cattle manure + plant waste (CP), and a poultry + cattle mixture (PC)—applied at 15, 30, 45, and 60 t ha⁻¹, alongside control and NPK treatments. Liquid digestates significantly increased kernel yield compared with the control, with clear differences among digestate types and application rates. Under PP, CP, and PC treatments, yield increased from 2195.2 to 2717.9 kg ha⁻¹, from 2352.2 to 2850.9 kg ha⁻¹, and from 2393.7 to 2807.0 kg ha⁻¹, respectively, with maximum values observed at 30 t ha⁻¹. NPK consistently produced high yields (2807.9-2977.1 kg ha⁻¹). Yield components improved under digestate applications. Digestate applications improved several yield-related traits across all digestate types. Harvest index, plant height, spike length, peduncle length, stem + spikelet weight, spikelet kernel number, spikelet kernel weight, and thousand kernel weight generally increased under digestate treatments compared with the control, although the magnitude of response varied according to digestate source and application rate. Kernel quality traits varied moderately, with crude protein (12.94-16.01%), wet gluten (24.73-36.0%), and Zeleny sedimentation (39.0-62.0 mL). Under PP digestate application, K and Ca levels in wheat kernels were significant (p < 0.01), whereas CP and PC showed limited effects, with significance observed only for Fe. Multivariate analyses indicated that net income was primarily driven by kernel yield and its components. Economic evaluation showed that digestate applications increased profitability, with the highest net income under CP at 30 t ha⁻¹ ($955.2 ha⁻¹ yr⁻¹). Although the highest yield and net income were generally obtained around 30 t ha⁻¹, 15 t ha⁻¹ may represent a safer option where salinity risk and long-term soil effects are major concerns. Overall, biogas liquid digestates—especially CP and PC applied at moderate rates—represent effective and economically viable nutrient sources for wheat production in semi-arid systems. However, further multi-year studies are required to assess long-term impacts on soil properties, nutrient dynamics, and environmental sustainability.