Abstract

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.

Keywords: Soil fertility, anaerobic digestate, wheat kernel yield and quality, economic evaluation, semi-arid conditions.

References

AACC, 2010. AACC Approved Methods of Analysis. 11th Ed. 46-30.01 Crude protein—Combustion method. Cereals & Grains Association. St. Paul, MN 55121 USA. Available at [Access date: 13.01.2026]: https://www.cerealsgrains.org/resources/Methods/Methods/46-30.pdf

Al Seadi, T., Rutz, D., Prassl, H., Köttner, M., Finsterwalder, T., Volk, S., Janssen, R., 2013. 12 - Biogas digestate quality and utilization In: The Biogas Handbook: Science, Production and Applications. Wellinger, A., Murphy, J., Baxter, D. (Eds.). Woodhead Publishing Series in Energy. pp.267-301.

Alaboz, P., Demir, S., Dengiz, O., Öz, İ., 2021. Effect of biogas waste applications on soil moisture characteristic curve and assessment of the predictive accuracy of the Van Genuchten model. Eurasian Journal of Soil Science 10(2): 142–149.

Alburquerque, J.A., de la Fuente, C., Bernal, M.P., 2012. Chemical properties of anaerobic digestates affecting C and N dynamics in amended soils. Agriculture, Ecosystems & Environment 160: 15-22.

AOAC, 1995. Official methods of analysis. 16th ed., Association of Official Analytical Chemists. Washington, D.C., USA.

AOAC, 2005. Official methods of analysis. 18th ed., Association of Official Analytical Chemists. Washington, D.C., USA.

APHA, 2017. Standard methods for the examination of water and wastewater (23rd ed.). American Public Health Association, American Water Works Association, Water Environment Federation, USA.  Available at [Access date: 13.01.2026]: https://www.standardmethods.org/doi/book/10.2105/smww.2882

ASAE, 2003. Moisture measurement-unground grain and seeds. ASAE Standards. American Society of Agricultural Engineers, USA.

Bachmann, S., Uptmoor, R., Eichler-Löbermann, B., 2016. Phosphorus distribution and availability in untreated and mechanically separated biogas digestates. Scientia Agricola 73: 9–17.

Barłóg, P., Hlisnikovský, L., Kunzová, E., 2020. Effect of digestate on soil organic carbon and plant-available nutrient content compared to cattle slurry and mineral fertilization. Agronomy 10(3): 379.

Blake,  G.R., Hartge, K.H., 1986. Bulk Density. In: Methods of Soil Analysis: Part 1 Physical and Mineralogical Methods, 5.1, Second Edition. Klute, A. (Ed.). American Society of Agronomy, Soil Science Society of America, WI, Madison, USA. pp. 363-375.

Bouyoucos, G.J., 1951. A Recalibration of the hydrometer method for making mechanical analysis of soils. Agronomy Journal 43: 434-438.

Bremner, J.M., 1996. Nitrogen-total. In: Methods of Soil Analysis: Part 3 Chemical Methods, 5.3. Sparks, D.L. Page, A.L., Helmke, P.A., Loeppert, R.H., Soltanpour, P.N., Tabatabai, M.A., Johnston, C.T., Sumner, M.E. (Eds.). SSSA Book Series No. 5. ASA-SSSA Madison WI, USA, pp. 1085– 1121.

Crespo-Herrera, L., Crossa, J., Huerta-Espino, J., Vargas, M., Mondal, S., Velu, G., Payne, T., Braun, H., Singh, R., 2018. Genetic gains for grain yield in CIMMYT’s semi-arid wheat yield trials grown in suboptimal environments. Crop Science 58: 1890–1898.

Donald, C.M., Hamblin, J., 1976. The biological yield and harvest ındex of cereals as agronomic and plant breeding criteria. Advances in Agronomy 28: 361-405.

EPA, 2007. Microwave assisted acid digestion of sediments, sludges, soils, and oils. United States Environmental Protection Agency (EPA). USA. Available at [Access date: 13.01.2026]: https://www.epa.gov/sites/production/files/2015-12/documents/3051a.pdf

FAO, 2017. The future of food and agriculture – Trends and challenges. Food and Agriculture Organization of the United Nations (FAO), Rome, Italy. Available at [Access date: 13.01.2026]: https://www.fao.org/3/i6583e/i6583e.pdf

Gooding, M.J., Ellis, R.H., Shewry, P.R., Schofield, J.D., 2003. Effects of restricted water availability and increased temperature on the grain filling, drying and quality of winter wheat. Journal of Cereal Science 37(3): 295–309.

Häfner, F., Hartung, J., Möller, K., 2022. Digestate composition affecting N fertiliser value and C mineralisation. Waste Biomass Valorization 13: 3445–3462.

Hijazi, O., Abdelsalam, E., Samer, M., Amer, B.M.A., Yacoub, I.H., Moselhy, M.A., Attia, Y.A., Bernhardt, H., 2020. Environmental impacts concerning the addition of trace metals in the process of biogas production from anaerobic digestion of slurry. Journal of Cleaner Production 243: 118593.

Hillel, D., 1982. Introduction to soil physics. Academic Press.

ICARDA., 2019. Wheat Phenotyping Protocols. Available at [Access date: 13.01.2026]: https://icarda.org 

ICC, 1994. Standard Methods 101/1, 105/2, 116/1, 155. International Association for Cereal Science and Technology Vienna. Available at [Access date: 13.01.2026]: https://icc.or.at/icc-standards/standards-overview

Inan, İ.H., 2008. Agricultural enterprise management and planning. Tekirdağ, Türkiye.

ISO 5529:2007, International Standard ISO 5529. Wheat-Determination of sedimentation index-Zeleny test. International Organization for Standardization (ISO), Switzerland. Available at [Access date: 13.01.2026]: https://cdn.standards.iteh.ai/samples/40524/27aaf8e2b6bb4b67bbfa7780c9b1a568/ISO-5529-2007.pdf

Kacar, B., 2014. Plant, soil and fertilizer analysis – 2 (1st Ed.).Nobel Publications, Ankara, Türkiye. [in Turkish]

Köppen, W., 1900. Versuch einer Klassifikation der Kli mate, vorzugsweise nach ihren Beziehungen zur Pflanzen welt. Geographische Zeitschrift 6: 593–611, 657–679.

Lal, R., 2020. Managing soils for resolving the conflict between agriculture and nature: The hard talk. European Journal of Soil Science 71(1): 1–9.

Möller, K., Müller, T., 2012. Effects of anaerobic digestion on digestate nutrient availability and crop growth: A review. Engineering in Life Sciences 12(3): 242–257.

Möller, K., Stinner, W., 2009. Effects of different manuring systems with and without biogas digestion on soil mineral nitrogen content and on gaseous nitrogen losses (ammonia, nitrous oxides). European Journal of Agronomy 30(1): 1–16.

Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Analytica Chimica Acta 27: 31–36.

Namlı, A., Akça, H., Akça, M.O., 2023. Components and their assessment in different biogas slurries for enhanced waste management. Eurasian Journal of Soil Science 12(1): 10–18.

Nkoa, R., 2014. Agricultural benefits and environmental risks of soil fertilization with anaerobic digestates: A review. Agronomy for Sustainable Development 34(2): 473–492.

Olsen,S.R., Dean, L.A., 1965. Phosphorus. In: Methods of soil analysis. Part 2. Chemical and microbiological properties. Black, C.A., Evans, D.D., White, J.L., Ensminger, L.E., Clark F.E. (Eds.), Soil Science Society of America. Madison, Wisconsin, USA. pp. 1035-1049.

Pratt, P.F., 1965. Potassium. In: Methods of soil analysis. Part 2. Chemical and microbiological properties. Black, C.A., Evans, D.D., White, J.L., Ensminger, L.E., Clark F.E. (Eds.), Soil Science Society of America. Madison, Wisconsin, USA. pp. 1022-1030.

Richards, L.A., 1954. Diagnosis and improvement of saline and alkali soils (Agriculture Handbook No. 60). U.S. Department of Agriculture, Washington, DC.

Rockström, J., Williams, J., Daily, G., Noble, A., Matthews, N., Gordon, L., Wetterstrand, H., DeClerck, F., Shah, M., Steduto, P., Fraiture, C. de, Hatibu, N., Unver, O., Bird, J., Sibanda, L., Smith, J., 2017. Sustainable intensification of agriculture for human prosperity and global sustainability. Ambio 46: 4–17.

Sadras, V.O., Calderini, D.F., 2015. Crop physiology: Applications for genetic improvement and agronomy. Academic Press.

Sieling, K., Kage, H., 2006. N balance as an indicator of N leaching in an oilseed rape–winter wheat–winter barley rotation. Agriculture, Ecosystems & Environment 115(1–4): 261–269.

Slafer, G.A., Savin, R., Sadras, V.O., 2014. Coarse and fine regulation of wheat yield components in response to genotype and environment. Field Crops Research 157: 71-83.

Sogn, T.A., Dragicevic, I., Linjordet, R., Krogstad, T., Eijsink, V.G.H., Eich-Greatorex, S., 2018. Recycling of biogas digestates in agriculture: Effects on soil quality and plant growth. International Journal of Recycling of Organic Waste in Agriculture 7: 49–58.

Soil Survey Staff, 2014. Kellogg soil survey laboratory methods manual. Soil Survey Investigations Report No. 42, Version 5.0, United States Department of Agriculture, Natural Resources Conservation Service, National Soil Survey Center, Kellogg Soil Survey Laboratory, Lincoln, Nebraska, USA. 1001p. Available at [Access date: 13.01.2026]: https://data.neonscience.org/documents/10179/2357445/KelloggSSL_MethodsManual_Report42Version5_2014/da9589dd-3278-402b-a5d4-02dc0c9c762c

Sutton, M.A., Howard, C.M., Erisman, J.W., Billen, G., Bleeker, A., Grennfelt, P., Van Grinsven, H., Grizzetti, B., 2011. The European nitrogen assessment: Sources, effects and policy perspectives. Cambridge University Press. 612p.

Swift, R.S., 1996. Organic matter characterization. In: Methods of Soil Analysis: Part 3 Chemical Methods, 5.3. Sparks, D.L. Page, A.L., Helmke, P.A., Loeppert, R.H., Soltanpour, P.N., Tabatabai, M.A., Johnston, C.T., Sumner, M.E. (Eds.). SSSA Book Series No. 5. ASA-SSSA Madison WI, USA, pp. 1011– 1069.

Tambone, F., Genevini, P., D'Imporzano, G., Adani, F., 2009. Assessing amendment properties of digestate by studying the organic matter composition and the degree of biological stability during the anaerobic digestion of the organic fraction of MSW. Bioresource Technology 100(12): 3140-3142.

Tambone, F., Scaglia, B., D'Imporzano, G., Schievano, A., Orzi, V., Salati, S., Adani, F., 2010. Assessing amendment and fertilizing properties of digestates from anaerobic digestion through a comparative study with digested sludge and compost. Chemosphere 81(5): 577-583.

Triboi, E., Triboi-Blondel, A.M., 2002. Productivity and grain or seed composition: A new approach to an old problem-invited paper. European Journal of Agronomy 16(3): 163–186.

US Salinity Laboratory Staff, 1954. Diagnosis and improvement of saline and alkali soils. US Department of Agriculture Handbook 60, Washington, DC.

Walkley, A., Black, I.A., 1934. An examination of Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Science 37(1): 29–38.

Walsh, J.J., Jones, D.L., Chadwick, D.R., Williams, A.P., 2018. Repeated application of anaerobic digestate, undigested cattle slurry and inorganic fertilizer N: Impacts on pasture yield and quality. Grass and Forage Science 73: 758–763.