Effect of poultry manure and chemical fertilizers on soil chemical and biological properties in millet, sorghum, and maize

This study evaluated the effects of poultry manure and chemical fertilizer on soil chemical and biological properties in pearl millet ( Pennisetum glaucum ), sorghum ( Sorghum bicolor ), and maize ( Zea mays ) at the Research Farm of the University of Kurdistan, Iran, during 2022 and 2023. The experiment was conducted as a split-plot arrangement based on a randomized complete block design with three replications. The main plot factor included three crops (pearl millet, sorghum, and maize), while the subplot factor consisted of five fertilizer treatments, including control, poultry manure, chemical fertilizer, and combinations of poultry manure with urea and triple superphosphate at varying rates. The results showed that, among the fertilizer treatments, the highest soil organic carbon levels across all three crops were observed in the F2 treatment (poultry manure). Soil nitrate levels were higher under pearl millet (11.75 mg kg⁻ 1 ) and maize (11.23 mg kg⁻ 1 ) than under sorghum (10.53 mg kg⁻ 1 ). The highest soil potassium concentration (139.9 mg kg⁻ 1 ) was recorded in the full chemical fertilizer treatment (F5), whereas the lowest value (118 mg kg⁻ 1 ) was observed in the control treatment. Poultry manure significantly improved soil nutrient content, increased acid and alkaline phosphatase activities. The highest acid phosphatase activity (132.83 μg PNP g⁻ 1 h⁻ 1 ) was observed with poultry manure application, while the lowest activities were recorded in the control (79.45 μg PNP g⁻ 1 h⁻ 1 ) and chemical fertilizer (88.2 μg PNP g⁻ 1 h⁻ 1 ) treatments. Although poultry manure increased soil EC, its benefits for soil fertility and biological activity indicate that it may be suitable under controlled application rates and regular EC monitoring.