Research Article

The Effects of Long-Term Organic and Inorganic Fertilisation on Soybean Yield, Carbon and Nitrogen Content

Feyzullah Öztürk^*, Seher İlhan and Ibrahim Ortaş

Department of Soil Science and Plant Nutrition, Faculty of Agriculture, Çukurova University, Türkiye

*Corresponding author e-mail: ozturk2421@gmail.com

(Received: 30/08/2025; Revised: 02/10/2025; Accepted: 15/10/2025; Published: 20/12/2025)

ABSTRACT

The soybean plant, with its high protein and oil content, plays a vital role in both human nutrition and animal feed, and is a strategic agricultural product, particularly due to its ability to fix nitrogen in the soil. The application of various long-term sources, such as mineral fertilisers, compost, manure, and mycorrhiza, plays a significant role in increasing soybean yield by directly affecting both the plant’s productivity and carbon sequestration in the soil. The experiment was established in 1996 within the Soil Science and Plant Nutrition Research Area of the Research and Application Farm at Çukurova University’s Faculty of Agriculture, utilising a randomised block design. The current research began with Soybean (Glycine max (L.) Merr.) cultivation in the 2022-2023 production year. Before cultivation, control, mineral fertilizer (NPK), animal manure (25 tons ha^-1), compost (25 tons ha^-1), and compost + mycorrhiza (10 tons ha^-1) were applied. After harvest, different parts of the soybean were harvested. The nutrient content of different parts of the soybean plant was analyzed. Total, inorganic and organic carbon concentrations in the soil were investigated. Also, CO₂ fixation through photosynthesis was determined. The highest grain yield and total biomass were found in soybean plants treated with compost application. In general, compost, compost+mycorrhiza, and subsequently manure applications produced higher yields and biomass than mineral fertilizer and control plots in the soybean plant environment. Additionally, total carbon concentration and total CO₂ fixation in the soil were highest in the compost application. The total organic carbon (TOC) in the soil was highest following manure application. Agricultural sustainability and carbon sequestration in soil are recommended for further research to mitigate the potential negative effects of climate change through the use of manure, compost, and mycorrhizae. Future studies should examine the impact of these applications under different plant species and soil types. These findings could play an essential role in shaping environmental policies related to carbon sequestration, the carbon cycle, and soil health.

Keywords: Soybean, Soil organic carbon, Nutrient uptake, Mineral fertilizer, Mycorrhiza, Compost, Manure