Soil properties and greenhouse gas emissions in a long-term wheat fertility study

Long-term field studies have been vital sources of information regarding the effects of amendments on soil properties because they account for natural variability and complexities of experimental conditions over time. This study was conducted to evaluate the effects of soil fertility amendments on soil physical and chemical properties and greenhouse gas (GHG) emissions at a long-term continuous wheat soil fertility experiment which was established in 1892 on Oklahoma prairie soils. Samples for analysis of soil chemical and physical properties were collected prior to planting of the 2023 wheat crop while the analyses of some physical properties were performed in situ. Collection of gas samples for GHG analysis was performed within the 17-month study period. Manure application led to higher pH and soil organic matter (SOM) content. Continued phosphorus and potassium applications seemed to cause their accumulation on the surface while nitrogen application led to nitrate leaching all the way to the 45 cm depths. Although there were observed trends in treatment effects on physical properties, most were not statistically different likely be due to the overwhelming tendency of continuous conventional tillage to homogenize soil physical properties. Carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions were influenced by soil temperature and rainfall. Emissions of both GHGs were appreciably higher in the N-applied and the manure-applied treatments. The study showed that long-term continuous fertilizer application influenced GHG emissions, soil physical and chemical properties, as well as the distribution of nutrients in the soil profile.