Pyrolysis temperature effects of tomato stems biochar on leaching dynamics of ammonium, nitrate, and dissolved organic carbon in sandy soil

The study objectives are to examine the effect of doses of tomato stems biochar (TSB) produced at different pyrolysis temperatures (250, 400, and 600 °C) on the leaching of nitrate, ammonium, and dissolved organic carbon, as well as quality indicators of sandy soil. The column experiment was including these treatments; control (no biochar added), 1% TSB250, 2.5% TSB250, 5% TSB250, 1% TSB400, 2.5% TSB400, 5% TSB400, 1% TSB600, 2.5% TSB600, and 5% TSB600. Each plastic column was filled with 1 kg of sandy soil. Tomato stems biochar was applied at three doses (1%, 2.5%, and 5% w/w). Soil available nitrogen increased significantly relative to the control treatment by 9.50%, 31.69%, 46.71%, 69.07%, 15.24%, 37.43%, and 75.57% under applying 1% TSB250, 1% TSB400, 2.5% TSB400, 5% TSB400, 1% TSB600, 2.5% TSB600, and 5% TSB600 treatments, respectively. Results showed significant decreases in cumulative leached ammonium over the control treatment by 20.77%, 27.04%, 37.09%, 34.04%, 40.43%, 48.61%, 18.26%, 25.26%, and 32.94% for 1% TSB250, 2.5% TSB250, 5% TSB250, 1% TSB400, 2.5% TSB400, 5% TSB400, 1% TSB600, 2.5% TSB600, and 5% TSB600 treatments, respectively. The amount of cumulative leached nitrate decreased significantly relative to the control treatment by 8.27%, 8.56%, 8.91%, 8.61%, 8.42%, 8.66%, 28.37%, 31.63%, and 34.40% for 1% TSB250, 2.5% TSB250, 5% TSB250, 1% TSB400, 2.5% TSB400, 5% TSB400, 1% TSB600, 2.5% TSB600, and 5% TSB600 treatments, respectively. The effectiveness of biochar treatments in reducing the cumulative leaching of ammonium decreased in the order TSB400 > TSB250 > TSB600. However, the effectiveness of biochar treatments on the cumulative leaching nitrate was in the order of TSB600 > TSB400 ≈ TSB250. Applying TSB at all pyrolysis temperatures and levels in sandy soil led to a significant increase in the cumulative leaching of dissolved organic carbon compared to the control treatment. Utilizing tomato stems biochar as a soil amendment is a promising strategy for significantly enhancing the quality indicators of sandy soil and reducing the leaching of ammonium and nitrate. This would reduce the loss of nitrogen fertilizers added to the soil and preserve groundwater from pollution.