Abstract
The utilization of biochar's as soil amendments for enhancing nutrient retention in subsoils present potential limitations. To address this issue, we conducted a greenhouse experiment to assess the effects of various biochar's derived from animal manures (swine manure, poultry litter, cattle manure) and plant residues (rice straw, soybean straw, corn straw) when applied to surface of an acidic soil. Our study focused on wheat crops under a no-tillage system, with a subsequent evaluation of the residual impacts on soybeans. The experimental design involved the application of biochar's at different rates i.e. 10 and 20 Mg ha-1, followed by the assessment of their influence on NPK levels, pH, and exchangeable Al in stratified soil layers (0-5, 5-10, 10-15, and 15-25 cm). Furthermore, we investigated the interplay between biochar doses and the application of nitrogen (N) in the top 5 cm of soil, specifically examining NO-3<math><msubsup><mtext>NO</mtext> <mrow><mn>3</mn></mrow> <mo>-</mo></msubsup> </math> , NH+4<math><msubsup><mtext>NH</mtext> <mrow><mn>4</mn></mrow> <mo>+</mo></msubsup> </math> , P and K levels. Our findings revealed that in the top 5 cm of soil, biochar doses and N application significantly affected NO-3<math><msubsup><mtext>NO</mtext> <mrow><mn>3</mn></mrow> <mo>-</mo></msubsup> </math> , NH+4<math><msubsup><mtext>NH</mtext> <mrow><mn>4</mn></mrow> <mo>+</mo></msubsup> </math> , P and K concentrations. However, in deeper soil layers, no significant differences were observed among biochar doses with or without N application. Interestingly, K levels were impacted throughout all soil depths, regardless of the presence or absence of N application. Moreover, biochar application up to a 5 cm depth induced favorable changes in soil pH and reduced exchangeable Al. In contrast, deeper layers experienced a decrease in soil pH and an increase in exchangeable Al following biochar treatment. In conclusion, our study demonstrates that biochar's can effectively retain NPK nutrients, enhance soil pH, and decrease exchangeable Al, independent of the type and dosage of application under a no-tillage system. Nonetheless, the efficacy of biochar amendments may vary with soil depth and type of nutrient, warranting careful consideration for maximizing their benefits in sustainable agricultural practices.