[Effects of Returning Nitrogen by Biochar Loading on Paddy Growth, Root Morphology, and Nitrogen Use Efficiency].

Building a nutrient channel between eutrophic water and agricultural fields could reduce nutrient input into fields and alleviate eutrophication by returning nitrogen. In order to determine the feasibility of returning nitrogen by biochar loading, a rhizobox experiment was conducted with two nitrogen applied methods, namely SN (applied nitrogen by nitrogen fertilizer solution) and BN (applied nitrogen by nitrogen-loaded biochar). The results showed that BN, in comparison with SN, decreased the biomass and nitrogen uptake of the aboveground paddy by 16% and 14%, respectively, increased biomass root-shoot ratios by 25%-27%, and reduced nitrogen recovery use efficiency. Two nitrogen application methods affected the length and volume of paddy adventitious roots. Paddy underground biomass and nitrogen uptake were positively correlated with soil ammonium content, whereas paddy aboveground nitrogen uptake was negatively correlated with root tips. It was suggested that the paddy biomass and nitrogen uptake would be influenced when nitrogen was applied solely by nitrogen-loaded biochar. However, no affinity and no significance in nitrogen use efficiency were found for plant uptake between chemical nitrogen and biochar-loaded nitrogen. Additionally, biochar promoted soil mineral nitrogen content for further plant uptake. Therefore, biochar could be used as the carrier for returning nitrogen from waterbodies to fields. The replacement rate of chemical nitrogen fertilizer is the key to influencing plant growth and needs future study.

[Influence of Calcium Carbonate and Biochar Addition on Soil Nitrogen Retention in Acidified Vegetable Soil].

In Taihu Lake region, more and more paddy fields are being converted to vegetable fields, which cause serious soil acidification and decreased soil nitrogen retention. In this study, calcium carbonate and biochar were used as acidification amendments to test their ability on soil acidification remediation and soil nitrogen retention improvement. Calcium carbonate and biochar addition rates were determined by pH buffering curves. An incubation experiment with and without nitrogen fertilization and multi-leaching simulation tests were conducted. The soil nitrogen mineralization rate, dynamics of the nitrogen content in soils and leachates, and soil pH were measured. The results showed that 3.92×10-2 mol·kg-1 calcium carbonate and 27.73 g·kg-1 biochar should be added into the tested acidified vegetable soil to recover the original pH value. Without nitrogen fertilization, the addition of calcium carbonate increased the soil nitrogen mineralization rate by 37% but had no significant effect on mineral nitrogen content. However, biochar addition significantly improved the soil nitrogen mineralization rate by 35%-44% and nitrate content by 42%-58%. Nitrogen leaching loss was cut down by 42%-57% in biochar addition treatment because of the lower leachate volume and nitrogen concentration, while calcium carbonate addition increased nitrogen leaching loss by 12%-76% because of the higher leachate nitrogen concentration. After leaching, the soil pH decreased for all the treatments. The soil pH change was the lowest for calcium carbonate addition treatment under no nitrogen fertilization and the lowest for biochar addition treatment under nitrogen fertilization. This result suggests that calcium carbonate is more applicable for seriously acidified soils which are fallowed and biochar is more suitable for the intensified vegetable fields because it can improve the soil nitrogen retention and soil pH, and reduce the nitrogen leaching loss.