Biochar enhances nut quality of Torreya grandis and soil fertility under simulated nitrogen deposition

•Additional N deposition increased nut quality, but caused soil acidification and decreased soil fertility.•Biochar application showed acid neutralization with increased soil pH.•Biochar strongly interacted with N addition by increasing both nut quality and soil fertility.

Torreya grandis, an economically important nut tree in Southeast China, is being subjected to increasing atmospheric nitrogen (N) deposition, and thus far its impact on nut quality remains unknown. Also, studies evaluating nut quality response to biochar application (commonly used as soil amendment) to soils under N deposition conditions are rare. Here, we investigated changes of nut physical characteristics (i.e., nut weight, length and width and kernel weight) and nut nutritional components (i.e., lipid, protein, starch and total soluble sugars) under a factorial combination of biochar application (0, 20 t ha−1) and simulated additional nitrogen deposition (0, 30 and 60 kg N ha−1 yr−1) treatments in a growing season (approximately 7 months). Results showed that N addition had a direct fertilizing effect, with a significant increase of nut weight, nut size, kernel weight, and nut nutritional components in terms of lipid, protein, starch and total soluble sugars. However, soil chemical properties were negatively affected by N addition with significant decreases in soil pH and available N, P and K. Biochar application showed a liming effect, with a significant increase of soil pH which was significantly correlated with nut weight and the main nut nutritional components. Additionally, biochar strongly interacted with additional N deposition by increasing the availability of N, P and K in soil. Our study suggested, for the first time, that the 'win-win' can be achieved, both nut quality of T. grandis and soil fertility can be improved by biochar application to soils suffering from N deposition. Results are relevant for the successful improvement of nut crop quality and development of sustainable agriculture under accelerated N deposition worldwide.