Nano calcium carbonate improves wheat nitrogen accumulation and grain yield by enhancing soil nitrogen supply and flag leaf photosynthetic characteristics

Over-application of chemical fertilizers to attain optimal crop yields has resulted in an environmental issue of global concern. To mitigate this, reducing nitrogen (N) application and enhancing fertilizer use efficiency is crucial, and nano-fertilizers offer a promising solution. However, there is a paucity of studies examining the use of nano-fertilizers in fields. This study aimed to assess the impact of different dosages of nano calcium carbonate (NCC) mixed with compound fertilizer (CF) on soil N supply, enzyme activity, microbial ecology, as well as photosynthetic characteristics, N accumulation and yield of wheat plants. The effects were examined through a soil column leaching experiment and a two-year field experiment conducted from 2020 to 2022. Five treatment groups were established, namely CK (CF), T1 (CF + 0.15% NCC), T2 (CF + 0.30% NCC), T3 (CF + 0.45% NCC), and T4 (CF + 0.60% NCC), to determine the optimal ratio of NCC to CF. All NCC treatments resulted in reduced leaching of soluble N. Nevertheless, the 0.45% and 0.60% NCC treatments (T3 and T4) posed a risk of migration through water runoff, leading to nutrient losses. The simultaneous application of NCC and CF increased the content of soil nitrate N (NO3--N), as well as the activity levels of urease and protease during the anthesis stage. Additionally, it elevated the abundance of various microbial communities, including Actinobacteria, Acidobacteria, Chloroflexi, Cyanobacteria, and Nitrospirae. NCC application reduced the content of Na+/K+ and malondialdehyde (MDA), while elevating the activities of flag leaf superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), nitrate reductase (NR), and glutamine synthetase (GS). Additionally, it increased stomatal conductance (Gs) and net photosynthetic rate (Pn). The 0.30% NCC treatment showed significantly higher N accumulation in the stem, leaf, and spike compared to CK at the maturity stage. Moreover, 0.30% NCC treatment exhibited a significant increase in the number of grains per spike and higher yields compared to CK. In particular, 0.30% and 0.45% NCC treatments accomplished yield boosts of 29.6–34.7% and 19.9–26.0%, respectively. NCC enhanced wheat plant N accumulation and yield through regulation of N release rate and increased soil N content, enzyme activity, and microbial community diversity and abundance. Additionally, NCC boosted flag leaf photosynthesis rate during the anthesis to maturity stage of wheat. This research highlights the potential of NCC to improve wheat crop production. And 0.30% NCC is the optimal application concentration for NCC.