Context: Maize plays a crucial role in global food security, while extensive use of nitrogen (N) fertilizers in maize production has posed severe environmental risks. The challenge of optimizing N fertilizer applications to obtain high maize yield, high NUE and low N losses has received considerable attention but lacks evidence from longterm field experiments. Objective: This study aims to quantify the influences of long-term continuous N applications on soil mineral N (SMN) and their subsequent effects on root growth, aboveground biomass accumulation, yield formation, and environmental benefits of maize, and determine the optimal N rate that ensures sustained high maize yield and environmental sustainability over the long-term. Methods: A winter wheat-summer maize double cropping system was established in the North China Plain (NCP) in 2010. This included five continuous N fertilizer treatments during the maize season, comprising 0, 75, 150, 225 and 300 kg N ha-1, which were denoted as N0, N75, N150, N225 and N300 in the study. Results: Increasing N rates resulted in higher N surpluses and SMN, leading to much higher aboveground biomass and maize yield, but also caused reduced NUE over the 12-year period. Specifically, the mean maize yield was 6.7, 8.8, 9.9, 10.4 and 10.1 Mg ha-1 for the N0-N300 treatments during 2011-2022, respectively. The low yield in the N0 treatment was mainly because long-term zero N inputs led to low SMN thus restricting roots growth, aboveground biomass accumulation and yield formation. In contrast, high SMN inhibited roots distribution, which subsequently negatively influenced post-silking dry matter remobilization and yield and thus caused a much lower harvest index (HI) in the N300 treatment. Effects of N fertilizer on maize yield intensified along with increasing experimental duration, thus requiring more N to achieve high yields in the latter years. The optimal N rates showed a strong positive correlation with the annual maximum yields over the experimental period, averaging 153 kg N ha-1 in achieving high yield, high NUE and low surplus. Conclusions: Our findings demonstrated that the prolonged low N input could result in soil depletion, limiting maize growth and thereby compromising yield sustainability. Conversely, excessive N application led to SMN accumulation and higher N loss risks. The optimal N rate is 153 kg N ha-1 that can obtain long-term high maize yield stability while minimizing environmental costs in the NCP. Implications: Our long-term experimental results provide robust evidence for optimizing N fertilizer applications in achieving high yield and high NUE with low N surplus in maize production in the wheat-maize double cropping in the NCP and similar cropping systems worldwide.

The optimization of nitrogen (N) fertilization has become an ever more important global challenge with the aim of achieving high crop yields and high N use efficiency (NUE) with low environmental risks. The North China Plain (NCP) is China's most important wheat (Triticum aestivum Linn.) production region, and a global hotspot for N fertilizer use. How much nitrogen can be saved compared to the farmers' level that would not influence wheat yield, and lead to high NUE with low N surplus? It is still challenging as there are not enough evidences from the long-term experiments. Thus, continuous detailed observations from an ongoing long-term experiment in the NCP since 2010 with five N rates, namely 0 (N0), 60 (N60), 120 (N120), 180 (N180) and 240 (N240) kg N ha-1, were included in the study. Our results indicated that stable high wheat yield cannot be achieved without enough N inputs from the long-term, because of severely depleted N pool in the N0 and N60 treatments seriously influenced root growth and wheat development thus damaged wheat yield. Though highest wheat yield was obtained in the N240 treatment, the high N rate caused lowest NUE and largest N surplus with high soil mineral N (SMN) with the mean value of 143 kg N ha-1 at the 0-60 cm layer at harvest. Besides, both root weight density (RWD) and root length density (RLD) were much lower in the N240 treatment compared to that in the N180 treatment. Our integrative analyses clearly indicate that the optimal N application for achieving high yield, high NUE and low environmental risks in wheat production was 180 kg N ha-1 based on long-term observations. Our results should be beneficial for promoting sustainable wheat production in the NCP and similar regions with wheat-based double cropping over the world.

Context: The North China Plain (NCP) is China's largest peanut producing area, where winter-wheat summer peanut is an important double cropping system. Excessive nitrogen (N) applications are widely used leading to declined N use efficiency (NUE) and biological N fixation (BNF). However, the influence of excessive fertilizer N inputs on yield and BNF of summer-peanut remains uncertain.Objective: The study aims to evaluate the impacts of different fertilizer N inputs on yield and BNF of summer peanut in the NCP, and explore the optimal N rates for achieving high NUE and low N losses without sacrificing yield. Methods: A three-year field experiment and pot experiment involving five N treatments (N rates with 0, 50, 100, 150, and 200 kg N ha-1, defined as N0, N50, N100, N150 and N200 in the study, respectively) were conducted in the NCP. The jointing use of field experiment and pot experiment were adopted to measure BNF of summer peanut, and the partial least squares path model and a nightingale rose diagram were both included in the study.Results: Summer-peanut yield increased quadratically with increasing N application, but N rates larger than 150 kg N ha-1 caused inadequate seed filling and thus led to slightly reduced yield. Generally, increased N applications significantly increased soil mineral N (SMN) between 0 and 60 cm depth, and dramatically reduced BNF as high SMN strongly inhibits biological nitrogenase activity.Conclusions: The N application required to obtain an optimum yield of 3915 kg ha-1 with relatively high NUEoi (the ratio of N output and N input, 73.0%) and low N losses in the summer-peanut production was 150 kg N ha-1 in the NCP.Implications: The sustainable development of summer-peanut systems will involve reduced N application rates, and N optimization in the winter-wheat summer-peanut rotation should receive further attention considering the N legacy effects.

Enhancing soil organic carbon (SOC) while concurrently reducing greenhouse gas (GHG) emissions and without compromising yield is a contemporary challenge for many agricultural sectors across the globe. In China, resolving the "carbon-food" nexus is a key pillar of government policies aimed at constraining "Carbon Peak" and delivering "Carbon Neutrality". The present study explores the potential to increase SOC stocks while reducing GHGs emissions, without sacrificing crop yields considering crop rotation optimization under different irrigation managements in the North China Plain (NCP) based on a 6-year experiment. We found higher crop yields for the irrigated treatments compared with the rainfed treatments, demonstrating that rainfed crops were constrained by water deficit stress in the region. Yield was highest in the winter wheat-summer maize rotation (WM), followed by yields of the winter wheat-summer soybean (WS), while the average yields of winter wheat-summer maize -spring maize (WMMs) were lowest. SOC stocks in the surface soil (0-20 cm) increased for the irrigated treat-ments, but soil carbon sequestration (i.e. the rate of SOC stocks change over time) for the rainfed treatments decreased for all treatments. SOC stocks for WMMs was greatest of all treatments, leading to the highest carbon sustainability index (CSI) for this treatment. Nitrous oxide (N2O) emissions were 23-57% higher in the irrigated treatments than the rainfed treatments for the three rotations, which was highest in WMMs and lowest in WS. Carbon footprints (CFs) were highest in WS and lowest in WMMs. Overall, we found that increasing SOC stocks reduced CFs and increased yield. WMMs with irrigation was the most effective treatment for promoting SOC sequestration and mitigating GHG emissions with relatively high yield in this study, suggesting that crop rota-tions that are (1) more intensive and (2) grow more aboveground biomass are more likely to promulgate lower CFs and contribute towards national emissions abatement targets, such as those aimed at Net Zero.

Achieving a pathway for green development is a critically important challenge for agriculture in China and beyond. The current study evaluates the effects of a range of management interventions including planting, fertilizer nitrogen (N) rate optimization and increasing farm size to promote agricultural green development across the North China Plain (NCP) based on large-scale farm surveys. Our results showed that the mean annual N fertilizer rate for wheat-soybean rotation was much lower than that of wheat-maize and wheat-peanut. Interestingly, our study indicated strong pre-crop effects of summer soybean (Glycine max (Linn.) Merr.) on the following winter wheat (Triticum aestivum Linn.) in N saving compared to summer maize (Zea mays Linn.) and summer peanuts (Arachis hypogaea Linn.), the low N rate for summer soybean and its 'legume' carryover effects led to the low N rate, N surplus and N footprint, and high N use efficiency (NUE) in wheat-soybean. The survey results showed that the optimal N rates for achieving maximum yield of summer maize, summer peanuts and winter wheat were 229, 249 and 236-260 kg ha(-1) across the NCP, respectively. Moreover, better N management is beneficial for reducing the N surplus and leads to higher NUE and lower N footprint. Generally, large farms applied less N fertilizer than small farms, thus leading to a lower N surplus and higher N partial factor productivity with the same yield level. Here we show for the first time that the combinations of crop rotation design, optimizing N rate application and increasing farm size are very efficient in reducing N fertilizer applications and the N footprint with stable crop yields. N management should play a more important role in agricultural green development across the NCP and similar regions around the world.