Growing evidence indicates that climate change has significant impacts on crop production. However, the spatial variability and extent of the impacts on N concentrations in crops have yet to be explicitly described, although N concentration is a critical element of both the nutritional value of food and the planning of appropriate field management procedures. We present multi‐tiered evidence showing that warming increases N concentration in rice and reduces internal N use efficiency (iNUE), thereby increasing N uptake in crops and encouraging greater N fertilizer use. First, we mapped current N concentrations and iNUE for single‐season irrigation paddy rice production in 975 counties across China using data from 1,637 on‐farm experiments and Random Forest regression modeling. Current N concentrations in rice grain and straw have increased with increasing temperatures from northern to southern China. The global meta‐analysis provided further direct evidence that warming increases N concentration in rice. Future warming projections indicate that N concentrations in grain will increase by 5%–9.6% and that iNUE will decrease by 9%–14% under scenarios RCP4.5 and RCP 8.5 although higher CO₂ and other factors may also affect N concentrations. Overall, these data demonstrate that N uptake by rice will need to increase by 7.8%–13.6% to maintain current grain yields across China based on warming alone. Our findings indicate that warming associated with increase in N concentration and reduction in iNUE would be expected to encourage N application, raise the urgency of measures to prevent excessive N application, and stronger counteracting measures need to be enacted.

In China, deep tillage (DT; to >20 cm soil depth) has increased crop yields by improving soil properties, while no-tillage (NT) has been recommended to reduce the labor and machinery costs. Local farmers are willing to adopted rotary tillage (RT; harrowing to 10–15 cm depth) for easy management. However, the effects of these tillage management methods on agronomic productivity, greenhouse gas (GHG) emissions, soil organic carbon (SOC) sequestration, and economic return have not been quantified systematically, and their effectiveness remains in question. Here, we present a meta-analysis of the effects of these methods using 665 paired measurements from 144 peer-reviewed studies. The results indicated that DT significantly increased crop yields by 7.5% relative to RT, and even greater increases were observed in regions with low temperatures and with a wheat cropping system. In contrast, NT resulted in a yield reduction of 3.7% relative to RT, however, controlling for the appropriate temperature and long extension duration (>15 yr) could reduce yield losses and even increase the yield. Both DT and NT significantly enhanced SOC sequestration relative to RT. Adoption of DT would lead to both higher total GHG emissions (N₂O and CH₄) and increased energy costs, while NT reduced GHG emissions. DT management exhibited a positive net profit for all cropping systems; NT decreased the net profit for rice and wheat but increased the profit for maize. Our study highlighted the agronomic, environmental, and economic benefits and trade-offs for the different tillage methods and should enable investors and policymakers to ensure the best tillage management decisions are made depending on the location-specific conditions.

Effective spatial arrangement in maize population can reduce inter-plant competition, promote root development, and enhance nutrient uptake. This study aimed to clarify how planting density and row spacing affect maize growth and yield. A four-year field experiment (2011–2014) was conducted using three planting densities (50,025, 67,500, and 100,050 plants ha⁻¹) combined with two row spacings. Grain yield increased with higher planting density, whereas plant dry weight and nutrient (N, P, K) contents declined. Higher density restricted root growth both vertically and horizontally, particularly in the 0–10 cm soil layer and inner root zone. Narrower row spacing increased grain yield, plant dry weight, and shoot nutrient contents and improved vertical and inner-zone root growth while reducing growth in the outer root zone. At the highest density, these effects were most pronounced in fine roots (<2 mm diameter), with significant increases in root length and surface area in the 0–10 cm layer in both vertical and inner horizontal zones. Overall, higher density intensified root competition and inhibited root development, whereas narrower row spacing alleviated such competition, enhanced nutrient acquisition, and improved crop yield. These results highlight the central role of fine roots in mediating maize responses to planting density and row spacing, suggesting that a moderate planting density (~67,500 plants ha⁻¹) combined with narrower row spacing is optimal for balancing root development and yield.