Plant population density (PPD) and nitrogen (N) application rate (NAR) are two controllable factors in cotton production. We conducted field experiments to investigate the effects of PPD, NAR and their interaction (PPD × NAR) on yield, N uptake and N use efficiency (NUE) of cotton using a split-plot design in the North China Plain during 2013 and 2014. The main plots were PPDs (plants m⁻²) of 3.00 (low), 5.25 (medium) and 7.50 (high) and the subplots were NARs of 0 (N-free), 112.5 (low), 225.0 (moderate) and 337.5 (high). During both 2013 and 2014, biological yield and N uptake of cotton increased significantly, but harvesting index decreased significantly with NAR and PPD increasing. With NAR increasing, internal nitrogen use efficiency(NUE) decreased significantly under three PPDs and agronomical NUE, physiologilal NUE, nitrogen recovery efficiency(NRE) and partial factor productivity from applied nitrogen (PFPN) also decreased significantly under high PPD between two years. Lint yield increment varied during different PPDs and years, but NAR enhancement showed less function under higher PPD than lower PPD in general. Taken together, moderate NAR under medium PPD combined higher lint yield with higher agronomic NUE, physiological NUE, and NRE, while low NAR with high PPD would achieve a comparable yield with superior NRE and PFPN and high NAR under high PPD and medium PPD produced higher biological yield but lower harvest index, lint yield and NUE compared to moderate NAR with medium PPD. Our overall results indicated that, in this region, increasing PPD and decreasing NAR properly would enhance both lint yield and NUE of cotton.

Background: Long-term rotary tillage has led to the deterioration of cotton production in northern China. This deterioration is due to the disturbance of topsoil, a dense plough pan at the 20–50 cm depth, and the decreased water storage capacity. A 2-yr field experiment was performed from 2014 to 2015 to explore a feasible soil tillage approach to halting the deterioration. The experiment consisted of four treatments: replacing the topsoil from the 0–15 cm layer with the subsoil from the 15–30 cm layer (T1); replacing the topsoil from the 0–20 cm layer with the subsoil from the 20–40 cm layer and subsoiling at the 40–55 cm layer (T2); replacing the topsoil from the 0–20 cm layer with the subsoil from the 20–40 cm layer and subsoiling at the 40–70 cm layer (T3); and conventional surface rotary tillage within 15 cm as the control (CK). Results: The results indicated that the soil bulk densities at the 20–40 cm layer in T2 were 0.13 g·cm^− 3 and 0.15 g·cm^− 3 lower than those obtained from CK in 2014 and 2015, respectively. The total nitrogen (N) and the available phosphorus (P) and potassium (K) contents from the 20–40 cm layer in T2 and T3 were significantly higher than those in CK and T1. The amount of soil water stored in the 0–40 cm layer of T2 at the squaring stage of cotton was 15.3 mm and 13.4 mm greater than that in CK in 2014 and 2015, respectively, when the weather was dry. Compared with CK, T2 increased cotton lint yield by 6.1 and 10.2 percentage points in 2014 and 2015, respectively, which was due to the improved roots within the 20–60 cm layer, the greater number of bolls per plant and the higher boll weight in the T2 treatment. Conclusions: The results suggested that soil replacement plus subsoiling would be a good alternative to current practices in order to break through the bottleneck constraining cotton production in northern China. Replacing the topsoil in the 0–20 cm layer with the soil from the 20–40 cm layer plus subsoiling at the 40–55 cm layer would be the most effective method.

Background: The one-time combined application of conventional urea (U) with controlled-release urea (CRU), manure (M), or nitrification inhibitors (NIs) offers sustainable nitrogen (N) management options. However, their comparative performance under equivalent N inputs remains unclear. We conducted a two-year micro-plot field experiment to evaluate their effects on cotton yield, yield stability, nitrogen use efficiency (NUE), and soil mineral nitrogen (N _min ) dynamics. Treatments included a control (CK, no N) and four iso-N strategies: U (conventionally split-applied, with 40% applied basally and 60% at the first flowering), U + CRU (30% U + 70% CRU, one-time basal application), U + M (70% U + 30% M, one-time basal application), and U + NI (one-time basal application). Results: Both the U + CRU and U + M treatments increased shoot biomass by 53%–155% relative to the CK treatment. The highest biomass was observed in the U + M treatment in 2020 and in the U + CRU treatment in 2021. Under heavy rainfall in 2021, U + CRU enhanced N uptake in reproductive organs by 31.9%–56.1% compared with other treatments, suggesting greater resilience to high-precipitation conditions. Although U + CRU and U + M performed similarly in 2020, U + CRU outperformed all other treatments in 2021, increasing yield by 6.7%–42.3%, largely through a higher boll number, and exhibiting greater yield stability across both years. Soil data revealed consistently higher N _min from flowering to boll opening under U + CRU, consistent with increased shoot N uptake and biomass. In contrast, residual N _min in the 0–0.6 m soil layer was 10.4%–24.0% lower under U + CRU across both years, indicating a reduced risk of N loss. U + CRU achieved the highest NUE in 2021, exceeding that of other treatments by 43.4%–74.6%. Conclusions: Overall, at the evaluated N application rate, the one-time basal application of U with CRU (30% U + 70% CRU) synchronized N supply with crop demand, thereby improving yield and yield stability while reducing residual soil N _min . This strategy represents a potential climate-resilient approach for sustainable cotton production under high-precipitation conditions.