Oilseed rape (Brassica napus L.) is a crucial source of edible oil and livestock feeding, and is a promising biofuel crop. The increasing demand for oilseed rape requires strategies to increase yield while retaining quality. Field experiments were performed in southern China to evaluate the impacts of fertiliser level and planting density on dry matter accumulation, seed oil and protein content (%) and yield (per ha), oil quality, and the profitability of oilseed rape. Fertiliser treatments contained nitrogen (N), phosphorus (P), potassium (K), sulfur (S) and boron (B) at four increasing rates, compared with nil fertiliser, and there were six planting densities (range 7.5–45 × 104 plants ha–1). Dry matter accumulation significantly (P < 0.05) increased in response to increasing plant population and fertiliser level, whereas harvest index decreased, suggesting that increasing the production of oilseed rape is limited to improvement of population quality. Seed oil and protein contents were significantly affected by fertiliser level rather than planting density. Increasing the fertiliser rate increased seed protein content, simultaneously slightly decreasing oil content. Glucosinolate content of rapeseed slightly decreased with increasing fertiliser but erucic and oleic acid contents were not affected, indicating that increasing the fertiliser rate might not reduce oilseed rape quality. Manipulation of fertiliser level was more effective than altering planting density for increasing seed oil and protein yields. Highest seed oil and protein yields resulted from the highest fertiliser application of 240 kg N, 52.4 kg P, 174.3 kg K, 15 kg S and 1.2 kg B ha–1, under a planting density of 22.5 × 104 plants ha–1. Maximum economic gain occurred with the two highest fertiliser levels, whereas planting density has no significant effect on profitability. A balanced application of NPKSB fertilisers should be employed with direct-sowing cultivation of oilseed rape, aimed at building a suitable population structure that balances plant population density and individual growth.

Rapeseed (Brassica napus L.) is a major oil crop in China, with the world’s largest planted area and total yield. Rapeseed has a high demand for nitrogen (N), and nitrogen deficiency in soil is an important limiting factor for rapeseed production. However, rapeseed responds to N deprivation by regulating its own morphology, structure, and physiology. We carried out the current experiment by utilizing low N (LN: 0.3 mM NO₃⁻) and normal N (CK: 6.0 mM NO₃⁻) treatments using Brassica napus as the experimental material. The study results showed that low N induced root elongation in rapeseed, and the root length of LN treatment was 2.37 times that of HN treatment. The dry matter of roots also significantly increased due to low N treatment. Meanwhile, low N treatment decreased photosynthetic pigment (including chlorophyll a, chlorophyll b, and carotenoids) contents and dry mass accumulation of leaves. A higher root/shoot ratio and N physiological efficiency were observed under low N treatment. The changes in cell wall components (pectin, cellulose, hemicellulose, and lignin), related enzymes, and genes’ transcription levels in roots were determined and the results suggested that low N promoted the demethylation of ion-bound pectin (ISP) and covalently bound pectin (CSP), the content of CSP and cellulose. The promoted pectin methylesterase (PME) activity, inhibited pectin and cellulose degradation enzymes, and up/downregulation of related genes also confirming the results of cell wall components. The low N-increased demethylation degree of pectin and content of pectin and cellulose in cell walls was conducive to cell wall loosening and cell wall synthesis during cell division and elongation, ultimately promoting root-adaptive elongation. The study revealed a possible mechanism in which the alteration of cell wall component content and structure participates in cell elongation and expansion, which directly induces root elongation under N deficiency. The successful implementation of this research may be conducive to facilitating the development of rapeseed cultivars with high N use efficiency through root-based genetic improvements and improving plant adaptability to low N.

Environmental acclimation ability plays a key role in plant growth, although the mechanism remains unclear. Here, we determined the involvement of Arabidopsis thaliana PLANT DEFENSIN 1 gene AtPDF1.5 in the adaptation to low nitrogen (LN) levels and cadmium (Cd) stress. Histochemical analysis revealed that AtPDF1.5 was mainly expressed in the nodes and carpopodium and was significantly induced in plants exposed to LN conditions and Cd stress. Subcellular localization analysis revealed that AtPDF1.5 was cell wall- and cytoplasm-localized. AtPDF1.5 overexpression significantly enhanced adaptation to LN and Cd stress and enhanced the distribution of metallic elements. The functional disruption of AtPDF1.5 reduced adaptations to LN and Cd stress and impaired metal distribution. Under LN conditions, the nitrate transporter AtNRT1.5 expression was upregulated. Nitrate transporter AtNRT1.8 expression was downregulated when AtPDF1.5 was overexpressed, resulting in enhanced transport of NO₃⁻ to shoots. In response to Cd treatment, AtPDF1.5 regulated the expression of metal transporter genes AtHMP07, AtNRAMP4, AtNRAMP1, and AtHIPP3, resulting in higher Cd accumulation in the shoots. We conclude that AtPDF1.5 is involved in the processing or transmission of signal substances and plays an important role in the remediation of Cd pollution and LN adaptation.

Nitrogen fertilization and planting density are two key factors that influence the yield of rice. Reducing nitrogen fertilizer input and increasing planting density will help to improve nitrogen use efficiency and stabilize yield. Field and ¹⁵N tracer method in plot experiments were conducted to study the trends of yield, nitrogen use efficiency (NUE) and nitrogen transfer of hybrid rice and conventional rice under dense planting with a reduced nitrogen rate (DPRN) and sparse planting with a high nitrogen rate (SPHN). Among the nitrogen in rice plants, the proportion of nitrogen from fertilizer under the DPRN was reduced by 1.8–13%. The late-season rice (LSR) had a higher rate of decrease compared with the early-season rice (ESR). The uptake efficiency of nitrogen fertilizer was significantly higher under the DPRN than that under the SPHN, with an increase of 7.7–21.9%. The accumulated nitrogen and translocated ratio under the DPRN before the heading stage were 6.1–10.8% and 2.0–9.6% higher than those under the SPHN, respectively. The yield did not change under different treatments. Those findings suggest that the DPRN could guarantee a stabilized yield while increasing the NUE and the amount of translocated nitrogen in the double-cropped rice system.

Under the current rice cropping system, excessive nitrogen application has become a major issue that needs to be changed, and nitrogen reduction has become a hot research topic in recent years. The use of optimum planting density is becoming a common agronomic management system in addition to nitrogen reduction, especially under double cropping rice systems. In this paper, changes in rice yield, nitrogen-use efficiency (NUE) and net N mineralization under dense planting with a reduced nitrogen rate (DPRN) were studied. By comparing DPRN with high-nitrogen sparse planting (SPHN), we found that the population tiller number (tiller number per unit area) increased by 9–27% under DPRN cultivation. Nitrogen accumulation under DPRN treatment of double-cropped rice was basically stable. NUE under DPRN was significantly higher by 1.3–22.7% compared to SPHN. The partial factor productivity of applied N (PFP_N) was significantly higher than that of SPHN, with an increase of 4.3–22.8%. The net N mineralized of double-cropped rice under DPRN increased at different stages, and the increase in late-season rice (LSR) was greater than that of early-season rice (ESR). The highest net N mineralized in double cropping rice at different stages was found in the dense planting treatment (DP) and N₂ (120 kg N h⁻¹). In conclusion, DPRN cultivation of double-cropped rice could be accepted as a proper management strategy for reducing nitrogen input, improving NUE and promoting soil nitrogen mineralization under given conditions.