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Xinjuan Chen, Zhujun Zhu, Joska Gerendás and Nadine Zimmermann

Brassica campestris vegetables play an important role in the Chinese diet. The objective of this study was to evaluate the composition and content of glucosinolates (GSs) in five species of Chinese Brassica campestris vegetables by high-performance liquid chromatography. The compositions and contents of GSs varied significantly among and within species and cultivars. The contents of total GSs were 100 to 130 mg/100 g fresh weight (FW) in turnip (B. rapifera), 50 to 70 mg/100 g FW in purple cai-tai (B. chinensis var. purpurea), and 14 to 35 mg/100 g FW in Chinese cabbage (B. pekinensis), choysum (B. chinensis var. utilis), and pakchoi (B. chinensis var. communis). In Chinese cabbage, the predominant individual GSs were glucobrassicin for both cultivars, neoglucobrassicin only for ‘zaoshuwuhao’, and gluconapin only for ‘zaoshuwuhao’. The predominant individual GSs were glucobrassicanapin and gluconapin in purple cai-tai and choysum and gluconapin in pakchoi and turnip. The relative content of total aliphatic GSs was 80% to 90% in purple cai-tai and choysum, 60% to 65% in pakchoi and turnip, and 17% to 50% in Chinese cabbage. The relative content of total indolic GSs was 37% to 75% in Chinese cabbage, 25% to 27% in pakchoi, and 5% to 17% in purple caitai, choysum, and turnip. The relative content of aromatic GSs was 28% to 36% in turnip, 8% to 14% in Chinese cabbage and pakchoi, and 2% to 4% in choysum and purple cai-tai. These results suggest that there are significant genotypic variations in composition and content of glucosinolates in Chinese Brassica campestris vegetables.

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Shichao Wang, Xinlu Bai, Jianbin Zhou and Zhujun Chen

Overapplication of nutrients and water is common in intensive greenhouse systems. A 2-year experiment (2011–13) was conducted to study the effect of different nutrient and water treatments on the growth and yield of tomato (Lycopersicum esculentum Mill.) and on soil nutrient accumulations in solar greenhouses in South Loess Plateau, China. The treatments included 1) current fertilizer and water practices (FW), 2) formula fertilizer and water 1 (FW1), 3) formula fertilizer and water 2 (FW2), and 4) farmer’s practice (FP). Compared with FW, FW1 and FW2 had yields not significantly different from grower control treatments; however, they saved 35% to 46% of the nitrogen (N) fertilizer, 40% to 54% of the phosphorus (P2O5) fertilizer, 19% to 35% of the potassium (K2O) fertilizer, and 15% to 21% of irrigation water. The economic profits of FW1 and FW2 were greater than those of the FW and FP treatments. The two formula treatments also reduced soil electrical conductivity (EC) and the accumulation of nitrate, available P, and available K in soil. However, the soil nutrients are still above optimal levels. Obvious N surplus in the greenhouse was observed in different treatments, mainly because of high N input from manures. This study revealed there is great potential to reduce nutrient and water use while maintaining the same yield in a greenhouse system.

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Shichao Wang, Zhujun Chen, Jun Man and Jianbin Zhou

In China, greenhouse soils often receive large rates of different manures and have a high content of soil organic matter (SOM). Understanding changes in nitrogen (N) mineralization in soils of newly built greenhouses after their construction is important for managing N. Soil samples were obtained from solar greenhouses of different ages (0, 1, 2, and 3 years) located in the south edge of the Loess Plateau, China, at 0- to 20- and 20- to 40-cm depth. N mineralization in the soils was measured with the Stanford and Smith long-term aerobic incubation method over 30 weeks. SOM, total N, and the mineralized N in the 0- to 20-cm and 20- to 40-cm soil layers were significantly increased in the older greenhouses. The cumulative mineralized N in the 0- to 20-cm soil layer in different cultivation years was increased in each year since the greenhouses were established. For the greenhouses with the same age, the cumulative mineralized N in the 0- to 20-cm soil layer was greater than that in the 20- to 40-cm layer. The potentially mineralizable N (N0) both in the 0- to 20-cm and the 20- to 40-cm soil layers increased with the greenhouses’ age. Regression analysis indicated that when SOM increased 1 g·kg−1, N0 in the 0- to 20-cm and 20- to 40-cm depth increased 22.6 and 8.4 mg·kg−1, respectively. Therefore, as the N supply in soil increases with the age of the solar greenhouse, we suggest that the application rates of manure and synthetic fertilizer be reduced.

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Huixia Li, Zhujun Chen, Ting Zhou, Yan Liu, Sajjad Raza and Jianbin Zhou

The interaction between potassium (K) and magnesium (Mg) in plants has been intensively studied. However, the responses of different tomato (Solanum lycopersicum L.) cultivars to high K levels at low temperatures remained unclear. Herein, a complete randomized hydroponic experiment was conducted to evaluate the effects of temperature (25 °C day/18 °C night vs. 15 °C day/8 °C night) and K concentrations (156 mg·L−1 vs. 468 mg·L−1) on the growth and Mg nutrition of tomato cultivars Gailiangmaofen (MF) and Jinpeng No. 1 (JP). Compared with the control temperature (25 °C day/18 °C night), the low temperature decreased total biomass, shoot biomass, and Mg uptake in shoot by 17.3%, 24.1%, and 11.8%, respectively; however, the root/shoot ratio was increased. High K had no significant effect on plant growth or biomass compared with the control K concentration (156 mg·L−1); however, Mg concentrations and uptake in shoot were significantly lower under high-K treatment. Significant difference was observed for K uptake, but not for Mg uptake, between the two cultivars. There was no significant interaction between temperature and high K on Mg uptake of tomato, so a combined stress of low temperature and high K further inhibited Mg uptake and transport. Low temperature and high K increased the risk of Mg deficiency in tomato.