Calcium-rich vegetables in diet could minimize calcium deficiency and maximize good health and well-being. The aim of the present study was to determine the effect of different levels of foliar application of CaCl2 on lettuce (Lactuca sativa L.) growth and calcium concentrations with the application of organic and conventional fertilizers. Pot experiments were conducted with three calcium levels (60, 120, and 180 mg·L−1 of CaCl2) of an organic fertilizer (3N–0.8P–3.5K) and commercial conventional fertilizer (15N–15P–15K). Calcium in whole oven-ashed samples of shoots was analyzed by atomic absorption spectrometry. Nine lettuce cultivars including butterhead, romaine, and loose-leaf phenotype were tested. These results revealed that the calcium concentration in lettuce significantly increased as calcium levels increased from 60 to 180 mg·L−1. Elevated calcium concentrations in organic and conventional fertilizers increased the concentration of calcium in lettuce from 1.82% at 60 mg·L−1 to a mean of 2.15% at 120 and 180 mg·L−1. The concentration of calcium in the loose-leaf phenotype was 2.17%, 2.47%, and 3.80% higher than that in the butterhead and romaine phenotypes at 60, 120, and 180 mg Ca/L, respectively. Furthermore, the significant difference in calcium concentration among cultivars ranged from 1.27% to 3.05%. ‘Perilla Green’, ‘Breen lettuce’, and ‘Salinas’ had the highest calcium concentrations followed by ‘Jericho lettuce’, ‘Salad Bowl’ and ‘Crisp’, and ‘Kaiser’, whereas ‘Valmaine’ and ‘Rosa Green’ had the lowest calcium concentrations. The present study revealed that selecting fertilizers and cultivars with high calcium concentration can increase the total calcium content of lettuce.
Efficient nitrogen (N) fertilizer management is crucial for ensuring the maximum economic yield and reducing the risk of environmental pollution. The objective of this study was to determine the effect of N fertilizer management on root yield and N uptake of radish in southern China by using 15N isotope tracing. A 2-year field experiment was conducted with three N rates (0, 60, and 120 kg N/ha) and two different application proportions, viz, A [50% at basal, 20% at 15 days after seeding (DAS), 30% at 30 DAS] and B (30% at basal, 20% at 15 DAS, 50% at 30 DAS) for each N rate, which were expressed as N0, N60A, N60B, N120A, and N120B, respectively. The results showed that root yields were significantly increased with N rates increasing from 0 to 120 kg N/ha. The root yields for N120A and N120B were 67.60 t·ha−1 and 72.50 t·ha−1 at harvest, 64.07% and 66.67% higher than those for the treatments of N60A and N60B, respectively. Mean radish recovery of N fertilizer ranged from 25.90% at N120A to 32.60% at N60B, and N fertilizer residual rate in the soil ranged from 11.50% at N120A to 14.90% at N60B. About 17.50% to 35.70% of total uptake of 15N derived from basal fertilizer was absorbed at seeding stage. However, 61.87% to 80.18% of total uptake of 15N derived from topdressing fertilizer absorbed at root expanding stage. Therefore, appropriate nitrogen application with increasing topdressing nitrogen amount could increase root yield of radish and the nitrogen recovery efficiency. Nitrogen fertilizer application recommended was 120 kg N/ha with 30% for basal, 20% for 15 DAS and 50% for 30 DAS in this study.