Xiangmin Rong

Tobacco readily accumulates cadmium (Cd), an unnecessary and poisonous element. A total of 107 soil and tobacco leaf samples were collected from South China, to clarify the quantitative relationship between soil properties and Cd content in tobacco leaves. The results showed that 86.9% of the total sampling points had soil cadmium in excess of standard value, and the ratio of active Cd content to total soil Cd content was 24.0%. The enrichment factor of tobacco Cd was 3.43. There was a significant positive correlation between Cd concentration in tobacco leaves and soil Cd content. Soil pH, organic matter and cation exchange amount were negatively correlated with the Cd enrichment factor of tobacco. This present study has provided a regression model of tobacco Cd content based on soil factors, which could accurately predict Cd content in different parts of tobacco.

Urea is commonly over‐applied as a nitrogen (N) fertilizer to crops in southern China and has a low utilization efficiency due to the high precipitation and high temperatures in this region. This has led to a need to optimize the management of N fertilizer use in maize crops on the subtropical hilly uplands of southern China. We investigated the effects of applying different amounts of N in the form of polymer‐coated urea (PCU) on the yield of maize and gaseous losses of N from soils in the form of NH₃ and N₂O. The field plots used in this trial had zero‐added N (0 kg N ha⁻¹), the addition of urea (240 kg N ha⁻¹) and four levels of fertilization with PCU (1 PCU, 0.9 PCU, 0.8 PCU and 0.7 PCU), which represented a 0%, 10%, 20% and 30% reduction, respectively, in the application of PCU‐N relative to the urea plot. Compared with the urea plot, there was little variation in the yield of maize for all the PCU‐N treatments, with a significant improvement in the utilization efficiency of N (up to 46.0‐51.2%) with a 0‐30% reduction in the application of PCU‐N. Significant effects in the mitigation of the N₂O emission flux and the accumulation of N₂O‐N were observed in the 0.8 PCU and 0.7 PCU plots. The application of PCU‐N significantly reduced the flux and total amount of NH₃‐N lost to the environment: as the application rate for N decreased by 0‐30%, the NH₃ loss was significantly reduced by 12.7‐36.1%. Our findings suggest that the use of PCU could allow a reduction in the application of N of 20‐30% compared with traditional agricultural practices in this area with the same yield of maize, but with significantly decreased NH₃ and N₂O losses and the increased utilization of N.

To understand the relative importance of plant community composition and plant-induced soil properties on N transformations, the soil N mineralization, ammonification and nitrification characteristics of natural secondary forests (Quercus mongolica-Juglans mandshurica forest: QJF, and Quercus mongolica-Populus davidiana forest: QPF) and the adjacent larch plantations (Larix kaempferi forest: LF1 and LF2) were studied during the growing season. All of the forest types showed seasonal dynamics of N mineralization rates. The total cumulative N mineralization was significantly higher in QPF (73.51 kg hm⁻²) than in LF1 (65.64 kg hm⁻²) and LF2 (67.51 kg hm⁻²) (p < 0.05). The total cumulative nitrification from May to November was significantly higher in QJF (65.16 kg hm⁻²) and QPF (64.87 kg hm⁻²) than in LF1 (52.62 kg hm⁻²) and FL2 (54.17 kg hm⁻²) (p < 0.05). Based on the variation partitioning, independent soil properties were the primary determinants of the N transformations (13.5%). Independent climate conditions explained 5.6% of the variations, while plant variations explained 3.2% of the variations in N transformations. We concluded that different forest types with various plant community compositions have different influences on the litterfall quantity and quality and the nutrient availability, and these differences interact with seasonal climate conditions that in turn drive the differences in N mineralization.