No abstract

Nitrogen (N) and phosphorus (P) use and losses in China's food chain have accelerated in the past three decades, driven by population growth, rapid urbanization, dietary transition, and changing nutrient management practice. There has been little detailed quantitative analysis of the relative magnitude of these driving forces throughout this period. Therefore, we analyzed changes in N and P flows and key drivers behind changes in the food (production and consumption) chain at the national scale from 1980 to 2010. Food (N and P) consumption increased by about fivefold in urban settings over this period but has decreased in rural settings since the 1990s. For urban settings, the integrated driving forces for increased food consumption were population growth, which accounted for ∼60%, and changing urban diets toward a greater emphasis on the consumption of animal products. Nutrient inputs and losses in crop and animal productions have continuously increased from 1980 to 2010, but the rates of decadal increase were greatly different. Increased total inputs and losses in crop production were primarily driven by increased crop production for food demand (68-96%) in the 1980s but were likely offset in the 2000s by improved nutrient management practices, as evidenced by decreased total inputs to and losses from cropland for harvesting per nutrient in crop. The contributions of animal production to total N and P losses to waters from the food chain increased by 34 and 60% from 1980 to 2010. These increases were caused mainly by decreased ratios of manure returned to cropland. Our study highlights a larger impact of changing nutrient management practice than population growth on elevated nutrient flows in China's food chain.

In order to study the effect of corn kernel composition and physical structure on moisture distribution and transfer process and obtain the optimal tempering-drying parameters of corn kernel, a physical model was constructed with four different components as follows: seed coat, horny endosperm, farinaceous endosperm and embryo. The drying model was established based on the assumption of different diffusion coefficients and same thermal conductivity for the four components. The software of COMSOL Multiphysics was used to simulate the heat and mass transfer process inside the corn kernel during the thin-layer drying. The results showed that the least total drying time and the best drying quality were achieved under the multistage circulating drying of 10 min hot air drying and 60 min tempering, and the tempering degree was up to 0.9207.