Yun Xie

Regions of land that are brought into crop production from native vegetation typically undergo a period of soil erosion instability, and long term erosion rates are greater than for natural lands as long as the land continues being used for crop production. Average rates of soil erosion under natural, non-cropped conditions have been documented to be less than 2 Mg ha−1 yr−1. On-site rates of erosion of lands under cultivation over large cropland areas, such as in the United States, have been documented to be on the order of 6 Mg ha−1 yr−1 or more. In northeastern China, lands that were brought into production during the last century are thought to have average rates of erosion over this large area of as much as 15 Mg ha−1 yr−1 or more. Broadly applied soil conservation practices, and in particular conservation tillage and no-till cropping, have been found to be effective in reducing rates of erosion, as was seen in the United States when the average rates of erosion on cropped lands decreased from on the order of 9 Mg ha−1 yr−1 to 6 or 7 Mg ha−1 yr−1 between 1982 and 2002, coincident with the widespread adoption of new conservation tillage and residue management practices. Taking cropped lands out of production and restoring them to perennial plant cover, as was done in areas of the United States under the Conservation Reserve Program, is thought to reduce average erosion rates to approximately 1 Mg ha−1 yr−1 or less on those lands.

Soil erosion is a major environmental problem in China. Planning for soil erosion control requires accurate soil erosion rate and spatial distribution information. The aim of this article is to present the methods and results of the national soil erosion survey of China completed in 2011. A multi-stage, unequal probability, systematic area sampling method was employed. A total of 32,948 sample units, which were either 0.2–3 km2 small catchments or 1 km2 grids, were investigated on site. Soil erosion rates were calculated with the Chinese Soil Loss Equation in 10 m by 10 m grids for each sample unit, along with the area of soil loss exceeding the soil loss tolerance and the proportion of area in excess of soil loss tolerance relative to the total land area of the sample units. Maps were created by using a spatial interpolation method at national, river basin, and provincial scales. Results showed that the calculated average soil erosion rate was 5 t ha−1 yr−1 in China, and was 18.2 t ha−1 yr−1 for sloped, cultivated cropland. Intensive soil erosion occurred on cropland, overgrazing grassland, and sparsely forested land. The proportions of soil loss tolerance exceedance areas of sample units were interpolated through the country in 250 m grids. The national average ratio was 13.5%, which represents the area of land in China that requires the implementation of soil conservation practices. These survey results and the maps provide the basic information for national conservation planning and policymaking.

Parameters describing processes of crop growth and yield production provide modelers with the means to simulate crops and provide breeders with a system of comparing cultivars. Such values for rice ( Oryza sativa L.) are especially important for some regions in the southern USA. Accordingly, the objective of this study was to quantify key biomass and yield production processes of four rice cultivars common in this region. We measured the leaf area index (LAI), the light extinction coefficient ( k ) for Beer's law, N concentrations, and the harvest index (HI) for the main and ratoon crops in 1999 and 2000 at Eagle Lake, TX. Dry matter was linearly related to intercepted photosynthetically active radiation (IPAR) for all of the data sets. The mean radiation use efficiency (RUE) was 2.39 g aboveground biomass MJ −1 IPAR. Maximum LAI values ranged from 9.8 to 12.7, and the mean k value for the main crop was 0.37. The highest main crop yields were 7.04 Mg ha −1 for Cocodrie in 1999 and 7.22 Mg ha −1 for Jefferson in 2000. Yield differences among cultivars were due to HI differences and were not related to RUE values. The mean HI was 0.32 for all four cultivars over the two harvests in each of the 2 yr. Consistency in values of RUE, k , N concentrations, and HI among the cultivars in this study and between this study and values reported in the literature will aid modelers simulating rice development and yield and aid breeders in identifying key traits critical to rice grain yield improvement.