Simulating Net Primary Production Of Agricultureal Vegetation In China

Plant net primary production (NPP) of agriculture vegetation represents the capacity of sequestrating atmospheric CO2 in agro-ecosystem, and plays an important role in terrestrial carbon cycling. In comparison with natural ecosystems of forest and grassland, agro-ecosystem is much complex due to human being activities. To batter understand the contribution of agro-ecosystem to regional carbon budget, the simulation models of crop NPP have been developed well since 1970s. However, few models are successfully put into practice in the agro-ecosystem of China, which is mainly due to the unavailability of model inputs and the verification of reliability in different regions of China. The objectives of this paper are to establish a crop NPP model that could be put into practice in the agro-ecosystem of China and to make sensitivity analysis of the model. Then validate this model and to estimate crop NPP in China by employing it.In light of a preliminary model established by the authors that simulates net primary production of rice and wheat crops, a model named as Crop-C was developed. Crop-C is dedicated to simulating net primary production of rice, wheat, maize, cotton, rapeseed and soybean crops those planted in approximately two thirds of agricultural soils in China. The model includes two main functional modules: photosynthesis and respiration, and nitrogen transport within soil-plant system. The processes of photosynthesis and respiration are mainly driven by environmental variables of temperature, solar radiation, precipitation, atmospheric CO2 concentration and crop tissue nitrogen. The transportation of nitrogen within soil-plant system is determined by simulating the processes of crop nitrogen uptake, soil nitrogen mineralization and synthetic nitrogen release.Model sensitivity analysis suggests that the sensitive significance of Crop-C to input parameters is in descending order of temperature, PAR, atmospheric CO2 concentration, soil nitrogen consentration, rate of nitrogen application and precipitation when the input parameters vary -10% and 10%, respectively. In addition, global wanning would have a negative effect on net primary production of agriculture vegetation in China based on the model sensitivity analysis.Models for simulating crop net primary production (NPP) have been developed well over the last tree decades, while few of them are successfully put into practice in the agro-ecosystem of China. The objectives of this paper are to validate an existing model Crop-C developed by the authors, and to estimate crop NPP in China by employing Crop-C.Crop-C was validated against independent measurements from literatures and the derived NPP from crop yields documented in national statistical yearbooks. Six crops of rice, wheat, maize, cotton, soybean and rapeseed, planted in approximately two thirds of agricultural soils in China, were involved in the validation. Model validation indicated that NPP of the six crops can be well simulated from weather, soil and N fertilization in various regions of China. A comparison between the simulated and the observed NPP resulted in a correlation coefficient (R~2) of 0.76 (n=786).To estimate net primary production of agricultural vegetation in China, data of model parameters were interpolated or rasterized into grid layers which had the same frame, that is, the same cell size (10km×10km), the same original point (low-left point of the frame) and the same rows and columns for all data layers.By linking the Crop-C to GIS database, crop NPP in mainland China was estimated from 1980 to 2000. The GIS database includes soils, weather, N fertilization and some other related...