Development of Wide-area Assessment Methodologies for Carbon/Nitrogen Balance Associated with Agricultural Activity

Background and Objectives

In East Asia, the rapid population increase and economic growth in recent years have increased the demand for food, and agricultural production is booming. Moreover, the dramatic increase in energy demand may require cultivation of crops for energy use. Such acceleration of agricultural activity will promote decomposition of organic materials accumulated in the soil and raise atmospheric CO₂ concentration. In turn, input of animal manure, straw and other organic farm materials into farmland will help return to the soil the carbon atoms that plants have absorbed from the atmosphere and fixed in their bodies. Excessive application of nitrogen fertilizers and other organic materials for the purpose of increasing production lead to the pollution of groundwater and eutrophication of lakes and coastal waters. In fact, serious water pollution is reported in the eastern part of China and other areas. Thus, the balance between the inflow and outflow of carbon and nitrogen in farmland (carbon/nitrogen balance) associated with agricultural activity has a significant bearing on the global environment. It is therefore vitally important for sound management of global environment that the carbon/nitrogen balance are estimated accurately and the optimal amounts of fertilizer application and other organic inputs are computed.

In this research project, we aim to clarify the relationship between crop production/consumption and environment in Japan and East Asia, from the perspective of the movement of carbon and nitrogen. For this purpose we will develop models to estimate the change in carbon accumulation in the soil, and will assess the impact of climate change and effects of organic materials input in Japan and East Asia. In addition, we will analyze the current flows of carbon and nitrogen as function of farm production and food demand in East Asia, in order to be able to predict, with the help of materials circulation models, future changes in the carbon/nitrogen balance in terms of the expected socioeconomic changes and climate change scenarios (Fig. 1).

Expected Outcomes

Carbon/nitrogen balance in farmlands of Japan and East Asia will be clarified, which will help formulate recommendations for more integrated farmland management techniques. It is also hoped that comprehensive forecast on the environmental impact of agricultural activity in East Asia will serve as basic information for future studies on food policy and environmental pollution prevention policy.

Relevant Outcomes to Date

Carbon accumulation change in soil by organic carbon dynamic model in soil

We have examined whether the soil carbon balance prediction model ( “RothC” ) developed by Rothamsted Research of the U.K. is applicable to soils in Japan. It was found that the carbon amount predicted by the model generally matched the actual measured values (Fig. 2). However, poor compatibility was observed with respect to Andosol that accounts for approximately 50% of the upland field soil in Japan. We have added certain modifications to the model to increase its accuracy.

Prediction of water quality changes due to increased food production and consumption in East Asia

On the basis of data by the United Nations Food and Agriculture Organization (FAO) and the statistics from various countries, we have developed a model to estimate on a continental scale the environment burden of nitrogen due to food production/consumption, and nitrogen concentration in ground water and river water. East Asia saw dramatic increases in crop production and fertilizer consumption as a result of population increase and dietary changes, especially increased meat consumption (Fig. 3). The model we have developed suggested a dramatic rise in nitrogen concentration in the groundwater and river water of upland agricultural areas in the lower reaches of the Yangtze and Hwang Rivers and other areas after year 1980 (Fig. 4). If this trend should continue, food demand will further climb by 2020, requiring approximately 1.4 times as much fertilizer as is required today. The estimates we arrived at correspond well with the trends of water quality data obtained by on-site studies in various parts of China and in Southeast Asia.