Case Study on Development of the Sustainable Agricultural System for Various Agro-ecosystems Through Assessment of Nitrogen Flow

Abstract

Importance in the sustainability of agricultural systems has long been recognized in relation to maintaining and improving agricultural productivity in harmony with the surrounding environment. In many cases, however, the sustainability is discussed rather qualitatively, not quantitatively. This is mainly because of lack of measurable indicators to express the degree of the sustainability in the system. The nutrient is an essential element for the agricultural systems and the appropriate management of such nutrient should be one of the key points for sustainable development of the system. Moreover, the nutrient flow within the system can be quantified at a certain degree and the nutrient budget that is a consequence of balance between input and output may be closely related to sustainability. Optimization of nitrogen cycling in the farm community is considered to be an important aspect as nitrogen is a major nutrient to increase agricultural production. In this paper, a whole picture of the nitrogen cycle for agricultural production that was constructed based on data collected from agricultural statistics, research reports, study reports, field observation, interview with farmers and information from experts, will be presented with particular focus on three areas in the East and Southeast Asian countries such as Shandong province in China, Northeast Thailand, and Mekong Delta. The obtained nitrogen budget is also discussed in order to improve sustainability of the system. Corresponding author: osamuito@jircas.affrc.go.jp Although various types of farming systems can be seen in East and Southeast Asian countries, the dominant systems in the region largely depend on local biophysical conditions, especially climatic factors that most affect agricultural production and can not be modified by the effort of the individual farmer. The agro-ecosystem in the region can be broadly classified into six categories according to the FAO definition as can be seen in Fig. 1. The FAO agro-ecological zoning system is based on simple parameters such as length of growing period, mean monthly temperature and daily mean temperature (Pingali et al, 1997). In this paper, an example of typical farming operation will be picked up from three agro-ecosystems (warm semiarid subtropics with summer rainfall, warm sub-humid tropics and warm humid tropics) and direction of sustainable development of farming systems will be briefly discussed based on research outcomes that have been produced by the projects that the Japan International Research Center for Agricultural Sciences (JIRCAS) conducted in the region. Special attention will be placed to analyze agricultural production from the viewpoint of nitrogen flow for its sustainable development. Chapter 1. Sustainable Bioproduction Systems 48 Fig 1 Agroecological zones in south, south east and east Asia (modified from Pingali et al. 1997) Estimation of Nitrogen Flow A whole picture of the nitrogen cycle for agricultural production in three target regions was developed based on data collected from agricultural statistics, research reports, study reports, field observation, interview with farmers and information from experts (Matsumoto et al, 2000, Matsumoto et al, 2003). Nitrogen Flow in Shandong Province in China The first example is from Lingxian County, Shandong Province, China that belongs to warm semiarid subtropics with summer rainfall (Yagi and Hosen, 2000). The intensive upland cropping is dominant with wheat, maize, vegetables and cotton as major crops. The regional analysis of the nitrogen flow indicated an excessive load of nitrogen to arable land and the environment (Fig. 2). The load is mainly due to increasing consumption of chemical fertilizer in addition to increasing manure application. The analysis of nitrogen budget based on statistics suggested that the balance between input and output of nitrogen in arable land was 288 kg N/ha/year in 1997. There was an increasing trend in the nitrogen load; for example, the balance in 1981 was 159 kg N/ha/year that accounted for 55% of that in 1997. Nitrate pollution to groundwater due to excessive application of nitrogen fertilizer should be a major concern in near future, but the present level of nitrate in the groundwater collected from wells is still within the acceptable range, indicating that the nitrate pollution has not been widely spread in the region despite increasing amount of nitrogen application. Warm serniarid tropics Warm subkarmid tropics