Nitrogen Cycling with Respect to Environmental Load in Farm Systems in Southwest China

Abstract

In Qibainong, a steep-mountainous karst region in southwestern China, self-sustaining societies have long existed, but increasing socioeconomic liberation has fuelled the recent rapid structural change of its economy. Consequently, environmental deterioration and exhaustion of resources have become problematic issues. We carried out a field survey in Qibainong in southwestern China and used both estimated and measured N flows and N balances from obtained results. Our results are summarized as follows (1) farmers used large amounts of chemical N fertilizers at intensities of 113–1124 kg N ha 1 ; (2) substantial application of chemical fertilizer in Qibainong has contributed to an increase in potential NO3-N leaching of 6–511 kg N ha 1 , followed by NH3 volatilization; (3) crop products are largely distributed to feed livestock, the products of which are a major income source; (4) this area has a great requirement for imported food; (5) in addition, unused manure N (up to 191 kg N ha 1 ) is generated by the increase in manure N production. Chemical fertilizer application, in addition to unused manure can be regarded as a major source of environmental damage. Based on the relationship between the N application rate and the NO3-N leaching potential, we estimated the critical limit of the N application rate of chemical fertilizer + manure to be 297 kg N ha 1 . In Qibainong, unused manure, which is an important nutrient resource, was applicable within the critical limit. We recommend that all manure N produced within the village be used effectively on arable land, and that any shortages be supplemented by chemical N fertilizer up to 297 kg N ha 1 to maintain water resource quality. Further improvement might be achieved through incorporating chemical fertilizers, P and K supplemented manure, and so on.