Degradation of Chinese mollisols: Agricultural and ecological aspects

Background/Question/Methods As a great grain contributor, the Northeast Plain of China dominated by Mollisols (Black soils) is a vital food and animal production basis to the nation. However, its sustainability has been decreasing during the past decades due to (1) farmland degradation mainly from severe soil erosion; (2) over-cropping with only chemical fertilizer but no organic material input; (3) bad seedling establishment due to severe spring drought and traditional tillage. In addition, transformation of the national economy from a centrally-controlled model to a free market economy has weakened the agricultural extension service. This also made the sustainability of agriculture more vulnerable in the region. Results/Conclusions The land degradation is attributed to the decline in the quantity and quality of soil organic matter (SOM). The SOM loss from cultivation was attributed to a combination of surface soil erosion and agricultural practices including tillage and removal of plant residues. Since the reclamation of the Mollisols land, the land has been intensively cultivated in an improper way, i.e. Chinese conventional cultivation system. Under this cultivation system all the aboveground crop residues are removed after harvest and used for heating and cooking because crop residues are almost the unique energy source in the countryside of the Mollisols region in the last decades. Consequently, the quality of the Mollisols has being deteriorated rapidly. This has become a serious problem in the region in both agricultural and ecological aspects. 1), SOM decrease is also a direct response to soil layer thinning caused by water and soil erosion. Loss of SOM resulted in poor soil properties, especially soil structure, which, in turn, led to more losses of water and nutrients by runoff. 2), The use efficiency of agricultural resources is low. The N fertilizer use efficiency is only about 30% on average, much lower than that in the Mollisolls area of the North America. Hence, more than 50% N fertilizer is lost to the environment. This causes a lot of ecological and environmental problems, for instance, ground water contamination and surface water eutrophication. 3), Studies showed that the SOM in the Mollisols land can be restored by conversion of tillage system from conventional to conservation ways. Therefore, the new knowledge and enhanced capacity for N management and carbon sequestration will be critical in improving and quantifying regional ecological performance with respect to the losses of NO₃^‑ to water system and N₂O/CO₂ to air within the global community.