Origin and cultivation history of rice in China

cies of cultivated rice in ancient China is possibly more northward than in the modern times. The earliest rice grains unearthed from the Neolithic sites existed along the lower and middle reaches of the Yangtze River. The later ones were found in Yunnan Province, South China and along the Yellow River reaches. Primitive rice cropping in the Taihu Lake region which is on the lower reach of the Yangtze River has already a 6,000-7,000 years history and the primitive tribes growing rice there are ancestors of the Yue Nationality since the beginning of the history, hence the Yue Nationality is the most important one for rice cropping in China. During the periods of Spring-Autumn and Warring States to Qin and Han Dynasties (from 722 B.C. to A.D.220 ), Yue people disseminated rice to Japan, Korea and other Southeast Asian countries by sea. In the period of over 3,000 years since the recorded history,the rice development in China has experienced changes from north to south and from south to north. As Chinese c

Spatial variation and driving mechanism of soil organic carbon components in the alluvial/sedimentary zone of the Yellow River

Alluviation and sedimentation of the Yellow River are important factors influencing the surface soil structure and organic carbon content in its lower reaches.Selecting Kaifeng and Zhoukou as typical cases of the Yellow River flooding area,the field survey,soil sample collection,laboratory experiment and Geographic Information System(GIS)spatial analysis methods were applied to study the spatial distribution characteristics and change mechanism of organic carbon components at different soil depths.The results revealed that the soil total organic carbon(TOC),active organic carbon(AOC)and nonactive organic carbon(NOC)contents ranged from 0.05–30.03 g/kg,0.01–8.86 g/kg and 0.02–23.36 g/kg,respectively.The TOC,AOC and NOC contents in the surface soil layer were obviously higher than those in the lower soil layer,and the sequence of the content and change range within a single layer was TOC>NOC>AOC.Geostatistical analysis indicated that the TOC,AOC and NOC contents were commonly influenced by structural and random factors,and the influence magnitudes of these two factors were similar.The overall spatial trends of TOC,AOC and NOC remained relatively consistent from the 0–20 cm layer to the 20–100 cm layer,and the transition between high-and low-value areas was obvious,while the spatial variance was high.The AOC and NOC contents and spatial distribution better reflected TOC spatial variation and carbon accumulation areas.The distribution and depth of the sediment,agricultural land-use type,cropping system,fertilization method,tillage process and cultivation history were the main factors impacting the spatial variation in the soil organic carbon(SOC)components.Therefore,increasing the organic matter content,straw return,applying organic manure,adding exogenous particulate matter and conservation tillage are effective measures to improve the soil quality and attain sustainable agricultural development in the alluvial/sedimentary zone of the Yellow River.