Effects Of Continuous Cropping Of Tobacco Planting On Soil Aggregate And Combined Carbon And Nitrogen

Disadvantages caused by continuous cropping of tobacco were one of the important problems faced by modern scale production of tobacco.To understand the negative effects caused by tobacco continuous cropping on soil fertility and structure changes,soil selected from a typical tobacco growing areas in Hanyang town Jiange County of Guangyuan city was studied;and contents of soil combination carbon and soil nitrogen,and soil aggregates were measured.All were for the purpose of providing theoretical basis and data reference on sustainable development of tobacco production.The results were as follows:1.The effects of different planting years of tobacco continuous cropping on soil organic carbon,carbon storage,total nitrogen and nitrogen storage in 0-20 cm soil were significantly higher than those in 20-40 cm soil.Long-term tobacco continuous cultivating(>15 years)was beneficial to increase organic carbon content,carbon storage,total nitrogen and nitrogen storage in 0-20 cm and 20-40 cm soil.The decrease of fertilizer application rate by tobacco planting caused that the soil organic carbon,total nitrogen and nitrogen storage were significantly lower than those in the CK,especially in the 0-20 cm soil of the 5,8,10 tobacco planting years.2.Compared with the CK,the tobacco continuous cropping significantly reduced the proportions of the water stable aggregates of the >5mm,2~5mm and 1~2mm and significantly improved those of the <1mm.As the planting years increased,the proportions of the water stable aggregates of the >5mm significantly decreased while those in other soil significantly increased;accordingly,Mean Weight Diameter(MWD)and Geometric Mean Diameter(GMD)in the soil water stable aggregates significantly decreased with the increase of the planting years;but Aggregate Deterioration Rate(ADR)showed in the contrary way.3.Compared with the CK,tobacco continuous cropping significantly reduced the organic carbon,nitrogen and nitrogen storage of the soil aggregates,but those in the different soil increased with the increase of the planting years.The contribution rate to the bulk soil from organic carbon and nitrogen of <0.25 mm micro-aggregates significantlyincreased with the increase of the plating years.The homogenization of organic carbon and total nitrogen in the aggregates was promoted under 10,15 and 26 planting years.4.The C/N of 0-20 cm soil was not significant by tobacco planting years,but that of20-40 cm soil was significant and the C/N in different aggregates was not significant by different planting years.5.The organic carbon and nitrogen were positively correlated with the aggregates fractions of >0.25 mm,while those of <0.25 mm showed in the contrary way.The aggregates fractions of >2mm were positively correlated with MWD,while those of <2mm were negatively correlated.The aggregates fractions of >1mm were positively correlated with GMD and negatively correlated with ADR.The contents of organic carbon and nitrogen in the soil aggregates were positively correlated with MWD and GMD,while those were negatively correlated with ADR.