| Flue-cured tobacco is an important economic crop.The production of tobacco for high yields and good qualities is related to farmers’ income,local finance and national tax in the poor areas of Southwest China.Tobacco is sensitive to continual cropping and rotation is necessary for soil health and sustainable development of agriculture in tobacco growing areas.To understand the source and fate of nutrients is beneficial to optimize the management of nutrient resources and to obtain the high yield of crops with good quality.Therefore,we spent 3 years to study the nutrient utilization and leaching from soils with continual cropping and rotation of tobacco with chemical fertilizer and mixture of chemical fertilizer and manure.The experiment was carried out in long-term experimental sites established in tobacco growing area of North Guizhou province.In the cropping systems,tobacco,maize and wheat were grown.The main objective is to provide scientific bases for rational management of soils nutrient resource and sustainable development of agriculture production.Following are the main results obtained.1.Rainfall was major water source for crops in North Guizhou,where the mean annual precipitation was 829.27mm from 2010 to 2012.Rainfall from May to September accounted for 61.7%of annual precipitation,which could meet the basic water requirement of tobacco and maize.The change of rainfall distribution in time and space,i.e.drought in spring and summer,influenced crop transplanting and growing.Heavy rains in summer,on the other hand,caused runoff and nutrient leaching.2.Rains were rich in nutrients.Inorganic nitrogen from rains accounted for 13.86%～21.53%of fertilizers added(16.21%～21.53%in tobacco seasons and 13.86%～18.21%in maize seasons)and potassium for 7.04%～27.75%of fertilizer supplied(7.04%～10.63%in tobacco seasons and 18.17%～27.75%in maize seasons).Potassium input from rains into soils was highest,followed by ammonia and nitrate,and with phosphorus lowest3.There was a positive correlation between underground runoff and rainfall.In each crop growing seasons,underground runoff was high at the beginning and less in the late stages.The underground runoff was higher in tobacco-maize rotation than continual tobacco cropping systems.In addition,chemical fertilization increased underground runoff compared to fertilization of chemical fertilizers combined with manure.4.Rainfall led nutrient leaching.The concentration of ammonia changed from 0.14mg/L to 1.52 mg/L,nitrate from 10.59mg/L to 35.35mg/L,and potassium from 11.3mg/L to 40.6mg/L.No phosphorus was detected in runoff,indicating this element remained mainly in soils.5.In different cropping models,tobacco-maize rotation in nutrient cycling condition was higher than that of flue-cured tobacco-continuous cropping,but tobacco-maize rotation in the nutrient cycling is more balanced,the input of fertilization was more than or much larger than output in flue-cured tobacco season,high nutrient input and the proportion of crop absorption disharmony caused by soil nutrient imbalance,may be one of the causes of continuous cropping of flue-cured tobacco production decline.Take on the treatment of fertilizer application reduced and combined fertilization treatment,nutrient digestibility increased significantly,rotation;nutrient apparent rate is higher than the continuous cropping area.6.The content of soil total nitrogen,total potassium under different planting patterns without too big change,the content of total phosphorus increased year by year,fertilization treatment increased the content of organic matter.The soil nitrogen and potassium content in flue-cured tobacco planting after content had the obvious rise,decline in the wheat planting,rotation model in nitrogen and potassium content decreased significantly after maize planting. |
