Effects Of Tobacco Cropping And Fertilization Patterns On The Growth Of Later Green Manure Plants And Benefits Of Returnning Green Manure To Soils

Tobacco is an important cash crop in hilly and mountainous areas in Guizhou Province.Tobacco cultivation is of great significance for shaking off poverty and increasing fiscal revenue.Tobacco mono-cultivation and tobacco-maize rotation are the main cropping models in the local area.Fallow in autumn and winter is quite common in tobacco mono-cultivation fields.The yellow soils are widespread in the local area for growing tobacco,which has a clay texture,lacks organic matter,and suffers from excessive fertilization,leading to cropping obstacles as well as other soil and environmental problems.The cultivation of green manure plants（GMPs）in the fallow season can effectively utilize light,heat,water,and soil resources.Besides,returning GMPs to the field can increase soil organic matter and reduce chemical fertilizer usage,being beneficial to the development of green and sustainable agriculture.Although many researchers have reported the advantages of cropping GMPs,little was known about the influence of previous tobacco on GMP growth,particularly the enrichment of residual nutrients from tobacco-grown soils by GMPs.Therefore,a long-term field experiment was established in 2004 in Zun Yi City,Guizhou Province,and the experimental treatments included)a blank control,ii)tobacco mono-cropping supplied with only chemical fertilizers,iii)tobacco mono-cropping supplied with organic fertilizer and chemical fertilizers,iv)tobacco-maize rotation supplied with only chemical fertilizers,and v)tobacco-maize rotation supplied with organic fertilizer and chemical fertilizers.GMPs ryegrass and vicia villosa were grown in the winter.In our present experiments,we recorded the growth of these two GMPs and detected GMP nutrient uptake in the recent five years.Simulation research was also carried out to realize the dynamic of MGP decay and enzymatic activities in the soil.Following were the main results obtained:（1）Fertilizing the planting patterns significantly affected the growth of ryegrass.Higher ryegrass biomass was achieved in the tobacco-maize rotation system than that in the field for growing tobacco only.The application of organic manures in combination with chemical fertilizers in the tobacco growing season also significantly increased the biomass of follow-up ryegrass,indicating an important role of cropping and fertilizing manners in the ryegrass growth.By contrast,cropping and fertilizing manners influenced little,if any at all,the growth of the leguminous vicia villosa.（2）GMPs efficiently enriched the nutrients from the tobacco field during their growth periods.In the fertilized tobacco-grown soil,the amount of nutrients enriched by GMPs arrived at 53.74 kg·hm^-1for N,3.84 kg·hm^-1for P,and 68.88 kg·hm^-1for K by ryegrass,and74.09 kg·hm^-1for N,3.66 kg·hm^-1for P,and 44.97 kg·hm^-1for K by vicia villosa.GMPs increased Na OH-hydrolysable N by 10.89%-11.3%and available P by 11.04%-14.9%in the unfertilized soils.However,CH₃COONH₄-exchangeable K in the soil decreased due to GMP uptake.The increased available N in the soil may come from biological nitrogen fixation.The higher available P in the soil could be explained by the improvement of microbial activity,mobilization of insoluble phosphorus,and extraction of P from the deep soil through the intensive roots of GMPs and then accumulation in the cultivated layer of soil.The higher nitrogen level in vicia villosa than that in ryegrass indicated a better ability to enhance available N in the soil due to biological N fixation.（3）The simulation experiment showed that the soil p H slightly increased by 0.03-0.19 units during the 15-45 days of GMP decomposition.Available N,P,and K in the soil significantly increased with 7500-22500 kg·hm^-1of GMPs added to the soil within 60 days of incubation.Microbial biomass and enzyme activities in the incubation soil also significantly increased.These results indicated that the application of GMPs at these rates was beneficial to the improvement of the test soil for growing tobacco.In addition,the soil p H changed little after 45 days of GMP addition,probably indicating no effects on crop growth and development at this time.（4）During the 5-year ryegrass cultivation in autumn and winter,the average tobacco leaf yield increased by 33.85%and the medium-and high-grade tobacco leaves by 11.92%in the yellow soil.The proportion of chemical components,including properly decreased nicotine levels and increased total and soluble sugar,is reasonable in the tobacco leaves.The agronomic efficiency of fertilizer utilization also increased at the same time.（5）After continuous cropping of ryegrass for 5 years in autumn and winter,the organic matter was increased by 5.27%,Na OH-hydrolysable N by 35.58%,Olsen P by36.08%,and CH₃COONH₄-exchangeable K by 27.78%in the yellow soil tested.The activities of sucrase,urease,phosphatase,and catalase in this soil were increased by 30.77,39.4,46.09,and 65.8%,respectively.Taken together,the cropping of GMPs in the fallow tobacco fields in autumn improved the yield and quality of tobacco leaves and soil properties to different degrees,which is conducive to sustainable tobacco cultivation.