Possible reasons for the occurrence of continuous cropping obstacle of sweet potato from soil nutrients
Continuous cropping obstacle is a critical problem during the cultivation of sweet potato,but the factors responsible for the occurrence of sweet potato continuous cropping obstacle are not clear.In this study,5-year,10-year,and 15-year continuous cropping sweet potato soils were collected,and soil pH,organic matter,cation exchange contents,total and available nitrogen(N),phosphorus(P)and potassium(K),and available medium and trace elements contents were analyzed,and the ratios of N/P,N/K,P/K were calculated.The results showed that,compared with their own control,5-year continuous cropping sweet potato increased soil pH,but 10-year and 15-year continuous cropping decreased soil pH.5-year continuous cropping sweet potato had little effects on the contents of soil organic matter,total and available N,whereas 10-year and 15-year continuous cropping increased their contents,and the organic matter contert in 15-year,total and available N contents in 10-year and 15-year were increased significantly.5-year,10-year and 15-year continuous cropping increased the contents of total and available P.There was no obvious law with regard to the effects of continuous cropping on contents of total and available K,and available medium and trace elements(Ca,Mg,S,Fe,Mn,Cu,Zn,Si).Continuous cropping sweet potato decreased the N/P ratio,but increased the N/K and P/K ratios,resulting in the imbalance of N,P,and K.The enrichment of N and P might induce the relative K deficiency and destroy soil microbiota,causing the occurrence of plant diseases and insect pests.Given that sweet potato is tolerant to poor soil conditions and K-preferring,it can be concluded that continuous cropping obstacle of sweet potato is attributable to soil acidification and N-P-K imbalance rather than decreased soil fertility.
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