Imbalanced Soil Chemical Properties and Mineral Nutrition in Relation to Growth and Yield Decline of Sesame on Different Continuously Cropped Upland Fields Converted Paddy

Sesame (Sesamum indicum L.) is an important oilseed crop, but is negatively affected by continuous cropping. There is still a lack of information on the effect of continuous cropping on soil chemical properties and mineral nutrition related to sesame growth and yield decline. Therefore, we investigated sesame growth and yield, nutrient concentration and soil chemical properties on five fields with continuous cropping history: non-continuous cropping (Year 0) and durations of two, four, five and six years on an upland field converted paddy in Tottori, Japan. Results show that plant height significantly decreased by 18.76%, 15.22%, and 13.64% in the Year 4, Year 5 and Year 6 fields, respectively, compared to Year 0. The effect of continuous cropping was more pronounced on the 1000-seed weight decline than seed yield. Compared to Year 0, seed yield decreased by 52.86% in Year 2 with no significant differences among the Year 2, Year 4, Year 5 and Year 6 fields, whereas the 1000-seed weight decreased by 6.68% and 12.20% in the Year 2 and Year 5 fields, respectively, compared to Year 0. Plant leaf tissue N concentration significantly decreased in the Year 2, Year 4 and Year 6 fields compared to Year 0, whereas leaf tissue K concentration decreased in the Year 6 field. The increase in duration of continuous cropping years gradually altered soil chemical properties. Soil pH, exchangeable Ca and Mg and cation exchange capacity (CEC) gradually increased in the long duration of continuous cropping, whereas total N and C, exchangeable NH4+-N, urease, dehydrogenase and catalase activities decreased. Our study suggested that the decrease in soil available N and enzyme activities, and decrease in K nutrition due to competitive ion effect as a result of increase in soil Ca and Mg could possibly contribute to the growth and yield decline of continuous sesame on upland field converted paddy.