Effects of a potato/maize intercropping system on physiological characteristics and total yield with two potato varieties at different row ratios

The intercropping of potato(Solanum tuberosum)and maize(Zea mays)is a traditional cropping pattern in southwest China.Potato/maize intercropping trials were carried out to determine the dynamic changes of photosynthetical active radiation(PAR),soluble protein content(SPC),proline content(Pro),malondialdehyde content(MDA),superoxide dismutase(SOD),peroxide dismutase(POD),and catalase activities(CAT)from the tuber initiation stage to the tuber expansion stage.The yield was also studied using monocropped potato as the control.Two potato varieties:Zhongshu 5(early-maturing variety with erect branches) and Mira(mid-late maturing variety with spread branches)were employed as well as two potato to maize ratios. The ratio 2∶2meant two rows of potato to two rows of maize and 3∶2meant three rows of potato to two rows of maize.Gradual decreases in PAR and SPC were observed from the tuber initiation stage to tuber expansion stages in both Zhongshu 5and Mira.However,there were gradual increases in Pro,MDA,CAT and a decrease in SOD in Zhongshu 5but decreases in MDA,CAT and a similar SOD activity in Mira.POD activity in Zhongshu 5and Pro and POD activity in Mira had different trends due to row ratios.In addition,intercropping led to lower SPC and higher Pro,SOD and POD in the two potato varieties.Lower PAR,higher MDA,and lower CAT at the tuber initiation stage and higher CAT at the tuber expansion stage in Zhongshu 5were also detected,as was a higher PAR and lower MDA and CAT in Mira compared with the monocropped plants.Moreover,higher PAR and CAT in the 3∶2intercropping system than in the 2∶2intercropping system were observed,as well as a similar SPC.Other parameters changed differently due to growth stages.Nonetheless,intercropping reduced the light environment in the Zhongshu 5/maize system but improved it in the Mira/maize system.A better light environment was found in the 3∶2than in the 2∶2systems.Mira was more tolerant to shade than Zhongshu 5while both Mira and Zhongshu 5were more tolerant to shade in the 3∶2combination than in the 2∶2one.In summary,a varied light environment in intercropping led to substantial changes in physiological characteristics of potato and a reduction in tuber yield at harvest.LERs were 0.88and 1.00in the 2∶2intercropping potato/maize system for Zhongshu 5and Mira,respectively,while it was 1.24and 1.40in the 3∶2system.It is suggested that there is no intercropping advantage in a 2∶2potato/maize system but an obvious advantage in the 3∶2system with better production in the latter.