The Effect Of Ridging Modes On Growth,Photosynthetic Physiology And Yield Of Sweet Potato In Relay-Cropping System

Sweet potato/maize relay-cropping represents a main cultivation mode of sweet potato in southwest China.Flat-planting,bed-planting and heap-up-soil cultivation are the main three cultivation modes in relay-cropping system.In terms of researches on ridging modes of sweet potato,the research on ridge cultivation was more and the heapup-soil cultivation was relatively rare.Some studies indicated that heap-up-soil cultivation had the advantage of increasing the yield of sweet potato,but the physiological mechanism about it was unclear.In addition,ridging modes which is more suitable for sweet potato production on the local area should be further studied.It is against this background that this work was conducted in order to improve the land comprehensive production efficiency and explore which ridge mode is more suitable for sweet potato production in relay-cropping system.Single factor random block design was used and ‘Xida 985'(the local maize cultivar)and ‘Yushu 33'(short tendril type cultivar of sweet potato)were used for the study materials.To study the effect of ridging modes on environment condition,ecological adaptability,response mechanism of photosynthetic physiology,soil nutrient and fresh tuber yield of sweet potato.The main results are as follows: 1.The environmental effect of heap-up-soil cultivation was more suitable for the growth of sweet potato under the condition of relay-croppingThe light condition of big-ridge with double rows and heap-up-soil cultivation were better than single-ridge under maize row,photosynthetic active radiation(PAR)value of heap-up-soil cultivation was significantly higher than single-ridge under maize row;Environmental CO2 concentration of single-ridging under maize row was highest,big-ridge with double rows came second and heap-up-soil cultivation was last.Heapup-soil cultivation had the largest air and soil diurnal temperature e difference(8.5 ? and 1.2 ?respectively)than other treatments;Water content of single-ridging under maize row was significantly higher big-ridging with double rows and heap-up-soil cultivation.2.Ecological adaptability of sweet potato wass the strongest in heap-up-soil cultivation,however,sweet potato in single-ridge under maize row was affected most by maizeThere were no significant difference in sweet potato leaf dry matter content(LDMC)and leaf area(LA)between big-ridge with double rows and heap-up-soil cultivation.The shade degree of single-ridge under maize row was the largest,its specific leaf area(SLA),LDMC and LA were higher than others,which could assures it had a utmost adaptability to more adverse growing conditions in order to meet its own growth.On the contrary,sweet potato grew in heap-up-soil cultivation had the lowest degree of stress,so its net assimilation rate(NAR)and relative growth rate(RGR)were significantly higher than single-ridge under maize row,but its RGR of underground part was lower than that during the period of relay-cropping.The advantage of heap-up-soil cultivation reflected in recovery ability after maize harvest,its RGR,NAR and root activity were significantly higher than the other two.3.Heap-up-soil cultivation had the strongest photosynthetic capacity;the percentage of light energy was the highest in that part of driving photosynthesisHeap-up-soil cultivation increased the values of net photosynthetic rate(Pn),stomatal conductance(Cond)and transpiration rate(Tr)and also increased effective photochemical quantum yields(Y(II))and maximum photochemical quantum yields(Fv/Fm)of PS II,which meant the light quantum capture efficiency of sweet potato in this mode was higher than the others when compared with them.While sweet potato in single-ridge under maize row was most affected by maize,its Chl b accounted for a higher proportion in photosynthetic pigment composition.The ratio of light energy that dissipated as heat was the highest,and the open extent of photosynthetic system II was the lowest in single-ridge under maize row.4.There was nutrient competition between maize and sweet potato in single-ridge under maize row;Heap-up-soil cultivation was more conducive to absorb phosphorus and potassium for sweet potatoThere were no significant differences in N,P and K uptake of maize between heapup-soil cultivation and big-ridge with double rows during the period of relay-cropping.Root of sweet potato and maize were so closely linked and existed nutrient competition to each other,sweet potato had a higher competition ability of N than maize while the uptake of P and K were not in competition with maize.There were advantages in the absorption of P and K for sweet potato in heap-up-soil cultivation,the total phosphorus content got the highest value in this ridge mode.5.Heap-up-soil cultivation was more advantageous to improve land use efficiency and commodity rate of sweet potatoThe three kinds of ridge modes in maize/sweet potato relay-cropping system were all shown to have the relay-cropping advantages in two years.Land equivalent ratio(LER)of single-ridge under maize row was significantly lower than heap-up-soil cultivation in two years.While the average LER of heap-up-soil cultivation was 1.3,which showed the obvious relay-cropping advantage.The differences of LER between big-ridge with double rows and heap-up-soil cultivation were mainly caused by the difference of fresh tuber yield.The fresh tuber yield(16802.34 kg×hm-2 on average)of heap-up-soil cultivation was significantly higher than the other two ridge modes.The commodity rates in heap-up-soil cultivation were the highest in two years,which was 73.42% on average.6.Correlation analysis between all indexes and the fresh tuber yieldThe correlation analysis between all indexes and the fresh tuber yield showed that sucrose-phosphate synthase(SPS)activity,root activity,ribulose-1,5-bisphosphate carboxylase/oxygenase(RuBisco)activity,Y(II),NAR,Pn and Cond were significantly and positively correlated with fresh tuber yield(ranked by correlation),while nonphotochemical fluorescence quenching(NPQ),chlorophyll b content,chlorophyll a/b,environmental carbon dioxide concentration and soil moisture content were negatively correlated with the yield(sorted by the absolute value of the correlation).Regression analysis showed that the best regression equation model contained five variables: SPS,Cond,qL,NPQ and total potassium(TK).The results showed that heap-up-soil cultivation could be used to reduce the light and nutrient stress of the sweet potato in relay-cropping system,and the sweet potato could obtain stronger photosynthetic capacity;The accumulation of photosynthetic product for root tuber was more favorable after maize harvesting than other ridge modes;The advantages of land utilization and fresh tuber yield were all the most obviously than the other two ridging modes,it was more suitable for sweet potato production in relaycropping system for the local area.