| In order to explore the rules of yield formation and high photosynthetic efficiency by different agronomic measures in maize/sweetpotato relay cropping system and get the best cultivation field configuration of sweetpotato production by establishing a mathematical model for high yield and high photosynthetic efficiency, this experiment using quadratic orthogonal rotating design, researched the influences of 5 factors(cutting section, nitrogen fertilizer, potash fertilizer, the density of sweetpotato and the time of cutting the top section) on growth vigor, absorption and conversion of solar radiation, photosynthetic carbon assimilation, accumulation and distribution of photosynthate,redistribution and allocation of dry matter of sweetpotato and the composite yield at two points between 2014 and 2015. Main conclusions are as follows:1. Influences on vine growth vigor of sweetpotato With the cutting section increased, vine length and branch numbers increased and basal branch numbers reduced, however the cutting section had little influence on LAI. With nitrogen fertilizer increased, vine length, stem diameter, branch numbers and LAI increased. With potassium fertilizer increased, vine length, branch numbers and LAI increased, however the potassium fertilizer had little influence on stem diameter. With the density of sweetpotato, vine length and stem diameter increased and basal branch numbers and LAI reduced. With lapse of cutting time, stem diameter, and LAI increased and vine length and branch numbers reduced.5 factors could regulate aerial part growth vigor of sweetpotato to some extent.The degree of influence to vine length, stem diameter and branch numbers were the density of sweetpotato>cutting section>the time of cut the top section>nitrogen fertilizer>potasium fertilizer. And the degree of influence to LAI was the density of sweetpotato,>the time of cut the top section>nitrogen fertilizer>potassium fertilizer>cutting section.There was no significant correlation between vine length, stem diameter and branch numbers.2. Influence on absorption and conversion of solar radiation Within certain realms, cutting section, nitrogen fertilizer, the density of sweetpotato, the time of cutting the top section could increase chla+chlb、q P and Fv/Fm; potassium fertilizer could increase chla+chlb, however had less influence on q P、Fv/Fm. q N changed like a parabola going upwards influenced by 5 factors.5 factors all could improve the capacity of absorption and conversion of solar radiation through increasing chlorophyll content and PSII reaction center openness and reducing heat dissipation. The most important factor to the capacity absorption and conversion of solar radiation was the density and the second was nitrogen fertilizer.3. Influence on photosynthetic carbon assimilation Within certain realms, cutting section, nitrogen fertilizer, potassium fertilizer, the density of sweetpotato and the time of cutting the top section could increase Ru Bpase activities, the values of Pn, Gs and Tr and reduce the values of Ci. Ci had significant negative correlations with Pn, Tr, Gs and Ru Bpase. Pn, Tr, Gs and Ru Bpase both had significant correlations with each other. 5factors all could improve sweetpotato’s photosynthetic carbon assimilation and the most important factor was the density and the second was nitrogen fertilizer.4.Influence on accumulation of photosynthate With the cutting section increased, the dry weight of sweetpotato’s storage tubers, SPSase activities and starch contents increased. With nitrogen fertilizer increased, tubers’ dry weight and SPSase activities reduced, however nitrogen fertilizer had little influence on starch contents and marketable tuber percentage. With potassium fertilizer increased, tubers’ dry weight and starch contents increased, however potassium fertilizer had little influence on SPSase activities. With the density of sweetpotato, starch contents increased, however the density had little influence on tubers’ dry weight and SPSase activities. With lapse of cutting time, SPSase activities increased starch contents reduced and marketable tuber percentage changed little. 5.Influence on the yield of coin/sweetpotato relay intercropping system Marketable tubers weight, sweetpotato’ production and the composite yield changed like a parabola going downwards influenced by 5 factors.With the cutting section increased, marketable tuber percentage and maize yield reduced. With nitrogen fertilizer increased, maize yield reduced however nitrogen fertilizer had little influence on marketable tuber percentage. With potassium fertilizer increased, marketable tuber percentage and maize yield increased. The density of sweetpotato had little influence on maize yield and the time of cutting the top section could increased marketable tuber percentage. The interaction effect of potassium fertilizer and the time of cutting to sweetpotato’ production and the composite yield were both very significant. The degree of influence to sweetpotato’s yield was the density of sweetpotato>nitrogen fertilizer>the time of cutting the top section>potassium fertilizer>cutting section and the density and nitrogen fertilizer both had very significant on the yield. The degree of influence to the composite yield was the density>nitrogen fertilizer>the time of cutting the top section>cutting section>potassium fertilizerand the density and nitrogen fertilizer both had very significant on the yield and the density and nitrogen fertilizer both had very significant on the yield. 6.the correlative relationships between sweetpotato yield and the other indicators Stem diameter significantly and positively correlated with photosynthetic parameters and sweetpotato yield. The composite yield significantly and positively correlated with sweetpotato yield and marketable tuber percentage. The sweetpotato yield significantly and positively correlated with photosynthetic parameters and chlorophyll fluorescence parameters. What’s more, different agronomic measures had similar influence to the three indicators above.This showed that improving photosynthetic capacity is the key to improve the yield of sweetpotato. The composite yield very significantly and positively correlated with the indicators of absorption and conversion of solar radiation, photosynthetic carbon assimilation, accumulation and distribution of photosynthate and redistribution and allocation of dry matter,therefore, in maize /sweetpotato,improving the production of sweetpotato is the key to improve the composite yield.7.Production model optimization The regression equation between 5 factors and sweetpotato yield is Y=27046.63-6.50X1+ 517.87X2-30.20X3+1614.17X4+72.10X5-814.19X12-1401.46X22-539.96X32-1018.66X42-1327.08X52+463.21X1X4+633.25X2X4-583.28X3X5,The optimized cultivation measure(length of cutting seedling + nitrogen fertilizer+ potassium fertilizer + cutting density + topping stage) was “6-7 segment-length +166.7-203.8 kg/hm2+338.23-501.72 kg/hm2 +58037-61956 plants/hm2 +70 days after cutting” and the composite yield could achieve 26497.25 kg/hm2 under above configuration.The regression equation between 5 factors and the composite yield is Y=Y=19188.37-53.71X1-357.81X2+113.63X3+498.14X4-253.1X5-515.09X12-193.78X22-628.63X32-418.21X42-554.65X52-409.1X1X3+406.85X1X5-448.15X2X3-604.66X2X4-310.02X3X4.The optimized cultivation measure(length of cutting seedling + nitrogen fertilizer+ potassium fertilizer+cutting density+topping stage) was “5-6 segment-length +14.7-31.3kg/hm2+537.7-614.3 kg/hm2 +61329-63217plants/hm2 +65-68 days after cutting” and the composite yield could achieve 19229.08kg/hm2 under above configuration. |
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