| This study seeks for the effects of increasing nitrogen fertilizer and spraying hormone on the growth and development,photosynthesis,nitrogen absorption and utilization,yield and quality of relay-intercropping sweet potato,theoretical basis and practical production guidance were provided for effectively improving the growth potential,high yield and quality of sweet potato under the maize/sweet potato model.The experiment was carried out with yushu50 as the material,adopted the two-factor completely random group design with 3 levels of N and 4 levels of hormone.The nitrogen application amount was based on 75kg/hm~2(N1)and increased to 150 kg/hm~2(N2)and225 kg/hm~2(N3).The leaves of sweet potato were sprayed any hormone(H1),sprayed with GA3(H2),or 6-BA(H3),or GA3+6-BA(H4),and was repeated three times.Agronomic character,photosynthetic pigment,photosynthetic characteristic index,hormone content,nitrogen metabolism and physiological related enzyme activity,yield and quality were measured.The results were as follows:1 Effect on growth of symbiotic period and matter distribution of later stage of sweet potato in the relay-intercroppingSymbiosis period in the relay-intercropping,the length of the longest vine and the fresh weight of the stem of the sweet potato increased with the increase of nitrogen application amount,while the branch number was the most in N2 treatment,and the stem diameter was the least with N1 treatment.The longest vines were significantly longer in H2 and H4 treatments than H1 and H3 treatments.Branch number and stem diameter were significantly higher with H3 and H4 treatments than H1 and H2 treatments.In different hormone treatments,the fresh weight of stem and vine treated with H2,H3 and H4 was significantly higher than H1.The results showed that the increase of nitrogen fertilizer could increase the stem diameter,the length of the longest vine and the fresh weight of the stem of sweet potato;the exogenous application of GA3 could increase the length of the longest vine;the exogenous application of 6-BA could increase the branch numbers and the stem diameter of sweet potato;and both GA3 and 6-BA could increase the fresh weight of the stem and vine in the relay-intercropping period of the sweet potato.In the growth of later stage,the fresh weight of sweet potato stem and vine was significantly lower under N2 treatment than N1 and N3 treatments,while the tuber root and vine ratio(T/R)and the weight of per plant showed that were significantly higher under N2 treatment than N1 and N3 treatments.The fresh weight of stem and vine were significantly higher in H1 and H2 treatments than H3 and H4 treatments with different hormones,while the weight of per plant and T/R value were opposite to it.Exogenous spraying of GA3 would lead to the increase of fresh weight,while exogenous spraying of6-BA would reduce fresh weight and increase the weight of per plant in later stage of sweet potato,thus increasing T/R value.2 Effects on photosynthesis of sweet potatoThe experimental results showed that chlorophyll content,net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of leaves increased with the increase of nitrogen application.The SPS activity of leaves was the highest under N2treatment,followed by N3 treatment,and the lowest under N1 treatment.Among different hormone types,the content of chlorophyll a in leaves was significantly higher in H2 and H4 treatments than H1 treatments.Chlorophyll b has a maximum value in H3 or H4treatment,and a minimum value in H1 or H2 treatment.The total content of chlorophyll was higher in H3 and H4 treatments than H1 and H2 treatments.Pn showed that H4treatment was significantly higher than other treatments,H1 treatment was significantly lower than other treatments,and Gs,Tr and Ci were significantly lower than other treatments.The SPS activity of leaves was significantly lower in H1 treatment than in H2treatment,and in H2 treatment than in H3 and H4 treatment.The results showed that increasing application of nitrogen fertilizer could improve the chlorophyll content,Pn,Gs,Tr and SPS activity of leaves,and it was more beneficial to increase SPS activity of leaves of sweet potato with appropriate nitrogen than high nitrogen.Exogenous application of GA3 can increase the content of chlorophyll a in leaves,while exogenous application of 6-BA can increase the content of chlorophyll b and the total content of chlorophyll.Exogenous application of GA3 or(and)6-BA could improve Pn,Gs,Tr and Ci in sweet potato leaves,the SPS activity was also significantly increased in sweet potato leaves,especially 6-BA.If need to improve photosynthetic performance and coordinate matter distribution of relay-intercropping sweet potato,it could use 150 kg/hm~2 nitrogen with GA3 and 6-BA simultaneously.3 Effect on nitrogen and hormone metabolism in sweet potatoThe nitrate reductase activity and soluble protein content were significantly increased with the increase of nitrogen application at the symbiotic stage of relay-intercropping and later growth stage.In general,the nitrate reductase activity and soluble protein content of leaves were significantly higher in H2 and H4 treatments than H1 and H3 treatments under the same nitrogen application,and there was no significant difference between H2 and H4 treatments and between H1 and H3 treatments.The results showed that the nitrate reductase activity and nitrogen metabolism ability of sweet potato could be improved by adding nitrogen fertilizer and GA3.The contents of GA3 and 6-BA increased in leaves with the increase of nitrogen application.The content of GA3 showed that were significantly higher in H2 and H4treatments than H1 and H3 treatments under different nitrogen treatments.The contents of 6-BA showed that were significantly higher in H3 and H4 treatments than H1 and H2treatments under different nitrogen treatments.The results showed that increased nitrogen fertilizer and exogenous hormone spraying could regulate hormone metabolism in sweet potato,among which increased nitrogen fertilizer and exogenous GA3 spraying could increase GA3 content in leaves of sweet potato,while increased nitrogen fertilizer and exogenous 6-BA spraying could increase 6-BA content in leaves of sweet potato.4 Effect on yield and quality of sweet potatoThe study showed that effects of different nitrogen application and hormone were significant on yield of sweet potato.The yield of sweet potato was significantly higher in N2 treatment than N3 treatment,while N3 treatment was significantly higher than N1treatment.Under the same nitrogen application,H4 was significantly higher than other treatments,and H1 was significantly lower than other treatments.Both the dry matter content and soluble sugar content were higher in N2 treatment than N1 and N3 treatments,while the soluble protein content increased with the increase of nitrogen application.The dry matter content of H3 and H4 were higher than H1 and H2 treatments,and H3treatment was the highest.The soluble protein content of H2 and H4 was significantly higher than H1 and H3 treatments.The soluble sugar content of H4 treatment was the highest,followed by H3 treatment,and H1 treatment was the lowest.The results showed that the yield of sweet potato could be increased by appropriate nitrogen application and exogenous application of GA3 and 6-BA.Exogenous application of GA3 can significantly increase the soluble protein content of tuber root of sweet potato.Exogenous application of 6-BA can significantly increase the dry matter content and soluble sugar content.In summary,the treatment that was medium nitrogen application and exogenous spraying of GA3 and 6-BA can growth batter at the relay-intercropping symbiosis stage,photosynthetic capacity and nitrogen metabolism were stronger,matter distribution was more coordinated in later stage,and yield and quality was higher.Using 150 kg/hm~2 of pure nitrogen and spraying GA3 and 6-BA can improve the yield of sweet potato in relay-intercropping... |
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