| Ecological stoichiometry is the science that studies the chemical elemental composition of biological organisms and the material balance of ecosystems.In agricultural ecosystems,it has been proven that ecological stoichiometry can be used to guide agricultural production practices.Different fertilization treatment will change the content and availability of the Carbon,Nitrogen,and Phosphorus,but it is still unknown how these changes will impact on the stoichiometric ratio of C,N,and P in citrus leaves,and on fruit yield.Therefore,this paper makes use of an nitrogen fertilizer application experiment which lasts for 6 years,setting four different nitrogen fertilizers usage amount:no nitrogen fertilizer(N0),70% of the local nitrogen fertilizer application(N70),85% of the local nitrogen fertilizer application(N85),and local nitrogen fertilizer application(N100).And meanwhile applying with cake fertilizer(N0+C),(N70+C),(N85+C),(N100+C)and green manure(N0+G),(N70+G),(N85+G),(N100+G)three types of fertilizers,a total of 12 kinds of fertilization treatment are set in this nitrogen fertilization experiment.This paper studies the effects of different amounts of nitrogen fertilizers,and that of nitrogen fertilizers combined with organic fertilizers on the soil carbon,nitrogen,and phosphorus content and on the stoichiometric ratio of orange orchards.And this paper tries to make clear of the effects of soil carbon,nitrogen,and phosphorus content on the stoichiometric ratio of leaf carbon,and the impact of stoichiometric ratio of nitrogen,and phosphorus,and the carbon of leaves in different periods on citrus fruit yield and quality.Below are the main research findings:1.Effects of different nitrogen fertilizer treatments on soil carbon,nitrogen and phosphorus content and stoichiometric ratio in citrus orchardsThe application of nitrogen fertilizer significantly changed the contents of organic carbon(SOC),nitrogen(TN)and phosphorus(TP)in the soil,but the effects of different nitrogen fertilizer application rates and its combination with organic fertilizer were different.Nitrogen fertilization reduced,but not significantly,SOC and TN content of the soil,and increased soil TP content significantly.There was no significant difference in soil SOC content among the nitrogen application rates combined with cake fertilizer application,but the increase in nitrogen application rate significantly reduced soil TN content and largely increased soil TP content.There was no obvious change in the soil SOC content among the different nitrogen application rates under green manure application.With the increase of nitrogen application rate,the soil TN content in the germination stage decreased significantly,and the soil TP changed insignificantly,but the soil TN and TP content in the mature stage increased significantly.With application of single chemical fertilizers,the stoichiometric ratio of soil carbon,nitrogen,and phosphorus did not change significantly at the germination stage of citrus.The soil TN: TP and SOC: TP of the N70 treatment at the maturity stage were significantly lower than those of other nitrogen treatments.With cake fertilizer application,the C: N: P ratio of citrus soil at germination stage did not change with the increase of nitrogen application rate,while the soil SOC: TN of N85+C treatment at maturity stage was significantly lower than that of other nitrogen application rates.Combined with green manure application,the soil SOC: TN in the germination stage of citrus rose up significantly with the increase of nitrogen application,and the soil TN: TP and SOC: TP in the treatment of N85+G in the mature stage of citrus decreased significantly.2.Effects of different nitrogen fertilizer treatments on the leaf stoichiometric ratio and the relationship between soil-leaf stoichiometric ratioUnder single chemical fertilizer treatment,with the increase of nitrogen application rate,the content of carbon(C),nitrogen(N)and phosphorus(P)in the leaves decreased significantly at the germination stage,flowering stage and young fruit stage,while the C,N,P content in the leaves increased significantly in the fruit expansion stage and mature stage.Under the combined application of cake fertilizer and green manure,the content of C,N,and P in the perennial leaves increased significantly,and the content of C,N and P in annual leaves was significantly reduced with the increase of nitrogen application in the germination,flowering,and young fruit stages,and decreased significantly in the fruit expansion and mature stages.The changes of C,N,P content in the soil and their stoichiometric ratio significantly affected the C,N,P content in the leaves and their stoichiometric ratio,and the leaf nutrient content was easily affected by external nutrient input.The C,N,P stoichiometric ratios of leaves were significantly non-linearly correlated with soil C,N,P stoichiometric ratios at flowering and young fruit stages,and were significantly linearly correlated with soil C,N,and P stoichiometric ratios at fruit expansion and mature stages.3.Effects of different nitrogen fertilizer treatments on the stoichiometric ratio of leaves and fruits and fruit yield and qualityRegardless of the single application of chemical fertilizers or combined application of chemical fertilizers and organic fertilizers,the nutrient content of carbon,nitrogen,and phosphorus in fruits increased significantly with nitrogen application,but there was no significant change in fruit yield and fruit quality.Compared with single application of chemical fertilizer,combined application of cake fertilizer significantly improved the content of carbon,nitrogen and phosphorus nutrients in fruits.There was no significant difference in fruit carbon,nitrogen and phosphorus content,fruit yield and quality between green manure combined application and single application of chemical fertilizer.The stoichiometric ratio of carbon,nitrogen,and phosphorus in leaves at the flowering stage was significantly correlated with the stoichiometric ratio of carbon,nitrogen,and phosphorus in the leaves at the later stage.The TC: TN in the leaves at the flowering and young fruit stages was significantly correlated with the fruit yield and quality.The TC:TN in the leaves at the fruit expansion and ripening stages was significantly correlated with the fruit yield and quality.Leaf stoichiometric ratios at young and ripening stages were most closely related to citrus fruit yield and fruit quality,and there was a significant relationship between soil-leaf-fruit stoichiometric ratios at mature stages.In conclusion of the research results,it is feasible to confirm the supply and balance of soil nutrients and the yield and quality of citrus fruits according to the stoichiometric ratio of carbon,nitrogen and phosphorus in citrus leaves.The stoichiometric ratio of carbon,nitrogen and phosphorus in mature leaves is an important basis for scientific fertilization in orangery,when the annual and perennial leaves TC: TN,TN: TP and TC: TP were494.14: 18.11: 1 and 639.45: 19.40: 1,respectively,the yield and quality of citrus fruits were higher. |
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