Effects Of Phosphorus Levels And Fertilization Methods On Growth And Development Of Navel Orange

Citrus is the most widely planted and most productive fruit crop in China,which is mainly distributed in the hills and mountainous areas of Guangxi,Sichuan,Hunan,Guangdong,Hubei,Fujian,Jiangxi,Chongqing,Zhejiang and other provinces and cities.it has played a very important role in poverty alleviation and rural revitalization and development of agriculture and rural areas in southern China.The citrus orchard has complex site environment and diverse topography,especially blind or excessive fertilization,improper fertilization and low fertilizer use efficiency in citrus production management.to a certain extent,it restricts the healthy and sustainable development of citrus industry.Therefore,the 8-year-old（planted in 2011）’Nevilina navel orange’grafted on orange rootstock（Citrus junos Sieb.in Nanchong City,Sichuan Province.Ex Tanaka）was used to study the effects of five phosphorus supply levels[0（P0）,0.15 kg/tree（P1,calculated by P2O5）,0.30kg/tree（P2）,0.45 kg/tree（P3）,0.60 kg/tree（P4）],four fertilization depths[0（D0）、15cm（D15）、30cm（D30）、45cm（D45）]and two root-cutting fertilization[no root cutting fertilization（Q1）and root cutting fertilization（Q2）]on citrus growth and development,nutrient absorption and utilization,fruit yield and quality and soil physical and chemical properties,so as to provide theoretical basis and technical support for suitable phosphorus application and high-quality and high-yield fertilization management in hilly and mountainous navel orange orchards.The main results are as follows:（1）The results of the experiment on the level of phosphorus supply showed that compared with no phosphorus application（P0）,phosphorus application could effectively promote the shoot growth,nutrient accumulation,yield and quality formation of Nevilina navel orange;the leaf length,width,leaf perimeter,leaf area,leaf chlorophyll content and branch length increased at first and then decreased with the increase of phosphate fertilizer application,and reached the peak at P2 treatment.The accumulation of nitrogen,phosphorus and potassium in shoots treated with P2 was the highest.According to the curve between phosphorus application rate and nutrient accumulation,the maximum accumulation of nitrogen and phosphorus in shoots（in terms of P2O5,the same below）was 0.31 kg/tree/year,and the maximum accumulation of potassium was 0.25 kg/tree/year.Phosphorus application effectively increased the accumulation of nitrogen,phosphorus and potassium in fruit,among which the accumulation of nitrogen,phosphorus and potassium in P2 treatment was the highest,which increased by 82.70%,42.25%and 43.09%respectively compared with P0treatment.The yield of Nevilina navel orange was increased by 53.30%compared with P0,and the best phosphorus amount to obtain the maximum yield was 0.26 kg/tree/year.P1 treatment had the highest fruit chromaticity,which was helpful to fruit coloring;P3treatment had the highest contents of soluble solids（（TSS））,solid-acid ratio（TSS/TA）and vitamin C;phosphorus application had a significant effect on the enrichment of soil nutrients,and P2 treatment was the most effective,which increased the contents of organic matter,alkali-hydrolyzable nitrogen,available phosphorus and available potassium in soil,and significantly decreased soil p H.Based on the annual growth and development of navel orange,it is concluded that the annual P₂O₅ dosage of navel orange is 0.15-0.30kg/tree.（2）The results of fertilization depth experiment showed that compared with surface application（D0）,fertilization at 30cm soil layer（D30）significantly promoted the development of spring and autumn shoots of Nevilina navel orange,increased leaf length,width,leaf perimeter,leaf area,leaf chlorophyll content and branch length,and increased the accumulation of dry matter and nitrogen,phosphorus and potassium in spring and autumn shoots.When the fertilization depth is too shallow or too deep,the development of branches is slow and the accumulation of dry matter becomes smaller.Deep fertilization in 30cm significantly increased the contents of nitrogen,phosphorus and potassium in Nevilina navel orange fruit,which increased by 66.90%,58.01%and73.71%respectively compared with D0 treatment.The yield-increasing effect of D30treatment was obvious,which increased by 52.87%compared with D0 treatment,increased fruit weight per fruit,decreased fruit acidity,increased fruit vitamin C content,increased pulp moisture content and fruit firmness,but also increased pericarp thickness.Reduced the edible rate of the pericarp.With the increase of fertilization depth,the fruit yield decreased,titratable acid increased and vitamin C decreased.According to the fitting curve,it was found that the fertilization depth was closely related to a large number of indexes in the growth process of Nevilina navel orange,from which it was concluded that the range of fertilization depth of organic and inorganic compound fertilizer suitable for each index was 15-30cm.（3）The results of root cutting experiment showed that after root cutting,the leaf development of spring shoot increased and the leaf development of autumn shoot decreased;the dry matter accumulation and nutrient absorption of nitrogen,phosphorus and potassium in spring and autumn shoots increased;the nutrient content of fruit decreased,which had the greatest effect on fruit potassium content;compared with the treatment without root cutting,the yield of Nevilina navel orange increased by 22.84%on average.The fruit chromaticity was better,the pericarp thickness decreased,the soluble solids,solid-acid ratio,vitamin C content,juice yield and edible rate increased significantly,the titratable acid content decreased,and the fruit had stronger marketability.