Preliminary Studies On Recommended Fertilization For Nitrogen,Phosphorus,Potassium Of Newhall Navel Orange

The distribution area of citrus in China is extensive.It is widely planted and distributed in Guangxi,Hunan,Jiangxi,Hubei,Sichuan,Chongqing and Yunnan Provinces.Since the citrus trees are mainly planted in mountainous and hilly areas with an obvious spatial variation in soil fertility,and the nutrient requirements vary considerably in different parcels of orchards.Previous researchs have shown that the managements of nutrient resources in most citrus ochards in China are irrationally and blindly fertilized,which have caused decline in citrus production and quality,increase in environment pollution and waste of fertilizer resources.With regards to the issues above,outdoor investigations for fertilization managements and lab data analyses of soil,leaf and fruit samples were conducted to figure out the scarcity and abundance of nutrient,fruit yield and quality of main Newhall navel orange orchards in Jiangxi Province and Chongqing municipality to clarify the existed problems of fertilization.So we will learn about the main limiting factors of high yield,quality and fertilizer utilization efficiency of Newhall navel orange,providing basic data for the exploration of the optimal nutrient management system.At the same time,2-year-old Newhall navel orange（Citrus sinensis Osbeck cv‘Newhall’）trees on trifoliate orange（Poncirustrifoliata（L.）Raf.）root stocks with nitrogen controlled treatments were selected to explore the nutrient uptaking rules of young Newhall navel orange trees and the convenient and fast leaf nutrient diagnosis methods.The main results were as follows:（1）Most orchards mainly applied with chemical fertilizers,and organic fertilizers were used in a low percent of which 42.86%of total ochards didn’t use organic fertilizers.The application of organic fertilizers affected the yield of Newhall navel oranges to some extent.The application of fertilizer was the highest in Fengjie without organic fertilizer,and the yield was the lowest.The total input of fertilizer in Xinfeng was the second with the highest organic fertilizer application,and its yield was significantly higher than the other ochards.The results of the sample investigation showed that the nitrogen,phosphorus,and potassium inputs of the Newhall Navel Orange ochards in areas of Jiangxi（Anyuan county,Xinfeng county,Xunwu county）,Chongqing（Yunyang county,and Fengjie county）were generally higher.The average annual applications were 730 g/plant（calculated with the content of pure N）,451.73g/plant（calculated with the content of P₂O₅）,and 519.44 g/plant（calculated with the content of K₂O）.The amount of suitable orchards accounted for 1.74%,0%and 7.14%of the total orchards.The proportion of nitrogen,phosphorus and potassium nutrients inputs in most orchards was unbalanced,but only the ranges of Fengjie and Anyuan were suitable（1:0.5-0.7:0.7-1.7）.（2）There were some differences among the nutrient of soil,leaf,and fruit in the five major producing areas,with large coefficient of variations.Among all the soil samples of Chongqing and Jiangxi,73.24%and 94.59%were short of soil available nitrogen,43.66%and 30.43%were short of soil available phosphorus,47.89%and57.97%were short of soil available potassium.1.41%and 17.39%were short of soil soil organic matter.Among all the leaf samples of Chongqing and Jiangxi 0,87.33%were short of nitrogen,87.33%and 98.59%were short of phosphorus,98.59%and1.45%were short of potassium.There were also significant differences among the nutrient uptake of fruits in different orchards.The nitrogen uptake in Xinfeng was the highest,with an average of 3.07 kg pure nitrogen per 1000 kg of citrus fruit,the amount of phosphorus and potassium uptake in Yunyang ochards was the highest with0.87 kg pure phosphorus（calculated as P₂O₅）and 1.68 kg pure potassium（calculated as K₂O）per 1000 kg citrus fruit.And we probed into the influence and interrelation of different physiological indicators on fertilization by partial least square regression.The results showed the most important impact factor of the application of nitrogen was soil pH.phosphorus and potassium fertilization was the content of organic matter.（3）The results of the controlled nitrogen experiment of 2-year-old Newhall navel orange indicated that the input of nitrogen was beneficial to the citrus growth above ground with 25 g pure nitrogen per tree used in this experiment of which fertilizer utilization rate was 6.77%.The content of nitrogen in spring shoots of different treatments was significantly higher than autumn shoots.The content of potassium in spring shoots was significantly lower than autumn shoots.With the increasing of nitrogen fertilizer application,the nitrogen content in spring shoots showed an increasing trend while the potassium content showed a decreasing trend.The leaf nitrogen content in autumn shoots was the same as spring shoots,and it increased with the nitrogen fertilizer application.However the trend of phosphorus and potassium content was opposite.With the increase of nitrogen fertilizer application,the content of phosphorus in leaves of autumn shoots decreased while the potassium content increased significantly.The nutrient contents of nitrogen and potassium in each organs of the trees were significantly higher than phosphorus,and the content of nitrogen was the highest in the root.The content of phosphorus and potassium was the highest in the shoot.The use efficiency of fertilizer is low in sandysoil citrus orchards.They should be（4）The spring shoot leaves were collected from Newhall navel orange.The nitrogen content of all samples ranged from 1.63%to 4.67%,the phosphorus content was 0.03%-0.23%,and the potassium content was 0.78%-2.02%.The calibration models of N concentration of spring shoot leaves were established by using the characteristic fluorescent parameters,partial least square（PLS）method and internal cross-validation.The PLS model for nitrogen content with prediction set was with MRE=9.48%,RPD=2.01,accuracy of regression model=78.57%.The feature bands of the leaf spectrum reflectance measured by the Fieldspec4were 1407 nm,1620 nm,1750 nm,1905 nm,2175 nm and 2309 nm respectively.The PLS model established by characteristic spectral reflectance for nitrogen was with MRE=4.05%,RPD=3.168,accuracy of the regression model=86.71%after the preprocessing of first-order derivative and multiple scatter correction method（FD+MSC）.