Effects Of Nitrogen Fertilizer On Satsuma Mandarin Fruit Yield, Quality And Nitrogen Use Efficiency

Satsuma mandarin has been grown as a specialized industry in Danjiangkou, it forming a two hundred miles citrus belt on both sides of the reservoir area, and increasing a rate of two acres per annum.However, in the long process of planting, the local farmers blind pursuit of economic interests, has resulted in widespread excess nitrogen use, decreased nitrogen use efficiency and damage of the local environment by nitrogen loss. Field trials and pot experiments have been used to study the effects of different nitrogen levels on satsuma mandarin nitrogen use efficiency, yield and quality of the fruit。The main results abtained are as following:(1) Increasing nitrogen within the adequate range, has improved satsuma mandarin fruit yield significantly. In2012-2013,the fruit yield of each treatment from field trials result was shown as N1.25﹥N1.5﹥Nl﹥N0.75﹥N0,and the pot experiment shown the same result as field trials. Field test results shown that, compared with the conventional fertilizer treatment N1.0,N0andN0.75treatment fruit yields were reduced by67%、22%, N1.5were increased by28%、26%.Pot test results showed similar results as the field trials.Fruit yield of the blank NO treatment was significantly lower than the other treatments, the N0.75, N1.0, N1.25andN1.5teartments increased the fruit yield5.26,5.15,5.82and4.92times more than the NO treatment respectively.The relationship between of total amount of nitrogen applied and fruit production can be expressed as: y=179.5+48.83x-0.571x2(R2=0.992, P﹤0.05),(y=fruit yield;x=N applied).(2) The results shown that, NO processing fruit titratable acid content increases, the solid acid ratio decreases, edible fruit fertilization rate was significantly lower than the fertilizer processing. Under nitrogen deficient conditions, satsuma mandarin fruit quality has declined and appears bark large fruit.(3) With amount of nitrogen in the adequate range, satsuma mandarin leaf chlorophyll content showed a positive correlation with the amount of nitrogen fertilizer applied. With increased use of nitrogen fertilizer, soil nitrogen nutrient supply increases significantly, trees absorb more nitrofen and provides adequate material for the synthesis of chlorophyll.Thus chlorophyll content increased gradually with increasing nitrogen rate, but at a high amounts of nitrogen fertilizer the chlorophyll content of spring shoots reach a maximum and did not increase further.(4) With amount of nitrogen in the adequate range, satsuma mandarin spring shoots leaf photosynthesis exhibited with increasing nitrogen rate and growing trend under low nitrogen conditions,Satsuma mandarin leaf photosynthetic rate, transpiration rate and stomatal conductance were significantly lower than the high nitrogen conditions, the difference was significant, but with the increasing amount of fertilizer, Satsuma mandarin leaf photosynthesis reaches a critical value, afer which most photosynthesis increases with longer use of fertilizer to increase. Under conditions of different nitrogen levels, the carbon and nitrogen containing photosynthetic compounds showed inconsistent results. The soluble protein and free amino acids i showed an initial ncreaser with increasing nitrogen followed by a decreasing trend, there was a negative correlation between the soluble sugar and nitrogen content.(5) With amount of nitrogen in the adequate range, increasing nitrogen increases the nitrogen content of satsuma mandarin leaves,showing a positive correlation. Under experimental conditions, in both field trials and pot experiment and each year, Satsuma mandarin fruit pulp showed nitrogen nutrient content increase with nitrogen rate used. Satsuma mandarin pulp showed large differences between nitrogen treatments at low and high nitrogen levels.(6) Nitrogen deficiency and excess significantly affects satsuma mandarin nitrogen use efficiency under field test conditions. The relationship between nitrogen fertilizer rate and nitrogen use efficiency can beexpressed by the equation:y=-0.14+0.098x-0.00009x2(R2=0.921, P﹤0.05).Satsuma mandarin nitrogen fertilizer nitrogen use efficiency increased to a maximum with increases N applied and then decreased at higher levels.(7) The results show that, soil total nitrogen and effective nitrogen content increased significantly with increasing fertilizer use. Under field test conditions,although this trend was observer each year, the size of the increases differed between years.