Study On Soil Nutrient Status Of Citrus Orchards And Optimization Fertilization In Chongqing Area

The ecological environment in Chongqing is ideal for the growth of citrus, the total area of which currently is nearly 1.26×105 hm2, with the output of 1.8×106 t,1.3 billion RMB production approximately every year. The citrus industry has now become the main economic sector in Chongqing. However, the low rate of good citrus as well as the low quality and output has greatly constrained the development of citrus industry, having the average yield only 12 t/hm2 each year. Therefore, how to solve these issues has become the priority for Chongqing citrus industry. Hill dominated geography with the poor soil quality, lack of the systematic knowledge of the soil fertility, experience based fertilizer application, such as excessive application, deficient application, wrong application are the main hindrance as well as the neglecting of the organic fertilizer importance. With regards to the problems above, field experiment combined with outdoor investigation and lab analysis were conducted to study the citrus orchard fertilizer application and the citrus output in Chongqing area, aiming at learning about the current citrus production state and the existing problems affecting the citrus output and the nutrient absorption. The systematic soil investigation using samples and lab data analysis were conducted to look into the scarcity and abundance of the soil nutrient so that proper theory basement can be provided for the citrus orchard soil cultivation and efficient fertilizer application methods based on the soil nutrient measurement. And the field experiment was implemented to explore the optimum nutrient management system and citrus special fertilizer for citrus.The results of sample investigation showed that the application of N 408.5 kg/hm2, P 228.3 kg/ hm2and K 260.1kg/hm2 were applied with an improper proportion N:P2O5:K2O=1:0.56:0.64, excessive N, lack of K, random P application. The fertilizer application failed to follow the time schedule of citrus growth, that is, the low application of fruit expanding fertilizer hardly met the nutrient demand of citrus at the fruit period. Fengjie had the highest output due to its highest fertilizer application, while Yougchun ranked NO.2, due to its highest organic fertilizer application in spite of a low level of fertilizer. For the other counties which applied the fertiler or organic fertilizer averagely, they had the average performance.The nutrient analysis showed that the soil pH had an decreasing trend from northwest to southwest along the Yangze river area,83.5% of which is suitable for the citrus growth.53% orchard had a low organic matter content in the whole city aear,89.7%,51.6% and 55.6% for instant N, P, K respectively.which are primary nutrient,8.6%,9.1% and 46.4% for Ca, Mg, and S respectively which are secondary nutrient,36.2%,24.8%,5.1%,42.7% and 98.6% for Fe, Mn, Cu, Zn and B respectively. Wu monutain area showed an scarcity of most nutrient, among all the samples within the 10 main citrus area,71% of which are short of P,78.6%,92.1%,86.85 and 94.7% for K, Fe, Zn and B respectively.Fengjie orchard had the good soil fertility except an low amount of N, Fe, Mn and B, caused by the high fertilizer application.The different nutrients have a close relationship, promoting or prohibiting. The disequilibrium of one element would affect the nutrient efficiency of another element, then affecting the crop development. Therefore, proper application with an ideal proportion of various elements can greatly increase the citrus output.The field experiment based on the optimum nutrient management system and the citrus exclusive nutrient match showed that compared to the traditional application method, the citrus output has increased 18.9% and 15.5% respectively during the 2 years successive optimum nutrient management, for VC,0.69% and 7.66% increase respectively,1.2% and 13.75% decrease for intritable acid respectively. Meanwhile, the SSC/TA and the fruit shape index increased too, greatly improving the citrus flavor. The optimum management effectively promoted the growth of the spring vegetable shoot and main stem and decreased the physiological fruit dropping number, which were good for the citrus growth and to improve the citrus output and quality.Controlled release treatment displayed the good effect too, increasing the output 14.7% and 11.8% respectively while rising the content of Vc and SSC/Tc, and decreasing the intitrable acid, which proved that controlled nutrient release treatment can meet the citrus nutrient need at different development stage. The effect of specialty fertilizerⅠandⅡhad no significant effect, which needed It is therefore concluded that 0.525kg N,0.515kg P,0.434kg K are the optimum combination for each citrus (6 years old) each year, with 30% of the total amount apllied in March,40% in May, and 30% in November, the effect of which will be greatly improved by the application of organic fertilizer.