| In the majority of hilly mountainous regions in southern China, especially in Chongqing Three Gorges Reservoir, citrus plays an important role in the rural economy. Due to the contrasting nutrient distribution caused by complex topography of hilly mountainous regions, it is difficult to materialize the precise fertilization, resulting in obvious difference in fruit quality and yield per tree, low orchard overall yield, lower fertilizer efficiency and larger non-point source pollution risk, thereby affecting the enhancement of citrus industry efficiency and sustainable development in this region. This study targeted to the main hilly citrus orchard of Chongqing Three Gorges reservoir area, took the citrus groves in the Fengjie Tiefo villege (refered to as area A) and the Zhongxian Yangliu villege(refered to as area B) as experimental regions to investigate the soil nutrient levels, spatial distribution and responses of citrus tree to fertilization in the mountain citrus orchard, and to explore the generation technology of the nutrition status graph and variable fertilizer prescription map in the hilly orchard. Our aims are to provide theoretical basis and scientific technology for the scientific fertilization and precision management in hilly citrus orchard. The main research contents and results are as follows:1. The nutritional status and the relationship between nutrient elements in orchard were studied, and the spatial distribution map of the soil nutrition were drawn through the examples of the two test area soil samples. It showed the nutritional status of hill orchard and laid a good foundation for the variable fertilization prescription map drawing. The results showed that:(1) The soil nutrient spatial distribution is extremely uneven in the test area. The variation coefficients of soil available P content was greatest in both of A and B area. For A area, the variation coefficient of soil available K is the lowest. The average available N, available P, available K content was suitable, suitable and high range, respectively.70.2%and80.3%of the soil samples were in the appropriate-high levels of available N, available K levels, and62.7%in the lack to shortfall level of available P. The results showed that N and K element was more abundant and P was lack in general. For B area, the coefficient of variation of soil available nitrogen is the lowest. The average available N, available P, available K content of the samples was in the lack, suitable and high range, respectively.89.4%and58.9%of the total soil samples were in the lack-shortfall level of available N and available K content, while92.2%was in appropriate-high levels of available P content. The levels of N and P nutrition in this park was a general lack, K was more abundant in general or become excessive.(2) The results showed that the soil pH value of areaA and B were4.41-6.91and4.41-8.88respectively, which more soil samples pH, were acid in area A, and most soil samples were alkali in area B. The soil pH and the soil nutrient content were significantly or highly significantly negative correlation in both areas. There was a very significant positive correlation between the soil nutrient elements in both experimental areas. This trial indicated that there was very close relationships between the soil nutrients.(3) Based on the test areas geographic information, the sampling point accurate positioning information and soil sample nutritional contents, the soil nutrient distribution maps based on the micro scale of two test areas was firstly established in China. The soil nutrient distribution maps showed the actual situation of the spatial distribution of soil nutrient test area and laid a foundation for the variable fertilization prescription map drawing.2. Select a typical hilly mesa mountain in Zhongxian citrus area, the soil nutrient condition and spatial distribution were systematically studied. Results are as follows:(1) Soil pH was in the appropriate-alkaline range; available N, available P, available K content of the soil samples were in the lack, suitable and high range, respectively. The minimum of the soil pH and the maximum of the soil nutrient were found in the lower foot places. The lowest soil nutrients content appeared at the top of the hill. The soil nutrient content of the southern slope was higher than that of the north. (2) The model fitting of the soil nutrient levels and the elevation, based on the three-scale of southern slope (sunny), the northern slope (shady) and the entire mountain, showed that the best-fit equation were cubic functions of the soil pH, nitrogen, available phosphorus, available potassium content with site elevation. This inferred the entire orchard soil nutrient levels and space distribution can be fine-draw by less sampling and chemical analysis.3. Regard the A area Chislett late-maturing navel orange growing areas as a platform, the impacts of different fertilizer treatments on citrus plant nutrition, yield and fruit quality were studied. The results provided a basis for the establishment of the fertilization decision model and drewing of the fertilizer prescription map.(1) The results showed that a significant or extremely significant positive correlation prented between the nitrogen applying levels and the1eaf SPAD value, N and P content, fruit weight, thickness and longitudinal diameter of pericarp, fruit shape index and yield showed, while it showed a significant or extremely significant negative correlation to the total acid, TSS, Vc of the citrus fruit. A significant or extremely significant positive correlation were showed between the Phosphate applying levels and leaf SPAD value, P content, fruit weight, TSS, fruit vertical, horizontal diameter and fruit yield, while showed a significant negative correlation to the leaf K content, fruit Vc content and chromaticity of angle(H). Potassium applying levels showed a significant or extremely significant positive correlation with leaf SPAD value, K content, titratable acidity, fruit weight, thickness of pericarp, fruit vertical and horizontal diameter and yield, while a significant negative correlation with total K content, fruit acid Vc and chromaticity of angle(H).(2) The results of the six fertilization treatment in Fengjie trial area showed:The leaf potassium utilization were44.68%higher when the citrus were treated by T1(organic fertilizer:fertilizer=50%:50%) than other treatments. The yield was about91.67%when the citrus were treated by T2(organic fertilizer:fertilizer=25%:75%). When the citrus were treated by T3(organic fertilizer:fertilizer=75%:25%), the quality of the fruit was better than other treatments, the TSS and solid acid ratio increased by8.08%and22.27%separately, while the thickness of pericarp and titratable acidity content decreased by23.43%and25.86%than the control respectively. Phosphorus utilization was the highest when citrus were treated by T4(only compound fertilizer) than other treatments, up14.67%. Nitrogen utilization was the highest when citrus were treated by T5(only organic fertilizer) than other treatments, up38.27%, besides, the color of the fruit was better. The overall efficiency of the best fertilizer treatments needed further exploration and research.4. Based on the above results, developed the prescription map of variable rate fertilization of this two test area.For area A, N, P and K fertilization demand generally displayed the decreasing trend from north to south.High volume and in the amount of N, P and K fertilizer requirement region accounted for30%,60%and17%of the total area oforchards.38%of the orchard area did not need potassium. For area B, N, P and K fertilization demand generally displayed a decreasing trend from southeast to northwest.High volume and in the amount of N, P and K fertilizer requirement region accounted for90%,60%and8%of the total area of orchards. About40%of the area did not need K fertilizer.In typical mountain of area B, high volume and in the amount of N, P and K fertilizer requirement region accounted for79%,54%and9%of the total area oforchards. About47.7%of the area did not need K fertilizer. |
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