Effects of N, P, K on Yield and Quality of Jujube in the Loess Hilly Region and Its Fertilization Model

The aim of this study is to explore the optimal N, P and K fertilization model suitable for pear-jujube in the mountain of northern Shaanxi in 2016 years. This experiment use 3-factor, saturated optimal design for quadratic fertilization scheme. The effects of different fertilization treatments on the yield and quality of pear-jujube were studied through field experiments. And comprehensive evaluation based on the quality of pear-jujube. The results showed that N1P3K3 has the highest yield, which is 48% higher than the control (CK). The effect of nitrogen, phosphorus, and potassium on yield is potassium fertilizer (positive effect)> phosphate fertilizer (positive effect)> nitrogen fertilizer (negative effect). Phosphate and potassium fertilizers have significant effects on increasing the content of soluble solids. Application of potassium fertilizer alone can significantly increase the content of reduced Vitamins c. The combined application of nitrogen, phosphorus, and potassium reduced the content of reduced Vitamins c. N3P3K1 treatment can significantly increase the total sugar content in fruits. Single application of phosphate and potassium increases the content of organic acids in fruits. Other fertilization treatments have significant effects on reducing the content of organic acids in fruits. The sugar-acid ratio of N3P3K1 is significantly higher than CK, which had an important effect on improving the taste. A high amount of potassium fertilizer has a significant effect on increasing the total flavonoid content in fruits. The interaction of nitrogen and phosphorus will reduce the total flavonoid content. The effect of nitrogen, phosphorus, and potassium on quality is potassium (positive effect)> nitrogen (positive effect)> phosphate (positive effect). Comprehensive analysis, the optimal fertilization amount when the target yield is 23000 ∼ 27000 kg·hm-2 and the quality score is above 85 is nitrogen (N) 406.93 ∼ 499.31 kg·hm-2, phosphorus (P2O5) 203.94 ∼ 297.08 kg·hm-2, and potassium (K2O) 285.47 ∼ 322.82 kg·hm-2.


Introduction 37
The ecological environment of the Loess Plateau in northern Shaanxi is fragile. The main 38 reason is that vegetation is scarce; soil erosion and land desertification are more serious. The improve fruit yield and quality. Fertilizer input is crucial for sustainable agricultural production 46 that provides sufficient food for the world [2] . And it plays an important role in food safety [3] . The quality of fruit is an important aspect of the value of the commodity. Bie Zhixin et al [4] showed

78
Overview of the study site 79 The

117
Moisture content of fruit: The moisture content of fruit is determined by drying method.

119
Soluble solids were measured using a 2WAJ-Abbe refractometer. Reducing vitamin c was 120 determined by 2,6-dichloroindophenol titration [19]; the total sugar content was determined by  [26]. Six quality indicators of moisture, fruit shape index, soluble solids 128 content, sugar-acid ratio, reduced Vc and total flavonoid content were comprehensively scored in order of importance (out of 100 points). For each index, the best processing value is full marks.

130
The percentage of the measured value of the index in the optimal processing value of the 131 processing is the actual score of the processing index. The sum of the weight values of all the 132 quality index scores of each process is the overall quality score of each process. The total 133 flavonoid content weight is 0.3. The sugar-acid ratio and the reduced Vc weight are both 0.2. The

134
water content, fruit shape index and soluble solids weight are all 0.1.

135
Data statistics and analysis 136 The test data was compiled using Microsoft excel 2010 and SPSS.18.0, and drawing was 137 using MATLAB 7.1.

139
Effects of different fertilization treatments on the output of 140 pear-jujube 141 The yield of fertilization treatment is significantly higher than control treatment. The output 142 of K 3 , P 2 K 2 and N 1 P 3 K 3 is higher than that of other treatments. The yield of N 1 P 3 K 3 treatment is 143 the highest, reaching 25950.6 kg/hm 2 , 48% higher than the control. It shows that fertilization can 144 increase the yield of jujube trees. Among them, the increase of potassium fertilizer application has 145 a significant effect on increasing yield. Combined application of phosphorus and potassium can 146 further increase the output of red dates on the basis of single application of potassium fertilizer.

147
The reasonable combination of nitrogen, phosphorus and potassium is more beneficial to the 148 increase of jujube yield. (Table 2) 149

153
Effects of different fertilizer treatments on the quality of 154 pear-jujube 155 Fertilization can significantly increase the water content of jujube fruit. The N 1 P 3 K 3 156 treatment had the highest water content, which was 4.17 percentage points higher than the control.

157
P 2 K 2 treatment had the highest soluble solids content, which was 2.19 percentage points higher 158 than the control. Phosphate and potassium fertilizers increase the reduced Vc content of jujube 159 fruit and reduce the total sugar content. The total sugar content of P 2 K 2 treatment was significantly 160 higher than that of phosphate fertilizer and potassium fertilizer. Phosphate fertilizer and potassium 161 fertilizer will increase the organic acid content of jujube fruit. Single application of nitrogen 162 fertilizer or combined application can reduce the content of organic acids. The N 1 P 3 K 3 , N 3 P 1 K 3 and N 3 P 3 K 1 treatments had significantly lower organic acid content than the other treatments.

164
Therefore, balanced fertility can significantly reduce the content of organic acids in jujube fruit,

165
and has a significant effect on changing the taste of jujube fruit. The sugar acids treated with 166 N 3 P 1 K 3 and N 3 P 3 K 1 were 2.42% and 2.64% higher than the control, respectively. This has a lot to 167 do with their high sugar content and low acid content. The total flavonoid content of K 3 and 168 N 1 P 3 K 3 treatments was significantly higher than that of the other treatments. The total flavonoid 169 content of P 2 K 2 , N 2 K 2 and N 1 P 3 K 3 treatments was also higher than that of the control, indicating 170 that potassium fertilizer has a significant effect on increasing the total flavonoid content of pear 171 jujube. (Table 3) 172

189
The main effect analysis of each fertilization element was carried out. Since the regression  (Table 2) 223   (Table 6) 273

292
Chai [27] research shows that increasing the application of potassium fertilizer can increase 293 the sugar and vitamin C content in jujube fruit. The Vc content of K 3 was the highest in this 294 experiment, which is consistent with Chai's conclusion. But the highest total sugar content is 295 N 3 P 3 K 1 treatment. The sugar content of K 3 treatment was lower than the control 0.29g/100g. The 296 total sugar content of N 2 K 2 and P 2 K 2 treatments was not significantly different from N 3 P 3 K 1 297 treatment. Analyze the possible reason for the negative effect caused by excessive potassium 298 fertilizer. The specific mechanism needs further study. Lin et al [28] showed that the application 299 of phosphorus and potassium fertilizers on the quality of citrus showed that single application of 300 phosphorus, potassium fertilizer and combined application of phosphorus and potassium fertilizers 301 can increase the content of soluble sugar in citrus. In this study, single application of phosphate 302 fertilizer or potassium fertilizer had little effect on total sugar and reducing sugar content.

303
Combined application of phosphorus and potassium can significantly increase the content of total sugar and reducing sugar. Analyze the reasons for the difference between the results of Lin [28] 305 may be that the appropriate amount of potassium fertilizer is an important factor for increasing the 306 sugar content in jujube fruit, and excessive potassium fertilizer will have a certain inhibitory 307 effect. The specific mechanism needs to be further studied. Phosphate fertilizer and potassium 308 fertilizer alone will increase the acid content in jujube fruit. Other treatments can reduce the 309 content of organic acids in jujube fruit. High levels of phosphate and potassium fertilizers, and 310 low levels of nitrogen fertilizer have a promoting effect on the total flavonoids content in jujubes.

311
Therefore, proper fertilizer application should be paid attention to when applying fertilizers.

312
3-factor 2 times D-saturated optimal design has been successfully applied to Platycodon