# Effect of Different Ratios of Cow Manure and Chemical Fertilizers on Fruit Quality of Gala Apples
## 3 Results and Discussion
### Total Soluble Solids, Titractable Acid, Sugar-Acid Fraction  
Fruit flavour quality are significantly influenced by sugar and acid content, so metabolic regulation of sugar and acid plays a key role in fruit development. Figure 1 shows the effect of different ratios of cow manure and fertilizer on fruit glycolic acid and its components.  
Total soluble solids (Figure 1A) and titratable acid (Figure 1B) contents of fruits were not significantly different among fertilizer treatments, but were higher than those of non-fertilize treatments. Previous studies have shown that organic fertilizer treatments can increase the titratable acid content of fruits [32]. In the present study, the titratable acid content of fruits was higher in all fertilizer treatments than in the non-fertilize treatments, and the titratable acid content of fruits in different ratios of organic fertilizer and chemical fertilizer were higher in all treatments than in chemical fertilizer alone, which is consistent with the results of previous studies on lemon that organic lemons had a lower titratable acidity concentration than lemons grown in a conventional way [33]. It has also been suggested that organic fertilizer can reduce fruit acid content [34], that organic fertilizer application can reduce titratable acid content in passion fruit [35], and that organic fertilizer replaces chemical fertilizer to reduce titratable acid content in apple fruit [36].  
There are various fractions of sugars (Figure 1C-F) in apple fruit, mainly four, including sorbitol, glucose, fructose, and sucrose, with the highest percentage of fructose and sucrose. There are three main organic acid fractions (Figure 1G-I) in the fruit, including malic acid, quintic acid, shikimic acid, of which malic acid has the highest percentage and the rest of the acids are low [37]. Malic acid is an apple-specific acid and therefore the main source of sourness in apples, and quintic acid affects the astringency of apple fruit and plays an important role in the perception of sweetness [38]. A total of four sugars and three organic acids were identified in the apples of this study, in agreement with previous studies [39]. Fructose and sucrose accounted for a higher proportion of the sugar fraction, and malic acid was the highest in the organic acid fraction. Among the fertilization treatments, 50% CF + 50% CM treatment had higher content of each sugar fraction in the fruits.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Treatment** & **L** * & **a** * & **b** * & **C** * & **H0** \\ \hline
100\% CF & 67.79 \(\pm\) 4.23 & 22.41 \(\pm\) 2.41 & 22.08 \(\pm\) 2.67 & 32.09 \(\pm\) 0.99 & 45.21 \(\pm\) 4.98 a \\
75\% CF + 25\% CM & 70.47 \(\pm\) 0.38 & 21.81 \(\pm\) 1.06 & 21.59 \(\pm\) 0.91 & 31.06 \(\pm\) 0.76 & 46.29 \(\pm\) 5.06 a \\
50\% CF + 50\% CM & 64.03 \(\pm\) 0.20 & 28.86 \(\pm\) 5.93 & 19.75 \(\pm\) 2.33 & 34.52 \(\pm\) 1.83 & 30.06 \(\pm\) 3.02 bc \\
25\% CF + 75\% CM & 68.57 \(\pm\) 3.12 & 23.33 \(\pm\) 6.39 & 19.69 \(\pm\) 2.63 & 31.13 \(\pm\) 2.76 & 36.02 \(\pm\) 3.86 b \\
100\% CM & 62.94 \(\pm\) 8.78 & 29.36 \(\pm\) 9.72 & 19.51 \(\pm\) 4.03 & 35.77 \(\pm\) 3.91 & 26.38 \(\pm\) 2.93 c \\ CK & 70.22 \(\pm\) 1.22 & 20.80 \(\pm\) 2.47 & 23.42 \(\pm\) 2.82 & 32.33 \(\pm\) 1.73 & 50.27 \(\pm\) 4.57 a \\ ANOVA & NS & NS & NS & NS & * \\ \hline \end{tabular} Note: Values followed by different letters, within the same column, were significantly different (* means that \(p<0.05\)). NS means no significant difference.  
\end{table}
Table 4: Effect of different ratios of cow manure and chemical fertilizers on the colour of the shade side of fruits.  
The results of this study showed that the treatment of cow manure with chemical fertilizer could increase the fructose and sucrose contents of fruits, and significantly increase the malic acid content of fruits compared with chemical fertilizer alone. The results were consistent with previous studies on blueberry fruits [40].