Abstract:

To understand the characteristics of citrus orchard soil acidification in western Zhejiang for providing reference for citrus orchard acid soil improvement and sustainable development, 26 citrus orchards in western Zhejiang were selected for soil investigation. The composition of soil exchangeable acids, acid buffering capacity and their relationship with soil properties were analyzed. The applicability of five lime demand estimation methods, namely SMP buffer method, exchangeable acid neutralization estimation method, calcium hydroxide mixed titration method, calcium chloride exchange calcium hydroxide neutralization titration method and estimation method based on soil physical and chemical properties, were evaluated with reference to the lime demand determined by soil lime adding cultivation method. The results showed that the soil pH of the investigated orchard was pH 3.11-6.52, and 88.5% of the soil pH was lower than the suitable growth range of citrus (pH 5.0-6.5). The soil pH (pH 4.80) developed from purple sandstone was higher than that of other parent materials, followed by the soil developed from diluvium (pH 4.41), river alluvium (pH 4.36), quartz sandstone (pH 4.24) and acid rock (pH 4.23). The content of exchangeable acid in the soils was 0.05-6.66 cmol/kg, and the content of hydrolytic acid was 2.24-16.05 cmol/kg. The content of potential acids in the soils developed from purple sandstone, river alluvium and diluvium were relatively low. Soil acid buffer capacity was significantly positively correlated with free iron oxide content, cation exchange capacity, exchangeable calcium, total base ions, and base saturation (P<0.05), and negatively correlated with soil exchangeable Al³⁺content (P<0.05). Among them, soil exchangeable calcium and free iron oxide contributed the most to soil acid buffer capacity. Soil developed from purple sandstone had higher exchangeable calcium and free iron oxide content, so the buffer capacity was higher. With the increase of garden age, the contents of active acid and potential acid increased, while exchangeable base and soil acid buffer capacity decreased. The results with different estimation methods of lime demand showed that SMP method was more accurate in estimating the soil with higher lime demand, and the calcium hydroxide mixed titration method had the highest linear correlation with the results of incubation experiments. These two methods were relatively suitable for the estimation of soil lime demand of orange orchards in western Zhejiang.

Key words: western Zhejiang, citrus orchard, acid soil, acid buffer capacity, lime application rate