The strata exposed in Huangyan area are mainly Mesozoic volcanic rocks of Upper Jurassic Gaowu Formation (J3g) and Xishantou Formation (J3x), volcanic sedimentary rocks of Lower Cretaceous Guantou Formation (K 1g) and Chaochuan Formation (K 1c), and quaternary loose sediments.
Due to the influence of paleoclimate, neotectonic movement, sea level fluctuation and other factors, the Quaternary strata in mountainous areas and plains are quite different in lithology, genesis and thickness, which are synchronous and heterogeneous deposits respectively. The exposed parts of the mountain surface are mainly Pliocene flood alluvial deposits, alluvial deposits and Holocene alluvium. The surface of the plain area is mainly Holocene marine deposits and alluvial deposits.
Comparing the types of soil-forming parent materials in huangyan district and the distribution of citrus in huangyan district, it can be clearly seen that citrus is mainly distributed in Holocene marine sediments (mQ4) and alluvial-diluvial sediments (alQ4), and a certain amount is also distributed in Pleistocene slope alluvial-diluvial sediments (dl-plQ3), while citrus in hilly areas is mainly distributed in weathered residual sediments of Upper Jurassic Xishantou Formation (J3x) (Figure
The research shows that when a large number of Pliocene (Q3) proluvial, proluvial and slope deposits appear in Quaternary sediments, it is the most suitable stratum for planting citrus and other fruits, which is quite different from the Middle Pleistocene (Q2), which is reflected in the soil development related to plant growth. In Pliocene (Q3), proluvial, proluvial, slope deposits and other soil-forming materials developed in sub-yellow gluten mud. The sub-yellow ribbed soil with alluvial, alluvial and diluvial parent materials developed in the Upper Pleistocene (Q3) is weak in reddening, light in texture, weak in acidity, high in silicon-aluminum ratio, high in substitutability, good in fertilizer conservation, rich in salt base and good in tillage, which is beneficial to the growth of fruit trees such as citrus.
Although citrus can grow on all kinds of soil (including saline-alkali land), and even the requirements for soil pH can be wider, ranging from 5.0 to 8.5, citrus still has certain requirements for soil conditions, because different soil types have significant effects on the trial operation date, fruit state, quality and yield of citrus. According to relevant data, when the average salt content in 100cm soil is more than 0.003%, it can't be planted. The light salty clay with salt content of 0.00 1% ~ 0.003% needs to be planted for one year or light exotic soil, which indicates that the growth of young oranges is poor and the fruiting period is delayed. However, in the film-covered loam or loam sandy soil with low salt content (< 0.00 1%), it can bear fruit after three years of planting, and the trees are strong, with high yield and good quality, which shows the importance of soil.
Figure 5- 1 Lithology and pedogenic parent material types of citrus in huangyan district, Zhejiang Province
Table 5-2 Comparison of Main Properties of Soils Developed in Q3 and Q2 Strata in Huangyan Area of Zhejiang Province
The fluvo-aquic soil distributed on both sides of Yongning River and at the junction of mountainous areas and plains is the main soil type in local citrus producing areas. The parent material of soil is mainly marine sediments, followed by flood alluvium, and the soil layer is deep. The main soil types are film-covered mud ploughing sand, mud ploughing sand and river mud. Due to the different degrees of tidal influence, it can be divided into three types: micro-calcareous fluvo-aquic soil (coated loam sand), non-calcareous fluvo-aquic soil (loam sand) and calcareous fluvo-aquic soil (river mud). The soil layer is deep, generally greater than 1 ~ 2m. The soil is heavy to medium clay, with good ventilation and water permeability, and the subsoil is affected by tides, which lies in the daytime and comes out at night and is slightly alkaline. Topsoil contains high-efficiency nutrients, among which citrus planted on calcareous fluvo-aquic soil and non-calcareous fluvo-aquic soil has developed root system, lush foliage, high yield and good quality, which is especially suitable for planting early orange, local early orange and slow orange.
Coastal light saline soil is mainly distributed in the newly formed beach zone, which is a newly developed citrus planting area in recent 10 years. The planting area is small, accounting for only 0.68% of the total citrus area in the whole region. Due to the short time of soil formation, the soil generally has no obvious development level and the soil structure is poor. The whole soil layer contains soluble salt and is calcareous. When the pH value exceeds 8, most of the iron, manganese and zinc compounds in the soil are insoluble, and the citrus trees turn green seriously or even die, and the yield and quality are relatively poor.
Citrus planted on red soil is mainly distributed on hilly slopes with an altitude of about 25 meters. The parent material of the soil is mostly weathered tuff, and the thickness of its soil layer, including semi-weathered materials, can reach more than 1 ~ 2m. The soil type is mainly red soil, and the soil texture is medium to light clay.
(2) Effect of Huangyan soil on citrus quality.
Huangyan tangerine has thin skin, red flesh, high fruit yield and edible rate, and the ratio of sugar to acid is as high as 13.0. Its main cultivated variety "native jujube" is mainly distributed in the first terrace and floodplain on both sides of Yongning River in Huangyan, and citrus is mostly distributed in the lower reaches of Yongning River, where the terrain is low and the marine sediments are most widely distributed. The soils developed by alluvial parent materials in Quaternary rivers can be divided into coated silt soil and coated silt soil. However, the quality of citrus fruits on Tuhe soil, which is greatly affected by tides, is the second, and the ratio of sugar to acid of citrus fruits on clay heaped soil and red gravel soil is low, and the taste is not good. According to Liang et al.' s research (1988), the pH value of citrus orchard soil is lower than 5.28, and the pH value is lower than 4. 1. Exchangeable aluminum seriously affects the availability of various nutrients in the soil, especially phosphorus. Although available zinc has increased, potassium, calcium and magnesium are insufficient, which leads to an obvious increase in acid content in the fruit and affects the quality. It is found that the content of calcium in the parent material and soil of high-quality orange orchards is obviously higher than that of ordinary orange orchards (Table 5-3), which shows that appropriate calcium content in the soil has a certain effect on improving the quality of oranges.
Table 5-3 Contents of Elements in Citrus Planting Soil in Zhejiang Province
There is a close relationship between soil types and citrus quality in Huangyan citrus producing area, and the geochemical characteristics of different soil types affect citrus quality. According to the field investigation, the soil types of Huangyan citrus orchard are mainly fluvo-aquic soil, coastal light saline soil and red soil. The soil texture is medium to medium clay, and the soil reaction changes from acidic to alkaline, among which fluvo-aquic soil has the longest cultivation history. Citrus planted in fluvo-aquic soil in this area has high sugar content and sugar-acid ratio (Table 5-4), good quality, high yield and the largest planting area.
Table 5-4 Relationship between Tidal Soil and Local Early Fruit Quality in Huangyan Citrus Orchard, Zhejiang Province
From the geochemical characteristics of different soils (Table 5-5), it can be seen that, compared with red soil and saline soil, fluvo-aquic soil is richer in mineral components than other soils, with geochemical characteristics of high P, Si, Mg, Ca, Na and K and low al, Fe, Co and Ba. The contents of organic matter, available nitrogen, phosphorus, potassium, available magnesium, zinc, copper and other nutrients in soil increased obviously from the core layer to the surface layer, reflecting the height of soil cultivation and fertilization. Therefore, fluvo-aquic soil is the main soil type for cultivating high-quality citrus.
Table 5-5 Contents of Related Elements and Oxides in Citrus Planting Soil in Zhejiang Province
Note: The content unit of oxide is%, and the rest is mg/kg.
Effect of groundwater on citrus quality
In Huangyan and Jiaojiang areas, shallow groundwater in coastal plain generally belongs to brackish water, and the salinity of groundwater is mostly 1 ~ 2g/L, which can reach more than 2.7g/L. The hydrochemical type of groundwater in this area is piedmont HCO3. Sodium calcium or chlorine carbonate? Na type, gradually transitioning from offshore to HCO3 Cl? Na Mg type, near the sea is cl? Na type. In the vertical direction, the salinity of water gradually increases from top to bottom.
According to the determination, the pore phreatic water of Holocene alluvium is HCO3? Na Ca type, pH value is about 6.5, and the pore water type of Pliocene diluvial, alluvial and diluvial sediments is HCO3? Ca type, pH 6.6, suitable for citrus growth. However, it is worth pointing out that these groundwater are rich in calcium, which has an important impact on the improvement of citrus quality. Predecessors have come to the conclusion that there are more high-quality fruits in the areas where the groundwater in citrus orchards is affected by tidal waves, and the underground salt water is beneficial to improve the quality of citrus in the prosperous period and the fruiting period. In fact, calcium in groundwater may play an important role.