Detailed Explanation of Rice Paddy Soil Types and Nutrient Status in Sanming City
Our city has relatively abundant land resources, with a total land area of 34.44 million mu, of which cultivated land area is 2,563,100 mu, accounting for 7.4% of the total land area (of which paddy field area is 2,441,900 mu, accounting for 7.1% of the total land area, and agricultural land is 121,200 mu, accounting for 0.3% of the total land area). Due to differences in distribution terrain, paddy soils can be divided into four types: plain fields, sloping terraced fields, mountain valley fields, and streamside fields, with a ratio of 4.6:5:6.2:1 among them. Plain fields are dominated by hydromorphic paddy soil, including grey mud fields, grey sandy fields, black sandy fields, black mud fields, etc.; sloping terraced fields are permeable paddy soil, including yellow mud fields, yellow muddy sand fields, grey-yellow mud and purple mud fields, etc.; mountain valley fields are mainly gleyed paddy soil, including deep and shallow mucky fields, greenish mud fields, etc.
1. Hydromorphic paddy soil:
Hydromorphic paddy soil covers an area of 1,232,300 mu, accounting for 50.61% of the paddy soil area, and is the main type of paddy field soil in our city. It is distributed in river valley plain fields, streamside fields on both sides of streams and rivers, and broad mountain valley fields in hilly valleys across all counties.
In the process of soil formation, hydromorphic paddy soil is affected by both surface irrigation water and groundwater, producing a hydromorphic process, that is, the oxidation-reduction process in paddy soil formation. The cultivated horizon of hydromorphic paddy soil is relatively thick. According to analysis and statistics of 128 soil samples, the average is 214.5+-1.70cm (C.V. 11.72%),<0.01mm物理性粘粒43.35±14.22（Ｃ.Ｖ32.80％），质地适中，多为轻壤至中壤；土壤肥力较高，养分较为丰富，有机质为2.59±0.44％（Ｃ.Ｖ16.98％）、全氮0.157±0.&127;081&127;％（Ｃ.Ｖ51.59％）、全磷0.082±0.037％（Ｃ.Ｖ45.12％）、全钾2.59±0.44％（Ｃ.Ｖ16.99％）、代换量7.72±2.50me／100g土（Ｃ.Ｖ32.28％）。根据母质类型的差异，可划分为灰泥田、潮沙田、石灰田、乌泥田等四个土属。
2. Permeable paddy soil:
Permeable paddy soil covers an area of 777,000 mu, accounting for 31.91% of the paddy soil area. It is widely distributed in mountainous areas, hilly slopes, hilly upland fields and high terraces of river valleys across all counties. Most of it originates from red soil, and there are also slope deposits, flood-alluvial deposits and Quaternary red clay from yellow soil and purple soil as parent materials. It is located at higher terrain positions, the soil body is less affected by groundwater, and soil water is mainly supplied by rainfall and irrigation water, belonging to the surface water type.
The cultivated horizon of permeable paddy soil undergoes frequent alternating dry and wet conditions, which is conducive to the decomposition of soil organic matter. The organic matter content is lower than that of other subtypes, with an average of 2.17+-0.34% (n=117, C.V. 15.67%). The average ratio of humic acid to fulvic acid is 0.78+-0.21 (n=8, C.V. 26.92%), lower than that of hydromorphic and gleyed paddy soils. The soil is strongly acidic, with an average pH of 5.13+-0.47 (n=117, C.V. 9.16%). Available nutrients are relatively deficient. Based on differences in parent material types, permeable paddy soil can be divided into six soil genera: yellow mud fields, red earth fields, purple mud fields, brown mud fields, white soil fields, and sandy fields.
3. Gleyed paddy soil:
Gleyed paddy soil covers an area of 425,830 mu, accounting for 17.49% of the paddy soil area. It is found in all counties, mostly distributed in spring overflow zones of mountain and hill valleys, or low-lying areas of plains. In the process of soil formation of gleyed paddy soil, due to low-lying terrain, poor drainage, and high groundwater levels, generally above 50 cm, and even overflowing onto the surface to inundate rice fields, the soil body is in a saturated state or is soaked by groundwater year-round, and reduction processes dominate throughout the soil.
According to analysis and statistics of 228 profile points across the city, the average organic matter content of gleyed paddy soil is 3.37+-0.46% (C.V. 13.65%),<0.01mm物理性粘粒46.41±12.84（Ｃ.Ｖ27.67％），&127;全氮0.174±0.046％（Ｃ.Ｖ26.44％）,全磷0.074±0.034％（Ｃ.Ｖ45.94％）,全钾2.843±1.205％（Ｃ.Ｖ42.38％）,碱解氮179±44ppm（Ｃ.Ｖ24.58％）,&127;速效磷4±2ppm（Ｃ.Ｖ50.0％），速效钾65±41ppm（Ｃ.Ｖ63.07％），&127;代换量9.48±2.68me／100g土（Ｃ.Ｖ28.27％）,pＨ5.0±0.42（Ｃ.Ｖ8.4％）。根据水文地质条件和潜育程度不同，划分为青泥田、冷烂二个土属。