四川盆地是我国重要的柑桔产区之一。其紫色土面积占四川盆地总面积的55％,约16万km~2。这些紫色土是由湖相沉积的砂岩、页岩风化而成的幼年土壤,富含磷、钾等元素,但由于含有或多或少的碳酸钙(CaCO_3),致使土壤呈微碱性乃至较强的碱性反应。特别是紫色砂、页岩新风化出的土壤含碳酸钙较多,有的高达10％～15％,有效态的二价铁离 Sichuan Basin is one of the important citrus producing areas in China. Its purple soil area accounted for 55% of the total area of ​​the Sichuan Basin, about 160,000 km ~ 2. These purple soils are formed by lacustrine sedimentary sandstone and shale weathered young soils that are rich in elements such as phosphorus and potassium. However, due to the presence of more or less calcium carbonate (CaCO3), the soil is slightly alkaline and even more alkaline Strong alkaline reaction. Especially the purple sand, shale newly weathered soil containing calcium carbonate more, and some as high as 10% to 15%, the effective state of ferrous