凡是为提高作物产量和品质、提高土壤肥力而施入土壤用以供给植物营养的物质都叫肥料。直接供给作物必需营养的那些肥料称为直接肥料，如氮肥、磷肥、钾肥、微量元素和复合肥料都属于这一类。而另一些主要是为了改善土壤物理性质、化学性质和生物性质，从而改善作物的生长条件的肥料称为间接肥料，如石灰、石膏和微生物肥料等就属于这一类。然而，这两类肥料有时是不能截然分开的，如有机肥料既是直接肥料又是间接肥料。

All materials that are put into the soil to provide nutrients for plants in order to increase crop yield and quality and to improve soil fertility are called fertilizers. Fertilizers which directly supply essential nutrients to crops are called direct fertilizers, such as nitrogen, phosphorus, potassium, trace elements and compound fertilizers. Other fertilizers which are mainly used to improve the physical, chemical and biological properties of soil, thus improving the growth conditions of crops, are called indirect fertilizers. Such as lime, gypsum and bacterial fertilizers.sometimes the two kinds of fertilizers can not be completely separated. For example, organic fertilizer is both direct fertilizer and Indirect fertilizer.