What Is a Compound Fertilizer? Advantages and Precautions of Mixed Application

What is a compound fertilizer? What are the advantages of mixed application? What precautions should be taken? Compound fertilizer refers to a chemical fertilizer that simultaneously contains the three elements nitrogen, phosphorus and potassium, or contains only any two of these elements. For example, a compound fertilizer containing any two of the three elements is called a binary compound fertilizer, while a fertilizer simultaneously containing the three elements nitrogen, phosphorus and potassium is called a ternary compound fertilizer. 

Fertilizer mixing refers to a fertilizer made by mechanically mixing two or more single-element fertilizers or compound fertilizers together. Its advantages are:

① Suitable fertilizer varieties can be selected according to different soils and different crops, and blended in appropriate proportions;

② Applying fertilizers with multiple components at one time can both bring into play the interactive effects among nutrients and save labor for fertilization;

③ It can improve certain undesirable physical and chemical properties of fertilizers, such as moisture absorption, caking and high free acid content.

Note: Precautions for mixed use

① Fresh compost and barnyard manure can be mixed with plant ash and lime because the former produces organic acids during decomposition, which affects the activity of microorganisms; adding 2%-3% lime or 5% plant ash can regulate the acidity and promote the decomposition of the fertilizer. 

② Superphosphate can be mixed with an appropriate amount of plant ash because superphosphate usually contains 5% free acid; if mixed with plant ash at 5% of the phosphate fertilizer application rate, the adverse effects of the free acid in the phosphate fertilizer can be eliminated, while the effectiveness of the phosphate fertilizer and potassium fertilizer will not be reduced. 

③ Plant ash cannot be mixed with decomposed human excrement and urine for application, because the main component of plant ash is potassium carbonate, whose aqueous solution is alkaline, while the nitrogen in decomposed human excrement and urine exists in the form of ammonium carbonate; when it encounters alkali, it volatilizes ammonia, thereby causing nitrogen loss and reducing fertilizer effectiveness. According to experiments, after mixing 1 part plant ash with 1.5 parts human excrement and urine and leaving it for 3 days, the nitrogen loss can reach 27%. 

However, not all fertilizers can be made into mixed fertilizer. When considering mixing several fertilizers, 3 principles should be followed:

① It should not cause loss of fertilizer nutrients or reduce their availability. For example, ammonium nitrogen fertilizers such as ammonium sulfate or compound fertilizers containing ammonium nitrogen, as well as water-soluble phosphate fertilizers such as superphosphate, must not be mixed with alkaline fertilizers such as plant ash and calcium cyanamide, so as to avoid nitrogen loss and reduced phosphorus availability;

② It should not produce undesirable physical properties;

③ It should help improve fertilizer effectiveness and work efficiency and reduce the cost of fertilizer application.