What is controlled-release fertilizer?

　　Controlled-release fertilizers are coated with various polymers; the micropores in these coatings typically measure only a few hundred nanometers. Liquid water cannot pass through the membrane and can only enter it in the form of water molecules. Consequently, while water molecules can freely move in and out of the coating, the fertilizer granules remain completely isolated from the external environment, and nutrients are released primarily via osmotic pressure across the membrane. As a result, the rate of nutrient release depends solely on the mobility of water molecules and the size of the membrane’s micropores, and when… Controlled-release fertilizer When applied to the soil (with micro‑porous placement), the release of controlled‑release fertilizer is governed solely by the mobility of water molecules. The rate at which water moves depends on temperature, while factors such as soil microbial activity and pH do not influence the fertilizer’s release in any way. By contrast, with conventional fertilizers, rapid early nutrient release often outpaces the plant’s ability to absorb them, leading to substantial nutrient accumulation in the soil—where it may volatilize, be lost through rainfall, leach into groundwater, or become immobilized in the soil. As a result, average fertilizer use efficiency hovers around 35%, with nutrient deficiencies emerging later. Controlled‑release fertilizers, on the other hand, effectively capture nutrients that would otherwise remain unavailable in the early stages and make them available to plants over an extended period. They also minimize losses due to leaching, microbial degradation, and soil fixation, essentially providing a steady, sustained supply of nutrients. Consequently, fertilizer use efficiency can reach approximately 70%, with root‑zone utilization rates as high as 80%.

　　 Controlled-release fertilizer In reality, it is a nutrient source that continuously releases over a 24-hour period, with the release rate depending on ambient temperature: higher temperatures during the day accelerate release, while lower nighttime temperatures slow it down. Meanwhile, plant resources are most abundant when daytime temperatures are high, thanks to vigorous photosynthesis. Some experts argue that the nutrient-release profile of controlled‑release fertilizers aligns with plant needs—an appealing notion—but in practice, it is merely an approximation of such a curve.

　　There are three types of release‑pressure curves for controlled‑release fertilizers.

　　1. High release (the first half of the parabola): In the early stages, it develops and releases rapidly; such membranes are typically thin or made from materials with poor performance characteristics.

　　II. Under a fixed temperature—specifically, at a given temperature—the daily release of students’ basic information remains essentially unchanged. If the temperature fluctuates, the differences are negligible, primarily because coating materials like ours do not exhibit thermal expansion; consequently, the size of the micropores or pores remains constant.

　　Third, the release curve of “S.” This is a highly desirable curve for China. Typically, this type of fertilizer employs two approaches: an initial slow release followed by a rapid late‑stage release, thereby achieving an S‑shaped release profile. One approach involves using thick coating materials; however, the material itself and its performance are relatively weak. As the thick film swells and micropores or gas pores expand, the water‑soluble resin developed at South China Agricultural University adopts precisely this management strategy. With a very low coating ratio, the early stage exhibits ultra‑low release rates, while the swelling of the thick film and the enlargement of micropores or gas pores lead to a marked acceleration in the release rate.

　　The S-shaped curve is the most favorable nutrient-release profile for plant growth. During the early seedling stage, plants have relatively low nutrient requirements; as their growth rate accelerates, their demand for nutrients increases accordingly. The S-shaped release curve is an exceptionally ideal pattern. Controlled-release fertilizer The release duration can be precisely matched to the length of the plant’s growth period and the specific conditions of its growing environment.