Studies on controlled potassium fertilizers I. Relative effectiveness of various hardly soluble potassium compounds as source of slow-release

Abstract

Relative effectiveness of various hardly soluble K materials as sources of slow availability for plants was compared by uptake of K in Brassica seedlings grown in quartz sand-nutrient medium with occasional leaching, and by the release pattern of K. Material characteristics exert a great influence on K availability. Water solubility is not a dominant factor for controlling the availability of K to the plants, but particle sizes and the reaction of K in fertilizers with nutrient ions in the medium play a significant role in the release pattern of K. Moreover, the plant roots have an ability to accelerate K release from such hardly soluble aources as fused potassium phosphate, KMgPO4, and K2CaP2O7. According to the results obtained, that is, total dry matter production, pattern of K uptake through four successive croppings and loss of K by leaching the examined materials appear to be divided into the following three groups: a) Materials having a high degree of slow availability-KMgPO4 (+3 mesh), fused potassium phosphate (+28 mesh and -65 mesh), K2CaP2O7 (+3 mesh), and calcined potassium phosphate (-7+14 mesh). b) Materials having a mid degree of slow availability- KCaPO4 (+3 mesh), liparite potassium. Sulphur coated KCl, calcined potassium phosphate (-32 mesh), K2CaP2O7 (-32 mesh), KMgPO4 (-32 mesh), and KPO3 (+3 mesh). c) Materials having a low degree of slow availability-KCaPO, (-32 mesh), KPO, (-32 mesh). © 1974 Taylor & Francis Group, LLC.