Nitride-based controlled-release fertilizers and process for making same

Abstract

A controlled-release solid nitride fertilizer from fly ash and a method for making are described. The fertilizer includes a nitrogen source including at least one solid nitride combined with at least one precipitation-inhibiting agent and with at least one moisture-retention agent, all compressed together to form a porous release structure that in contact with water releases ammonium ions as a nitrogen nutrient at a substantially uniform release rate over a selected release period and thereby maximizes nitrogen-use efficiency by plants.

What is claimed is: 
     
         1 . A controlled-release soil fertilizer composition, comprising: a homogeneous blend comprising at least one solid nitride, at least one precipitation-inhibiting agent, and at least one moisture-retention agent, combined in a porous structure that releases ammonium ions at a substantially uniform release rate over a selected period of time 
     
     
         2 . The composition of  claim 1  wherein the at least one solid nitride is selected from the group consisting of AlN, Ca3N2, Ca3AlN3, CaAlSiN3, and combinations thereof, and the at least one precipitation-inhibiting agent is selected from the group consisting of Ca2P2O7, Ca3(PO4)2, CaH4(PO4)2, K2HPO4, KH2PO4, K4P207, KHCO3, Na4P2O7, and combinations thereof. 
     
     
         3 . The composition of  claim 1 , wherein the at least one moisture retention agent is selected from the group consisting of starch, cellulose, and combinations thereof. 
     
     
         4 . The composition of  claim 1  further comprising at least one hydrolysis catalyst selected from the group consisting of CaO, K2O, Na2O, CaCO3, Ca(OH)2, and combinations thereof. 
     
     
         5 . A process for making a solid nitride-containing fertilizer, comprising the step of compressing a homogeneous blend comprising at least one solid nitride comprising aluminum (Al), calcium (Ca), or Al and Ca, at least one moisture-retention agent, and at least one precipitation-inhibiting agent together under a selected compression load. 
     
     
         6 . The process of  claim 5 , wherein the step of compressing a homogeneous blend includes extruding a wet and congealed form of the homogeneous blend through an extrusion device.