Abstract

The process for the production of a slow-release micronutrient fertilizer is described. The compound contains zinc, iron, manganese, and copper as micronutrients and is produced by polymerizing a system containing phosphoric acid, zinc oxide, hematite, pyrolusite, copper sulfate, and magnesium oxide followed by neutralization of the polyphosphate chain with ammonium hydroxide. Changes in temperature, density, and viscosity of the reaction system during polymerization were studied. Reaction kinetics was studied at three different temperatures. Rate curves revealed a multistage process with essentially linear rates at each stage. Thus, each stage displayed zero order kinetics. The product was crystalline and revealed ordering of P-O-P chains. It had low solubility in water but high solubility in 0.33 M citric acid and 0.005 M DTPA. Three different field trials showed significant yield increments using the slow-release micronutrient fertilizer compared to the conventional micronutrients. Yield increments in rice were in the range of 10–55% over control (with no micronutrient) and up to 17% over the conventional micronutrient fertilizers. There were significant increases in total uptake of zinc, iron, and manganese in the grain. Slow-release fertilizers also produced significant yield increases in potato as well as significant increase in vitamin C content of the tuber.

Highlights

  • Micronutrients are essential components of proteins and enzymes and are vital for increasing crop yields as well as improving the nutritional quality of food

  • Slow-release functionality has been achieved by encapsulation of water soluble materials within a membrane or conversion to polymers of the urea aldehydes [1, 2]

  • A glassy phosphate produced by fusing oxides of micronutrients in phosphoric acid at 800∘C has been described in a patent [5]

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Summary

Introduction

Micronutrients are essential components of proteins and enzymes and are vital for increasing crop yields as well as improving the nutritional quality of food. Slow-release fertilizers (which have low water solubility) are, considered as the solution to the problem. We report the process for production of slow-release multimicronutrient fertilizer of Zn, Fe, Mn, and Cu. Studies on polymerization kinetics, process parameters, changes in physical properties, and product characterization were done.

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