Eficiência agronômica de micro e macro nutrientes recuperados da urina humana no cultivo de milho (zea mays)

Abstract

The continuous growth of the population has significantly increased the demand for phosphate fertilizers in addition to the addition of residues in the environment. The recovery of nutrients (nitrogen and phosphorus) from human urine through the crystallization of struvite (NH₄MgPO₄.6H₂O) is an expanding practice in the world. The objective of this study was to characterize a struvite-based fertilizer obtained from the chemical precipitation of human urine in Jar test, detect the presence of possible heavy metals, compare its agronomic efficiency with conventional fertilizer in the cultivation of corn plants, as well as, monitor nutrient concentrations in cultivated soils and corn plants. The microstructural characterization of the struvite-based fertilizer was performed in an X-Ray Diffractometer (XRD) and 31P solid-state Nuclear Magnetic Resonance Spectroscopy (NMR). Elemental and heavy metal characterization was performed on an Inductively Coupled Plasma Atomic Emission Spectrometer (ICPOES). Their P forms were determined through their variable solubility by the Standard Measurement and Testing (MTP) protocol. The kinetics of P release in water was evaluated at different pHs. Five P rates (30, 80, 160, 240 and 320 mg kg −1) provided by the struvite and monoammonium phosphate (MAP) based fertilizer were evaluated and compared in a greenhouse under corn cultivation for 45 days. At the end, the production of dry mass (DM), the concentrations of nutrients deposited in the cultivated soils and the levels accumulated in the tissues of the plants were determined, in addition to the relative agronomic efficiency (EAR) of the fertilizer evaluated in relation to the MAP. A comparison of the treatments was performed by the Mean Comparison Test (Friedman Test) with its post-hoc (Nemenyi) and by the Mann-Whitney U test.Among the results obtained, struvite was the predominant phase in the material. (79.54%). A newberyite phase was detected by NMR, however, NMR was not able to identify other impurities, evidencing the need for the association of methods when it is intended to carry out P speciation. Cd, Pb, Cr and Hg were below the permitted by Brazilian regulations. in all treatments with MAP, MS productions were higher. However, do not observed statistical differences when comparing the averages of the same treatment (significance level 0.05). P uptake was higher in plants of corn fertilized with MAP. On the other hand, soils treated with fertilizer based on struvite showed higher concentrations of remaining P. EAR was low for dosage of 30 mg of P/kg of soil. At dosages of 80, 160 and 240 mg of P/kg of soil, the EAR were above 85%, but this proportion reduced in the dosage of 320 mg of P/kg of soil. The results indicated that the fertilizer at struvite base can be considered an alternative and safe source for the supply of nutrients to the corn crop due to its chemical composition meet the nutritional demand and not present high concentrations of metals heavy.