The unrestricted growth of nitrifying bacteria, such as Nitrosomonas and Nitrobacter, causes an increase in the rate of nitrification. The effect of inhibitors is aimed at inhibiting the action of these microorganisms, by directly acting to reduce the speed of biological processes. As a result, the period of availability for plants of the ammonium form of fertilizer increases. This will increase the yield of agricultural crops due to the fact that this form is fixed by the soil and is not washed out of the reach of the root system. In addition, the ecological risk of environmental pollution will decrease.
In this way, leaching of the nitrate form of nitrogen, which pollutes river and lake waters, will decrease and the level of its accumulation in agricultural products will decrease. Therefore, the production of nitrification inhibitors with greater activity will reduce the cost of growing plants and provide the market with new, more effective drugs in the future.
For this purpose, according to the developed methodology, coordination compounds Cu(II), Zn(II), Co(II), Mn(II), Fe(II) were synthesized and isolated in the solid state with different amounts and ratios of ligands (1:1, 2:1, 1:2, 2:2) for their use as new nitrification inhibitors.
Crystal hydrates of metal sulfates were used for the synthesis of these complexes: ZnSO4 ∙ 7 H2O; CuSO4 ∙ 5 H2O; CoSO4 ∙ 7 H2O; MnSO4 ∙ 5 H2O; FeSO4 ∙ 7 H2O, and well-known nitrification inhibitors - dicyandiamide (DCD) and 4-amino-1,2,4-triazole (ATC) were used as ligands with the content of the main substance at least 93 and 95 %, respectively.
With the help of IR spectroscopy, the structural elements of both ligands were detected and identified. Based on the shift and activity of the vibrational bands, it was established that ATC addition is realized by 1,2-coordination through the N1-N2 atoms of the triazole ring. Coordination of metals to ATC is carried out via the azole cycle. In turn, DCD coordination in the Cu(II), Co(II) and Mn(II) complexes was confirmed by the shift and decrease in intensity of the C≡N peaks. For Zn(II) complexes, DCD addition is implemented through the C=NH group.
The formation of complexes of the predicted form was confirmed for most substances on the basis of: comparison of masses during synthesis; final mass of thermal decomposition and isothermal aging; determined metal content, taking into account the 1,2-coordination of one of the ligands. The formation of other types of complexes in each of the groups was also revealed.
Thermal analysis confirmed some literature data related to the decomposition of ligands and revealed the uniqueness of the formation of ZnS during the decomposition of zinc complexes.
It was established that the solubility in water and KAS-28 solutions of all complexes, except for Mn(II), is lower than that of 4-amino-1,2,4-triazole and dicyandiamide. The addition of KAS increased the solubility of substances and provided a sufficient amount of them to inhibit the nitrification process.
During the work on the research, a number of regularities were discovered:
- increase in biological activity and duration of action of synthesized complexes in comparison with original commercial drugs;
- it is shown that depending on the proportion of 4-amino-1,2,4-triazole in complex compounds, there is a different effect on all parameters of nitrification;
- the decrease in the loss of ammonium cations is proportional to the increase in the proportion of dicyandiamide.
Therefore, we can conclude about the influence of the ratio of ligands on nitrification indicators - the complex with the ratio of ligands 1:2 (ATC:DCD) acts better on the first phase of nitrification, and the ratio 2:1 in the composition of the complex has a better synergy of action on both phases.
According to these results of the laboratory experiment, it was established that among the synthesized compounds, ENIs-2 showed the highest efficiency. They are more effective than commercial nitrification inhibitors.
As a result of conducting field research, it was established that the use of the most effective synthetic substances together with RKD 10-34-0 and urea provides a significant increase in corn yield. ZnNIs-2 significantly affected plant growth and yield, and MnNIs-2 relatively well on yield.
