Trace Element Contents in Maize following the Application of Organic Materials to Reduce the Potential Adverse Effects of Nitrogen

The plants cultivated in loamy sand contained less iron, manganese, copper, cobalt, nickel, and zinc while containing more chromium, lead, and cadmium than in sand. This study was launched to use organic materials in the form of humic acids (HA) to reduce the potential negative effects of excessive nitrogen fertiliser (ammonium nitrate, urea, and urea and ammonium nitrate solution-UAN) application rates (160 mg N kg^-1 soil) on the trace element contents in maize in two soils differing in granulometric composition. HA were applied into the soil three times during the maize vegetation: before the sowing, at the five-leaf unfolded stage, and at the intensive shoot growth stage. The HA doses amounted to 0, 0.05, 0.10, and 0.15 g kg^-1 soil. Urea fertilisation increased the cadmium, lead, chromium, and nickel contents and reduced the iron content in maize on both soils. UAN contributed to an increased chromium content being higher than that caused by urea and to reduced iron content in the aboveground parts of maize, as compared to the objects with ammonium nitrate. In the series with ammonium nitrate, the highest dose of HA reduced the manganese, zinc, iron, and cobalt contents in maize on both soils. In the series with urea, however, their reducing effect on the copper and iron contents in maize on both soils was noted. The study also demonstrated a positive reduction in the contents of many other trace elements in maize under the influence of the application of HA (particularly, their highest dose). However, it only concerned one of the soils under study. The application of HA into the soil can be effective in reducing the trace element content in plants and can mitigate the adverse environmental impact of intensive agricultural production.

Use of Organic Materials to Limit the Potential Negative Effect of Nitrogen on Maize in Different Soils

This study was launched to test organic materials in the form of humic acids (HA) applied to soil to improve the effect of nitrogen on maize, and to determine an optimal dose of HA, which will be ecologically safe and will counteract potential negative (phytotoxic) influences of excessive nitrogen fertiliser doses, on two soils with different textural composition. The maize plants grown on the loamy sand were characterised by a higher value of the SPAD leaf greenness index, yields, and a lower content of total-N and sulphate sulphur in maize. Urea, and especially UAN, promoted higher SPAD leaf greenness index values during the stem elongation stage and particularly during the tassel emergence stage. The effect of urea on maize yields was positive on both soils, but UAN had a positive effect on this parameter only on the loamy sand. HA tended to increase the SPAD leaf greenness index. The impact of HA on plant height and yields (especially medium dose) was generally positive. However, a negative effect of the interaction of HA with UAN on the plant height and maize yield on the sand was observed. HA caused an increase in the total-N content, and their highest dose also decreased the sulphate sulphur content in maize. The application of HA to soil has a positive influence on the growth and development of plants and can create positive effects by mitigating adverse consequences of intensive agricultural production in the natural environment.

Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.