Mikroelem-terhelés hatása a sárgarépára (Daucus carota L.) karbonátos homoktalajon | The effect of microelement load on carrot (Daucus carota L.) on calcareous sandy soil

Summary We examined the effect of 0, 30, 90, 270 kg ha ⁻¹ microelement loads on carrot on calcareous sandy soil in the Danube-Tisza mid-region. We applied the salts of microelements at the beginning of the experiment in Cr ₂(SO ₄) ₃, K ₂Cr ₂O ₇, CuSO ₄, Pb(NO ₃) ₂, Na ₂SeO ₃ and ZnSO ₄ forms in the spring of 1995. 6 elements × 4 loads = 24 treatments × 3 replications meant 72 plots of 7 × 5 = 35 m ² size. As it can be expected of sandy soils, the production site has bad water management, it is drought-sensitive and it is weakly supplied with NPK. The ploughed layer contains 0.7–1.0% humus, 2–3% CaCO ₃. The soil water is at a depth of 5–10 m. As a basic fertiliser, we applied 100 kg ha ⁻¹ N, 100 kg ha ⁻¹ P ₂O5 and 100 kg ha ⁻¹ K ₂O in the whole experiment every year. Main results: During the six months long growing period of carrot, there was only 234 mm precipitation. July and August (the period of intensive root development) were droughty. Of the applied microelement salts, Cr (III), Cu and Pb were ineffective. The depressive effect of Zn could be observed in the case of 90 kg ha ⁻¹ and 270 g ha ⁻¹ loads. The toxicity of Cr (VI) and Se was more expressed in the case of 30 kg ha ⁻¹ load, whereas doses above this led to the reduction of plant number and dying out of plants. As a result of higher Cr (VI) and Se loads, even weed species disappeared and the soil became infertile. In the sample taken from a young leaf on 6 ᵗʰ June, the amount of Se, Cr, Cu and Pb was higher by one magnitude than the control plant, whereas the Zn content of the shoot became five times higher. During harvest, on 11 ᵗʰ September, the concentrations decreased in general. Se was an exception, as its amount increased by three times its previous value in the respective treatments. The Cr, Cu and Se content of the root was lower than that of the leaves, it was somewhat more protected from element enrichment. Nonetheless, the average Pb and Zn content did not significantly differ from the leaves' Pb and Zn content. The Cr content of the roots and leaves produced in the toxic Cr (VI) treatment exceeded the Cr content of the carrot grown in the Cr (III) treatment. On unpolluted control soil, the root yield around 20 t ha ⁻¹ + 5 t ha ⁻¹ fresh leaf yield indicated the following uptakes: 88 kg K; 57 kg Ca; 54 kg N; 14 kg Mg, Na and P; 11 kg S; 5–6 kg Fe and Al. Furthermore, we measured the following amounts: B: 145 g, Zn: 41 g, Cu: 27 g. Our data can serve as a guide in calculating the element demand of carrot in technical advice. The “total” Cr, Pb, Cu and Zn content of the ploughed layer estimated with cc.HNO ₃ + cc.H ₂O ₂ exploration well represented the amounts applied, the load. As for Se, the soil analysis indicated a 50% enrichment after the first year. The watersoluble selenate might have leached under the ploughed layer or it might have partially escaped into the air. This issue calls for further analyses. 5. On polluted soil in Cr (VI) and Se treatments, we obtained the uptake maxima of 3 g ha ⁻¹ Cr and 51 g ha ⁻¹ Se in the 30 kg ha ⁻¹ treatment. In the case of unchanged conditions, the phytoremediation of 30 kg ha ⁻¹ Se, Cr would take ten thousand years, whereas the uptake of 30 kg ha ⁻¹ would require 585 years. In the Cr (III), Pb, Cu and Zn treatments (which do not cause yield loss), the 270 kg ha ⁻¹ element uptake would take 17 thousand Cr years, ten thousand Pb years, four thousand Cu years and 1570 Zn years. As regards a stronger, point source pollution, phytoremediation cannot be a real alternative, even in the case of a suitable hyperaccumulator plant species. 6. The carrot root became unsuitable both for human and animal consumption, due to the harmful Pb and Se element enrichment.