The processes of growth and development as well as the yield quality of crops depend on the abundance of soil nutrients and the ability of the plants to uptake nutrients. Nutrients can be taken up more efficiently after application of a biostimulant. The effect of biostimulants depends on the content of their active substance as well as the dose, timing and frequency of their application. In 2009-2011, a controlled field experiment was conducted in the Kuyavian-Pomeranian Province (53°13′N; 17°51′E). The objective was to analyse the effect of the timing and doses of foliar application of the biostimulants: Kelpak SL (seaweed extract containing phytohormones) and Asahi SL (a mixture of phenolic compounds) on the content of macroelements: Mg, P, Ca, N, Na and K in the storage roots of carrot directly after harvest and after storage (for 6 months in chambers with controlled conditions: temp. +1°C, Rh 95%). Kelpak SL was applied once in a dose of 3 or 2 dm3 ha-1, twice in doses of 3+2 dm3 ha-1 or 2+2 dm3 ha-1 at intervals of two or four weeks, as well as three times in doses 3+2+2 dm3 ha-1 or 2+2+2 dm3 ha-1, every two weeks. Asahi SL was applied twice in doses 0.5+0.5 dm3 ha-1,at a two-week interval. The first application of biostimulants was always performed at the 4-leaf stage. The study showed that the biostimulants Kelpak SL and Asahi SL, irrespective of the dose and frequency of application, increased the N concentration in the carrot roots. An increase in the Mg, P, Na and K concentrations was observed after a single application of Kelpak SL in a dose of 2 dm3 ha-1, and in the Ca concentration after a dose of 3 dm3 ha-1. Asahi SL did not affect the Mg, P, Ca and Na concentrations but increased the K content in the roots. After storage, the content of Mg, Na and K decreased, whereas the concentration of P, Ca and N did not change. Directly after harvest and after storage, positive correlation between N and K and between N and Na, as well as between Na and K was indicated.
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