With the uptake of organic farming the importance of green manures increases, and the cultivation of cover crops plays an ever important role both in agriculture and in horticulture. The fertilizer value of plants cultivated for green manures is largely dependent on the biomass produced, and also the nutrients that were accumulated within it. The aim of this work is to determine the influence of weather conditions in the second half of summer on the fertilizer value of catch crops intended for cultivation of vegetables. The research included: spring rye (Secale cereale), oats (Avena sativa), common vetch (Vicia sativa), white mustard (Sinapis alba), tancy phacelia (Phacelia tanacetifolia), buckwheat (Fagopyrum esculentum), fodder sunflower (Helianthus annuus). The catch crop plants, cultivated as a pre-crop for the cultivation of vegetables proved to be a rich source of organic matter and nutrients for the following crops. The course of weather had a major influence on the volume of biomass, and the chemical composition and fertilizer value of cover crops. Shortage of water and high temperatures after rainfalls, causing the formation of crust on the soil did mostly limit the growth of catch crops. The biggest biomass among the investigated catch crops was created by sunflowers, phacelia and rye, the lowest by common vetch. White mustard and sunflower provided the biggest amount of nitrogen in their role as catch crops. The sunflower proved to be a rich source of K, Ca and Mg. The most Ca was left in the field by tancy phacelia, which also proved to be a good source of K. The biomass of buckwheat provided large amounts of Mg, but it was poor in N, P and S. Rye and oats proved to be a rich sources of P, but they also contained small amount of Ca and Mg. The most sulphur was left over by the biomass of white mustard. The common vetch proved to be the most weather-sensitive of all plants. Its biomass left the least P, K, Mg and S in the field, the Ca content was also small, compared to other catch crops. Nitrogen content of dry matter of common vetch was high, but not the highest in the three year average.

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