Sweet corn grain is rich in nutrients. There are many factors, fertilization being one of the most important, which influence the quality of the grain. A special role in improving soil fertility is ascribed to catch crop plants when they are incorporated into the soil. A field experiment was carried out in central-eastern Poland to investigate the effect of phacelia and amaranth catch crops used as green manures on dry matter, sugars and ascorbic acid contents in sweet corn kernels. Catch crops were sown at three dates: 21^st July, 4^th and 18^th August, and incorporated in late October. Sweet corn was cultivated in the first year following manuring. The effect of the green manures was compared to farmyard manure applied at a rate of 40 t∙ha^-1 and a non-manured control. The highest average dry matter content (27.5%) was determined in corn kernels cultivated without manuring, significantly lower after farmyard manure (26.4%). Catch crops incorporation did not cause significant changes in dry matter content in corn. Corn cultivated after catch crops had higher or similar contents of sugars compared with cultivation after farmyard manure. The most total sugars (8.12% f.m.) were found in corn cultivated after phacelia sown on the 21^st of July, the least (7.04% f.m.) in the non-manured control. The highest monosaccharides content was in corn following amaranth sown on the 21^st of July and 4^th of August (2.50% f.m.), it was significantly lower (2.27% f.m.) after farmyard manure. The highest ascorbic acid content was determined in corn after phacelia sown on the 4^th of August (8.88 mg·100^-1 g f.m.) and in amaranth sown on the 21^st of July (8.98 mg·100^-1 g f.m.). Significantly less ascorbic acid was found following phacelia sown on the 18^th August and in the non-manured control. Ascorbic acid contents in corn from the remaining treatments did not differ significantly. ‘Sweet Wonder F₁’ was characterized by higher contents of dry matter and total sugars in kernels than ‘Challenger F₁’.

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