The use of cheese whey in agricultural applications is an option to reduce the environmental impact caused when it is dumped without control. The purpose of this work was to measure the phytotoxicity of the sweet whey that is generated during the production of fresh cheese using seeds and seedlings of alfalfa (Medicago sativa L.) and corn (Zea mays L.) as test-object organisms. The variables evaluated were the lethal concentration (LC50) due to the inhibition of germination in both seeds, and the sublethal concentration (CSL) due to the decrease in the development of sprouts and seedlings. Four individual experiments were carried out under controlled laboratory conditions, both in Petri dishes with culture medium and in germinators with support, in a completely randomized experimental design (DECA) with five treatments (4, 8, 12, 16 and 20% of whey and a drinking water control) with a total of 252 experimental units. The results obtained indicate that sweet whey has an LC50-5 of 53% and a CSL-10 of 12% in alfalfa seeds (p<0.05) and an LC50-60 of 20% in alfalfa seedlings and an LC50-20 of 20% in corn seedlings. It was observed at 60 days that at concentrations between 4 and 6%, sweet whey has a growth-promoting effect on corn seedlings (p<0.05), concluding that it is possible to safely use diluted whey in sustainable agricultural practices.

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