The study aims to assess seed yield of yellow lupine, seed chemical composition, weed infestation of lupine crop, and contents of organic C and total N in the soil cultivated in the conventional tillage (CT), reduced tillage (RT), and no-till (NT) systems. The experiment was established on sandy-clay soil classified as Rendzic Phaeozem. It was set up in a randomized blocks design in 3 replicates having size of 75 m × 6 m. The lupine seed yield was higher in the CT system than in the RT and NT systems, due to a higher plant number m−2, pod number m−2, and seed number m−2. The tillage systems had little effect on the contents of protein, phosphorus, magnesium, and calcium in the seeds; however, ash content of the seeds increased and that of potassium decreased in the NT system compared to the CT and RT systems. The tillage systems also affected lupine infestation by weeds. A higher weed number m−2 and their air-dry weight were determined in the RT system compared to the CT and NT systems. The NT and RT systems system increased contents of organic C and total N in the soil compared to the CT system.