After potato, ulluco and oca; mashua is an important carbohydrate resource in the diet of the highland people of Peru. This andean crop is grown on poor soils and it had never been grown along the coast, hydroponically or in any other way. This is the first experience with soilless culture. To establish N, P and K uptake, mashua plants were grown under simulated marginal nutritional and winter conditions at the International Potato Center (CIP), Lima, Peru. Nutritional conditions were controlled by growing the plants in subirrigated sand. The plants were supplied with four different nutrient solutions: 1) control (100 ppm N, 15 ppm P and 150 ppm K), 2) low nitrogen (50 ppm), 3) low phosphorus (5 ppm) and 4) low potassium (50 ppm). There was no significant difference in growth between the control and low K treatments. Low N and P treatments reduced growth. Plants started to produce tubers between 30 th and 60th days after tuber-seeding and vegetation period was shortened from seven to five months. The highest harvest index (HI) and leaf area index (LAI) values were obtained at 90th and 120 th days, respectively. Mashua absorbs K efficiently even under marginal nutritional conditions, taking up sufficient K but neither N nor P. The highest N, P and K uptakes were obtained in low K treatment. There was a higher K level in tubers than in leaves at low K level. It was concluded that potassium would be more important for tuberization and frost resistance.