The total sugar content in potato tubers was significantly modified by intercrop fertilization and straw fertilization (table 9). Intercrop fertilization significantly decreased the concentration of total sugars in potato tubers. The lowest its content was recorded in potato tubers fertilized with a mixture of white clover with Italian ryegrass and phacelia plowed down in the autumn and left till spring in the form of mulch. The content of reducing sugars in potato tubers fertilized with white clover and Italian ryegrass did not differ significantly from their concentrations observed in tubers fertilized with farmyard manure. However, on control object, the content of total sugars in potato tubers was significantly higher than in the potato fertilized with farmyard manure. Straw fertilization also significantly modified the content of total sugars in potato tubers. At the sub-block without straw content of total sugars in potato tubers was significantly lower than at the sub-block with straw.

3.3.6 Vitamin C content in potato tubers

The vitamin C content in potato tubers was significantly differentiated by the examined factors of experiment and their interaction (table 10). Intercrop fertilization in comparison with control object caused a significant increase of vitamin C content in potato tubers. Indeed, the highest concentration of vitamin C were characterized in potato tubers fertilized with phacelia in the form of mulch and white clover. The vitamin C content in potato tubers fertilized with a

mixture of white clover with Italian ryegrass and phacelia developed at a similar level as in the potato fertilized with farmyard manure. Straw fertilization also significantly differentiate the concentrations of vitamin C in potato tubers. On objects with straw the content of vitamin C in tubers was significantly higher than on the objects without straw. From the interaction between studied factors shows that the highest concentration of vitamin C were characterized by potato tubers fertilized with phacelia both plowed down in the autumn, and left till spring in the form of mulch, in combination without straw and with straw, and white clover and white clover with straw, and the lowest in potato tubers from control object.