The content of true protein in potato tubers was significantly differentiated by the intercrop fertilization, fertilization with straw and their interaction (table 12). The highest concentration of true protein in potato tubers was noted in potato tubers fertilized with phacelia and white clover both plowed down in the autumn, and left till spring in the form of mulch. The concentration of true protein in potato tubers fertilized with a mixture of white clover with Italian ryegrass remained at a similar level, such as on farmyard manure.

However, true protein content in potato tubers fertilized with Italian ryegrass was significantly lower than in tubers fertilized with farmyard manure. Straw fertilization also significantly differentiate true protein content in potato tubers. At the sub-block with straw concentration of true protein in potato tubers was significantly higher than on sub-block without straw. Investigated the interaction of factors we can see that the highest true protein content had potato tubers fertilized white clover, white clover with straw, and phacelia both plowed down in the autumn, and left till spring in the form of mulch in combination without straw and with straw, and the lowest potato tubers harvested from control object, without intercrop fertilization.