Variations in the rates of nitrification and denitrification during the growth of potatoes (Solanum tuberosum L.) in soil with different carbon inputs and the effect of these inputs on soil nitrogen and plant yield

Summary A potato crop (Solanum tuberosum L. cv. Maris piper) was grown in a soil to which N was added, as NH₄NO₃, with or without added C, as sucrose or straw. Shortly after amendment the soil, in all treatments, contained only relatively low levels of mineral N. However, these levels increased later. The increase, which was greatest in the absence of added C and least with added sucrose, occurred before the emergence of the plant canopy. The addition of C to the soil had no effect on plant yield, measured either as dry matter or total N content. The potential nitrification rate was high early in the season, and decreased significantly as the plants developed. The potential denitrification rate showed two significant peaks in activity, possibly related to plant development, the first to the development of new roots and the second to root senescence. It seems probable that the amount of C released by the potato plants was only about one-quarter of that required for the maximum microbial activity.