The effect of CCC, nitrogen and potassium on the growth and yield of two varieties of potatoes

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Abstract
The two experiments described here were the 3rd and 4th in a series of experiments investigating the effect of time of application of nitrogen and potassium on the growth and yield of potatoes.The effect of applying all the fertilizer nitrogen in the seed bed was compared with applying all the nitrogen at the time of tuber initiation or dividing the dressing between these times. Similar times of application were tested for potassium. CCC was applied after a leaf area index of 3 had been reached (on all but the no N treatments) in order to offset the tendency for late nitrogen to increase stem growth, but to avoid any tendency for CCC to depress yield by reducing leaf area indices (L) below an assumed optimum value of 3. These treatments were applied in separate experiments to a second early variety (Craig's Royal) and a maincrop variety (Pentland Dell), planted a month later.In both crops the response to nitrogen was large and delaying or splitting the application of nitrogen increased tuber yield compared with nitrogen applied in the seed bed. Responses to potassium were small, but there was a tendency for split applications to be superior to late or early applications.The beneficial effect of delayed or split applications of nitrogen was associated with an improvement in the recovery of nitrogen in the crop which was largely ascribed to a reduction in loss due to leaching. Total and tuber dry-matter yields were linearly related to leaf area duration (D) in both crops, although the earlier variety was more efficient per unit of D. High values of L (6) were recorded for both crops, but there was no indication of an optimal value of L; consequently CCC which reduced L also reduced yield. D was closely related to the maximum quantity of nitrogen accumulated in the leaves per unit area of ground.