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This article in AJ

  1. Vol. 70 No. 1, p. 51-57
    Received: Aug 15, 1977

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Analysis of Potato Growth under Differing P Regimes. I. Tuber Yields and Allocation of Dry Matter and P1

  1. R. E. McCollum2



High rates of P fertilization for potatoes (Solarium tuberosum L.) over many years have resulted in significant increases in total and extractable soil-P reserves. While fertilization practices for other crops grown in rotation with potatoes reflect both plant demand and soil-test P, many producers continue to fertilize potatoes with little regard to crop requirements nor to existing soil-P levels. If neither potatoes nor crops grown in rotation with them require such high rates of directly-applied P, a considerable saving in fertilizer costs could be realized. This hypothesis was tested in two field experiments (on a Typic Umbraquult, fine-loamy, mixed, thermic soil) designed to measure tuber yields and trace patterns of dry matter and P accumulation by ‘Pungo’ potatoes in response to row-applied fertilizer P[FP (1969) = 0, 24, 48, and 72 kg/ha; FP (1970) = 0, 28, and 56] on soil with 35, 66, and 110 kg of extractable soil P/ha. The latter objectives were accomplished by weekly samplings and appropriate analyses of tops and tubers during tuber bulking. When soil P was low (35 kg) or medium (66 kg), row-applied P increased yields by 38 and 22%, respectively; but no response to fertilizer P was obtained if initial soil P was high (110 kg). At tuber initiation, P concentration in whole plants ranged from 0.20% under severest deficiency to 0.45% under optimal nutrition; it dropped to less than 0.20% at harvest, regardless of treatment. On low-P regimes (SP < 66, FP = 0) rates of dry matter and P accumulation were still positive at 84 days after emergence; but plants on other treatments had lost most of their leaves—and many haulms were dead—at 79 days. At tuber initiation, plants with and without row-applied P had accumulated 20 and 10%, respectively, of their 72-day total P. Dry matter at tuber initiation was about 10% of the 72-day total for all treatments. About 75% of the total accumulated P and 70-75% of total dry matter was in tubers at harvest. While massive P applications to these low P soils are needed to make them productive, my results suggest that even high-demand crops like potatoes require relatively modest amounts of row applied P to maintain maximal productivity once the initial deficiency is eliminated.

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