Analysis of Potato Growth Under Differing P Regimes. II. Time by P-status Interactions for Growth and Leaf Efficiency1
- R. E. McCollum2
Few full-season studies of potato (Solarium tuberosum L.) growth under mid-latitude environments have been conducted. Furthermore, published reports about effects of nutrient status on leaf efficiency in any species are inconclusive. Hence, the effects of factorially combined levels of initial soil P (SP = 35, 66, and 110 kg/ha) and row-applied fertilizer P (FP = 0, 28, and 56 kg/ha) on dry matter accumulation, leaf-area generation, leaf efficiency, and partitioning of assimilates by potatoes were studied via growth-analysis concepts. Tops and tubers of field-grown ‘Pungo’ potatoes (40,000 plants/ha on Portsmouth fsl—Typic Umbraquult, fine-loamy, mixed, thermic) were harvested weekly, and all parameters essential to a detailed growth analysis were derived.
Growth curves for P-adequate plants (Sp ⋝ 66, FP > 0) were typically sigmoidal with three post-emergent ontogenetic phases: 1) pre-tuber vegetative (emergence − 28 days); 2) tuber initiation and early bulking concurrent with rapid leaf growth (28 to 50 days); and 3) continued tuber growth during rapid leaf loss followed by death of haulms. Plants on the low-P extreme (SP = 35, FP = 0) never entered the third phase; they produced in 80 days only 50% of the “normal” leaf canopy (LAI = 1.6 vs. 3.2 at optimal P) and lost none of it. Curves for plants with moderate P supplies lay between these extremes. Row-applied P enhanced early growth; but it also hastened leaf senescence and, if initial soil P was low, shortened the duration of tuber bulking.
Leaf growth rate was maximal with 0.35% P in foliar tissue. Tuber growth rate was a quadratic function of leaf area during most of the tuber bulking period, but the estimate of 3.4 as optimal LAI was tenuous because no treatment generated a LAI greater than 3.2. Tuber yield was linearly related to leaf-area duration (LAD); doubling the LAD resulted in a 45% increase in yield.
Phosphorus deficiency reduced mean net assimilation rate (
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