Analysis of Potato Growth Under Differing P Regimes. II. Time by P‐status Interactions for Growth and Leaf Efficiency1

Abstract

AbstractFew full‐season studies of potato (Solanum 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 (NAR) during early growth, had no statistically measurable effect during mid‐season [NAR (35 to 63 days) = 7.76 gm−2 day−1], but markedly increased NAR during late growth stages. Instantaneous estimates of NAR derived from growth equations suggested that effects of low P on leaf efficiency were even more severe and longer‐lasting than indicated by NAR's. Initiation of tubers as an additional metabolic sink halted a downward trend in NAR, and partitioning of assimilates between tops and tubers during bulking depended on P supply and the manner of supplying it.