Heavy metals in waste materials added to agricultural soils can severely inhibit subsequent crop growth. This study was conducted to evaluate the variation in tolerance among cultivars of an agriculturally important plant species to phytotoxic levels of added soil Zn. Twenty soybean (Glycine max L. Merr.) cultivars were screened, through greenhouse pot studies, for their growth response to Zn at pH 5.5 and 6.5 on a Sassafras sandy loam (Fragiudult) amended with 1.31 (control), 131, and 262 ppm Zn. Significant differential responses were found, and the cultivars were grouped into several tolerance and uptake classes, based on the results of the pH 6.5, 262‐ppm Zn treatment: tolerant (9 to 18% leaf dry weight yield reduction [YR], 5 cultivars), normal (20 to 32% YR, 12 cultivars), sensitive (33 to 48% YR, 3 cultivars); accumulator (696 to 730 ppm trifoliolate leaf Zn, 5 cultivars), normal (549 to 675 ppm Zn, 11 cultivars), and excluder (389 to 540 ppm Zn, 4 cultivars). Soil Zn additions significantly increased root and foliar Mn contents to reported phytotoxic levels at both pH 5.5 and 6.5, but did not influence DTPA‐TEA extractable soil Mn. Significant cultivar differences in root and leaf Mn contents were observed. The results of this work illustrate the importance of cultivar selection, not only for field planting of Zn‐enriched soils, but also for its influence on experimental results.

Two Coastal Plain soils were used to evaluate the effects of organic matter and Fe and Mn hydrous oxides on Zn phytotoxicity, and on Zn, Cd, and Mn uptake by soybean seedlings. Fertilized Pocomoke sl and Sassafras sl were limed to pH 5.5 and 6.3 with CaCO3 when adding Zn (six levels between 1.3 and 196 mg/kg at pH 5.5; seven levels between 1.3 and 524 mg/kg at pH 6.3). Cadmium was added at 1% of the added Zn. ‘Beeson’ soybean (Glycine max L. Merr.) was grown 4 weeks, and the trifoliolate leaves evaluated for dry weight yield and for their Zn, Cd, and Mn concentrations.The higher organic matter Pocomoke soil was more effective than the Sassafras soil in reducing metal uptake and Zn phytotoxicity. Foliar Zn levels associated with yield reduction of soybean grown on Pocomoke differed with soil pH. Cadmium uptake was significantly lower on the Pocomoke soil. Foliar Mn increased to reported phytotoxic levels (>500 mg/kg) with increased added Zn only on the Sassafras soil at pH 6.3.DTPA‐extractable Zn and Cd were linear functions of added Zn and Cd for both soils; 0.01M CaCl2‐extractable Zn and Cd were curvilinear (increasing slope) functions for the Sassafras and linear for the Pocomoke soil.Thus, soil type can strongly influence Zn, Cd, and Mn uptake, as well as Zn phytotoxicity to soybean. Soil organic matter appears to be more important than hydrous oxides of Fe and Mn in moderating the effects of excessive soil Zn and limiting Zn and Cd uptake. Induced metal toxicities (Mn) may depend on many factors, and should be considered an integral part of any characterization of specific metal phytotoxicities (e.g. Zn).

This investigation was part of a general characterization of Zn tolerance among cultivars of an agriculturally important plant species. Greenhouse studies were conducted to further evaluate the effect of soil Zn additions on soybean (Glycine max L. Merr.) cultivar differences in Zn tolerance, as well as plant Zn, Mn, Fe, and P contents. Four cultivars selected from a previous Zn tolerance screening trial (‘Wye’ and ‘Hudson Manchu’, tolerant; ‘York’, sensitive; ‘Columbus’, normal) were grown for 4 weeks on a fertilized Sassafras sandy loam (Fragiudult) amended with a wide range of Zn additions at pH 5.5 (nine additions between 1 and 131 ppm Zn) and 6.5 (10 additions between 1 and 524 ppm Zn). Leaf dry weight reductions were curvilinear across the Zn additions at each pH, with yield increases occurring at the lower Zn treatments. For all cultivars, root dry weight was unaffected by the Zn additions at the lower pH and significantly reduced at the higher pH by Zn additions greater than 262 ppm. Significant cultivar differences in leaf dry weight yields were observed at the higher Zn treatments. Leaf and root Zn contents increased linearly with increasing soil Zn at each soil pH (root r2 > 0.92, leaf r2 > 0.93 for all cultivars). The soil pH strongly influenced plant Zn contents; at an equivalent Zn addition, tissue values at pH 6.5 were approximately one‐third as great as at pH 5.5. Differential absorption and translocation of Zn was shown by the cultivars; at both pH levels, Hudson Manchu absorbed more Zn but translocated less than the other cultivars. Generally, leaf yield reductions of 20% corresponded to leaf Zn contents greater than 620 ppm at both pH levels; however Hudson Manchu had only 370 ppm Zn in its leaves at 20% yield reduction at pH 6.5. Cultivar differences in both soil and leaf Zn contents at a 20% reduction for leaf dry weight illustrate the inherent weakness of foliar analysis as a monitoring tool for available metals at toxic levels. Root Mn was increased linearly by soil Zn additions at both pH levels, while leaf Mn increases were curvilinear at pH 5.5 and linear at pH 6.5. Leaf Mn concentrations at both pH levels reached reported toxic levels (> 500 ppm) illustrating the complex nature of Zn phytotoxicity. DTPA‐extractable Mn was unaffected by soil Zn additions at both pH levels. Foliar (combined trifoliolate leaves) Fe, at pH 5.5 and 6.5, and P at pH 6.5, decreased with increasing soil Zn, but did not approach reported deficiency levels. Similar amounts of Fe and P were found in Zn‐tolerant and Znsensitive cultivars. These results illustrate the complex nature of Zn phytotoxicity and the importance of cultivar selection for cropping soils amended with metal‐containing wastes.

Reciprocal grafts were used to determine the relative importance of the roots and shoots of soybean (Glycine max L.) in tolerance to excess soil Zn. Grafts, in all combinations, were made between ‘Wye’ (Zn‐tolerant) and ‘York’ (Zn‐intolerant) soybean cultivars. For plants grown at soil pH 6.2 and soil Zn additions of 1.31, 131, and 393 ppm, the results showed that the scion genotype controlled relative Zn tolerance, while the rootstock genotype controlled Zn absorption and translocation. Differences in foliar Zn concentrations were not responsible for differential Zn tolerance of these two soybean cultivars.

Experiments were initiated to document the effect of cultivar, GA4+7, and number of fruit/spur on appendage number and flower bud initiation in apple. `Pacific Rose' is strongly biennial, `Braeburn' and `Fuji' are moderately biennial, and `Royal Gala' is not biennial. In the cultivar study, buds were sampled every 18 days starting at 50 days after full bloom and continuing through until leaf fall to determine the rate of appendage formation and appendage number in relation to doming. Because of the tendency for `Pacific Rose' to exhibit biennial bearing, the rate of appendage formation and the timing of doming were compared on nonfruiting trees, trees carrying a commercial crop, and trees sprayed with 300 PPM GA4+7 applied 14 days after full bloom. Number of appendages for the treatments were similar up to 100 days after full bloom. Presence of fruit on a spur has been demonstrated to inhibit flowering of apple. Spurs of `Pacific Rose', `Splendor', and `Royal Gala' were labeled with zero, one, two, and three fruit per spur and sampled three times during the season. As buds were harvested to count appendage number, the number of fruit per spur and the number of total seeds per spur were recorded. Correlation between number of seeds per spur and rate of appendage formation were done.