Differential Cultivar Tolerance in Soybean to Phytotoxic Levels of Soil Zn. I. Range of Cultivar Response¹

Abstract

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.

Zinc Phytotoxicity

“…Polson and Adams (1970) found bean cultivars differed, and White et ai. (1979a;1979b;1979c) found that soybean cultivars differed in susceptibility, but not by as much as two-fold. Boawn and Rasmussen (1971) compared Zn uptake and phytotoxicity in a range of economic species (Table 1), and Boawn (1971) reported on a field study with leafy vegetable crops grown on neutral pH soil amended with ZnS0 4 • Among the leafy vegetables, spinach and chard accumulated Zn more strongly and were more susceptible than other crops.…”

“…Smelter (Zn, Pb, Cu) and incinerator emissions, excessive applications of Zn fertilizers and pesticides, use of highly contaminated sewage sludges and some livestock manures, dispersal of Zn (and Pb and Cu) mine and beneficiation wastes, and release of Zn from galvanized (Zn plated) surfaces can cause Zn contamination of soils sufficient to cause Zn phytotoxicity, at least at low soil pH. As soil pH falls, Zn concentration in the soil solution and plant uptake increase, and the potential for Zn phytotoxicity is more severe (Chaney et aI., 1975;White et aI., 1979a;1979c;Francis et aI., 1985). Thus, Zn phytotoxicity is a potential problem whenever Zn-rich soils become acidic.…”

Translocação de zinco e crescimento radicular em milho

“…O zinco aparentemente é retido nos vacúolos, complexado com ácidos orgânicos, o que pode prevenir a toxidez (Krotz et al, 1990). Por outro lado, em soja, foi notada redução na produtividade com teores de Zn nas folhas variando de 400 a 730 mg kg -1 (White et al, 1979).…”

PEA (Pisum sativum L.) CULTIVARS WITH LOW ACCUMULATION OF HEAVY METALS FROM CONTAMINATED SOIL

“…A high intraspecific polymorphism in HM content in several crops, including legumes, was also described. Significant varietal differences have been shown in soybean [6,12], peanut [6] and beans [6,13] for Cd accumulation, in soybeans [14] for Zn accumulation, and in beans [13] for Pb and Zn accumulation from contaminated soil. However, many experiments compared a limited number of varieties (from 2 to 20) that did not reflect the diversity, domestication and history of cultivation of the species, which reduces the value of such studies in terms of trait polymorphism.…”