Plant species and varieties within species differ in their response to mineral stresses and toxicities. To achieve maximum yields, the plant and the soil must be compatible. In the past, the soil has been changed to fit the plant. In this study, we consider changing the plant to fit the soil, recognizing that plant species and varieties within species have specific nutrient requirements. Ten soybean (Glycine max (L.) Merr.) varieties, representing the germplasm currently used in soybean production in the United States, were subjected to Fe, Zn, and Cu stresses; and Mn and Al toxicities to determine their nutrient requirements or tolerance to mineral elements. Seven soils, which had produced the above nutrient stresses and toxicities in other crops, were used in this study. The soybean varieties showed a differential response to Fe stress by developing severe (‘Forrest’), moderate (‘Hodgson’), or no Fe chlorosis (‘Bragg’). Leaves dropped from Forrest and Bragg soybeans as they developed severe Mn toxicity symptoms. In contrast, ‘Lee’ soybean developed only slight Mn toxicity symptoms. Most soybean varieties grew well when subjected to Zn and Cu stresses, or when grown on Al-toxic soil. Care should be taken to select the proper soybean variety to be grown on soils where Fe stress or Mn toxicity may be a problem.

Fifteen cotton varieties (Gossypium hirsutum L.), representing germplasm recommended for different areas of the United States, were subjected to Fe, Zn, and Cu stresses and Al and Mn toxicities to determine their nutrient requirements. They were grown on the seven different soils described in part I of this study for soybeans. All cotton varieties grown on Quinlan soil (Fe stress) developed deficiency symptoms that were similar to symptoms produced in cotton grown on Shano and Taunton soils (Zn stress). On Quinlan and Taunton soils, the plants responded to both Fe and Zn. Iron added to Taunton soil decreased the uptake of Fe and increased the uptake of Zn by the plants. Lime added to Richland soil induced a Zn deficiency that increased Fe uptake by the plants. When Zn was added to this soil, yields increased and Fe uptake decreased in the plants. All 15 cotton varieties grew poorly on acid Bladen soil (Al toxic), and yields were doubled by liming and yield of C-7105, 73-319 doubled again by adding Cu. Best yields, with no toxicity symptoms, were obtained on Richland soil (Mn toxic). Cotton and soybean had different nutrient requirements. For example, cotton was Cu and Zn inefficient and Mn tolerant, whereas soybeans were Cu and Zn efficient and Mn intolerant in most varieties tested.

Previous observations indicate that the adaptability of certain wheat (Triticum aestivum L. em Thell) cultivars to strongly acid conditions is due to their ability to tolerate high levels of free aluminum. Studies were conducted to determine the differential response of cultivars to high levels of exchangeable Al in soil and to correlate these data to nutrient solution screening techniques. Field plots were located on a naturally low pH (4.5) Wooster silt loam soil (fine, loamy, mixed, mesic Typic Fragiudalf) in which pH levels, and, thus, available Al were controlled by liming. Data on yield, height, maturity, and winter survival of 43 wheat cultivars and experimental lines and two barley (Hordeum vulgare L. emend.) cultivars were obtained in 1973, 1974, and 1975. Field results were related to measurements of root length, weight, and number, leaf length and top weight of plants grown for 10 days in nutrient solutions containing O and 8 ppni Al. Many cultivars developed in the eastern USA appeared to have been selected unconsciously for Al tolerance. ‘Fultz’, ‘Trumbull’, ‘Fulcaster’, ‘Thorne’, ‘Seneca’, ‘Lucas’, ‘Butler’, ‘Fulton’, ‘Atlas 66’, ‘Blueboy’, and ‘Pennoll’ were classified as tolerant; whereas, most Indiana developed varieties such as ‘Abe’, ‘Arthur’, ‘Arthur 71’, ‘Redcoat’, ‘Reed’, and ‘Riley’ tended to lack aluminum tolerance. ‘Logan’, ‘Fairfield’, ‘Ruler’, and many of the experimental lines exhibited intermediate degrees of tolerance, indicating that this trait was not simply inherited. Root length in nutrient solutions containing Al was a good indicator of varietal response to the high acid conditions of the field. Nutrient solution techniques provide an efficient nondestructive screening method for use in the development of Al-tolerant wheat cultivars.