374 SUBBARAO ET AL.TABLE 5 Effect of Sodium Applied as a Nutrient on Several Crops
Degree of benefit in Degree of benefit in Degree of benefit in Degree of benefit in
deficiency of K deficiency of K sufficiency of K sufficiency of K
None to slight Slight to medium Slight to medium Large
Group I Group II Group III Group IV
Buckwheat Asparagus Cabbage Celery
Corn Barley Celeriac Mangel
Lettuce Broccoli Horseradish Sugar beet
Onion Brussels sprouts Kale Swiss chard
Parsley Caraway Kohlrabi Red beet
Parsnip Carrot Mustard Turnip
Peppermint Chicory Radish
Potato Cotton Rape
Rye Flax
Soybean Millet
Spinach Oat
Squash Pea
Strawberry Rutabaga
Sunflowers Tomato
White bean Vetch
Wheat
Source: Ref. 13.
TABLE 6 Concentrations of K in the Edible Portions of Some Crops and Estimates of Na
Replacement [Source: Ref. 10]
Crop K (%) in edible plant part % of K replaced with Na (estimate)
Red beet 10 b 90
Chard 10 a 90
Celery 10 a 75
Lettuce 10 b 25
Spinach 9 b 50
Radish 9 25
Tomato 5 25
Potato 2.5 40
Sweet potato 2.5 40
Wheat 0.5 1
Rice 0.2c 1
Soybean 1.7c 1
Peanut 0.7 1
aEstimations based on our experience with some of the above crops and other published sources.
bBased on studies at Kennedy Space Center.
cFrom Duke and Atchley [163].
Source: Ref. 10.tions, minimum tissue K levels can be determined only when Na is supplied adequately. For red beet, it
was shown that tissue K levels of certain tissues can drop from 100 g kg^1 dwt (normal tissue K levels
for these tissues with unlimited availability of K and Na) to 4 g kg^1 dwt when low K and high Na are
provided [3]. This decrease in tissue K occurred without any short-term effect on growth, suggesting that
4 g kg^1 dwt in the tissue is near the critical K level for these tissues. For spinach, these low K levels are
about 30 g kg^1 dwt, whereas for lettuce the low K levels are near 65 g kg^1 dwt (Figure 3). Similarly,
for red beet, the leaf Na levels reach 100 g kg^1 dwt without negative effects on growth rates, whereas
for spinach the level was 17 g kg^1 dwt and for lettuce it was 4.9 g kg^1 dwt (Figure 4). For Rhodes grass,