Effects of a combination of potassium deficiency and salt stress on the growth of maize. 1: K-present Hoagland's nutrient solution; 2: K-present Hoagland's nutrient solution + 40 mmol L−1 NaCl; 3: K-present Hoagland's nutrient solution + 80 mmol L−1 NaCl; 4: K-present Hoagland's nutrient solution + 120 mmol L−1 NaCl; 5: K-deficient Hoagland's nutrient solution; 6: K-deficient Hoagland's nutrient solution + 40 mmol L−1 NaCl; 7: K-deficient Hoagland's nutrient solution + 80 mmol L−1 NaCl; and 8: K-deficient Hoagland's nutrient solution + 120 mmol L−1 NaCl. Treatments with different letters indicate significantly different values (p < 0.05). Values represent means ± SE, n = 20.