Published online by Cambridge University Press: 27 March 2009
In a pot experiment, the growth of sugar beet on one soil with three levels of exchangeable Na ceased when the intensity of K measured as the activity ratio aK/√[a(Ca + Mg)] in the equilibrium soil solution had fallen to 6 × 10–4 (mole per litre)½;, the intensity of Na, aNa/√[a(CaH-Mg)], to between 1·7 and 4 × 10–3 (mole per litre)½;and exchangeable Mg to 0·14 m-equiv per 100 g soil. It was concluded that both the Na and the K intensities were exhaustion values but that K supply was preventing further growth. The additions of Na did not affect either yield or the uptake of K, Mg and Ca, but more Na was taken up from soils with higher Na levels.