EFFECTS OF INSOLATION AND SOIL CHARACTERISTICS ON TISSUE FLUID REACTION IN WHEAT

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Abstract
Tissue fluids from entire wheat tops showed diurnal acid periodicity, free acidity reaching a minimum in the evening and a maximum in the early morning. Sap acidity of wheat plants on acid soils was much greater than that of plants on the same soils after applications of CaCO3 to correct acidity. The general level of free acidity was much lower in plants on an untreated, low mineral humus than in those on an acid loam higher in mineral matter. Symptoms of acid toxicity appeared in the tops of 8 week old wheat on the untreated acid humus. Following correction of soil acidity with lime, the pH of the sap of plants on the humus was reduced more than in those on the loam. The sap acidity of strongly insolated plants on limed humus soil fell below the level necessary for iron mobility, as shown by chlorosis and absence of Fe in the leaves. When chlorosis had persisted for 2 or more weeks, leaves gradually lost their turgor and acidity rose rapidly as the moisture content diminished.