Calcium Deficiency and Ammonia Toxicity as Separate Causal Factors of (NH4)2HPO4‐Injury to Seedlings

Abstract

AbstractShort term experiments were conducted in a growth chamber with seedlings of sudangrass (Sorghum sudanensis) and cotton (Gossypium hirsutum L.) on a Lucedale sandy loam surface soil treated with different rates of MgO, CaO, (NH4)2HPO4, K2HPO4, and Ca(H2PO4)2. Sudangrass seed was planted in treated soils and the seedlings were allowed to grow for 14 days, during which time they were observed for symptoms of Ca deficiency or NH3 toxicity. Cotton seed was planted in a layer of untreated soil that was underlain by treated soil in glass‐front boxes for direct observation of root growth. The depth to which each primary root of cotton extended into the treated soil was measured periodically for 3 days after the root entered the treated soil. Results were related to ionic composition of soil solutions in situ. Calcium deficiency symptoms and reduced growth occurred on all soils with aCa/Σacation i ratios in soil solutions of 0.15 or less. Ammonia toxicity symptoms on foliage were caused by only one treatment although toxic concentrations of NH3(aq) were present in three other soil solutions. These solutions were also deficient in Ca. When conditions conducive to Ca deficiency and NH3 toxicity existed in the same soil solution, Ca deficiency symptoms dominated except at the highest NH3(aq) concentration.