ANALYSIS OF MACRO-ELEMENTS AND TRACE-ELEM ENTS IN HORTICULTURAL SUBSTRATES BY THE CACL2 DTPA-METHOD .9. SODIUM/

Impatiens Neu Guinea Hybrids were grown with increasing amounts and di fferent forms of sodium (NaCl, Na2SO4, NaNO3, Na2CO3) to test the suit ability of the CaCl2/DTPA method for estimating Na in horticultural su bstrates. 1. Na2SO4, NaNO3 and Na2CO3 applications of more than 400 mg Na/l substrate caused growth reduction; with NaCl 400 mg Na/l substra te were already toxic. 2. With all salt containing extraction solution s (CaCl2, CaCl2/DTPA, NH4-acetate) the added amounts of Na were recove red nearly completely, independent of the form of Na supplied. 3. By e xtraction with water somewhat lower Na contents were found with NaCl, Na2SO4 and NaNO3 as Na source compared to salt containing extraction s olutions.4. Large differences between water and salt containing extrac tion solutions were found with Na2CO3 as Na source. With water only a small percentage of added Na was recovered. 5. Extraction with water l eads to the risk of underestimation, Low sodium contents may be found which however may be toxic. Water extraction is therefore not well sui ted for the estimation of sodium content of horticultural substrates. 6. The extraction with CaCl2/DTPA is suited for the estimation of sodi um in horticultural substrates. No difference to other salt containing extraction solutions (CaCl2, NH4-acetate) has been found. The critica l value for Na toxicity is 400 mg/l substrate.