7: 



digested sample was then determined by a conventional, semi -micro 

 Kjeldahl distillation procedure. 

 5.1.2 Total Nitrogen in Soils 



Total N in soils was determined by the same method as total N in 

 plant tissue. Soil samples were finely ground for 5 minutes using a 

 mechanical mortar and pestle. A 0.2-g sample was weighed and digested 

 on an aluminum digestion block for 3 hours after the solution cleared. 

 Ammonium was determined by a semi-micro Kjeldahl procedure. 

 5.2 SULFUR 



5.2.1 Tissue Digestion for Total Sulfur 



Plant tissue was digested using a Mg(NCL) /HNO solution on a hot 



Q 



plate followed by heating in a muffle furnace at 500 C for 2 hours. 

 The procedure is a slight modification of the methods of Butters and 

 Chenery (1959) and Chaudry and Cornfield (1966) and is similar to the 

 digestion procedure for the gravimetric determination of S as given by 

 the Association of Official Analytical Chemists (1970). A preliminary 

 study indicated that this method resulted in more complete digestion 

 of the tissue and gave comparable recovery of added S when compared to 

 the HNO /HC10 / wet digestion technique described by Beaton et al . 

 (1968). Sulfate S was determined on the digested tissue by the 

 turbidimetric procedure of Massoumi and Cornfield (1963) and Chaudry 

 and Cornfield (1966) and will be given in a later section. The 

 digestion procedure is given in Appendix A. 



5.2.2 Soil Extraction for Sulfate Sulfur 



Extractable sulfate S was determined on air-dried, screened soils 

 by extracting 10 g of soil with 25 ml of a 0.01 M Ca(K PO ) ? -2H 

 solution. Soil and extractant were Dlaced in 100-ml bottles and 



