had equal or greater amounts of these cations than the opening plots (table 3) . The 

 fire-treated soil had appreciably greater amounts of extractable potassium and manga- 

 nese than all other treatment soils during the entire growing season. 



Table 5 .- -Treatment effects on soil nutrients from June to September ^ 1975 









Nutrient 



concentrations 





Treatments 



: Mn : 



K 



: Mg 



: NH / : NO " 





vg/g 



Fire treatment 50-100 715-1195 150-265 26-76 2.0-7.5 27-35 

 Pine -associated 



treatments 15-80 480-880 165-200 4-7 1.5-4.0 18-28 



Opening treatments 10-65 240-410 145-170 4-7 1.5-5.0 8-26 



Probably because of increased mineralization of organic nitrogen, fire-treated 

 soil had an extremely high ammonium ion content that varied with fire intensity. The 

 fire plots that burned the hottest, causing the greatest litter reduction, had the 

 highest NH4"^ concentrations. There was very little difference in NH^"*" and NO3" levels 

 between the rest of the pine-associated plots and the opening plots (table 3) . The 

 increased amounts of NH4+ in the fire treatments did not lead to excessively high N03~ 

 concentrations, but the nitrate values were slightly higher than those found in most 

 other treatments. 



The phosphate content was noticeably higher on the tree-associated sites than in 

 the openings (table 3) . The fire treatment appeared to raise the P04"-^ concentration 

 slightly over some treatments and greatly over others. 



These analyses indicated that the nutrient content of the soils within the pine 

 stand was comparable to or exceeded that in the openings. Rating the treatments in 

 terms of seedling growth potential on the basis of nutrients is very difficult. How- 

 ever, the fire-treated plots do stand out from the other treatments in their high nutri- 

 ent content, but this was expected (Christenson and Muller 1975; Viro 1974). Of 

 particular interest was the increase in nitrogen (NH4+) , because this, along with other 

 nutrients, can have a significant influence on the growth of ponderosa pine seedlings 

 (Cochran 1972; Vlamis and others 1957) and may play a role in the drought-resistant 

 capabilities of ponderosa seedlings (Loewenstein 1970) . The particular form of nitrogen 

 may also be important. Ponderosa seedling growth studies indicate that NH^+ is the pre- 

 ferred source over NO^" and urea (Wollum 1968, 1970) . 



All treatments had similar soil pH values, except for the fire plots which, as 

 expected, had much higher values. In all cases, pH values were highest in June and con- 

 tinually decreased throughout the summer. The average soil reaction for the opening 

 plots for June 4 was 5.5 compared to 5.6 for the pine-influenced plots. On September 3, 

 the average pH had fallen to 4.7 in the opening treatments compared to 4.9 for the 

 others. Average fire treatment pH dropped from a June 4 high of 6.5 to a September 3 

 low of 5.5, probably due to leaching of the oxides and carbonates found in the ash. 



9 



