Steam Sterilization on Water-Soluble Matter in Soils. 257 



two steamed soils is entirely reversed, as is also the percentage of nitrogen, 

 Soil No. I at the end of seven months yielding more than Soil No. 2, 

 but having a lower percentage of nitrogen. This illustrates the difference 

 in the length of time required for different soils to recover from the 

 steaming process. 



Fig. 69 — Second crop grown after steaming. Showing continued benefit 



G A O — Soil No. I , unsteamed 

 G A S — Soil Xo. I , steamed 

 P A S- — Soil Xo. 2, steamed 

 P A O — Soil Xo. 2, unsteamed 



il\n experiment with the growth of wheat seedlings in the extracts 

 of steamed and unsteamed soils throws some light upon the cause of 

 the unfavorable effect of the freshly steamed soil upon plant growth. 



Soil Xo. I was steamed and an extract made of the steamed and also 

 one of the unheated soil. One part of water to one part of soil was used 

 in making the extracts. Wheat seedlings were grown for four weeks 

 in the extracts, both undiluted and diluted by adding three parts of 

 water to one of extract. Table V shows the nutrients present in the 

 extracts diluted and undiluted. It will be noticed that the PO4 and 

 K are much higher in the extract of the steamed soil, while the nitrates 

 arc lower. However, nitrogen was doubtless supplied in ample amount 



9 



