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on plots which had been prepared by disking only. Milder deficiency 

 symptoms were observed on these same plots even where 300 pounds 

 of 0-14-7 had been placed in the row at planting time. The air space 

 porosity in these plots was only 14.2 per cent as compared with 26.9 

 per cent for adjacent plowed plots, which showed no potassium de- 

 ficiency symptoms. These two adjacent plots were comparable except 

 for the one variable of tillage in preparing seedbeds. 



Bower, Browning, and Norton (14) obtained symptoms of both nit- 

 rogen and potassium deficiencies in the first reported experiment which 

 demonstrated that tillage had a direct effect upon availability of nu- 

 trients. They observed definite nitrogen deficiency symptoms on corn 

 which was growing on land prepared by disking or subsurface tillage, 

 even where nitrogen fertilizer was applied. Corn on plowed land 

 showed almost no evidence of nitrogen deficiency. Similar results were 

 obtained with potassium, but the differences were not quite so clear 

 cut. Where no fertilizer was applied, however, the potassium content 

 of plowed corn was 70 per cent higher than the average of corn grown 

 by the other three treatments. Significantly, they found no difference 

 in exchangeable potassium content of the soils between these plots, yet 

 the potassium was definitely more available to the corn plant from the 

 plowed plots. They indicated that tests showed more ferrous iron (indi- 

 cating lack of aeration or reducing conditions) in the soils of those 

 plots which were not plowed and on which potassium deficiency was 

 observed. 



Lawton (46) made a study of the effect of aeration on absorption of 

 nutrients in pots in the greenhouse, where different degrees of com- 

 paction, different water levels, or forced aeration could be maintained. 

 He found that where pore space was reduced, either by compaction or 

 increase in water content, absorption of potassium was much less than 

 from a normal soil. Under these conditions root growth was also seri- 

 ously reduced. Forced aeration eliminated the distinct potassium de- 

 ficiencies, even though air was forced through the soil for only 30 min- 

 utes a day. He observed that absorption of potassium is more dependent 

 upon soil aeration than is uptake of nitrogen, calcium, magnesium, or 

 phosphorus. This is in agreement with the findings of several investi- 

 gators working with solution cultures. 



Smith and Cook (6j) studied the effect of soil aeration and compac- 



