High levels of both N and K from fertilizer were required to obtain optimum yield of timothy and also to maintain timothy as the dominant species in a grass sod. Phosphorus was required in relatively small amounts. Timothy degenerated when an imbalance of N and K was induced through fertilization and did so most rapidly when N was applied without K. Increasing N applications generally increased N content but the extent of the increase was modified when K was also applied, similarly K application increased K content but levels were modified downward when N was also applied. P content was affected only slightly by P application but levels were lowered when yields were increased by a combination of N and K. Critical nutrient concentrations of 1.6, 0.20, and 1.2% for N, P, and K respectively were determined for first-crop timothy cut at the fully headed stage. Higher levels of N and P were observed in second-cut material.

In a greenhouse experiment, yields of Charlottetown 80 and Herta barley decreased with increasing rates of aluminum applied to a Caribou loam soil. The decline in yield was greater with the Herta variety. At the same time, this variety did not exhibit symptoms of aluminum toxicity as had been encountered on the same soil m field trials.A nutrient solution experiment established that Charlottetown 80 and Herta possessed a differential tolerance to aluminum and indicated that regional barley production problems were due to high concentrations of this element. Typical aluminum toxicity symptoms were encountered which appeared at lower aluminum concentrations in the Herta variety. Top and root yields of both varieties declined with increasing aluminum treatment but the effect was more pronounced with Herta.Phosphorus and calcium decreased in the tops and increased in the roots with increasing aluminum concentration. The effect was greater in Herta at intermediate aluminum concentrations than in Charlottetown 80. It was concluded that aluminium depressed the translocation of these elements within the plant rather than their adsorption by the roots.

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'78. Native clay-fixed ammonium content, and the fixation of added ammonium of some soils of Eastem Canada. A study was made of the native clay-fixed NHa+ of some typical soils of Eastern Canada. Usually the amount of fixed NHa+ was related to the clay contents and increased down the profile but there were frequent exceptions to both of these generalizations. The amounts found ranged from l2to 450 p,g fixed NH++-N/g soil.In general, with some cultivated soils, the cropped areas had lower native fixed NHa+ contents than areas that were in sod. The capacity to fix added NHa+ was usually low in the sandy soils and in general the B and C horizons fixed more NHa+ Can. J. Soil Sci. 58: 27-38 (Feb. 1978) fixed NHa+ was found in the silt fraction. That many soils have the ability to fix NHa+ that is added to soil has been known for a long time (Nommik 1957(Nommik , 1965

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