To determine the residual value of previous applied Mo and determining the critical concentration of Mo in youngest fully emerged blades.

 A series of experiments started in late 1970'S to the earlier 1980 on very acidic yelllow sands that are deficient in Mo.  

Yellow  acidic sandy earths with  soil pH (CaCl2) of <4.5. Mo trioxide at nil, 140 & 280 g/ha was applied on original nil Mo plots.

Summary of the Mo on very acidic yellow soils:

 With ammonium nitrate the recommended rate of Mo (140 g Mo trioxide) was  inadequate for wheat grain 2 -3 years later.. 

Mo effectiveness rapidly declines with 2 to 3 years after the application.

A general conclusion for this experimental series:_  The residual effectiveness of Mo for cereal is likely to vary widely in different situations depending on soil pH, soil content of free iron, aluminium and manganese and the rate and type of nitrogen fertliser applied to the crop.

Critical Mo concentratin in wheat YEB s appeared to be 0.03 - 0.06 mg/kg. The evaluation of Mo in the YEB as a reliable tissue test but suggested continuing testing into future years.