Lime contains Calcium - Ammonium Nitrate is pure nitrogen. These two substances when added dry to one another form a chemical bond with is very difficult to break. This is why when you buy your 20-20-20 in all cases it is void of Calcium. When you add these two together in bulk and then add them to water they form hard clumps which float to the bottom of your bucket and will remain there. In order for plants to use elements they must be insolution. As far as toxicity goes if you put these two together in their dry form the result would be toxic. However if you mix the right amount of each in two different five gallon buckets. Ca in one bucket, N in another bucket and then poured both into a 10 gallon bucket this would be fine.

Herbus