some questions about rock fertilization

[simy1]

1) would you put furnace slag in your garden? if you google "slag chremical composition" the first hit is from our own group and there are sites linked from there that support the idea of using slag as a source of micronutrients, specifically Mg, Mn, Fe, and S (there is also lots of Ca and some K, but given that I already spread wood ash, those are unneeded)

2) what is the cheapest source of P, per pound of P?

[Bill]

Beer?

[Pat Kiewicz]

Some people would worry about heavy metals. Here's something from Penn State:

"Some slags may contain elevated concentrations of trace metals such as iron, cadmium, chromium, copper, lead, molybdenum, nickel, and zinc. Concentrations of these metals will vary in slags from different sources. All of these metals occur naturally in soil, and many are essential plant nutrients. If concentrations in the slag are similar to soil concentrations, they present no problem. If they are present at substantially higher concentrations in the slag than in the soil, repeated application of the slag could significantly increase soil concentrations of the metal in soil. This possibly could lead to plant toxicity, increased plant uptake and transfer of metals to animals or humans, or to other environmental problems. Before using a slag, be sure to obtain several laboratory analyses of the total concentrations of these trace metals in the slag."

>2) what is the cheapest source of P, per pound of P?

Cheapest?

Probably concentrated superphosphate (AKA triple superphosphate or triple phosphate). This concentrated of P2O5 derived from rock phosphate, 0-46-0. Not organically certified.

Ground rock phosphate would be 'organic' in that it is a natural source. It is very slowly available (best in slightly acid soils with good organic matter content). But it is bulky and expensive to ship around. Contains maybe 20% P (varies by source) but only 4% available P (so it's rated 0-4-0)

You can buy 5 pounds of triple (0-46-0) for $4.95 and 10 pounds of rock phosphate (0-4-0, *very* long run 0-20-0) for $6.25, using some web prices (and not including shipping, which can be by weight on bulky items).

[Penelope Periwinkle]

You owe me a new keyboard, young man.

Penelope

[simy1]

and transfer

I worked briefly in the past for a mining company, and chemical composition of the rock was an issue. I was amazed at the difference in heavy metals concentration between iron ore and granite rock. Iron ore typically has 100 times less lead, mercury, or uranium than granite. It is a very pure rock, as far as toxic stuff is concerned.

I understand that if the foundry is used to smelt lead all bets are off, and of course I had not thought of Cd and was originally worried about Al (the other elements will not be a problem for a light application). On the other hand, anyone eating local foods in red clay tropical areas intake far more aluminum than I would intake. In a Michigan acid sandy soil, my guess is that slag mainly serves a purpose of providing Mg and perhaps Ca.

[Bill]

LOL, glad you got a laugh out of it!

Bill

[Pat Kiewicz]

Dolomitic limestone will provide Mg and Ca, but no other trace minerals.

Langbienite is a mineral which will provide Mg and K. This naturally occurring mineral is the source for 'Sul-Po-Mag' also sold as 'K-Mag' (sulfate of potash magnesia). It is 22% K and 22% Mg by weight.

Kelp is the gold standard for trace mineral composition. The most cost effective way of buying it and applying IMO is Maxicrop powder mixed into foliar sprays. Kelp meal is expensive, but when we were a little more flush (cash-wise) I bought and used it when planting corn. The effects seemed obvious. The seed germinated more quickly and grew more robustly. I wish it were more *affordable* to as a soil amendment!