Rice Husk Ash (RHA)

[agroventuresperu]

What do you know about this as a fertilizer/soil amendment? We have a huge rice industry here as well as a brick industry. The brickyards mostly all use rice husks for fuel. Some places give away the resultant ash.

Some concerns I have are that the rice production is subjected to lots of chemicals: pesticides, fungicides. I would assume all of this would be volatilized when burned, but maybe not? I also can't really find any proper analysis that would mention the percentage of N P K Ca Mg S and its CaCO3 equivalence. Softwood ash has about a 30% lime equivalence, but a short-term residual liming effect, so it doesn't seem like it would be very effective to decrease subsoil Aluminum saturation. I can't imagine that rice husk ash would have a significantly longer term effect than wood ash.

Here's one source:
The rice husk ash (RHA) was produced from rice husks pellets (6 mm in diameter) burned in a boiler with a rotary grate, specially designed for producing biofuels. The burning temperature inside the combustion chamber was kept below the melting temperature of the ash and reached 980 to 1030 °C. The combustion temperature at the outlet of the chamber ranged from 750 to 920 °C. The time of complete combustion of the rice husks was in the range of 4 to 6 min. The pH of the used RHA was 10.7 and the material contained 0.27% of N, 4.02% of C, 1.45% of P, 0.6% of Mg, 3.88% of K, 0.51% of Ca, 0.05% of S and 0.08% of Na.

No idea the temperatures used here and all those other parameters, but those nutrients percentages are very low.  By comparison, the Umass.edu table
shows wood ash (guessing its hardwood)
Wood ashes - N0 P2 K6 Ca20 Mg1

Maybe if I can talk to the airforce to do a flyover and get them to drop a few tanker loads worth of the stuff, I think it could be promising.

[Seanny]

I use rice hulls for their 18% silica.
That’s the number missing on RHA.

[agroventuresperu]

Here's a decent article from Brazil:
https://www.redalyc.org/journal/3052/305257981008/html/




So, 1.1% Potassium? Am I reading that right? That's very underwhelming.

I really tripped and stumbled throughout the whole article. It looks like it even got published in a journal despite no apparent proofreading of the English.

Here's their concluding remark:
"As corrective of soil acidity, the residual effect of RHA comes down to the time needed to occurs the natural process of reacidification and leaching of basic cations, about 33 months for soils and weather conditions similar to this work."

And my proposed revision:
Regarding the amelioration of soil acidity, the residual effect of RHA is determined by the time required for the natural processes of reacidification (pH) and the leaching of basic cations (Base Saturation) to arrive at levels equal to those measured prior to the application of RHA. We infer that this residual effect is about 33 months in soil and weather conditions similar to those of this study.

[Tropicaltoba]

Any studies on accumulation of toxic metals? I went through the same process looking up birch ash. I think for rice leaf cadmium etc may be of concern for bioaccumulation.

[agroventuresperu]

Any studies on accumulation of toxic metals? I went through the same process looking up birch ash. I think for rice leaf cadmium etc may be of concern for bioaccumulation.

If you know where it's grown you can soil test for Cd and other metals. Will a given species bioaccumulate a given metal? There are probably studies with the most common crop species. There's even some literature that says Brazil Nuts bioaccumulate Selenium. No idea how they found that out or tested/proved it. What would be the source of the Cd?

One thing I've always wondered, but haven't ever taken the time to do a deep dive is with soil Aluminum saturation, which is extremely common in the tropics. I know some species have different strategies to cope with the presence of Al3+, some exclude it completely from the roots, but I've also read that other species can accumulate it and isolate it in certain tissues. Not sure what that means for fruits and other foods grown in such soils - if it translates to humans ingesting significant levels of Aluminum? I would think if it were really a big issue, than it would be something well-known, and people in tropical areas would be plagued with the related health problems, but I've never heard of such a thing.

[Tropicaltoba]

Have you look into converting it to biochar? I’m sure there is specs on the them temp needed to do it with rice husk. You can then “activate” it (make it a nutrient resevoir) by running bokashi leachate through it. Bokashi is basically fermented organic waste. The easiest way to make it is using lactobacillus (kombucha bacteria) to convert the sugars from fruit waste into a moderately acidic potassium rich solid waste which is easily composted. The liquid runoff is super acidic and the possum ions will bind to the carbon rich char and the acidity will neutralize any alkaline ash.

There is some potential/theoretical risk with producing poly aromatic hydrocarbons but these are also made by some natural wood decomposition.

[agroventuresperu]

Have you look into converting it to biochar? I’m sure there is specs on the them temp needed to do it with rice husk. You can then “activate” it (make it a nutrient resevoir) by running bokashi leachate through it. Bokashi is basically fermented organic waste. The easiest way to make it is using lactobacillus (kombucha bacteria) to convert the sugars from fruit waste into a moderately acidic potassium rich solid waste which is easily composted. The liquid runoff is super acidic and the possum ions will bind to the carbon rich char and the acidity will neutralize any alkaline ash.

There is some potential/theoretical risk with producing poly aromatic hydrocarbons but these are also made by some natural wood decomposition.

I think there's a municipality that actually does that. I'm not too interested at this point though.