Posts Tagged ‘soil’

Q&A: Tofu left-overs feed the soil

Question from Shlomy Goldman in Cranston, Rhode Island:

I’m inspired by what you guys are doing. I’m growing my first garden ever this season (I’m on the east coast) and I’m doing it veganic! I brought in some leaf mold compost which I put on top of turned sod to start my garden. I think the compost is a bit carbon rich. I’ve already got a mixture of vegetables beginning to grow. Can you make a recommendation on amendments I should add? I am about to start making my own tofu. would the okara, the left over pulp from making soymilk be nitrogen rich? Is okara different from soybean meal? how would I use it for the crops? Any other suggestions?

Answer by Greg Litus, Animal Place horticulturist:

I had assumed that the leftovers from tofu manufacturing would be depleted of proteins and most other minerals.  However, that isn’t the case. In a study about the various uses of okara published by the Journal of Agricultural and Food Chemistry, Characteristics and Use of Okara, the Soybean Residue from Soy Milk Production, the okara was found to be high in crude fibers but also contains 25% protein and other minerals as described in the article.  The one thing missing from the article is okara’s potential as fertilizer.

Okara would be useful as a fertilizer in the same way that your leaf mold compost is a good soil amendment.   All organic rich soil amendments depend on healthy soil microbial activity to break down the carbon.  That process takes time and can initially cause a reduction in available nutrients to plants as the soil microbes sequester those nutrients.  For that reason it is usually best to apply amendments like okara a few weeks to months before it is time to plant.   That time period allows microbial action to take organic forms of nitrogen and phosphorous and make those nutrients available to the plant in an inorganic or mineralized form.

In the case of nitrogen, microbial activity will eventually cause slow denitrification while excess water will leach some nitrogen out of the root zone.  Therefore, more nitrogen needs to added depending on the rate of loss.  That can be achieved by growing green manures such as legumes (beans and peas) that have a symbiosis with bacteria that actually fix nitrogen into the soil from the atmosphere.  When those crops are turned into the soil, the process of mineralization and denitrification starts all over again.  In lieu of the green manures many of us just add compost or other plant-based amendments such as leaf mold compost, alfalfa or okara.  These plant-based amendments will also add other nutrients like phosphorous that will not be lost to the atmosphere but have their own specific cycles in the soil/plant environment.  The best gardens are ones that develop good fertility over time such that new additions of compost and other amendments replace the elements lost through harvest.

Even when focusing on long-term soil development, there are times when we get it wrong and the plants starve because we intercepted the soil nutrient cycles at the wrong time.  In those cases, readily available nutrients must be added to the soil to assure good plant growth.  At our micro-farm we keep alfalfa tea brewing for that purpose.  We also use very small amounts of synthetic fertilizers occasionally.   One teaspoon of 10-10-10 goes a long way on young seedlings.  When small amounts of synthetic fertilizer are applied to soils rich in organic matter and healthy microbial activity the whole system is enhanced.  The negative side of synthetic fertilizer is obvious but when directly compared to blood and bone meals and fish emulsions the synthetic fertilizers have less environmental impact.

Like you, we have a strategy for long-term soil fertility that will eventually eliminate need for any emergency inputs.  FYI we add soybean meal directly to the soil and take all other plant waste from the field and kitchen directly to the compost heap.

For those able to travel to Grass Valley, Greg will be giving a free introductory course on veganic farming at Animal Place on Tuesday, June 5, 6:30-8:30pm.

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