Applying Compost Tea Post-Harvest Substantially Reduces Nutrient Loss

Most of us know compost tea has outstanding effects on fertility throughout the growth cycle of the plant. But some farmers are finding that it has significant benefits in the rot cycle when applied post-harvest, under certain conditions.


After harvesting most crops, some of the plant remains above ground. This residual can be treated in various ways, but most of them leave harvest-damaged organic matter exposed to the air and thus allow release of nutrients during both respiration (which continues for a while post-harvest) and decomposition. The real opportunity comes primarily from capturing the material that initially wants to evaporate out of the plant because it is the simple compounds that easily volatilize into the air.

First, let’s discuss what kind of extract will make the most beneficial treatment. Humus, which can be produced by a managed process on the farm, is a very powerful substance that attracts soil particles in such a way as to open pore space and enhance tilth. In addition to this physical change, humus also contributes to the mineral balance and diverse biological activity. This biological activity has three primary functions: recycling nutrients, providing nutrients in plant-friendly forms, and impacting the soil structure via lifecycle by-products.

Because there is such a variety of soil conditions, organic materials, and mineral contents, we want the widest possible variety of microbial life. In addition, we want that life to have the potential to expand rapidly — doubling a minimum of 30 times. Humus provides the nutrients, space, moisture, and other factors that allow the needed species to reproduce and become available to perform their functions.

In dealing with crop residue, several things should be considered. One is that the residue has an abundance of organic matter that has been built up by the plant into complex structures. Another factor is that the natural respiration of the plant involves movement of additional, less complex, and more volatile compounds up and down (mostly up!) the roots, stalks, and stems of the plant. Both the “standing” organic matter and the “flowing” compounds contain vital nutrients that can be available for future crops if they are treated properly.

Applying tea immediately following harvest can help to “lock in” the nutrients, preventing their loss to the atmosphere via respiration. The microbes then do their work on the residual organic matter, accelerating and enhancing decomposition (the rot cycle). Because this is a controlled process, the nutrients thus captured are restored to the soil the plants exist in. The net effect is to improve the health of the soil at a low cost and provide “free” nutrients to the next crop. This is especially necessary and beneficial on a farm emphasizing organic fertility.

To enhance this effect even further, incorporate residues into the soil or use a roller to put the stalks in contact with the soil, which is especially helpful in no-till operations, so that the activity can become integrated with the soil’s natural biological cycles.

One farmer reports that in his tests, running the tea applicator immediately behind the harvester results in an increased yield of several bushels in the year following (all other things being equal). It is important that application must be within hours of harvest, as that is the time when the respiration is continuing most strongly.

Obviously the quality of the tea is important to this process. Smaller operators can use the GSI tea machines, while larger farms would probably need a high-volume tea extractor such as the one available from Midwest Bio-Systems. In either case, an activator, also available from Midwest Bio-Systems, will enhance the output. Some agronomists also call for fish molasses as an additive prior to application.

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