Fungal superhighways operate underground to decompose minerals and nutrients from soil and deliver them to plants. For this reason, fungi are powerful, yet too often overlooked additions to plant production. Many industrial agricultural techniques damage these fungal communities, resulting in less than optimal crop yields, reduced crop nutrition, and increased need for agrochemicals. As a result, many organic farmers, and even many health conscious home gardeners are turning to organic methods to minimize exposure to agrochemicals. These growers will have the most success when they manage soil to support healthy fungal communities.
Cucurbits (squash, cucumbers, pumpkins, etc.) like those shown in the picture above are known for their vigorous summer growth and their preference for a rich nutrient base. Growing cucurbits in thin, desert soils may require soil amendments, but adding mineral salts to desert soils is not recommended. The plants shown here are being grown organically on a calcium carbonate rich, loamy clay desert soil that was mulched the previous year with well decayed wood chips to retain moisture. Humic acids have been added as soil conditioners. Low growing native astragalus plants have been allowed to remain on the site as a natural green manure and cover crop. In addition, an organic, fish emulsion based foliar fertilizer has been applied every two weeks to four (A-D) of the five plants shown. These four plants were planted Memorial Day weekend in 2017.
After planting, a Johnson-Su composting bioreactor (see video below) was constructed on the same site. The design was as described by Dr. David Johnson, except that the irrigation timings followed the cycle set for the garden as a whole, rather than the twice daily schedule Johnson recommends. The reactor was filled with a sawdust and green leaf substrate to create a fungal rich compost. The longer, less frequent irrigation resulted in small amounts of water draining from the reactor during watering, so Big Max pumpkins were planted under the reactor to harvest the nutrient rich leachate. This pumpkins were planted in mid-June.
Photograph E, in the middle of the picture above, shows the pumpkin growing on the leachate. Leaves are clearly greener, thicker, and fuller than the leaves of other cucurbit varieties grown. Although this was not designed as a scientific test, the impressive difference in apparent plant health and vigor is aligned with our general expectations for what a fungal rich compost will contribute to plant health. Microscopic examination of the compost tells us a diverse fungal and protozoan community is developing. Although the compost itself is not yet mature (sawdust has not degraded), we will be using it as a starter for compost teas in the weeks ahead. This will allow us to innoculate the remaining cucurbits with some of the microbes contained in the developing compost in time for a rich, late summer harvest of nutrient dense produce. In the fall, we will apply the completed compost to seedlings for our winter garden.
How to make a fungal rich compost.
Composts will develop diverse fungal communities when the starting material contains lignin rich substrates like dried leaves or sawdust, the compost is well aerated, and mixing is kept to a minimum. The self watering, self aerating Johnson-Su bioreactor, when filled with finely chopped and appropriate starting material, provides a perfect habitat for diverse dark-septate and mycorrhizal fungi. If you would like to make your own fungal rich compost, you can learn how by watching the video below.
If you would like to learn how to examine your compost and determine whether it has the fungi needed to help plant communities thrive, sign up for our Microbial Analysis for Growers online workshop, coming soon.