Leaves in vegtable garden

Asked December 31, 2019, 1:49 PM EST

I recently had a garden soil test done by Colorado State University and the test showed the Nitrogen level as high (86 ppm). I have been collecting my Ash and Sycamore tree leaves and placing them in the garden in the fall. Would this be a factor in this high nitrogen reading. This has resulted in small fruit on my plants and my hops have not produced any flowers for two seasons.
Would you have any suggestions for reducing the nitrogen.

Bernalillo County New Mexico

5 Responses

What state and county do you live in? If you tell me your county I can better route your question to the appropriate expert.

Thanks Ruth. I live in Bernalillo county of New Mexico - North Valley, Vista Del Norte neighborhood. This information was entered into the form I submitted my question on so I thought it went with the email. Sorry for the inconvenience.

Tree leaves have some nitrogen in them, however most of it is as organic nitrogen. As the leaves decompose, the organic nitrogen will convert to nitrate-nitrogen which is what is measured in the soil and appears on your soil test report. The amount of nitrate-nitrogen that the leaves put back into the soil is usually small, since the leaves usually contain low amounts of nitrogen at the end of the season and the conversion from organic-N to nitrate-N can be somewhat slow. Tree leaves are a good source of organic matter since they do supply some nitrogen and carbon to the soil and you should still add your leaves to your garden. The high nitrogen in the soil could be coming from any manure or other organic product that was added earlier in the season. The nitrate-nitrogen content in the soil in the spring should be about 50-60 ppm. To lower the nitrate-N content try planting a cover crop of annual ryegrass to help pull nitrogen from the soil. Cut the ryegrass with a lawn mower at its lowest setting when the ryegrass gets to about 5-6 inches tall (or taller if you want to wait). Collect the clippings with the mower and compost the clippings in a compost pile. The ryegrass will utilize the nitrogen in the soil and may reduce it to a level that would be more suitable for your garden.

Thank you for the information.
I'd like to ask your opinion on whether the leaves should be tilled in to the soil of just left as a cover on the garden? It seems like tilling is a practice we want to get away from because of the release of carbon dioxide.

The advantage of tilling in leaves allows the leaves to decompose in the soil and sequester carbon. Sequestering carbon refers to carbon being utilized by microorganisms within the soil or the conversion of carbon into compounds that can be held by the soil. Sequestering minimizes carbon loss by reducing CO2 evolution from the soil surface. Leaves left on the soil surface will eventually decompose, but they are exposed to the atmosphere more and are subject to decomposition by sunlight and heat resulting in CO2 release. The result is less sequestering of carbon and more carbon dioxide loss. Both management practices, however, are good ways to improve soil health. Tilling in leaves builds up the carbon in the soil for microbes and adds some nutrients and organic compounds to the soil. Adding leaves to the soil surface will also result in some decomposition of the leaves that will also add carbon and some nutrients as well as conserve moisture. Surface applied leaves will also serve to reduce weeds and make the crop or landscape more productive. Both management practices are good ways to make use of leaves as a readily available source of organic matter or mulch.