Leaves in vegtable garden
Bernalillo County New Mexico
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.
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.