Q. Sometimes I have seen gardens with compost and manure as the fertilizer of choice become very yellow. What causes this, and how do I avoid that happening to my garden?
A. What you have seen is “Induced Nitrogen Deficiency.” Soil amendments, including straw, tree bark, shavings or sawdust, peat moss, and manure (almost always containing a large percentage of bedding straw or sawdust) can induce a nitrogen deficiency on plants. The reason is that these materials are very high in carbon content, and therefore adding them into the soil raises the carbon to nitrogen ratio.
The carbon to nitrogen ratio is the amount of carbon in relation to the amount of nitrogen in the soil. This ratio should be 10:1 or lower. When the soil has ten parts of carbon, it should have at least one part of nitrogen or the plants will not be able to obtain the nitrogen they need. When carbonatious soil amendments are added, the amount of carbon is raised in relation to nitrogen. Micro-organisms in the soil attempt to break down the carbonatious material and in this process they use some of the nitrogen from the soil, making the ratio even worse. The micro-organisms have the ability to take the nitrogen before the plant can, so oftentimes adding soil amendments induces a nitrogen deficiency for the plant population. Therefore, whenever soil amendments are used, it is important to add some nitrogen, to bring the carbon to nitrogen ratio back to a ten to one, so that both the plant and the micro-organisms requirements are satisfied.