Sawdust and Cornstalk mulch - Knowledgebase Question

Marathon, IA
Avatar for rojohn
Question by rojohn
February 12, 1998
I would like to make use of the large amounts of sawdust I've acquired access to - some rotted but most not. I can see how incorporating large amounts of this in the soil would cause nitrogen depletion but have read that is not the case if it is usedas a mulch. I don't imagine a 2-3" layer would rot very much throughout one growing season but if it were to be left in place over winter, might it be sufficiently decomposed by spring to incorporate it without it so actively consuming nitrogen from the soil? If such is not the case, would a sprinkling of high N lawn fertilizer under the sawdust hasten decomposition and help to keep things in balance? Also, Last year I acquired 2 large round bales of cornstalks - several years old but not rotting - and to my amazement it spread easily and held well. I read in Burpee's latest book that dry corn stalks have a fertility analysis of 1.2 - .4 - 1.6, not a lot less than horse manure. Do you think 8-12" of this used as mulch and later incorporated every year would provide much of the nutrients needed for good crop growth and also enough nitrogen to self-sustain it's own decomposition? I wish I could compost it all but there's just too much and I'd rather take the easier route.

Answer from NGA
February 12, 1998
There are a lot of variables that affect rate of decomposition, but I believe your sawdust can still draw nitrogen from the soil after a winter on the garden. Rather than lawn fertilizer, which is water-soluble and will likely leach into the soil rather than remain near the surface with the sawdust, apply a slow-acting nitrogen source, such as alfalfa meal or corn gluten (which also inhibits weed seed germination!).

The corn stalks, on the other hand, sound like they will rot more quickly. They won't provide much in the way of nutrients for crops, but can contribute to soil organic matter, which is just as important, since organic matter is key to keeping nutrients available to plant roots. Hope this helps!

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