Re: grass clippings as mulch
- To: Gary Matson <m*@awwwsome.com>
- Subject: Re: grass clippings as mulch
- From: r* s* <r*@california.com>
- Date: Wed, 30 Jun 1999 16:05:48 -0700 (PDT)
Gary, How do your tomatoes (if you grow them) do with overhead watering?
Barbara
On Wed, 30 Jun 1999, Gary Matson wrote:
> I guess I must politely disagree with Susan's statement in this circumstance.
>
> It is my understanding, both from my reading in matters horticultural, and from
> personal experience with all kinds of mulch including fresh pine shavings, wood
> chips and high quality hay, that organic matter of any kind when just placed on
> the surface as mulch causes little or no nitrogen 'drawdown'. This is largely
> because there is no significant mechanism for transfer of nitrogen up out of the
> soil into the mulch. The mulch may, if very high in carbon relative to nitrogen,
> intercept small inputs of nitrogen from above moving into the soil (as bird
> droppings, spent spider dinners, lightening-fixed nitrogen, air pollution etc.)
> until the mulch can be broken down, at which time the inputs are released. So,
> even if grass clippings were low in nitrogen, they should cause no problem if
> placed on the surface.
>
> But grass clippings are very high in nitrogen. There is more than enough nitrogen
> in them to allow complete decomposition without any additional input needed. In
> fact, if grass clippings are too high a proportion of a compost mixture it can
> cause problems with ammonia release as the overabundance of nitrogen is not needed
> by the microorganisms. The municipal composting operation in the small city near
> us has had this problem since grass clippings are the majority of their
> 'greenwaste' in the summer months.
>
> The clippings have essentially the same nitrogen content whether dry or wet, since
> the N is bound in cell proteins and such. As they decay, this nitrogen is
> released. This decay can be mediated by lots of different organisms from mammals
> through invertebrates to fungi and bacteria. The drying just changes them enough
> physically that they usually do not mat down. This is especially the case in dry
> climates like central Spain and interior California.
>
> Our vegetable garden nowadays is under permanent mulch, and is not tilled at all.
> Every year we go out and trowel in the transplants, then place a layer of several
> thicknesses of newspaper on the surface and then cover that with flakes of hay,
> peeled off of rectangular bales and placed as tiles all over the area. Usually we
> get alfalfa-grass mix hay, but some years it is just various pasture grasses cut
> green, dried and baled, intended for livestock feeding.
>
> As the hay is wet by the sprinklers (all overhead water), the hay flakes expand to
> make a fluffy layer several inches thick, often as deep as 20 cm to start. By the
> next year, that has all disappeared and only a thin strewing is left on the
> surface, and weeds are again germinating. The decomposition of this hay layer
> provides most of the nutrients needed by the vegetables. Some years and with some
> crops, a slight addition of ammonium sulfate is sprinkled on and watered in
> sometime during the plants' growth. We do not add organic matter to the soil
> directly, but let the worms come up and drag it down in for us. The soil has
> become porous and friable in a way I would not have believed possible. (This is a
> stony,red, kaolinitic soil, with high content of iron and aluminum clays and a
> dense clay pan at a few feet of depth) I think the grass clippings should
> function in exactly the same way as the hay.
>
> I have never been aware of an allellopathic problem from anything I have used, and
> perhaps it is because, as was mentioned in another post (Jerry's I think--I've
> already deleted it from my machine), the substances don't persist very long.
> Concerns about allellopathy are more often expressed regarding living plants and
> their root exudates and leaf leachates. Living grass roots are especially
> inhibitory of trees and shrubs, I have read.
> -
> Gary Matson Far Northern California
> http://www.plantstogo.com
> Adapted Plants for Hot Summer Climates
>
> Damian Martin wrote:
>
> > However, I'm still unclear about this nitrogen business...
> >
> > Gary says...
> >
> > > Other than that, drying the clippings first converts them into
> > > essentially
> > > very short-cut, high quality hay, and eliminates sticking and matting in
> > > most cases. Tremendous nitrogen release as they decompose
> >
> > whereas Susan warns...
> >
> > > another problem might be the so called 'nitrogen draw down' effect
> > > (basically as raw materials rot/compost they use up nitrogen in the process)
> >
> > So does this mean that with dry clippings nitrogen is released *to* the
> > soil but that fresh clippings draw nitrogen *from* the soil?
> >
> > Finally, do dry clipping still contain those worrisome allelochemicals?
> >
> > Damian
> > Talavera, central Spain
>
> -
>
>
