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Garden Center Magazine: goodbye phosphorus!

June 9, 2011

“The company’s findings showed that most established lawns have enough phosphorous, and the element is essentially “recycled” when cuttings are left on the lawn to break down naturally.”

via Garden Center Magazine : Farewell phosphorous.*

This article describes the impending bans of P from lawn maintenance fertilizers for many states in the USA. It’s fascinating to note that even a fertilizer maker like Scotts (makers of “MiracleGroTM”) would be able to recognize P excess when it sees it. Unfortunately, for crops one can’t leave everything on the field to be recycled – the crop itself of course needs to be removed. But this does point out how return of unharvested biomass can maintain P balance and avoid unnecessary fertilizer application.

A couple of interesting side notes: Scotts fertilizer for starting a lawn would still contain P and Scotts brand of “organic” fertilizer, which is based on manure, would still contain P. Not entirely clear to me how that helps with the P runoff problem, but there you are.

Also fascinating is the fact that, in Wisconsin, P-containing Milorganite fertilizer will still be allowed under pending P ban legislation. Milorganite is the trade-name of a fertilizer produced in Milwaukee from biosolids from wastewater. It’s been produced for nearly 100 years. Old school sustainability!

*SIC: It’s “phosphorus” NOT “phosphorous”. Urgh.

3 Comments leave one →
  1. June 10, 2011 1:17 am

    but why do these lawns not need more phosphorus? just like in the grassland, the available P is very low,but it seems that grassland don’t need so much phosphorus.well,why?

  2. July 16, 2011 2:26 am

    I think the principle is that the lawn clippings, if left on the lawn, will be decomposed and their P can be used by the grass to make new grass (and be cut the next time, etc). A cycle!

    Note from the blog post that fertilizers for establishing a lawn will still contain P; this makes sense as the grass seeds need to make a lot of new roots and shoots in getting established. This might be tough if they are sown onto poor soil without much P. So, the idea, then, is that establishing a lawn might require a P subsidy but the established lawn, assuming the clippings are returned to the lawn, might not need any extra P. On the other hand, N is pretty easy to lose (as ammonia into the atmosphere, as nitrate moving in runoff water, as N2 gas if there are places where microbes can “denitrify” it) and might need to be continuously fertilized to keep the lawn nice and green but P is a bit “stickier” and doesn’t get lost at such high rates. Hope this helps.

  3. haiyang permalink
    July 25, 2011 2:27 pm

    If we clip the grassland year by year and not return the clippings back, as your “cycle hypothesis”, the grassland will become P-limited. I have a hypothesis: if the clipped grassland become nutrient-limited and retrogress, which is the major reason, N or P?

    Is the idea “the established lawn, assuming the clippings are returned to the lawn, might not need any extra P” means that as in the grassland, organic P is the major sources in the long term? some references think the NaOH-Pi is the one that sustain the ecosystem.
    anyway, thank you for your explain and suggestion.

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