Broadcasting compost within Orchards

Compost spreaders are working in almond orchards in this area.  The addition of composted organic matter – often composted yard waste — to soil should generally benefit soil physical and chemical properties.  However, it isn’t a source of short-term plant available nitrogen.  Research by UC Davis specialists Tim Hartz and Jeff Mitchell has shown that composted yard waste, when mixed with sand and held under constant, optimum moisture and temperature (the optimum conditions for mineralization of organic nitrogen) produces a very little plant available nitrogen (2% of total nitrogen in the compost) in the short run (12-24 weeks).  When compost is broadcast on the soil surface and not incorporated, plant available nitrogen should be even less.  Dr. Hartz did conclude that manures and composts had value in long-term soil building in vegetable crop production, where those materials are incorporated into the soil.  [Untreated/uncomposted manure use in almonds is a food quality risk and not supported by the almond industry.]

Why bring up compost use? Growers are willing to pay for it and seem happy with the results.  Here’s why.  If California agriculture ends up in a regulatory situation where nutrient budgets are required of growers, it should be recognized that the short term nitrogen benefits from composted yard waste are almost non-existent and the long term benefits are unknown.

Previous entries on compost applications can be found here and here.

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6 thoughts on “Broadcasting compost within Orchards

  1. I wish there was more research regarding the benefits of compost in almond production and whether or not it can substitute conventional fertilizer if used over a period of time. In speaking with different people in the compost industry it appears they are reluctant to fund research as they seem to have no problem selling compost. I am intrigued with the idea of substituting compost for conventional fertizers such as potassium and phosphorus as you not only gain the nutrient value but also a whole host of microbial benefits. However, I know that the release of P and K can take multiple years to become available and I would think that early on a compost program would have to overlap with a conventional program to see that the trees nutrient demands are met. I wish the compost industry would fund some of this type of research but for now I’ll just play around with it a little myself!

    1. Thanks for the comment. We are in the works of developing a project to review the long term benefits of compost applications. This is a very complicated issue, so there are many aspects that we are trying to cover. Most of our data is based upon annual crop work by Dr. Tim Hartz (UC Davis). What he has shown is that most nutrients are more readily available than we use to think. It is no longer the assumption of 33% in year one, 33% in year two, 33% in year three, but rather more like 90%, 8%, 2% over that same three year period. I reviewed his research in a previous entry, and would encourage you to view it to address the questions of potassium and phosphorous availability. Both of these nutrients (as well as nitrogen) do become available to the plant within the year of the compost application — much more quickly than we traditionally thought.

    1. Sara,
      Yes, it should be fine. We have applied relatively high rates of compost pre-plant and then incorporated the material into the berms. Within our rootstock trial, we applied 5 tons per acre to the berm (about 10 tons/treated acre), imediately disced in, pulled berms and planted about 2 months later. The amount to apply should vary depending on the type of compost, the amount of nitrogen, and the amount of salt. Keep in mind that too much may damage newly planted trees especially if it is too concentrated within the rootzone (Our’s was mostly OM, with minimal nitrogen). The risk can be reduced by incorporating the material a few months prior to planting.


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