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This graph shows the phosphorus levels of 147 sites, with each bar representing the phosphorus level of one site. The green bars are non-farm sites and generally have very low phosphorus. The red bars are growers using conventional growing methods and fertilizers, and fall mostly in the ideal range. Phosphorus levels for our organic growers are the yellow bars, and are generally quite high into the concerning range.
Phosphorus is a Goldilocks kind of nutrient. You don’t want too much OR too little. You want it just right. Plants need it to grow, but too much can pollute downstream waterways and cause plant nutrient deficiencies. Manure is a go-to fertilizer for our Front Range growers, and because organic farmers cannot use chemical fertilizers, they often apply large amounts of manure to boost their nitrogen levels. However, manure is also rich in phosphorous, which can build up in soils over time.
Excessive soil phosphorus is a common problem in organic production nation-wide and among CSSHP growers as well. Growers with very high phosphorus levels are advised to switch to low-phosphorus amendments, incorporate legume cover crops to boost nitrogen but not phosphorus, ensure adequate buffer strips along fields to slow and absorb nutrient run-off, and run plant tissue analyses for iron and zinc if deficiencies are suspected.
Elizabeth Black is the producer of the Citizen Science Soil Health Project