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Need to know: Manure and phosphorus management

Manure is a first-rate, albeit smelly, treasure trove of nutrients, with all the macro- and micronutrients plants need to grow (though not necessarily in the right concentrations). While phosphorus often plays second fiddle to nitrogen, it is a vital nutrient for plant growth and worth managing carefully. Understanding how manure phosphorus behaves after application is important to know how best to manage manure.

A crop farmer piped up from the back row of a meeting, “If phosphorus sticks to soil, why can’t I just bank it up in my soil and have it forever?” While it’s true that phosphorus is far less mobile in the soil than nitrogen, it can still be lost to the environment through runoff and erosion. In high-phosphorus soils, leaching can also occur. When excess phosphorus ends up in freshwater, it can cause harmful algal blooms and hypoxic zones where plants and animals can’t survive.

Phosphorus management in manure poses a unique challenge as the ratio of nitrogen to phosphorus cannot be adjusted to precisely meet the needs of the crop. Inevitably, phosphorus—and other nutrients—will be under- or over-applied when manure application rate is based on the crop’s nitrogen needs. Most forms of manure are notorious for over-applying phosphorus, leading to build-up in the soil and increasing the likelihood of phosphorus loss to the environment. | READ MORE

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