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Agronomic Crops > Crops Blog > Posts > Evaluating the phosphorus status of soil and the 590 phosphorus application criterion

‚Äč Animal manure has long been recognized as an important source of macro- (nitrogen, phosphorus, potassium) and micronutrients (boron, zinc, sulfur) for plants. In addition, manure application to agricultural lands can improve soil health and promote nutrient cycling. However, frequent applications of manure often result in phosphorus (P) buildup in soils and pose a risk to the environment via runoff or leaching to water systems. NRCS Nutrient Management Code 590 mandates soil testing and site assessment (using Phosphorous-index) to determine the suitability of a cropland to receive manure/litter. If the average soil test P and P-index for the field falls under "very high" range, manure application is discouraged. Currently the Code 590 is undergoing national revision.  Although P index and soil test phosphorus (P) levels are used for environmental assessment of P loss risk, these tools do not provide any information or prediction of the life span of application sites i.e. how long P can be applied safely before the site becomes a source of P to the environment. In addition, many Alabama soils are naturally rich in iron (Fe) and aluminum (Al) oxides, which can potentially render P unavailable for plant uptake as well environmental losses. 

The Alabama Animal Waste and Nutrient Management team at Auburn University along with the Alabama NRCS and Soil and Water Conservation Committee are working together to find ways to improve guidelines on P management while minimizing the risk of P loss to the environment. The animal waste and nutrient management team at Auburn University will conduct extensive soil sampling across the State of Alabama to understand the P status of the soils and their potential to act as a source or sink of P to the environment. The soil samples will be used to evaluate the current P application criterion and develop new tools for environmental P loss risk assessment. Growers are encouraged to participate and allow sampling of their fields. The information generated from the research will be shared with growers and will greatly benefit them. No site specific information will be shared with any other individuals/institutions. Please get in touch with the Alabama Animal Waste and Nutrient Management team at Auburn University via email or phone 334-734-4937.

Here are some frequently asked question.

  1. What type of sampling site is needed? Any field (row crop, pastureland or hay fields) that has received chicken litter or any manure in past 10 years.

  2. Does the site need to have had broiler litter for 1, 2, 3 or 4 years?   Number of years or manure type does not matter. If you have applied chicken litter or any other animal manure in past 10 years, the site will qualify for sampling.

  3. What type of crop rotation? Crop rotation does not matter. We would like to take samples from fields with diverse management practices such as crop rotation, no till, conventional till, grazing, cover crops, row crops, pasturelands etc.

  4. Does it need to have cover crops in rotation? If a cover crop was used in rotation, we would love to collect samples from that site.

  5. How many years will you need to sample the site? We will need to take soil samples only one time. We will not collect samples if the manure or chicken litter was applied within 14 days of sampling date.

  6. Describe the soil sampling procedure. We will map your field based on NRCS soil survey and determine the soil types. We will take 1 sample per map unit at three depths 0-6, 6-12 and 12-18 inches.

  7. What information will the grower receive? The growers will receive free soil test results for phosphorus and will be informed of the phosphorus holding capacity of their soils.

  8. Will the data be shared publicly? The data will not be shared publicly and will be kept confidential between the grower and the university. The information generated from data will be used for scientific purposes only.


Rishi Prasad, Ph.D., Assistant Professor and Animal Systems Environmental Specialist

Kent Stanford, Nutrient Management Specialist; Auburn University, Department of Crop, Soil and Environmental Sciences and Animal Sciences



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