Poultry Manure as a Garden Amendment

Poultry manure and litter (bedding and manure) from either your home flock or from a commercial flock is a great source of garden organic matter and nutrients. The organic nature of manure and litter have a number of advantages over inorganic or synthetic fertilizers such as improving soil structure by increasing the water holding capacity, providing pore spaces, and aeration for good plant growth. The organic matter in poultry manure lightens a heavy clay soil and prevents the clay particles from binding together.  They can also increase the cation exchange capacity, or a soil's ability to hold nutrients. The nutrients in organic fertilizers are more slowly released to the plants over a longer period of time and are less likely to leach away from the garden and into surface or ground waters causing pollution. Fortunately, poultry manure is a complete fertilizer because it contains the major nutrients of nitrogen, phosphorus, and potassium and the minor elements all crops require.

We surveyed poultry farms in 2016 for their current litter and manure nutrient concentrations as part of a greater project to document the potential nutrients for commercial application and obligations for proper management to protect water quality. Cage-free laying hens produce manure with 59, 62, and 31 lb/ton of total-N (nitrogen) – P₂O₅ (phosphate) – K₂O (potash) on an as-is basis (33% moisture). Broiler litter which comes from manure and bedding, most often wood shavings, contains 60, 49, and 53 lb/ton of nitrogen, phosphate, potash and about 27% moisture. Poultry manure and litter when applied to the soil undergoes "mineralization" which is the conversion of a nutrient from the organic (bound to carbon and hydrogen) form to the inorganic form. Nutrient mineralization in the garden takes some time and depends on soil temperature, moisture, and microbial activity.  While nitrogen mineralization and availability to the plants for poultry manure is only 55%, it is considerably lower for composted manure (~18%).  Phosphorus and potassium availability in poultry manure is equivalent to fertilizer and should be credited at 100%.  Given an adjustment for N availability, the fertilizer value of raw layer manure on a percentage weight basis would be approximately 1.6-3.1-1.5 (N-P-K ratio) and raw broiler litter approximately 1.6-2.4-2.6. 

A good fertilizer application rate to meet the nutrient requirements of mixed vegetables per 100 square feet of garden space is 0.23 lbs of available N, 0.11 lbs of P₂O₅, and 0.5 lbs of K₂O.  Using either raw layer or broiler manure to meet the N target would require 14 lbs of manure per 100 square feet.  If using composted manure, use 44 lbs of compost per 100 square feet.  Using a bucket or trash can to weigh the manure on a bathroom scale is a good way to calibrate the application rate to avoid excess nitrogen applied.  It should also be noted that these application rates will significantly over-apply phosphorus to the soil, which does not cause any harm to plants, but can be an environmental pollutant if runoff water or soil erosion from the garden area enters a local stream or pond.

Recommendation

In the fall of the year clean out your poultry coop and apply these nutrients in the garden after the harvest season to allow for proper mineralization and to be ready for spring planting. This is a good food safety practice to allow the good bacteria to take over the bad bacteria that can be in manures.  If you have been composting your poultry manure and litter along with table scraps and other organic matter from the garden, this mixture can be applied to the top of the garden in the spring then spaded into the soil prior to sowing seeds or planting.