Balancing biosolid nutrients with fertilizers

Dick Johnson, Nutrient Management Specialist, USDA – NRCS

Fertilizers can play an important role in balancing crop nutrient needs, even with biosolid (compost/manure) applications. Determine the nutrient requirement for each field based on the crop, soil test, soil type, and fertilizer history. Use the lowest-cost fertilizer materials and consider the following.

Biosolids are excellent sources of nutrients and should provide most of the nutrients needed for crops, depending on the nutrient, biosolid application rates and nutrient requirements of crops. Where biosolid applications are limited, there is greater reliance on fertilizers to provide the rest or balance of the needed nutrients. Nitrogen (N) is the fertilizer most likely needed when biosolids are not used, or used only to replace phosphorus removed in harvested crops.

For manured systems, develop a nutrient management plan (NMP) that is phosphorus (P)-based. In a P-based system, biosolids are applied at rates that provide no more P than is removed in harvested crops. This may not satisfy the N required for the crop, but fertilizer can provide the additional N if needed. Phosphorus-based manuring avoids the excessive P enrichment of soil.

Applying manures to satisfy all the N required for production will lead to:

1. P enrichment, soil test P exceeding 40 ppm

2. greater risk of P entering surface waters

Where biosolids do not provide enough phosphorus to meet crop requirements, consider a starter band application of fertilizer P to increase P efficiency. For row crops, band 2 inches below and 2 inches to the side of the seed furrow for maximum effectiveness. Starter fertilizers can injure developing plants at rates exceeding those in Table 1. ANM

—Excerpts from University of Idaho Nutrient Digest, Vol. 1, No. 2