Land application of organic materials for soil management in Nebraska is important for several reasons:

• Nebraska has about 1100 beef feedlots finishing a total of 5 million head per year.
• Beef manure N applied annually is equal to 150 lb/ac N applied to about 1.2 million acres (Figure 1).
• Other land-applied livestock manure, municipal wastes, and other organic materials contribute additional N for crop production.
• The availability of applied organic N and the fertilizer N substitution values of applied organic materials is not well predicted, although guidelines exist (Table 1).
• The uncertainty of applied organic N availability leads to over-application of fertilizer N, resulting in low N use efficiency of applied N.
• Organic N release varies with properties of the organic material, including the C:N ratio and cellulose and lignin content, with weather and soil conditions, and with management.

Research is underway to improve the prediction of the fertilizer N substitution values for organic materials.

• Eight organic materials of diverse properties are being evaluated at eight locations for three years under both irrigated and rainfed conditions. Treatments were applied in 2016.
  • One material, Novozyme, is a by-product resulting from an enzyme production process. The bacteria are killed by adding CaO. The by-product is composed of CaCO₃ and denatured microbial biomass with a low organic C to organic N ratio (C:N) and low lignin and cellulose content (low acid detergent fiber (ADF); Table 2).
  • The feedlot manures have the highest C:N but low ADF.
  • The municipal biosolid products have relatively high lignin and cellulose content (ADF).
  • Organic N applied varied with expected mineralization rate from 215 to 680 lb/acre; the sensor readings indicated that the amount available to the crop was similar for all organic materials.
• Each location has an N ramp, i.e. a series of N levels with no organic material applied for determination of N response functions.
• No fertilizer N was applied pre-plant for the organic material treatments, but N was applied in-season at V14 in 2016 and at V12 in 2017 according to NDRE canopy sensor guidance.
• The apparent recovery of organic material N (AONR) and fertilizer N replacement (FNR) for each organic material were calculated by relating the yield for each organic material receiving in-season N application to the N ramp for determining the fertilizer equivalent rate of N.

Research Findings

The apparent recovery of organic N (AONR) and fertilizer N replacement (FNR) (Table 2) from the applied organic materials in eastern Nebraska were:

• similar for rainfed and irrigated;
• 77% greater for a loamy sand compared with silt loam and silty clay loam soils;
• not affected by C:N ratio for these materials, but likely to be less if C:N is much higher;
• 2.34 and 2.29 times more, respectively, for livestock manures compared with municipal biosolid products; and
• not reduced by composting compared to not composting.

Compared with previous estimates of FNR (Tables 1, 2):

• FNR was 28% higher for cattle manure.
• FNR was 67% higher for compost.

Research is continuing and it is too early to draw conclusions. Results from 2017, the second crop after application, will also be reported at the Crop Production Clinics.