Fertilizer N Substitution Values of Land-Applied Organic Materials
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.
|Table 1. Current recommendation of estimated first-season availability (%) of manure organic-N.|
|% organic-N available in first year1|
|Source||Solid||Fresh liquid||Stored liquid|
1 Assumes spring-seeded crops; for fall-seeded crops, multiply values by 70% to account for delayed mineralization during cooler months.
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.
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.
|Stockpiled feedlot manure||10.3||226||0.27||0.32|
|Dairy manure compost||8.7||285||0.3||0.34|
|Lincoln municipal biosolid||7.1||387||0.13||0.15|
|Fremont biosolid composted||9.7||440||0.13||0.15|
|Fremont biosolid dewatered||8.3||378||0.1||0.11|
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.