Improved Use Efficiency of Applied Organic Nitrogen January 8, 2018
Land application of organic materials for soil management in Nebraska is important.
- Organic N applied annually to Nebraska cropland is equal to 150 lb/ac N applied to about 1.3 to 1.6 million acres.
- Beef feedlot manure is important but other livestock manure, but organic municipal and industrial wastes in total are also important. We refer to all as manure in the following.
- The availability of applied organic N and the fertilizer N substitution values of applied organic materials is not well predicted (Table 1).
- The uncertainty of applied organic N availability leads to over-application of fertilizer N resulting in low efficiency of applied N.
- Canopy sensor-guided in-season N application practices have been validated for corn produced on unmanured fields and may be a way to greatly improve N use efficiency for applied organic N.
- Application of 30 to 60 lb/acre of fertilizer N pre-plant followed by in-season fertilizer N application according to crop need may greatly improve applied N recovery and use efficiency.
- The canopy sensor practices may need calibration for manured fields, possibly with variations due to manure type and years since manure was applied.
- Validate or adapt canopy sensor-guided in-season N application practices for fields with manure or other organic material applied.
- Improve the prediction of the fertilizer N substitution values for organic materials
- Two sets of trials
- Set 1 trials were at Brule (2014-2016) and the Eastern Nebraska Research and Extension Center (ENREC) (2015-2017) with 0, intermediate and high levels of composted or stockpiled feedlot manure applied. Each manure level had a set of N ramp treatments with 27 lb/acre N rate increments to 107 lb/ac, and a high N reference strip of 178 lb/ac, applied before planting.
- Set 2 trials were at six locations in eastern Nebraska with eight organic materials during 2016 and 2017 (Table 2). No pre-plant fertilizer N was applied to the organic material treatments.
- The crop was continuous corn with no tillage
- Crop canopy reflectance was sensed for NDRE (Normalized Difference Red Edge Index) at V12 to v14 and plots were split for with and without sensor-guided in-season N application.
- The algorithm for interpretation of sensor readings was:
in-season N rate = 317√
- Grain yield and other variables were measured.
Results I. Crop canopy sensor-guided in-season N application for manured fields.
- The in-season N rate at ENREC was 43% and 17% less with manure applied compared with no manure for the year of application and for the mean of the second and third year after application, respectively. The in-season N rate was 23% less with manure applied at Brule.
- The sufficiency index algorithm over-estimated N need when the pre-plant N rate was 0 or 27 lb/acre (30 kg/ha) (Figure 1).
- Yield potential was lost if the crop was too stressed by low pre-plant N application.
- Pre-plant N of 55 lb/acre prevented excessive low N stress while allowing for NDRE differences expressive of crop N need and determination of in-season N application rates.
- The best time for canopy reflectance sensing was determined to be between V12 and V14.
- The above SI algorithm worked well (Figure 1). Data analysis has not yet finalized improvements to the algorithm either for manured or unmanured fields.
- In a preliminary comparison of the above algorithm with another used in Nebraska, the latter tended to under-apply in-season N. This needs further data analysis.
|% 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.
|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|
Results II. Improve the prediction of the fertilizer N substitution values for organic materials.
- 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 there was a big effect of cellulose and lignin contents so that N substitution was 2.3 times more for livestock manure compared with municipal biosolid
- Not reduced by composting compared to uncomposted.
Compared with previous estimates of FNS (Tables 1, 2)
- FNS was 28% higher for cattle manure.
- FNS was 67% higher for compost.