Abstract
A field nutrient balance (supplied minus harvested) can be an effective, end-of-season management evaluation tool. However, development of guidance for balance-based management requires knowledge of variability in balance inputs. To contribute to development of such guidelines, we evaluated the impact of corn silage hybrid selection, nutrient management, and growing conditions on field nitrogen (N) balances and documented variability in N and phosphorus (P) balances at the whole-farm, field, within-field levels. Variability in N removal among hybrids was evaluated using hybrid trials (5 locations, 4 years each). Variability in farm and field balances (4 farms, 2 years each) and within-field balances (2 farms, 2 years each) was assessed as well. Nitrogen supply comprised soil N (soil type-specific book values), rotation N, past manure N, and current year N (fertilizer and/or manure). Total N balances included all current year manure N while available N balances considered only plant-available N from manure. Phosphorus balances were derived as total P applied minus P harvested. Yield explained 81% of the variability in N uptake across hybrids. Nitrogen uptake intensity (NUI; N uptake per unit of yield) varied across locations and years, averaging 4.3 ± 0.1 kg N/Mg for short-season hybrids [≤95 days-to-maturity (DTM)] vs. 4.1 ± 0.1 kg N Mg−1 for longer-season hybrids. Whole-farm N balances ranged from 139 to 251 kg N ha−1 for total N and 43 to 106 kg N ha−1 for available N. Phosphorus balances ranged from 28 to 154 kg P ha−1. Balances per field ranged from −8 to 453, −66 to 250 kg N ha−1, and −30 to 315 kg P ha−1 for total N, available N, and total P, respectively, while within-field balances showed even larger ranges. We conclude that (1) variability in corn silage N and P balances at field and within-field scales and across year is large, emphasizing the need for field and within-field (where feasible) evaluation tools and management options, and (2) feasible limits for N balances should include both total and available N.
Highlights
Nitrogen (N) and phosphorus (P) are essential nutrients for plant growth and crop production, but if applied in excess of crop needs both nutrients can result in negative environment consequences
To allow for experimentation with N management on farms and to better understand and improve upon N management over time, a multi-agency partnership in NY consisting of Cornell University faculty and staff and staff from National Resources Conservation Service (NRCS), New York State Department of Environmental Conservation (NYSDEC) and NYS Department of Agriculture and Markets (NYSAGM) introduced an adaptive management policy for regulated farms in 2013 (Ketterings et al, 2013a,b) with an expansion of evaluation options in 2018 (NMSP, 2018)
Before N balance guidelines can be developed to extend the adaptive management option to corn grown for silage on animal operations where manure is a common nutrient source, research is needed to (1) determine degree of variability in N uptake by corn as impacted by hybrid selection, (2) evaluate total N vs. available N from manure when deriving N balances, and (3) determine variability in both N and P balances from farm to farm, year to year, field to field, and at the within-field level
Summary
Nitrogen (N) and phosphorus (P) are essential nutrients for plant growth and crop production, but if applied in excess of crop needs both nutrients can result in negative environment consequences. To allow for experimentation with N management on farms and to better understand and improve upon N management over time, a multi-agency partnership in NY consisting of Cornell University faculty and staff and staff from National Resources Conservation Service (NRCS), New York State Department of Environmental Conservation (NYSDEC) and NYS Department of Agriculture and Markets (NYSAGM) introduced an adaptive management policy for regulated farms in 2013 (Ketterings et al, 2013a,b) with an expansion of evaluation options in 2018 (NMSP, 2018). The 2018 adaptive management policy for NY allows farmers to apply N (manure and/or fertilizer) above Cornell University NMSP guidelines, even without any past yield records If this field-specific option is used the farmer is responsible for measuring yield annually moving forward and for conducting an evaluation to determine if the higher N rate resulted in a benefit (NMSP, 2018). Before N balance guidelines can be developed to extend the adaptive management option to corn grown for silage on animal operations where manure is a common nutrient source, research is needed to (1) determine degree of variability in N uptake by corn as impacted by hybrid selection, (2) evaluate total N vs. available N from manure when deriving N balances, and (3) determine variability in both N and P balances from farm to farm, year to year, field to field, and at the within-field level
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