Agustin J. Olivo1, Laura Klaiber2, Kirsten Workman1,3, Quirine M. Ketterings1
1 Department of Animal Science, Cornell University, Ithaca, NY, United States; 3William H Miner Agricultural Research Institute, Chazy, NY, United States; 3PRO-DAIRY, Department of Animal Science, Cornell University, Ithaca, NY, United States
Introduction
Optimizing phosphorus (P) application in corn silage production systems to align with crop P requirements while sustaining soil test P (STP) levels can help mitigate environmental risks and enhance farm profitability. Nutrient balances (supply minus uptake) can be an effective strategy to monitor P management in fields (Fig. 1). Sustained negative P balances (uptake > supply) can lead to a reduction in STP and negative impacts on crop productivity over time. Conversely, regular nutrient applications beyond crop removal can lead to increases in STP, which may be desirable in the short term to raise low STP, but undesirable if continued once soils reach optimum levels.
Data on P balances from 994 corn silage field observations across eight New York dairies were analyzed to characterize this metric and identify drivers that may point towards opportunities for improved management. Data on manure management practices that affect field P dynamics and nitrogen (N) availability for the crop were also evaluated, as well as the relationship between P balances and STP for four of the farms.
Key findings
Phosphorus balances were low, but with a wide range across farms and fields
On average, P balances across all fields were low (median of 7 lbs/acre), partially reflecting reductions in P surpluses on NY dairy farms over the last two decades as farm nutrient management has improved. However, there was a wide range across farm averages (-10 to 27 lbs/acre) and individual fields (-48 to 122 lbs/acre) (Fig. 2).
Manure P supply was the main driver of balances
Phosphorus supply was a more relevant driver of balances than P removed with harvest. Manure was the main source of P for all farms (Fig. 3), and farm to farm differences explained the largest portion of the variability in P supply. Higher P supply across farms was associated with higher manure application rates (driven partially by farm animal density) and higher manure P content connected to higher P rations.
Phosphorus was applied at higher rates to fields with adequate STP than to lower STP fields
Morgan-extracted STP levels varied across farms and fields, with averages of 9, 13, 22 and 22 lbs P/acre for Farms 1, 3, 4 and 5, respectively (the only ones analyzed in the study for Morgan-extracted STP). These values corresponded to sub-optimal (<9 lbs P/acre), optimal (9-19 lbs P/acre), and high (20-39 lbs P/acre) agronomic P levels, according to land-grant university guidelines. Across the entire database, P was applied at higher rates to fields with adequate STP levels, indicating potential opportunities to re-allocate P within farms (Fig. 4).
P-based manure applications could cover a large fraction of crop N requirements
Under management practices currently implemented by the farms assessed in the study, application of manure at N-based rates to corn would lead to large P balances for all farms, if utilized, due to a mismatch between manure available N to P ratio and corn N to P ratio needs. Similarly, P-based applications would cover only 51% of corn N requirements, on average. Increasing the rate of spring manure injection/incorporation or in-season injection on these farms could cover an average of 66 to 85% of corn N requirements, respectively, illustrating the greater N value of manure when more is incorporated/injected.
Conclusions
Results across the dataset showed low P balances on average, reflecting continued efforts from farms to efficiently manage manure nutrients and limit use of fertilizer P. Farms with large P balances may improve their performance by optimizing diet formulation to lower P excretion, reducing animal density, and/or exporting manure to move excess P off-farm. The data also showed potential opportunities to better allocate P within farms, re-allocating P from high or very high testing fields to P deficient fields. Combining appropriate rates of manure and N fertilizer or implementing manure treatment technologies that conserve N during storage and/or remove P, could help reduce P overapplication with N-based manure use. Similarly, spring or in-season manure incorporation or injection at P-based rates could recover a larger fraction of manure N, enough to cover almost all corn N requirements in some cases.
Full citation
This article is summarized from our peer-reviewed publication: Olivo A.J., L. Klaiber, K. Workman, and Q.M. Ketterings (2024). Characterization of phosphorus balances in corn silage fields from eight New York dairies. Agronomy Journal. https://doi.org/10.1002/agj2.21710.
Acknowledgements
We thank farmers and their certified crop advisors who shared farm data. This research was funded by a USDA-NIFA grant, funding from the Northern New York Agricultural Development Program (NNYADP), and contributions from the New York Corn Growers Association (NYCGA) managed by the New York Farm Viability Institute (NYFVI), and the Department of Animal Science, Cornell University. For questions about these results, contact Quirine M. Ketterings at qmk2@cornell.edu, and/or visit the Cornell Nutrient Management Spear Program website at: http://nmsp.cals.cornell.edu/.
