Saturday, 15 July 2006

Statewide, County-Based and Whole Farm Phosphorus Balances.

Quirine M. Ketterings, Caroline Rasmussen, Johan C. Mekken, and Karl J. Czymmek. Cornell Univ, 817 Bradfield Hall, Dept of Crop and Soil Sciences, Ithaca, NY 14853

            To date, nutrient management regulations in NY and most other states in the US are addressing the Clean Water Act by regulating Concentrated Animal Feeding Operations through implementation of the NRCS 590 standard for nutrient management. The NRCS 590 standard focuses on reducing risk to water quality by managing applications of fertilizer and manure; this is accomplished through development of plans that include the use of the P runoff index, the nitrate leaching index, and land grant university crop nutrient guidelines. However, a steadily increasing number of acres testing high or very high in P in NY and other states indicates that nutrient management practices need to do a better job of addressing importation and subsequent loading of nutrients onto farms and watersheds.

When the amount of P entering a field (or farm, or county, or state) exceeds the P removed with harvest this imbalance could lead to: (1) direct nutrient lost to the environment; and/or (2) increase in reserves in the soil, increasing the risk for future environmental losses. A phosphorus balance can be derived for an individual field, a farm, a county, a watershed, a region, a state or even an entire country. An analysis of the nutrient flows onto and off of the farm is essential to quantify current nutrient imbalances and identify farm practices which could be more efficient, thereby, increasing farm profitability and decreasing nutrient losses to the environment. As such, an imbalance may be an indicator of challenges and opportunities, current and future. The state- and county-wide balances have the potential to improve water quality protection by supporting activities that address the lack of balance between available nutrient supplies and potential nutrient uptake by crops. Such analyses are also the basis for measuring progress as farms make changes in management of soil, crop, fertilizer, feeds, and manure for watershed protection and long-term sustainability of our dairy industry.

To gain a better understanding of current balances, two studies were initiated: (1) state-wide and county-based assessment of P balances; and (2) individual farm mass nutrient balances for New York dairy and livestock farms. State-wide and county balances were derived as the difference between total amount of P in manure and fertilizer minus the amount of P in crop removal using the 2002 Census of Agriculture and NYS Agricultural Statistics Service data and following the same procedures used by the Mid-Atlantic Regional Water Program ( The whole farm mass balance assessments included quantification of imports through feed, fertilizer, nitrogen fixation from legumes, animals purchased and bedding and exports in the form of milk, animals and crops sold, and manure transported off the farm using a mass nutrient balance software tool (downloadable from To date, 38 farms participated in this study. The data were collated from available farm records which included farm financial records, crop recordkeeping and animal nutrition records. Acres of legumes, percent legume in the stand, yield and crude protein content were used to estimate N fixation.

            The total P balance for New York State amounted to +12.7 million kg of P (+19 kg of P2O5 per harvested ha of cropland) in 2002. Preliminary evaluation of farm mass nutrient balances showed that on average phosphorus imports (feed, fertilizer, animals and bedding) annually exceeded sales/exports(milk, meat, animals, crops, manure) by 50% resulting in an average excess of 29 kg of P2O5 per ha cropland. This raises questions related to causes of such imbalances and opportunities to address them. Our current work is focusing on gaining a better understanding of these pools and flows (and farm economics) to find ways to reduce balances and increase farm profitability.

Typically more nutrients come onto dairy and livestock farms as purchased feed and fertilizer than leave the farm as animal products and crops. Losses could be significantly reduced if fewer nutrients were imported onto the farm in the first place. The key solution lies in finding ways to increase nutrient use efficiency on farms and, thereby, decrease nutrient imports and reduce loadings to watersheds. Knowing a farm's mass nutrient balance is one step towards improving our understanding of nutrient movement onto, within, and away from the farm. A greater number of farms need to be included with multiple years per farm so we can quantify the impact of best management practices on overall balances.



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