Whole Farm Performance of Centrifuge Extraction of Phosphorus from Dairy Manure

Abstract

HighlightsA centrifuge can be used to extract manure phosphorus to a more concentrated form for easier transport.Extraction for more efficient transport to distant cropland reduced production costs in a scraped manure system.Use of a centrifuge in a flush manure system was less practical and economical due to handling of much more material.The cost of producing highly concentrated phosphorus material for export was greater than phosphate fertilizer prices.Abstract. As the size of dairy farms has increased, feeds produced on the farm as well as those purchased from off-farm sources can be transported long distances to feed the herd. Transporting the manure back to the cropland used to produce the feed can be difficult and uneconomical. Technology such as a centrifuge can be used to extract nutrients into a more concentrated form for more efficient transport. A dairy farm with 2000 cows and 1400 ha of land in Pennsylvania was simulated with the Integrated Farm System Model to evaluate the feasibility of extracting phosphorus (P) to reduce transport requirements on farm or to produce a concentrated P product for off-farm use. On this farm where manure must be transported to distant cropland to obtain uniform distribution, P extraction with a centrifuge provided a better ratio of nitrogen and P contents for use on nearby cropland and reduced transport costs for nutrients applied to more distant cropland. The centrifuge was found to be more practical and economical when used with manure scraped from the barn floor than with flushed manure because much less material was handled. Moving less material through the centrifuge both improved extraction efficiency and reduced electricity consumption, providing more economical P extraction. To avoid long-term accumulation of soil P on the farm with less land (2000 cows and 1100 ha) where concentrate feed (27% of total feed) was imported, centrifuge extraction provided a material with a high P concentration exported from the farm for other uses. Extracting the P for off-farm use cost about $2.51/kg P, which was greater than the price of phosphate fertilizer, but the extract also included other nutrients and micronutrients of value to crops. A centrifuge provides a useful tool for extracting and concentrating manure P, but the economic benefit to the producer depends upon the value of the full array of nutrient contents in the product, other manure handling practices, and the end use of the extracted material. Reducing the risk of eutrophication of surface waters provides additional benefit to society. Keywords: Dairy farm, Integrated Farm System Model, Manure handling, Manure management.