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Economics of capture of phosphorus from liquid dairy manure.

J. Harrison

Events

06-22-2020

Abstract:

104
Economics of capture of phosphorus from liquid dairy manure.
J. Harrison*1, K. Fullerton1, E. Whitefield1, K. Bowers2, S. Norberg3. 1Washington State University Puyallup, WA, 2Multiform Harvest Seattle, WA, 3Washington State University Pasco, WA.

A project was conducted with the goal of developing a nutrient recycling relationship between the dairy producers and alfalfa forage growers in Washington State. A mobile fluidized-bed cone (32,000 L) was used to evaluate the capture of P in the form of struvite (magnesium-ammonium phosphate) from undigested and anaerobically digested liquid dairy manure. Manure from ~30 dairies was evaluated and In 27 runs when reduction in ortho-P was positive, the average reduction in ortho- P was 32% with a range of 1 to 76%. The greatest capture rates were achieved with anaerobically digested manure since more of the P is in an inorganic form and captured in struvite. The factors that affected performance were: % suspended solids, Calcium, Fe, ratio of ortho-phosphate-P:total P, and ammonia concentration. When using data from the highest recoveries of P, the cost as calculated on a per cow per d basis when considering chemical costs were: $0.22 (anaerobically digested manure) to $0.39 (undigested manure). The use of a cost per cow per d metric for cost is not the most appropriate way to evaluate the cost to a given farm since the goal is to achieve a net zero balance of P imports and exports from any given farm. The net zero balance will be affected by factors such as: number of cows, number of acres utilized for manure application, phosphorus utilization by crops grown, double or triple cropping strategies, diet manipulation, and manure export off-farm. The factor having the greatest impact on achieving P balance is the land base for growing crops that utilize manure. When using the scenario of 1000 cows, 67 g per d per cow excreted P, and 27 kg P uptake by crops per year, the annual cost to achieve balance for respective hectares were: anaerobically digested manure 242 ha, $275,074; 283 ha, $182,693; 324 ha, $90,312; 344 ha, $44,122, and 362 ha, $2550. The annual cost to achieve balance for respective acres were: undigested manure 242 ha, $523,208; 283 ha, $347,494; 324 ha, $171,779; 344 ha, $83,922, and 362 ha, $4,851.

Keywords: manure, phosphorus, nutrient balance.