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United States Department of Agriculture

Agricultural Research Service

Title: Rapid on-Farm Analysis of Manure Nutrients Using Quick Tests

Authors
item Van Kessel, Jo Ann
item Thompson, R. - CSIC
item Reeves Iii, James

Submitted to: Journal of Production Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 3, 1999
Publication Date: N/A

Interpretive Summary: The nutrient content of manures applied to cropland is required when determining mineral fertilizer rates in order to minimize nutrient release to the environment and maximize crop production. Manure nutrient content is variable, and analysis of samples in a laboratory is time consuming. Quick Tests that enable a rapid, on-farm assessment of nutrient content could be valuable. For six available Quick Tests, this paper discusses the nutrients measured, describes the mode of operation, reviews assessments of accuracy, assesses ease of use and suitability to routine on-farm use, and evaluates the cost and availability. The Quick Tests considered are the hydrometer, electrical conductivity, ammonia electrode, Reflectometer, Agros N Meter, and Quantofix-N-Volumeter. The tests primarily measure ammonia, the rapidly available N. The hydrometer measures total N and P based on the specific gravity of the sample. Although accurate, the ammonia electrode is fragile and difficult to set up, and results with the hydrometer have been variable. Limited results with electrical conductivity have been promising for N. The Agros N Meter and Quantofix-N-Volumeter both measure N content based on the production of N2 gas when the manure is mixed with bleach. Agreement with laboratory analyses of N has been generally very good for wet manures. The reflectometer measures N based on a color-producing reaction; limited results with N in slurries are promising. Several Quick Tests have the potential for accurately measuring manure nutrients. They generally were more effective with slurries than solid manures. For each Quick Test, single farm or regional calibrations with laboratory analysis are required.

Technical Abstract: Quick Tests that enable a rapid, on-farm assessment of manure nutrient content could appreciably enhance manure management strategies. For six available Quick Tests, this paper: lists nutrients measured, describes the mode of operation, reviews assessments of accuracy, assesses ease of use and suitability to routine on-farm use, and informs of the cost and availability. The Quick Tests considered are the hydrometer, electrical conductivity, ammonia electrode, Reflectometer, Agros N Meter (or Nova meter), and Quantofix-N-Volumeter. The ammonia electrode provided accurate measurement of slurry NH4+-N; however, its fragility and the difficulty of setting it up, suggested limited suitability for on-farm use. The hydrometer indirectly measures total N and total P based on relationships with dry matter content and specific gravity. Results have been variable between regions and species. Electrical conductivity is used as an indirect measurement of NH4+-N and K; measurements are made with either a conventional probe or meter or with a small hand-held "conductivity pen". The limited results to date, with slurries, have been consistently good for NH4+-N, and variable for K. The Agros N Meter and Quantofix-N-Volumeter both directly measure NH4+-N and possibly some organic N. For both, when used with slurries, agreement with laboratory analyses of NH4+-N has been generally very good. The reflectometer measures the color intensity of test strips; limited results with NH4+-N in slurries are promising. Quick Tests were generally more effective with slurries than solid manures. For each Quick Test, single farm or regional calibrations with laboratory analysis are required.

Last Modified: 10/20/2014
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