Rapid On-Farm Analysis of Manure Nutrients Using Quick Tests

Quick tests enabling rapid, on-farm assessment of manure nutrient content could appreciably enhance manure management. The objectives of this study were to review the literature on the accuracy of quick tests, describe their operation, and to assess their ease of use and their suitability for routine on-farm use. These quick tests are the hydrometer, electrical conductivity (EC), ammonia electrode, reflectometer, Agros N Meter (or Nova meter), and Quantofix-N-Volumeter. The ammonia electrode provided accurate direct measurement of slurry ammonium; 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 (total solids) content and specific gravity. Results have been variable between regions and species. Electrical conductivity is used as an indirect measurement of ammonium and K; the limited results to date have been consistently good for ammonium N, and variable for K. The Agros N Meter and Quantofix-N-Volumeter both directly measure ammonium N and possibly some organic N. For both, agreement with lab analyses of ammonium N has been generally very good. The reflectometer measures the color intensity of test strips; limited results with ammonium N in slurries are promising. Several quick tests have the potential for accurately measuring manure nutrients on the farm. They generally were more effective with slurries than solid manures. For each quick test, single farm or regional calibrations with lab analysis are recommended, and in some cases necessary. Problem and Literature SummaryManures are often viewed as a waste disposal problem; however, manure nutrients can be effectively used to partially satisfy crop nutrient requirements, thereby reducing the purchase of mineral fertilizers. Manure management practices that do not fully consider manure nutrients in relation to crop requirements and soil and site characteristics may be economically inefficient and can result in nutrient losses to the environment. Using book values to estimate manure nutrient content can result in appreciable errors in manure application rates because of the potentially large variability in manure nutrient contents. If sampling is representative, analysis of samples in a commercial lab provides accurate results, but commonly involves waiting 1 to 2 wk for the results. Nutrient analyses performed rapidly on the farm using relatively cheap and robust equipment could be very useful. Several quick tests are commercially available for on-farm manure nutrient analysis. These tests measure either one or more of the following: ammonium N, total N, total P, and total K. Analysis usually takes less than 10 min, and the equipment is typically relatively simple to use. Lab analysis is accurate but time consuming, so the use of on-farm equipment to rapidly measure manure nutrients could be advantageous. The objectives of this paper are, for the current quick tests for analyzing manure nutrients, to: (i) review the literature on their accuracy in comparison with lab analysis, (ii) describe their operation, (iii) assess their ease of use, and (iv) assess their applicability for use on modern livestock farms. Study DescriptionThe seven quick tests considered in this study were the hydrometer, electrical conductivity meter and pen, ammonia electrode, reflectometer, Agros N Meter (or Nova meter), and Quantofix-N-Volumeter. A review of the literature was conducted and data were gathered on the accuracy and usefulness of quick tests. The quick tests were also evaluated in the lab for ease of operation when analyzing dairy slurries. Applied QuestionsCan quick tests be used to accurately measure manure nutrients? In general, the quick tests were more effective with slurries than with solid manures. 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. The ammonia electrode, Agros N Meter, and Quantofix-N-Volumeter, all show good agreement with lab results for measuring ammonium. Limited results are also promising for measuring ammonium with the reflectometer, conductivity meter, and conductivity pen. Are quick tests appropriate for use in a farm environment? For quick tests to be used routinely by producers, extension staff, or consultants, they must be simple to operate and easy to use. Although the conductivity meter and pen were the easiest quick tests to use, operation of the hydrometer, Agros N Meter, and the Quantofix-N-Volumeter was also relatively straightforward, and any of these tests would be very suitable for on-farm use. The reflectometer requires accurate timing and some dexterity, but is also reasonably easy to use. The ammonia electrode is comparatively expensive, quite fragile, and requires considerable effort to set-up and standardize prior to use. Therefore, the ammonia electrode is considered not suitable for routine on-farm use. What are the costs associated with purchase and use of the quick tests? The quick tests range in price from as low as $40 for a hydrometer to as much as $2000 for an ammonia electrode and meter. Purchase prices for the reflectometer, Agros N Meter, and Quantofix-N-Volumeter were $420, $330, and $330, respectively. The prices for conductivity meters vary from $400 to $1000, and a conductivity pen can be purchased for less than $150. Once the hydrometer and the conductivity meter and pen are purchased, there are little or no further costs associated with analyzing samples. The ammonia electrode, reflectometer, Agros N Meter, and Quantofix-N-Volumeter require consumables and therefore have additional costs (<$1.12) associated with each analysis. RecommendationQuick tests can be a useful addition to a manure management program. When used in conjunction with lab testing, quick tests can provide a practical means for monitoring the nutrient content of slurries as they are being applied to the fields, or for characterizing well-mixed slurries in storage facilities. They are less accurate than standard lab analyses and should not replace lab testing. Calibrations specific to individual farms or to regions in which common practices are used should be developed.