On-farm quick tests for estimating nitrogen in dairy manure

Manure nutrient analyses performed rapidly on the farm could be useful for nutrient management programs, The objective of this experiment was to evalu ate six quick tests for their accuracy in estimating total manure N or NH4-N. The quick tests included the hydrometer, electrical conductivity meter and pen, reflectometer, Agros N Meter, and Quantofix-N-Volumeter. The hydro meter was used to estimate total N, while the remaining tests were used to estimate NH4+-N. Samples (107) were collected from dairy farms in five nort heastern states. Samples were analyzed for total N and NH4+N by traditional laboratory methods and using each of the quick tests. Manure compositions ranged from 1.4 to 38.6% dry matter (DM), 0.9 to 9.5 kg/m(3) total N, and 0 .3 to 4.7 kg/m3 NH4+-N. The estimated concentration of total N or NH4+-N de termined by each quick test was regressed against laboratory-determined val ues. The hydrometer did not estimate total N accurately. The strongest rela tionship for estimation of NH4+-N was with the Quantofix-N-Volumeter follow ed by the Agros N Meter, the reflectometer, and the electrical conductivity meter and pen. When the samples were split into high (>12%) and low (less than or equal to 12%) DM groups, in all cases the r(2) for the regression e quation was higher for the low DM group than for the high DM group. The Agr os N Meter, the reflectometer, and the conductivity meter and pen did not p erform well for the high DM group. These data indicate that several quick t ests are viable options for measuring NH4+-N concentrations in dairy slurri es and solids.