The present status of “quick tests” for on-farm analysis with emphasis on manures and soil: What is available and what is lacking?

Abstract

There is an increasing interest in on-farm testing of a variety of materials, from soils to materials produced or utilized on the farm, including manure. Among the issues to consider are selection of constituents of interest, e.g., fiber and protein in forages versus inorganic-and organic-N and P in manures; the nature of the testing, e.g., conventionally based assays using solutions or test strips versus portable instruments; the potential advantages or disadvantages of on-farm versus conventional laboratory testing, such as speed, timeliness, waste generation, and cost. The availability of on-farm testing methods varies greatly with both the media in question and the analyte of interest. For example, for manures several quick tests exist for the determination of total ammoniacal N (TAN) which can be quite accurate ( R 2 of .9 or better versus laboratory determinations), fast and reasonably inexpensive, while no such methods exist for the determination of organic-N in the same samples. No quick test has been found satisfactory for the determination of P or K in dairy or poultry manures, although excellent results have been obtained for swine manure. Similarly, soil test kits have existed for years for determining N, P and K, but no such test exists for determining soil C content (organic or inorganic), and no inexpensive method exists for forage quality determinations (fiber, protein, digestibility). Spectroscopic methods such as near-and mid-infrared spectroscopy have found increasing use in the laboratory for the rapid analysis of a wide variety of products including feeds, manures and soils and offer great potential for on-farm determinations. This paper discusses the present state, and future potential, of methods suitable for on-farm testing of the wide variety of materials from soils to those materials utilized or produced on a farm, with emphasis on manures and soils and spectroscopic methods.