Determining Nutrient Recommendations for Agricultural Crops Based on Soil and Plant Tissue Analyses Between Different Analytical Laboratories

There is limited information concerning the disparities between soil and plant tissue testing laboratories. Soil and plant tissue analyses are crucial to determining nutrient applications for agricultural field crops. Accurate fertility inputs improve crop production and long-term agricultural sustainability. The over application of nutrients can potentially decrease yields and reduce profits. A study was established in 2016 at Louisiana State University at Alexandria (LSUA) in Alexandria, Louisiana to 1) assess and compare soil and plant tissue nutrient values, ratings and recommendations between research and commercial laboratories for field corn (Zea mays) and soybean (Glycine max), and 2) compare crop response and yields between the different recommendations provided by each laboratory. A survey was also conducted to identify soil and plant tissue testing procedures and methods followed by local growers. The majority of growers perform soil tests and do so regularly, while plant tissue analyses are conducted less often than soil. For fertility questions and recommendations, the option ‘other’ was most selected by responders, while the second option was equal between LSU AgCenter extension agents and agriculture consultants. The experiment was prepared in a randomized complete block design on a Coushatta silt loam soil. Soil and plant tissue samples were collected and analyzed for elemental levels using the Mehlich-3 extraction method (extractable Ca, Cu, K, Mg, Na, P, S and Zn). The soil was a Plant tissue agricultural metals, (Al, B, Ca, Cu, Fe, K, P, Mg, Mn, Mo, Na, S and Zn) were extracted using hydrochloric and nitric acid plant tissue digestion. Overall procedures and methods remained congruent among research and commercial laboratories. Following the elemental analyses of soil and plant tissue, nutrients were applied as recommended by each laboratory throughout the growing season. Ratings and recommendations were based on fertility method. The sufficiency approach to fertilization applied enough nutrients for the growing season; the build-up and maintenance method built the elemental concentration of soil until it reached the soil critical level and then maintained the amount of nutrients in the soil, so it was never limiting. For both field corn and soybean, commercial laboratories recommended higher nutrient applications for soil and plant tissue for each year of study, although elemental results remained similar in value between laboratories. Overall yield results exhibited minor variation between research and commercial laboratories. The results of the survey indicated soil and plant tissue testing are performed regularly by local growers, however, the distribution of sample analyses and information obtained varied. Agriculture sustainability and conservation was also rated high by participants