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Comparison of nutrient management recommendations and soil health indicators in southern Idaho

April B. Leytem, Christopher W. Rogers, David Tarkalson, Robert S. Dungan, Richard L. Haney, Amber D. Moore
Agrosystems, geosciences & environment 2020 v.3 no.1 pp. e20033
calcium carbonate, crop quality, crop yield, fertilizer rates, fertilizer requirements, irrigation, manure spreading, mineralization, nitrogen fertilizers, nutrient availability, nutrient management, phosphorus fertilizers, salt content, semiarid soils, semiarid zones, soil carbon, soil depth, soil nutrient dynamics, soil nutrients, soil quality, soil salinity, topsoil, Idaho
Advanced soil tests can improve the estimation of plant available nutrients to better match fertilizer additions with plant needs and, in some cases, provide a measure of soil health. In the present study, 334 samples from four separate studies were evaluated using the Soil Health Tool (SHT) vs. the standard regional (University of Idaho [UI] Guidelines) method for determining fertilizer application, assuming a crop of spring irrigated wheat. Recommended N applications using the SHT were ∼138 kg ha⁻¹ greater than the UI recommendations. Nitrogen mineralization predicted using the SHT (47 kg ha⁻¹) was similar to the N mineralization value used in the regional methodology (50 kg ha⁻¹). The P fertilizer recommendations were similar between the two methodologies with the SHT recommending, on average 4.7 kg ha⁻¹ less P than the regional method. The lower P recommendation are likely due to a lack of accounting for the effects of high calcium carbonate levels on the P availability from fertilizers in this region. The soil health score (SHS) was correlated with measures of soil C but was not positively correlated to crop yield. In some instances, increasing SHS were correlated with decreases in crop quality as the addition of manure increased soil C but also created issues such as high salt contents and release of late season N. With modification to more accurately represent irrigation conditions and including sampling to greater soil depths, the SHT may be tailored to better estimate soil nutrient status and provide better fertilizer recommendations for the region.