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

Authors: Leytem, April; Rogers, Christopher; Tarkalson, David; Dungan, Robert - Rob; Haney, Richard; MOORE, A - Oregon State University

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2020
Publication Date: 4/22/2020
Publication URL: https://handle.nal.usda.gov/10113/7019776
Citation: Leytem, A.B., Rogers, C.W., Tarkalson, D.D., Dungan, R.S., Haney, R.L., Moore, A.D. 2020. Comparison of nutrient management recommendations and soil health indicators in southern Idaho. Agrosystems, Geosciences & Environment. 3(1):e20033. https://doi.org/10.1002/agg2.20033.
DOI: https://doi.org/10.1002/agg2.20033

Interpretive Summary: Advanced soil tests are being developed to help improve the estimation of plant available nutrients in order to better match fertilizer additions with plant needs as well as provide a measure of soil health. In the present study, we compared the use of the SHT for making fertilizer recommendations vs. using the standard regional method as well as evaluated the SHT soil health score (SHS) relative to crop yields and quality. Use of the SHT to determine N fertilizer applications, without accounting for depth, would recommend greater N application than the current regional methodology. However, it does appear that by accounting for depth in the SHT can provide similar available N estimates. The P fertilizer recommendations were more similar, but slightly lower, with the SHT compared to 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 SHS was highly correlated with measures of soil C but was not positively correlated to crop yield. In some instances, increasing SHS resulted in decreases in crop quality as the addition of manure increased soil C but also created other potential problems 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, this test may be tailored to better estimate soil nutrient status and provide better fertilizer recommendations for the region.

Technical Abstract: Advanced soil tests are being developed to help improve the estimation of plant available nutrients in order to better match fertilizer additions with plant needs as well as provide a measure of soil health, in some instances. The Soil Health Tool (SHT) has been developed with both goals in mind, yet it has not been tested for use in semi-arid regions such as southern Idaho. In the present study, we compared the use of the SHT for making fertilizer recommendations vs. using the standard regional method as well as evaluated the SHT soil health score (SHS) relative to crop yields and quality. The SHT was designed to analyze samples for 0-15 cm depth and regional guidelines call for deeper soil sampling (0-30 cm or 0-60 cm). In order to determine N fertilizer applications, use of the tool without accounting for depth, would recommend greater N application (~138 kg/ha) than the current regional methodology. However, it does appear that by accounting for depth in the SHT can provide similar available N estimates for the top 30 cm of soil. While N mineralization was not well predicted utilizing the method included in the SHT or from the regional methodology, the average estimated available N for these soils (47 kg/ha) was similar to the N mineralization value used in the current regional methodology (50 kg/ha). The P fertilizer recommendations were more similar between the two methodologies with the SHT recommending, on average 4.7 kg/ha 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 SHS was highly correlated with measures of soil C but was not positively correlated to crop yield. In some instances, increasing SHS resulted in decreases in crop quality as the addition of manure increased soil C but also created other potential problems 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, this test may be tailored to better estimate soil nutrient status and provide better fertilizer recommendations for the region.