Postseason Diagnosis of Potassium Deficiency in Soybean Using Seed Potassium Concentration

Abstract

Core Ideas Seed‐K concentrations accounted for 60% of the variation in relative yield of unfertilized soybean for 100 site‐years in North America. The proposed deficient seed‐K concentration (<16.5 g kg−1) identified fields that responded positively to fertilizer K 77% of the time. Seed‐K concentration difference with and without fertilizer K decreased with the increase of soil K. Seed‐K concentrations can help diagnose reasons for low yields and correct K deficiency for subsequent crops. Soybean [Glycine max (L.) Merr.] seed nutrient concentrations may be useful for postseason diagnosis of nutrient deficiencies to identify reasons for lower‐than‐expected yields. Our objective was to determine the relationships between seed‐K and soil‐K concentrations and relative soybean yield and to develop potential seed‐K concentration thresholds for diagnosis of K deficiency as a yield‐limiting factor. Soil‐test K and seed‐K concentrations and yield data were collected from published and unpublished K fertilization research conducted in Arkansas (33 site‐years), Indiana (1 site‐year), Iowa (34 site‐years), Missouri (1 site‐year), Tennessee (6 site‐years), Virginia (1 site‐year), and Canada (24 site‐years). Seed‐K concentrations accounted for 66% of the variation in relative yield of soybean receiving no fertilizer K for Arkansas, 48% for Iowa, 78% for Canada, and 60% for North America from a database that included 100 site‐years. The critical seed‐K concentration ranges were 15.6 to 17.0 g K kg−1 for Arkansas, 17.4 to 20.0 g K kg−1 for Iowa, 14.6 to 16.2 g K kg−1 for Canada, and 16.5 to 17.7 g K kg−1 for North America. Seed‐K concentrations below the lower threshold for North America accurately predicted positive yield responses to fertilizer K at 77% of the sites classified as deficient. The difference between seed‐K concentration of soybean grown with and without fertilizer K decreased linearly as soil‐K concentration increased and plateaued when soil‐K concentration was ≥87, 139, 73, and 104 mg K kg−1 for Arkansas, Iowa, Canada, and North America, respectively. Results suggest that seed‐K concentrations can be used to aid in the diagnosis of K deficiency at maturity.

Mapping variability of soybean leaf potassium concentrations to develop a sampling protocol

“…Overall, each field had either similar levels of variability across sampling times or increased variability at the R2 growth stage compared to the later R4 growth stage (Table 3). The decreased variability in trifoliolate-K concentration at the R4 growth stage is likely due to the translocation of K from the leaves into the pods during reproductive growth (Bender et al, 2015;Parvej et al, 2016), decreasing the concentration and variability in the leaf-K. Similarly, for each field that was sampled at R4, the percentage which measured deficient increased from the R2 sample time to the R4 sample time (Table 3).…”

Broadening the Objectives of Future Potassium Recommendations

“…Genotype  Environment  Management (G  E  M) interactions can modify K uptake and KUE relationships. Parvej et al (2016) compiled seed K and grain yields for soybean grown at 100 site-years in North America. This included K-fertilized and unfertilized plots and soil test K levels that ranged from 30 to 408 mg K kg À1 soil that together, resulted in a wide range in seed K concentrations (12.7-24.3 g K kg À1 ).…”

“…Slopes of the linear regressions were statistically similar for the K-fertilized versus unfertilized plots. (Adapted from Parvej et al 2016) Interestingly, grain K concentrations are so conserved that G Â E Â M interactions often are inconsequential. For example, across species, K rates and application timings, and environments, the so-called "book values" for grain K concentrations were nearly as accurate at predicting K removal in grain as were lab-measured K concentrations and grain yields ( Fig.…”

“…The option to use book values for grain K concentration estimates has enabled K use and K nutrient budgets to be determined at various spatial resolutions ranging from local to national scales (http://nugis.ipni.net/Publication/). Parvej et al (2016) also explored the relationship between soil test K and seed K concentrations. Analysis including all site-years and fertilization groups revealed that seed K concentrations declined at soil test K levels below approximately 170 g K kg À1 soil; however, R 2 -values indicate that soil test K only explained 24 and 40% of the variability in seed K concentration for plots with and without K fertilizer, respectively.…”

Potassium management over 60 crops: A long‐term study on an Oxisol under no‐till

“…In Brazil, ∼90% of the total amount of K fertilizers is imported, generating a high external dependency. Increases of grains yield from 5 to 25% are frequent as a result of K inputs (Parvej, Slaton, Purcell, & Roberts, 2015;Parvej, Slaton, Fryer, Roberts, & Purcell, 2016 because of the high physiological K requirements of soybean and the high protein concentrations in its grains (Pettigrew, 2008). Although K fertilization is usually based on the exchangeable contents, non-exchangeable K influences the nutrient dynamics even in Oxisols with low cation exchange capacity and mineralogy dominated by kaolinite, quartz, and Fe-and Al-(hydr)oxides (Jalali, 2006;Moterle, Kaminski, dos Santos Rheinheimer, Caner, & Bortoluzzi, 2016).…”