Critical Trifoliolate Leaf and Petiole Potassium Concentrations during the Reproductive Stages of Soybean

Abstract

The critical K concentration in soybean [Glycine max (L.) Merr.] has been determined only for leaf tissue at the R2 (full bloom) stage. Our research objective was to develop critical K concentrations in soybean for both leaves and petioles across reproductive stages. Fifteen fully‐expanded, uppermost trifoliolate leaves with petioles plot−1 were collected 7 to 12 times from the V5 to R7 stages in five research trials that evaluated multiple fertilizer‐K rates and/or cultivars from different maturity groups (MGs). Both leaf‐ and petiole‐K concentrations, regardless of site‐year, cultivar, and fertilizer‐K rate, peaked around R2 stage and declined linearly with time at average rates of –0.198 g K kg−1 d−1 for leaves and –0.559 g K kg−1 d−1 for petioles. The leaf‐ and petiole‐K concentrations at the R2 to R6 stages explained 48 to 80% and 41 to 85%, respectively, of the variation in relative yield (RY). Petiole‐K concentration was a better predictor of RY than leaf‐K at the R2 stage where the predicted critical range (CR) concentrations were 14.6 to 19.0 g leaf‐K kg−1 and 30.1 to 38.3 g petiole‐K kg−1. The wider CR of petiole‐K at the R2 stage followed by a greater linear decline rate across reproductive stages indicates that growth stage as well as deficiency and sufficiency thresholds for petiole‐K could be more easily categorized than for leaves. Overall, the ability to interpret the K nutritional status in soybean tissues at numerous reproductive growth stages will improve K management. Critical soybean tissue‐K concentrations in the trifoliolate leaf and petiole can be developed for growth stages beyond the R2 stage by modeling the rate of tissue‐K decline across time. Petiole‐K concentrations are approximately twofold higher and decline at a greater rate than trifoliolate leaf‐K concentrations and may be equally as good or a better tissue to sample for the diagnosis of K deficiency. The ability to interpret the K nutritional status in leaves, petioles, or both tissues at numerous reproductive growth stages allows plant K status to be monitored and possibly corrected during the growing season across a range of growth stages.

Seasonal critical concentration and relationships of leaf phosphorus and potassium status with biomass and yield traits of soybean

“…The reduction in SY under P deficiency appeared to be closely related to the decreases in the number of pods and seeds per plant as deduced from the greatest CLPC (≈ 2.60 mg P g −1 ) found for these traits. The mean CLKC was also similar between TBM and SY (16.1 mg K g −1 ) and was within the range reported previously (14.6–19.0 mg g −1 ) in soybean ( Parvej et al, ). Factors such as genotype differences, growth conditions, whether the relationship of foliar nutrient status was established with the in‐season biomass or with the TBM and SY at maturity, and the age of plants are likely to influence the critical nutrient concentration.…”

“…Therefore, an early diagnosis of foliar P or K is useful in assisting the correction of deficiency before the nutrient uptake reaches the maximum. The timely diagnosis and remediation of nutrient deficiency also becomes important as the critical nutrient concentration among plant parts, including leaves, varies with the physiological and chronological age as shown in this study and elsewhere ( Bell et al, ; Parvej et al, ). Thus, the period of high demand for mineral nutrients during pod development or seed filling might decrease the foliar P or K concentration due to the remobilization of nutrients in to the developing seeds at later stage.…”

“…The rapid and early detection of nutrient stresses such as P and K deficiency are vital to the timely recommendation and application of fertilizers to avoid yield losses. Often, pre‐harvest tissue nutrient concentration exhibits a close relationship with the plant biomass accumulation and productivity at maturity ( Cure et al, ; Singh et al, ; Parvej et al, ; Singh and Reddy , ). The nutrient analysis of whole plants or organs such as leaf, petiole, composition of sap or activity of certain enzymes in plant, and the estimation of leaf color or photosynthetic pigments are some of the methods used to detect nutrient stress ( Scaife and Bray , ; Besford , ; Bell et al, ; Singh et al, ).…”

“…Moreover, losses in crop yield can occur even under moderate nutrient deficiency before a prominent deficiency symptom is observed ( Gerardeaux et al, ; Kanai et al, ; Singh and Reddy , ). Thus, leaf nutrient analysis is recommended for the early detection of K deficiency in crops and for nutrient management ( Bell et al, ; Crozier et al, ; Parvej et al, ). The tissue nutrient status in plant organs also differs at different growth stages ( Rao , ; Cure et al, ; Singh et al, ; Parvej et al, ; Singh and Reddy , ) which might lead to a stage‐dependent relationship with the overall crop productivity.…”

Do soil test levels and fertilization with phosphorus and potassium impact field crop tissue concentrations?

“…The relationship between STK and corn grain K in our study ( r 2 = .22) is inconsistent with an Iowa study that reported no relationship between soil test K and corn grain K, with STK values ranging between 75 and 275 mg kg −1 (Mallarino & Higashi, 2009). The relationship between STK and soybean grain K was weak in our study, but is generally consistent with a meta‐analysis drawing on studies conducted in Arkansas, Indiana, Iowa, Missouri, and Canada that found soybean seed K concentrations increased linearly as soil test levels increased up to 179 mg K kg −1 and seed K concentration plateaued at 18.8 g K kg −1 with an r 2 value of .40 (Parvej et al., 2016). To our knowledge, this is the first report of relationships of wheat tissue K concentrations and STK levels in the Midwest.…”