Irrigated soybean response to granular fertilizer potassium application timing

Abstract

Amelioration of K deficiency during the growing season requires knowledge of critical tissue concentrations and crop yield response to fertilization time. Our objectives were to characterize the yield and uptake responses of K-deficient irrigated soybean [Glycine max (L.) Merr.] to in-season fertilizer-K application time and rate, evaluate fertilizer-potassium-recovery efficiency (FKRE), and evaluate how leaflet-K concentration responds to K-fertilization time. Six trials were established on silt loam soils. Muriate of potash was applied pre-plant and compared to an equivalent K rate applied post-emergence on six or seven dates. Grain yield, trifoliolate-K concentration, and K uptake were measured. Relative soybean yields were regressed across days after planting (DAP) for two situations of K-responsive soybean: season-long K-deficiency symptoms or few symptoms (hidden hunger). The maximum yield increases from K fertilization ranged from 524 to 1948 kg ha −1 among trials producing relative yields that were 59−90% of the maximum yield produced with the greatest pre-plant-applied K rate. A linearplateau model showed maximal yields of soybean with hidden hunger could be produced with in-season fertilizer K applied as late as 83 DAP or 44 d after R1 stage (DAR1). For soybean experiencing season-long K deficiency, K fertilization from pre-plant until 60 DAP or about 20 DAR1 produced similar relative yields. The FKRE of pre-plant-applied fertilizer K ranged from 36 to 75% among trials. Regardless of the severity of K deficiency, fertilizer K applied post-emergence into the R2 development stage was taken up efficiently and produced similar yields as equal pre-plant-applied K rates.

Dynamic critical potassium concentrations in soybean leaves and petioles for monitoring potassium nutrition

“…Slaton et al (2020) reported that yields of K-deficient soybean may be increased by the application of fertilizer-K into the R5 development stage. Slaton et al (2020) reported no soybean yield loss when hidden hunger K deficiency was corrected before 44 DAR1, but more severe deficiency required earlier action to prevent yield loss associated with K deficiency. The petiole-K and trifoliolate leaf-K concentrations associated with 85 and 75% relative yields were also predicted across time to provide estimates of the degree of deficiency (Figures 1 and 2).…”

“…Parvej et al (2016) also reported lower correlations between tissue-K concentrations during early and late reproductive development stages and soybean relative yield. The weak correlation during the late vegetative and early reproductive growth of indeterminate soybean is attributed to the fact that flowering begins before plant shoots and roots are fully developed (Mitchell & Russell, 1971), rapid dry matter accumulation and nutrient uptake during subsequent growth may influence tissue nutrient concentrations (Bender et al, 2015), and K-deficiency may be effectively ameliorated through early to mid-reproductive development (Slaton et al, 2020). Although the tissue-K concentrations during early reproductive growth may be informational, tissue concentrations from samples collected beginning at the R2 stage or >15 DAR1 will most accurately characterize the plant-K nutritional status for management decisions regarding the need for additional fertilizer-K application.…”

“…These four site‐years were described by Slaton et al. (2020) (identified as site‐years B, C, D, and F, respectively, because the trials were used for multiple research objectives). Trials 16‐74, 17‐59, and 17‐60 followed soybean in rotation, measured 2.1 m wide and 9.1 m long, and were drilled in 38‐cm‐wide rows (Table 1).…”

“…The use of a single critical‐tissue‐K concentration to interpret K nutrition across all soybean growth stages leads to inaccurate assessments of plant‐K sufficiency for some growth stages. Potassium‐deficient soybean can benefit from in‐season K fertilization well into reproductive growth (Nelson et al., 2005; Slaton et al., 2020). However, the production system, especially regarding soil moisture and its influence on K uptake, may affect soybean yield response to in‐season K fertilization.…”

Profit‐maximizing potassium fertilizer recommendations for soybean

“…show symptoms of chlorosis beginning on the margins of the leaves, with yield loss caused by reductions in pods plant −1 , seed pod −1 , and seed weight along with increased seed abortion (Parvej, Slaton, Purcell, & Roberts, 2015, 2016). The severity of the deficiency dictates when and where on the plant the symptoms appear (Slaton, Roberts, Ross, & Richmond, 2020). Soybean can become more susceptible to plant diseases when K nutrition is low, such as seed decay caused by Diaporthe/Phompsis spp.…”