Assessment of Plant‐Available Potassium for No‐Till, Rainfed Soybean

Abstract

Temporal and spatial availability of K can influence soybean [Glycine max (L.) Merr.] productivity. This study quantified the impact of initial soil K concentrations, soil‐water content, and soybean K uptake on soil K pools (water‐extractable solution‐phase K [Ksol], 1 mol L−1 NH4OAc‐extractable K, referred to as exchangeable K (Kexch), and 5‐min sodium tetraphenylboron [NaTPB] extractable K [KTPB]) and compared predictions of plant K availability using the NaTPB vs. NH4OAc tests. Soil and soybean samples were collected five times between the VE and R6 development stages in 2003 and 2004 from fallow and cropped no‐till Toronto–Millbrook silt loam Alfisols at the Throckmorton Purdue Agricultural Center. Gravimetric soil water content was measured weekly during the growing season. Low‐, medium‐, and high‐K fertility plots were replicated four times. Initial Kexch levels ranged from 60 to 290 and from 50 to 90 mg kg−1 at the 0‐ to 10‐ and 10‐ to 20‐cm depths, respectively. Medium‐ and high‐fertility soils had the highest grain yields. The 0‐ to 5‐cm soil layer had the highest Kexch levels, water availability, and soybean K uptake. Compared with Kexch, Ksol levels were less stratified and the surface layer was less dynamic. The NaTPB extraction was a better predictor of soybean K uptake in 1 yr, but across both years, NH4OAc was superior. Potassium measurements in the 0‐ to 10‐cm soil layer provided slightly better estimates of plant K uptake than those in the 0‐ to 20‐cm layer. Greater water availability and K uptake in the 0‐ to 5‐cm soil layer suggest that under evenly distributed, intermittent rainfall conditions in somewhat poorly drained soils, vertical soil K stratification might not be a concern for no‐till soybean production.

Assessment of Soil Phosphorus and Potassium following Real Time Kinematic‐Guided Broadcast and Deep‐Band Placement in Strip‐Till and No‐Till

“…Th e decline observed only in the soil surface is likely related to crop removal as these fi elds had <2% slope and nutrient loss by runoff is unlikely. Th ese data agree with other studies that indicate crop nutrient uptake occurs mostly on the surface layer of the soil (Fernández et al, 2008Farmaha et al, 2012).…”

Root and shoot growth, seed composition, and yield components of no-till rainfed soybean under variable potassium

“…In no-till studies with a broad range of K levels (160-400 mg kg −1 ), K concentrations at the 0 to 5 cm layer were 1.5 to 2 times the values observed in the 5-to 10-cm layer and 2 to 2.5 times the values in the 10-to 20-cm layer (Buah et al 2000;Hargrove 1985). Recently, Fernández et al (2008) documented a 5:2:1 ratio for these same layers in a field with longterm no-tillage and broadcast K management. In the eastern corn belt of the United States, vertical stratification of K in soil is a particular concern for soybean as the crop is rarely irrigated.…”

“…In contrast, Ritchie et al (1994) found soybean accumulated only 50% of its total requirement by R4 at 70 days after emergence with 100% of uptake delayed until the very end of reproductive development (R7, 110 days after emergence). Furthermore, a typical soybean crop requires 73% more K in harvested grain when compared to maize (Fernández et al 2008 and references cited therein). However, existing recommendations do not account for crop differences in K demand (Purdue Crop Diagnostic Training and Research Center 2006); the advent of high fertilizer and crop prices has renewed interest in evaluating the need for crop-specificity in K recommendations.…”

“…No-till and conservation tillage often causes strong vertical stratification of K with highest concentrations in the surface 5 cm of the soil profile (Crozier et al 1999;Fernández et al 2008;Holanda et al 1998;Howard et al 1999;Karathanasis and Wells 1990). In no-till studies with a broad range of K levels (160-400 mg kg −1 ), K concentrations at the 0 to 5 cm layer were 1.5 to 2 times the values observed in the 5-to 10-cm layer and 2 to 2.5 times the values in the 10-to 20-cm layer (Buah et al 2000;Hargrove 1985).…”

Relationship of Soil Potassium Forms with Maize Potassium Contents in Soils Derived from Different Parent Materials

“…This advantage can increase accuracy in predicting plant K uptake, especially when plants obtain considerable amounts of K from nonexchangeable forms. On the other hand, some researchers reported that NaTPB has no advantage compared to the traditional methods for assessment of plant available K (Schindler et al, 2002;Fernandez et al, 2008). The effectiveness of solute used for assessment of available soil K seems largely dependent on the nonexchangeable K extracting power and extraction period of the method that different researchers employed.…”