Soybean [Glycine max (Merr.) L.] is considered relatively insensitive to B deficiency. However, B deficiency has recently become a common nutrient deficiency of soybean in northeast Arkansas. Field studies were conducted on four alkaline silt‐loam soils in northeast Arkansas to determine the influence of B application time and rate on soybean growth, tissue B concentration, and seed yield. Boron fertilizer was applied at 0, 0.28, 0.56, 1.12, and 2.24 kg B ha−1 near the V2 or R2 growth stages. Boron fertilization had no significant effect on soybean yield at one site but increased seed yields from 4 to 130% at three sites. At the most responsive site, B application at V2 increased yields by 13% compared with applications at R2. In contrast, at a site where leaf B concentrations were sufficient for soybean receiving no B, B applied at the R2 stage significantly increased seed yields by 5% compared with V2 B applications. Trifoliate leaf B concentrations at the R2 stage increased as B rate increased. Seed B concentrations also increased as B rate increased. Boron applied at the R2 stage resulted in equal or greater seed B concentrations than B applied at the V2 stage. Application of 0.28 to 1.12 kg B ha−1 during early vegetative or reproductive growth was sufficient to produce near maximal yields. The expected severity of B deficiency plus fertilizer and application costs associated with B fertilization should be considered when selecting the most appropriate B fertilization strategy.

The ability of soil tests to identify nutrient‐deficient soils and recommend fertilizer rates that optimize agronomic yield is essential for profitable soybean [Glycine max (L.) Merr.] production. Our objectives were to correlate relative soybean yield to Mehlich‐3 and 1 mol L−1 HNO3–extractable soil K and trifoliolate‐leaf K concentration at the R1 to R2 development stage and calibrate the K rates for Mehlich‐3‐extractable soil K. Experiments were established on silt loams at 34 site‐years planted with a Maturity Group IV or V cultivar and fertilized at five K rates (0–148 kg K ha−1). Mehlich‐3‐extractable soil K ranged from 46 to 167 mg K kg−1 and produced relative soybean yields of 59 to 100% when no K was applied. Eleven sites had Mehlich‐3‐extractable K < 91 mg K kg−1 and all responded positively to K fertilization. Soybean grown in soil having 91 to 130 mg K kg−1 responded positively at nine of 15 sites. Mehlich‐3 soil K explained 76 to 79% of the variability in relative yields and had critical concentrations of 108 to 114 mg K kg−1, depending on the model. The linear‐plateau model predicted the critical HNO3–extractable soil K to be 480 mg K kg−1 Trifoliolate‐leaf K concentration increased significantly, positively, and linearly as Mehlich‐3‐ and HNO3–extractable soil K increased, but Mehlich‐3 soil K explained only 49 to 53% of the variation in trifoliolate‐leaf K. Mehlich‐3‐extractable K is an excellent predictor of soil K availability for soybean grown on silt loams in eastern Arkansas.

Soil testing is an important tool for estimating soil K availability and determining how much fertilizer must be applied to realize crop yield potential and minimize fertilizer costs. Our primary objectives were to correlate relative rice (Oryza sativa L.) yield with Mehlich‐3 and 1 mol L−1 HNO3 extractable K, define sufficient whole‐plant K concentrations at panicle differentiation (PD) and early heading (HDG), and calibrate K‐fertilizer rates with Mehlich‐3 soil K in the direct‐seeded, delayed‐flood rice production system. Potassium rate experiments were established at 32 site‐years on silt loams in eastern Arkansas. Relationships between selected parameters were evaluated with linear, curvilinear, and linear‐plateau models. The relationships between relative yield regressed against Mehlich‐3 and HNO3 extractable K were significant and curvilinear. The final curvilinear models for Mehlich‐3 and HNO3 K explained 63 and 43% of yield variability among site‐years, with predicted critical soil concentrations to produce 95% relative yield of 99 and 390 mg K kg−1, respectively. Linear‐plateau models provided comparable critical soil K concentrations. Rice having whole‐plant K concentrations of 23.1 g kg−1 at PD and 13.0 g kg−1 at HDG were predicted to produce 95% relative yield. The predicted K‐fertilizer rates required to optimize rice grain yield depended on the model and ranged from 51 to 90, 41 to 70, 30 to 55, and 20 to 35 kg K ha−1 for soil having Mehlich‐3 soil K concentrations of 60, 70, 80, and 90 mg K kg−1, respectively. The suggested Mehlich‐3 soil and plant K critical concentrations should be appropriate for other U.S. mid‐South rice‐producing areas using similar cultural production practices.

Rice (Oryza sativa L.) cultivated with the direct‐seeded, delayed‐flood production system relies heavily on post‐emergence aerial application of N. The availability of a controlled‐release N fertilizer suitable for preplant application would offer rice growers an alternative N‐fertilization method and reduce the aerial application costs of N fertilization. Our objectives were to determine grain yield and N uptake of rice receiving preplant incorporated polymer‐coated urea (PCU) compared with urea applied preflood at the five‐leaf stage and characterize the N release of two PCUs. Field trials were conducted at five site‐years to evaluate rice performance when fertilized with preplant‐applied Environmentally Smart Nitrogen (ESN) and Duration Type 5 (D5) and preflood‐applied urea across N rates ranging from 0 to 168 kg N ha−1 Nitrogen release from PCU was evaluated in field incubations using a buried‐bag method at two site‐years. Nitrogen release was nonlinear across time and similar between site‐years but different between PCUs. The nonlinear relationships predicted that 75% of PCU N content was released by 36 d for D5 and 25 d for ESN. Nitrogen recovery at panicle differentiation averaged 30% for D5, 26% for ESN, and 72% for urea and at heading averaged 47% for D5, 37% for ESN, and 101% for urea. As the N rate increased, yields increased nonlinearly for rice receiving D5 preplant and urea preflood and linearly for rice receiving ESN preplant. Yield predictions for D5 were always lower than for urea at the same N rates. Results suggest that the N release from D5 and ESN is too rapid for rice cultivated in the direct‐seeded, delayed‐flood method.

Forage fertilization practices ate changing because of poultry litter use restrictions and reduced NH^NOj availability. Our objectives were to compare bermudagrass [Cynoàin dactylon (L.) Pers.] yield and N uptake among N sources and rates and evaluate the influence of N-fertilizer source on NH., volatilization. Four N sources, pelleted poultry litter (PPL), NH^NO,, urea, and urea + iV-(n-butyl) thiophosphoric triamide (NBPT) were applied at rates of 0 to 500 kg N ha" yr" to common bermudagtass from 2006 to 2008. Measurements included dry mattet yield and total N uptake ftom each N source applied at 400 kg N ha"' yr"'. A semi-open static chamber method was used to measure NH, volatilization for 15 d from each N source applied at 400 kg N ha" yr" in three split applications. Dry matter increased linearly in 2006 and curvilinearly in 2007 and 2008 as N rate increased, with maximum yields of 9910 to 14,328 kg ha" '. Forage fertilized with <300 kg PPL-N ha" ' yr" ' produced 78 to 96% of the dry matter as the same rates of NH^NO,. The addition of NBPT to urea showed no consistent benefit to yield or N uptake compared with urea alone. Urea-based fertilizers produced similar to slightly lower yields and N uptakes than NH^NOj. Cumulative NHj-N loss was greatest for urea (10.4-18.7% of applied N), intermediate for urea + NBPT (2.0-3.9%), and < 1.5% for PPL and NH^NOj. Given the limited availability of NH4NO3, restrictions on poultry litter use, and concerns about air quality, urea amended with NBPT is a suitable N source for bermudagrass.Abbreviations: NBPT, 7V-(n-hutyl) thiophosphoric ttiamide; PPL, pelleted poultry litter.