Minnesota is a leading corn ( Zea mays L.) producer in the United States, requiring substantial nitrogen (N) inputs for optimal yields. Using an in‐season critical soil nitrate (NO 3 − ‐N) concentration threshold to adjust fertilization rates can improve N management and reduce environmental impacts. This study assessed corn grain yield response to in‐season (i.e., V4–V6 corn development stage) soil NO 3 − ‐N concentration to establish a critical pre‐sidedress soil NO 3 − ‐N test (PSNT) under Minnesota conditions. Data included were obtained from 34 field experiments conducted from 2012 to 2019 across the major corn production regions of Minnesota. Relationships between PSNT and relative corn grain yield were analyzed using a quadratic‐plateau regression model. Across the entire dataset, a PSNT of 20 ± 2.5 mg NO 3 − ‐N kg −1 soil was the critical level to reach 97% of maximum corn grain yield. To increase suboptimum PSNT concentrations up to the critical threshold, application of 13.8 ± 2.4 kg N ha −1 is needed per 1 mg kg −1 increase in soil NO 3 − ‐N concentration based on pre‐/at planting N application, but validation is needed for actual sidedress applications. When precipitation was lower or greater than the 30‐year mean, the critical PSNT value was 21.5 or 17.4 mg kg⁻¹, respectively. Nonetheless, the 20 ± 2.5 mg NO 3 − ‐N kg −1 PSNT critical value is applicable across the state as limited model improvements were achieved when the data were segregated according to soil characteristics, location, corn material, and/or previous crop.

Starter fertilizers containing phosphorus (P) are applied to increase corn (Zea mays L.) early growth and ultimately grain yield. This study determined the rate of starter P needed to increase corn early plant growth and grain yield at differing starting soil test phosphorus (STP) concentrations with or without broadcast P application. Field trials were established at 10 site-years in Minnesota using a split-plot design. Main blocks consisted of 0 or 59 kg P ha-1 broadcast pre-plant. Sub-plots consisted of liquid starter fertilizer (10-15-0 N-P-K): 0, 29, 58, and 87 kg ha-1 applied on the corn seed. Analysis was conducted across sites after classifying each block per site (low, medium, high, and very high STP) according to University of Minnesota guidelines. Corn plant mass and P uptake at V5-V7 increased linearly as the rate of starter P regardless of where broadcast P was applied and initial STP concentration. Corn yield was increased by P when STP was in the low or medium STP classification, and application of starter P alone did not maximize grain yield in low P soils. The data indicate that 29 kg ha-1 of the starter applied in this study is sufficient to increase early plant growth and corn yield compared to broadcast P only when STP was medium or higher. Broadcast P is needed to maximize yield when STP was low, and varying starter rates more than 29 kg ha-1 will not result in a greater yield potential across sites versus broadcast P alone regardless of STP concentration.

Potassium (K) is a critical macronutrient for maximizing yields in agricultural crops. However, inconsistent responses to K fertilizer or soil test K levels have led researchers to question which soil properties influence K availability and cycling in soils. This study aimed to evaluate how K is retained in sandy soils. The specific objectives of this research were to (1) determine the influence of pH level on cation exchange capacity (CEC) and K sorption in coarse‐textured soils and (2) assess the impact of freeze–thaw cycling on K release across a range of agricultural soils. Soil was collected from 10 agricultural sites in Minnesota. Of these, four were used to evaluate K sorption and eight were used to assess K leaching following freeze–thaw weathering. Potassium sorption experiments revealed that sand‐textured soils exhibited limited K sorption as solution K increased, but a higher clay percent or CEC allowed for greater K sorption. The addition of calcium (Ca) in the sorption experiments resulted in K release for all sandy‐textured soils. In weathering studies, freeze–thaw cycling led to mixed effects on K leaching. Simulated irrigation water containing Ca and magnesium (Mg) significantly increased K leaching in comparison to deionized water. These studies indicate the need for tailored K recommendations in coarse‐textured, low‐CEC soils considering the limited K sorption capacity and influence of divalent cations.

It has been questioned whether the sufficient phosphorus (P)management approach could maximize potential grain yield in today's agricultural systems. The objective of this research was to establish six long‐term experiments across Minnesota to test phosphorus (P) management strategies on soils with a defined long‐term P history. Four soil test phosphorus (STP) interpretation classes were established as whole plots (low, medium, high, and very high). Split‐plots within each STP class consisted of one split‐plot that did not receive P (−P), and the second split‐plot received a broadcast application of P fertilizer (+P) at the rate of 73 (low), 44 (medium), 15 (high), and 15 (very high) kg P ha −1 . Grain yield, grain P concentration, and grain P removal were determined during corn ( Zea mays L.) (2015 and 2016) and soybean [ Glycine max (L) Merr.] (2017) growing seasons. Grain yield was increased by P fertilizer at 7 of 18 site‐years. Grain yields were similar between fertilized STP plots at the very low and low for corn and very low for soybean compared to nonfertilized or fertilized high and very high STP plots. No yield increase was noted for fertilized high or very high plots. Grain P removal was increased by applied P at 14 of 18 site‐years at the low and medium STP classes with no increase for the high and very high P testing soils. Results from this research indicate no greater yield potential for soils built to high or very high STP classes versus adequately fertilizing low‐ or medium‐testing soils.

Phosphorus (P) is essential to healthy plant development and is regularly applied in agronomic settings to ensure maximum crop yields. Sewage sludge incinerator ash (SSA) contains significant amounts of P and was investigated as a recycled P fertilizer in a 3‐year field study. Untreated SSA was applied at a range of agronomically appropriate rates based on water‐ and citrate‐soluble phosphate (WCSP) concentrations in a corn and soybean field study in Minnesota (Waukegan silt‐loam, pH 6.8) to determine the soil chemical effects of SSA amendment individually and compared with triple superphosphate (TSP), biosolids, and struvite. Concentrations of Olsen‐P and soil solution P ion fluxes from in‐situ plant root simulator probes increased with increasing rates of SSA and were significantly greater than control plots. Compared to the other P sources, SSA amendment increased soil test P at 50%–70% the increase observed with TSP amendment, while total P concentrations increased at 1.7–2.5 times the rate of increase with other P sources. This was due to the lower WCSP concentrations in SSA and the experimental choice to apply based on WCSP. Soil‐extractable concentrations and ion fluxes of copper (Cu) and zinc and total soil concentrations of Cu increased with SSA and biosolids application, indicating potential as a comprehensive nutrient source. Total concentrations of concerning elements including arsenic, cadmium, chromium, and lead did not increase above detection limits. Total mercury concentrations were statistically higher with SSA application compared with the control and other P sources, though the analytical sensitivity was significantly higher, and the increase was biologically marginal (an increase of 0.06 µg kg −1 P applied as SSA). Overall, soil chemical responses indicated that SSA increased concentrations of soil test P and some plant nutrients with minimal increases in concentrations of elements of concern.

Phosphorus (P) fertilizer recommendations based on the build and maintain (B&M) or the sufficiency philosophies were compared at six sites across Minnesota. Various levels of soil test P (STP) levels were established over four growing seasons. Applied P and P removed in harvested grain were monitored and used to develop a soil net P balance (Net P). Linear regression of net P with changes in STP was highly significant. Initial STP levels could be maintained at four of the six sites with a negative Net P. At those same sites, a zero Net P would tend to slowly increase STP over time. A sequential soil P fractionation analysis was conducted on soils from the six sites at the initiation and at the end of the 4-year period. Nine total soil P fractions were extracted that represented both inorganic P (Pi) and organic P (Po) in the labile and non or less labile soil P pools. A positive linear relationship between Net P and changes in Pi fractions was significant. As Net P increased, so did the changes in Pi in the Resin, BiCarb, and NaOH fractions. These three fractions accounted for 66% to >100% of the changes in Net P with Resin and NaOH accounting for the majority of Net P. Changes in Net P that were accounted for in the less labile P pools, Sonic and HCl fractions, variable, and difficult to determine. There was little effect of Net P on Po fractions.

Abstract Potassium (K) is an essential nutrient for plant growth. In K‐deficient soils, fertilization has been shown to increase herbage yield of alfalfa. The purpose of this study was to determine the effects of K fertilization on alfalfa leaf and stem yield, forage quality, nutrient removal, and plant health of a nonlodging experimental germplasm. Five alfalfa rotations had K fertilizer applied at three rates (0, 186, and 372 kg K ha−1) to soils already containing sufficient soil test K (223 mg kg−1). No overall yield differences were found related to K application rates, though K removal in total herbage increased by 30–58% with K fertilization, depending on alfalfa stand age. Leaf:stem ratios were not impacted by K fertilization. The concentrations of B, Ca, and Na decreased with K fertilization, while K concentrations increased, which may have resulted in B deficiencies. Leaf in vitro digestibility decreased significantly with the application of K. There was no benefit to crown rot disease resistance with increased K fertilization. This study supports that the addition of K to already sufficient soils does not lead to any additional economic benefits and may reduce productivity due to the reduction of B uptake and in vitro digestibility.

Currently, there are substantial knowledge gaps on the impacts of cover crops on soil resources in tree cropping systems, wherein they are typically planted in interrow alleys and maintained for multiple years. While cover crops uptake soil nutrients and water, they can also prevent soil water evaporative losses and return nutrients to soils via decomposition of plant residues and stimulation of microbial nutrient cycling. This field sampling study examined variances in soil conditions across 5- and 7-year-old, cover cropped pecan orchards. We collected soil beneath cover crops and beneath adjacent trees, where soil was kept bare, to evaluate impacts of cover on the soil biota, nutrients, carbon, and their dynamics across a production season. We employed routine soil chemical analyses, phospholipid fatty acid (PLFA) analysis, and high throughput sequencing of 16S rRNA genes and ITS regions for soils collected at four time points. We revealed that the cover cropped alley soils contained higher relative abundances of microbes that use labile soil substrates in resource rich conditions than did the tree row soils. Soil chemical analyses provided additional evidence that the cover crops did not deplete soil nutrients and reduce soil moisture, but rather, enhanced soil nutrient and moisture contents during many of the sampling time points. Notably, cover crop plant species correlated with soil nutrients and plant beneficial microbes, which may warrant consideration when selecting cover crop species. The tree row and cover cropped alley soils had different proportions of plant-beneficial mycorrhizal fungi. The tree rows supported higher numbers of ectomycorrhizal (ECM) fungi and alleys had higher relative abundances of arbuscular mycorrhizal (AM) fungi, suggesting potential benefits for tree species like pecan, which support dual colonization by AM and ECM Fungi. Altogether, the cover crops enhanced soil carbon, nutrients, and microbial populations in a pecan orchard and these impacts were frequently larger in a 7-year-old versus 5-year-old orchard.

Phosphorus (P) is an essential nutrient in agricultural production, yet its losses contribute to eutrophication in freshwater systems. To mitigate this, there is increasing interest in quantifying soluble P leaching losses and including them in P indices. The objectives of this research were (a) to evaluate water soluble P leaching loss from topsoils (0-15 cm) across a range of initial soil test P (STP) levels; (b) to determine the effects of soil type, physiochemical soil properties, and leaching volume on P leaching loss; and (c) to determine the predictability of P leaching losses from soil tests. Intact soil cores (3.81 cm in diameter, 0-15 cm deep) were collected from six agricultural fields in Minnesota and leached with deionized water offsite. Additional columns were collected to identify the influence of three leaching volumes on P leaching load. Phosphorus leaching loss was impacted by soil type, initial STP level, and the volume of the leaching event. Leachate P concentration increased with increasing STP level and remained consistent among leaching volumes. Concentrations were not diluted with increased leaching volumes. Consequently, leaching volume was the primary driver of total P load. Several linear and machine learning models were used to predict P leachate concentration. Phosphorus concentration was best predicted using a ridge regression model using two soil tests: the degree of phosphorus sorption and water extractable P (R-2 = .58, RMSE = 0.06). The model prediction of P leaching loss is promising, although further research on subsoil interactions is needed.

Active canopy sensing may improve corn (Zea mays L.) nitrogen (N) management, but little has been done to evaluate soil N content to improve the utility of sensors. This study investigated the usefulness of integrating canopy sensing tools and soil N content to estimate grain yield and N requirement at various corn development stages. Six to seven N rates at 35-45 kg urea-N ha(-1) increments were pre-plant applied in 12 sites throughout Minnesota. Canopy-sensing measurements were obtained at the V4, V8, V12, and R1 stages. Soil (0-30 and 0-60 cm) NH4-N and NO3-N concentrations were measured at the V4, V8, and V12 stages. Adjusting sensor measurements with soil NO3-N (0-30 cm) measured at the V4 stage provided the best trade-off between gains in prediction accuracy and practicality for soil sampling. At the V4 stage, predictions of N requirement with soil N alone (RMSE = 41.3 kg N ha(-1)) and soil-N-adjusted sensor measurements (RMSE ranging from 39.6 to 42.7 kg N ha(-1)) were similar but better than predictions with unadjusted sensor measurements (RMSE ranging from 61.0 to 72.9 kg N ha(-1)). Although the utility of canopy sensing without soil-N adjustments improved at later development stages, the most accurate predictions of N requirement were obtained with soil-N-adjusted sensor measurements collected at V8 and V12 (RMSE as low as 32.5 kg N ha(-1)). Our study shows that early-season canopy sensing (up to V8) coupled with soil N measurements may be a viable alternative to improve in-season N management.

Anaerobic potentially mineralizable nitrogen (PMN) combined with preplant nitrate test (PPNT) or pre‐sidedress nitrate test (PSNT) may improve corn ( Zea mays L.) N management. Forty‐nine corn N response studies were conducted across the U.S. Midwest to evaluate the capacity of PPNT and PSNT to predict grain yield, N uptake, and economic optimal N rate (EONR) when adjusted by soil sampling depth, soil texture, temperature, PMN, and initial NH 4 –N from PMN analysis. Pre‐plant soil samples were obtained for PPNT (0‐ to 30‐, 30‐ to 60‐, 60‐ to 90‐cm depths) and PMN (0‐ to 30‐cm depth) before corn planting and N fertilization. In‐season soil samples were obtained at the V5 corn development stage for PSNT (0‐ to 30‐, 30‐ to 60‐cm depths) at 0 kg N ha −1 at‐planting rate and for PMN when 0 and 180 kg N ha −1 was applied at planting. Grain yield, N uptake, and EONR were best predicted when separating soils by texture or sites by annual growing degree‐days and including PMN and initial NH 4 –N with either NO 3 –N test. Using PSNT (mean R 2 = .30)‐instead of PPNT (mean R 2 = .19)‐based models normally increased predictability of corn agronomic variables by a mean of 11%. Including PMN and initial NH 4 –N with PPNT or PSNT only marginally improved predictability of grain yield, N uptake, and EONR ( R 2 increase ≤ .33; mean R 2 = .35). Therefore, including PMN with PPNT or PSNT is not suggested as a tool to improve N fertilizer management in the U.S. Midwest.

The anaerobic potentially mineralizable N (PMN) test combined with the preplant (PPNT) and presidedress (PSNT) nitrate tests may improve corn (Zea mays L.) N fertilization predictions. Forty‐nine corn N response experiments (mostly corn following soybean [Glycine max (L.) Merr.]) were conducted in the U.S. Midwest from 2014–2016 to evaluate the ability of the PPNT and PSNT to predict corn relative yield (RY) and N fertilizer over‐ and under‐application rates when adjusted by PMN. Before planting and N fertilization, PPNT (0–30, 30–60, and 60–90 cm) and PMN (0–30 cm) samples were obtained. In‐season soil samples were obtained at the V5 development stage for PSNT (0–30, 30–60 cm) in all N rate treatments and PMN (0–30 cm) in only the 0 and 180 kg N ha−1 preplant N treatments. Increasing NO3–N sampling depths beyond 30 cm with or without PMN improved RY predictability marginally (R2 increase up to 0.20) and reduced over‐ and under‐application frequencies up to 14%. Including PMN (preplant only) with PPNT or PSNT improved RY predictability minimally (R2 increase up to 0.10) only for coarse‐ and medium‐textured soils, but N fertilizer over‐ and under‐application frequencies were not substantially reduced (≤12%). These marginal improvements in RY predictability and N fertilizer over‐ and under‐application frequencies, regardless of the variables used (e.g., fertilization, sampling depth, soil texture, and growing degree‐day categories), demonstrate that including PMN with soil NO3–N alone does not improve corn N fertilization need predictions enough to recommend their use. Disciplines Agricultural Science | Agriculture | Soil Science Comments This article is published as Clark, Jason D., Fabián G. Fernández, Kristen S. Veum, James J. Camberato, Paul R. Carter, Richard B. Ferguson, David W. Franzen et al. "Adjusting corn nitrogen management by including a mineralizable‐nitrogen test with the preplant and presidedress nitrate tests." Agronomy Journal (2020). doi: 10.1002/agj2.20228. Authors Jason D. Clark, Fabián G. Fernández, Kristen S. Veum, James J. Camberato, Paul R. Carter, Richard B. Ferguson, David W. Franzen, Daniel E. Kaiser, Newell R. Kitchen, Carrie A. M. Laboski, Emerson D. Nafziger, Carl J. Rosen, John E. Sawyer, and John F. Shanahan This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/agron_pubs/652 Received: 14 January 2020 Accepted: 26 March 2020 DOI: 10.1002/agj2.20228

Optical canopy sensing tools may improve corn (Zea mays L.) nitrogen (N) management, but their usefulness in far northern latitudes remains unclear. For this reason, the utility of SPAD, GreenSeeker normalized difference vegetation index (GS-NDVI), RapidSCAN normalized difference vegetation index (RS-NDVI), and RapidSCAN normalized difference red edge (RS-NDRE) were evaluated to predict corn grain yield, plant N accumulation, and plant N deficiency in 12 site-years throughout Minnesota. Six to seven N rates (35-45 kg urea-N ha(-1) increment) were pre-plant applied. Canopy sensing measurements and aboveground plant N accumulation were obtained at V4, V8, V12, and R1 stages. Regardless of the tool, low predictive power of grain yield, plant N accumulation, and N deficiency occurred at V4, likely because of low crop N demand and sufficient N supply. At V8, sensors provided good estimations of grain yield (R-2 = .75-.85) but underestimated the agronomic optimum nitrogen rate (AONR) by 33, 94, 102, and 46 kg N ha(-1) with the SPAD, GS-NDVI, RS-NDVI, and RS-NDRE, respectively. At V12 RS-NDRE measurements provided the most accurate estimations of grain yield (R-2 = .92) and AONR [R-2 = .84 and N rate differential from agronomic optimum nitrogen rate (dAONR) at -2 kg N ha(-1)]. At R1 SPAD also provided good estimations of grain yield and N deficiency. The mismatch between the best timings for predicting N fertilizer requirements (V12 and R1) and the best timings for sidedressing (V4-V8) highlight that sensing tools may have limited utility to improve the standard maximum return to N approach in the Upper Midwest.

Understanding the variables that affect the anaerobic potentially mineralizable N (PMNan) test should lead to a standard procedure of sample collection and incubation length, improving PMNan as a tool in corn (Zea mays L.) N management. We evaluated the effect of soil sample timing (preplant and V5 corn development stage [V5]), N fertilization (0 and 180 kg ha(-1)) and incubation length (7, 14, and 28 d) on PMNan (0-30 cm) across a range of soil properties and weather conditions. Soil sample timing, N fertilization, and incubation length affected PMNan differently based on soil and weather conditions. Preplant vs. V5 PMNan tended to be greater at sites that received < 183 mm of precipitation or < 359 growing degree-days (GDD) between preplant and V5, or had soil C/N ratios > 9.7:1; otherwise, V5 PMNan tended to be greater than preplant PMNan. The PMNan tended to be greater in unfertilized vs. fertilized soil in sites with clay content > 9.5%, total C < 24.2 g kg(-1), soil organic matter (SOM) < 3.9 g kg(-1), or C to N ratios < 11.0:1; otherwise, PMNan tended to be greater in fertilized vs. unfertilized soil. Longer incubation lengths increased PMNan at all sites regardless of sampling methods. Since PMNan is sensitive to many factors (sample timing, N fertilization, incubation length, soil properties, and weather conditions), it is important to follow a consistent protocol to compare PMNan among sites and potentially use PMNan to improve corn N management.

Estimates of mineralizable N with the anaerobic potentially mineralizable N (PMNan) test could improve predictions of corn (Zea mays L.) economic optimal N rate (EONR). A study across eight US midwestern states was conducted to quantify the predictability of EONR for single and split N applications by PMNan. Treatment factors included different soil sample timings (pre‐plant and V5 development stage), planting N rates (0 and 180 kg N ha−1), and incubation lengths (7, 14, and 28 d) with and without initial soil NH4–N included with PMNan. Soil was sampled (0–30 cm depth) before planting and N application and at V5 where 0 or 180 kg N ha−1 were applied at planting. Evaluating across all soils, PMNan was a weak predictor of EONR (R2 ≤ 0.08; RMSE, ≥67 kg N ha−1), but the predictability improved (15%) when soils were grouped by texture. Using PMNan and initial soil NH4–N as separate explanatory variables improved EONR predictability (11–20%) in fine‐textured soils only. Delaying PMNan sampling from pre‐plant to V5 regardless of N fertilization improved EONR predictability by 25% in only coarse‐textured soils. Increasing PMNan incubations beyond 7 d modestly improved EONR predictability (R2 increased ≤0.18, and RMSE was reduced ≤7 kg N ha−1). Alone, PMNan predicts EONR poorly, and the improvements from partitioning soils by texture and including initial soil NH4–N were relatively low (R2 ≤ 0.33; RMSE ≥ 68 kg N ha−1) compared with other tools for N fertilizer recommendations.Core Ideas Anaerobic potentially mineralizable N (PMNan) is a weak predictor of economic optimal N rate (EONR). Predictability of EONR by PMNan improves when accounting for soil texture. For coarse‐textured soils, PMNan at V5 improves EONR predictability. Increasing incubation length does not substantially improve EONR predictability. PMNan alone is not a reliable management tool for N rate determination.

Core Ideas Soil texture and precipitation largely impact split fertilizer application efficacy. Split fertilizer application consistently increased grain yield in irrigated sands. In fine‐texture and well distributed rain, split application should be done by V8. In fine‐texture and poor distributed rain, split application made no yield difference. Corn response to split application was greater in coarse‐textured than fine‐textured soils. In‐season N fertilization is increasingly being used as a management strategy to reduce risk of N loss to the environment. This study evaluated the optimal timing for a split N fertilizer application in corn ( Zea mays L.) across different environments and soil textural classes in Minnesota. Treatments consisted of pre‐plant (PP) urea applied at 0 to 270 or 315 kg N ha −1 on increments of 45 kg N ha −1 and five split applications (SA) of 45 kg N ha −1 urea ammonium nitrate as starter fertilizer and 90 kg N ha −1 of urea with an urease inhibitor applied at the V2, V4, V6, V8, or V12 stage of corn phenological development. Site‐years were grouped according to grain yield response to fertilizer timing. Irrigated coarse‐textured soils produced 1.5‐ to 1.9‐fold greater grain yield when fertilizer was split applied from V4 to V12 due to improved synchrony of N availability to crop demand and reduced potential for NO 3 –N leaching. Rainfed, fine‐textured soils had mixed results. Site‐years receiving well‐distributed precipitation produced greater grain yield when fertilizer was split applied from V2 to V8, but early season N deficiency reduced yield for the V12 application. Site‐years with limited precipitation during the late vegetative through grain filling stages of corn had no improvement in grain yield or N use efficiencies for SA because dry soil conditions likely interfered with root development and made N fertilizer positionally unavailable to the crop. This study highlights that the success of SA is largely dictated by soil texture and precipitation.

Sulfur is increasingly reported as deficient in many crops in the Upper Midwest of the United States. The objectives of this study were to determine if hard red spring wheat (HRSW) ( Triticum aestivum L. em thell.) varieties vary in response to S and to determine if plant tissue analysis can predict grain yield. Two studies were established in Minnesota. Study 1 compared two sources of S applied at four rates with and without in‐season S. Study 2 compared the response of six HRSW varieties to three rates of S (0, 8, and 16 kg S ha −1 ). Spring wheat grain yield and protein concentration were not affected by S rate, source, or timing with soil organic matter (SOM) >20 g kg −1 . For locations with SOM <20 g kg −1 , which were all sandy and irrigated, 8 kg S ha −1 maximized grain yield and protein concentration. Flag leaf S concentration varied among varieties separately from S rate applied. Wheat grain yield decreased when flag leaf S concentration was <4.1 g S kg −1 , and grain yield responses were likely with concentrations <2.8 g S kg −1 . There were negative relationships between tissue N/S concentration ratios and grain yield, but critical N/S concentration could not be determined. Application of S for HRSW should be targeted to soils with SOM <20 g kg −1 (0–15 cm). Sulfur rates sufficient to increase yield will result in an optimal protein concentration, and guidelines should not be varied based on the variety grown. Core Ideas Application of 8 kg S ha −1 increases hard red spring wheat yield on sandy soils. Flag leaf tissue S concentration will vary based on hard red spring wheat varieties. Variety variation in flag leaf total S concentration cannot predict variety sulfur requirements. Sulfur application rates should not be changed based on hard red spring wheat variety. Tissue total S concentration is a better predictor of grain yield than the N/S concentration ratio.

Nitrogen provided to crops through mineralization is an important factor in N management guidelines. Understanding of the interactive effects of soil and weather conditions on N mineralization needs to be improved. Relationships between anaerobic potentially mineralizable N (PMNan) and soil and weather conditions were evaluated under the contrasting climates of eight US Midwestern states. Soil was sampled (0–30 cm) for PMNan analysis before pre‐plant N application (PP0N) and at the V5 development stage from the pre‐plant 0 (V50N) and 180 kg N ha−1 (V5180N) rates and incubated for 7, 14, and 28 d. Even distribution of precipitation and warmer temperatures before soil sampling and greater soil organic matter (SOM) increased PMNan. Soil properties, including total C, SOM, and total N, had the strongest relationships with PMNan (R2 ≤ 0.40), followed by temperature (R2 ≤ 0.20) and precipitation (R2 ≤ 0.18) variables. The strength of the relationships between soil properties and PMNan from PP0N, V50N, and V5180N varied by ≤10%. Including soil and weather in the model greatly increased PMNan predictability (R2 ≤ 0.69), demonstrating the interactive effect of soil and weather on N mineralization at different times during the growing season regardless of N fertilization. Delayed soil sampling (V50N) and sampling after fertilization (V5180N) reduced PMNan predictability. However, longer PMNan incubations improved PMNan predictability from both V5 soil samplings closer to the PMNan predictability from PP0N, indicating the potential of PMNan from longer incubations to provide improved estimates of N mineralization when N fertilizer is applied.Core Ideas Relationships between mineralization estimates taken with the PMNan test and soil and weather conditions need to be improved. Soil sample timing and N fertilization minimally affected PMNan predictability by soil and weather parameters. Soil properties predict PMNan better than weather conditions. Soil and weather conditions combined explain up to 69% of the variability of PMNan. Longer PMNan incubations improve the relationship between soil and weather parameters and PMNan after N fertilization.

A Python package, "EONR", was developed for computing the economic optimum nitrogen rate (EONR) and its profile-likelihood confidence intervals (CIs) under economic conditions defined by the user. This work was motivated by the need to improve nitrogen fertilizer recommendations using the maximum return to nitrogen approach, specifically to make it easier for researchers and other practitioners to calculate uncertainty and consider externalities to the cost function while computing the EONR. The "EONR" package fits yield response data to a re-parameterized quadratic-plateau model, which is generally accepted as the most appropriate model for describing yield response to nitrogen in maize (the package also supports the quadratic model). Although grain price and fertilizer cost are typically the only economic factors producers consider for determining the EONR, this package allows the user to also consider variable costs and/or externalities. A general cost function may be desired if the user wishes to consider costs to the farm operation (e.g., equipment, technology, labor, etc.) or environmental costs/penalties that may result from excess fertilizer application (e.g., water treatment or health costs that result from pollution) in addition to the traditional fertilizer to grain price ratio. In addition to the development of the "EONR" Python package, the objectives of this work were to: (i) design an algorithm that utilizes a general cost function for computing the EONR and its profile-likelihood CIs for any crop and (ii) clearly document the methodology and algorithms used. The "EONR" Python package can be downloaded from the Python Package Index (https://pypi.org/), and installation instructions, tutorials, and supplementary background information can be found in the online documentation (https://eonr.readthedocs.io).

In a 6 x 3 x 3 factorial design, the effect of three sulfur fertilization rates (0, 8.4 and 16.8 kg/ha) on the properties of six spring wheat varieties grown in three locations in the US Midwest was evaluated. Dough properties were assessed via the Farinograph and GlutoPeak; contents of free amino acids and sugars in flour were determined by high-performance anion exchange chromatography. Bread volume and crust color were assessed as well. Overall, the main influence on flour, dough and bread properties was exerted by the growing location. However, sulfur fertilization rates significantly affected bread volume and the content of several free amino acids; the main ones being asparagine, glutamine, aspartate, glutamate, and alanine. At a fertilization rate of 0, 8.4 and 16.8 kg/ha, values ranged from 8.39 to 22.42, 7,92-22.563 and 6.67-25.05 mmol/kg, respectively, for asparagine, the precursor to the probable carcinogen acrylamide. GlutoPeak parameters appeared to be unaffected by sulfur fertilizer rate. Specific bread volumes ranged from 2.21 to 4.71 cm(3)/g. Across locations, the specific bread volume tended to be highest when samples had been grown at a sulfur fertilization rate of 8.4 kg/ha. Thus, the asparagine reductions achieved with the highest sulfur fertilization rate partially came at the expense of volume reduction.