Daniel W. Sweeney

Phosphorus, potassium, chloride, and fungicide effects on wheat yield and leaf rust severity

Abstract Plant nutrition and disease suppression are among the most important management tools for producers of hard red winter wheat (Triticum aestivum L.) in the central and southern Great Plains. This study was conducted to examine the effects of phosphorus (P) (0, 15, and 30 kg ha−1) and potassium (K) (0, 37, and 74 kg ha−1) fertilization, foliar fungicide application, and cultivar disease tolerance on wheat yield, yield components, and severity of leaf rust (Puccinia triticina Eriks.). Compared with no P, fertilizing with P increased yield by as much as 60% (>1.3 Mg ha−1 increase). Yield of cultivars susceptible to leaf rust was nearly 0.6 Mg ha−1 less without K than with K fertilization. Fungicide application resulted in mean yields of 4.8 Mg ha−1 for both resistant and susceptible cultivars, however, yield of susceptible cultivars was suppressed more than yield of resistant ones without fungicide. Although P fertilization had a moderately suppressive effect on leaf rust, the increased yield was primarily due to production of about 50% more heads m−2 apparently from more prolific tillering. Similarly, K fertilization appeared to reduce leaf rust severity and improve yield by increasing kernel weight, but this response may have been related partially to chloride (Cl) in the KCl fertilizer. Correlations suggested that improving dry matter production and N, P, and K uptakes at the boot stage by P and K fertilization can reduce leaf rust severity later in the growing season and increase wheat grain yield. These results indicate that especially P fertilization, but also K fertilization and fungicide application, are important management tools for reducing disease and increasing winter wheat yield.

Yield, nutrient, and soil sulfur response to ammonium sulfate fertilization of soybean cultivars

Abstract With the reduction of sulfur levels in high‐analysis nitrogen (N) and phosphorus (P) fertilizers and in atmospheric deposition, sulfur (S) fertilization may become more important, especially with intensive cropping systems. When high clay content is likely to limit root development into the subsoil, low extractable sulfate‐sulfur (SO4‐S) levels in the topsoil may suggest possible plant response to S fertilization. Even though ammonium sulfate [(NH4)2SO4] is widely used and readily available for plant uptake, field data are limited on the use of (NH4)2SO4 as an S source for soybeans [Glycine max (L.) Merr.]. A study was initiated to determine the effect of S fertilization as (NH4)2SO4 on: (i) the yield, seed weight, grain quality, and leaf and whole‐plant nutrient concentrations of four soybean cultivars grown on soils with high clay content subsoils; and (ii) selected soil chemical characteristics. Sulfur rates were 0, 28, 56, and 84 kg/ha, and soybean cultivars were two Maturity Group IV beans, ...

Response of tall fescue to fertilizer placement at different levels of phosphorus, potassium, and soil pH 1

Abstract Fertilizer application, particularly nitrogen (N), is important in cool‐season grass forage production. Subsurface (knife) placement of N often has resulted in higher forage yield and N uptake of tall fescue (Festuca arundinacea Schreb.) compared to surface‐broadcast fertilization, but further studies were needed to indicate whether soil pH, phosphorus (P), or potassium (K) modifies the response. Experiment I tested responses of forage yield and N and P concentration to N, P, and K amount and placement. Two types of fertilizer placement ‐ broadcast and knife ‐ were used with 13, 112, or 168 kg N; 0 or 19 kg P; and 0 or 37 kg K/ha in a factorial arrangement. Yields increased by 53% as N fertilization went from 13 to 112 kg/ha and by 69% as N increased from 13 to 168 kg N/ha. Forage yield was increased 26% from knife compared to broadcast fertilizer placement. P application increased forage production by 13%, but K application had no effect on yield. Forage N concentrations increased by 25% as N fe...

Calibration of the APEX Model to Simulate Management Practice Effects on Runoff, Sediment, and Phosphorus Loss

Process-based computer models have been proposed as a tool to generate data for Phosphorus (P) Index assessment and development. Although models are commonly used to simulate P loss from agriculture using managements that are different from the calibration data, this use of models has not been fully tested. The objective of this study is to determine if the Agricultural Policy Environmental eXtender (APEX) model can accurately simulate runoff, sediment, total P, and dissolved P loss from 0.4 to 1.5 ha of agricultural fields with managements that are different from the calibration data. The APEX model was calibrated with field-scale data from eight different managements at two locations (management-specific models). The calibrated models were then validated, either with the same management used for calibration or with different managements. Location models were also developed by calibrating APEX with data from all managements. The management-specific models resulted in satisfactory performance when used to simulate runoff, total P, and dissolved P within their respective systems, with > 0.50, Nash-Sutcliffe efficiency > 0.30, and percent bias within ±35% for runoff and ±70% for total and dissolved P. When applied outside the calibration management, the management-specific models only met the minimum performance criteria in one-third of the tests. The location models had better model performance when applied across all managements compared with management-specific models. Our results suggest that models only be applied within the managements used for calibration and that data be included from multiple management systems for calibration when using models to assess management effects on P loss or evaluate P Indices.

Electronically‐controlled, portable, cone penetrometer

Abstract An electronically‐controlled, portable, cone penetrometer was designed, built, and tested. The penetrometer was driven electrically through a linear actuator. Cone position was sensed by a 10‐turn potentiometer, and force was sensed with an electronic load cell. A laptop computer controlled the linear actuator and recorded signals from the sensors through a data logger equipped with a serial interface. The penetrometer was capable of driving the cone at 0.84 cms‐1 (±5%) over a load range of 0 to 180 kg. The system allowed force and position excursion limits to be set through software and provided data sets at 1‐cm increments to depths of 45 cm and forces to 2,000 N. The penetrometer demonstrated good repeatability among closely spaced probings when force per unit cone area was plotted against depth.

Multisite Evaluation of APEX for Water Quality: II. Regional Parameterization

Phosphorus (P) Index assessment requires independent estimates of long-term average annual P loss from fields, representing multiple climatic scenarios, management practices, and landscape positions. Because currently available measured data are insufficient to evaluate P Index performance, calibrated and validated process-based models have been proposed as tools to generate the required data. The objectives of this research were to develop a regional parameterization for the Agricultural Policy Environmental eXtender (APEX) model to estimate edge-of-field runoff, sediment, and P losses in restricted-layer soils of Missouri and Kansas and to assess the performance of this parameterization using monitoring data from multiple sites in this region. Five site-specific calibrated models (SSCM) from within the region were used to develop a regionally calibrated model (RCM), which was further calibrated and validated with measured data. Performance of the RCM was similar to that of the SSCMs for runoff simulation and had Nash-Sutcliffe efficiency (NSE) > 0.72 and absolute percent bias (|PBIAS|) < 18% for both calibration and validation. The RCM could not simulate sediment loss (NSE < 0, |PBIAS| > 90%) and was particularly ineffective at simulating sediment loss from locations with small sediment loads. The RCM had acceptable performance for simulation of total P loss (NSE > 0.74, |PBIAS| < 30%) but underperformed the SSCMs. Total P-loss estimates should be used with caution due to poor simulation of sediment loss. Although we did not attain our goal of a robust regional parameterization of APEX for estimating sediment and total P losses, runoff estimates with the RCM were acceptable for P Index evaluation.

Application of distillery waste anaerobic digester effluent to St. Augustinegrass

Abstract Effluent that results from methane anaerobic digestion needs to be disposed of or utilized. The objective of this glasshouse study was to examine the effect of rum distillery anaerobic digester effluent application rate on St. Augustinegrass (Stenotaphum secundatum Kuntze) growth and elemental uptake to determine the feasibility of land application. The initial application rates were 0, 0.22, 0.44, and 0.88 cm of the liquid effluent per week, equivalent to 0, 22, 44, and 88 g total solids (TS) per pot, respectively, for the first 4 months of the study. Because of apparent plant stress, effluent application was eliminated for the high application rate during the final 4 months of the experiment. Therefore, at the end of 8 months, effluent application totals were 0, 44, 88, and 88 g TS per pot, respectively for the four treatments. Since both of the two higher rate treatments received a total of 88 g TS per pot, treatments were designated as 0-[8mo], 44-[8mo], 88-[8mo], and 88-[4mo] to denote the time frame in which the total amount of effluent was applied. During the initial 4 months, St. Augustinegrass dry matter yield was more than 60% higher with the two lower application rates, 44-[8mo] and 88-[8mo], as compared with the higher 88-[4mo] application rate or the 0-[8mo] effluent control. By the end of the initial 4-month period, the high 88-[4mo] treatment had resulted in plant chlorosis and drying tissue and thus slightly lower cumulative dry matter yield than obtained with the control. During the second 4-month period, dry matter yield was similar for the 88-[8mo] and 88-[4mo] rates, but both were approximately one-half that obtained with the 44-[8mo] application rate. In general, uptake of measured elements increased with increased dry matter production. However, relative differences in K, Al, and Mn uptake appeared larger than observed with yield differences. As expected, soil concentrations of most elements measured were increased with effluent applications, especially K and Na. The addition of effluent, regardless of rate, raised soil pH from 6.5 to approximately 9, owing to increases in soil K, Na, Mg, and Ca levels. The data from this study suggest that the lowest effluent application rate, 44-[8mo] (equivalent to 0.22 cm week−1) may result in acceptable St. Augustinegrass growth. However, the apparent elemental buildup in the soil and the potential adverse effects on groundwater quality suggest that even lower rates may be necessary for longer-term continuous disposal of the distillery waste anaerobic digester effluent.

Legume and tillage effects on prairie soil nitrogen and penetration resistance

Abstract Legumes provide benefit in crop rotations, but data are limited on soil inorganic nitrogen (N) and soil strength responses to spring‐ or fall‐seeded legumes as green manures for grain sorghum [Sorghum bicolor (L.) Moench] production on the prairie soils of the eastern Great Plains of the United States. With increased emphasis on conservation tillage, information is also needed on combining conservation tillage with the use of legume cover crops. This experiment was established to examine the effects of i) red clover (Trifolium pratense L.) and hairy vetch (Vicia villosa Roth.) as previous crops to grain sorghum compared with continuous grain sorghum, ii) reduced or no‐tillage, and iii) fertilizer N rate on changes in soil inorganic N and soil strength. At two adjacent sites (Parsons silt loam; fine, mixed thermic Mollic Albaqualf) differing in initial pH and phosphorus (P) and potassium (K) fertility, soil nitrate‐nitrogen (NO3‐N) was as much as fourfold higher following kill‐down of red clover o...

Multisite Evaluation of APEX for Water Quality: I. Best Professional Judgment Parameterization

The Agricultural Policy Environmental eXtender (APEX) model is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of management practices. The current practice is to fully calibrate the model for each site simulation, a task that requires resources and data not always available. The objective of this study was to compare model performance for flow, sediment, and phosphorus transport under two parameterization schemes: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site-specific soil, weather, event flow, and water quality data. The analysis was conducted using 12 datasets at four locations representing poorly drained soils and row-crop production under different tillage systems. Model performance was based on the Nash-Sutcliffe efficiency (NSE), the coefficient of determination () and the regression slope between simulated and measured annualized loads across all site years. Although the BPJ model performance for flow was acceptable (NSE = 0.7) at the annual time step, calibration improved it (NSE = 0.9). Acceptable simulation of sediment and total phosphorus transport (NSE = 0.5 and 0.9, respectively) was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, uncalibrated use of APEX for planning or management purposes may be misleading. Model calibration with water quality data prior to using APEX for simulating sediment and total phosphorus loss is essential.

NITROGEN, PHOSPHORUS, AND POTASSIUM EFFECTS ON GRAIN SORGHUM PRODUCTION AND STALK ROT FOLLOWING ALFALFA AND BIRDSFOOT TREFOIL

Grain sorghum [Sorghum bicolor (L.)], grown on the often infertile claypan soils of the eastern Great Plains, requires attention to soil fertility. Experimental objectives were to determine the effects of phosphorus (P) and potassium (K) fertility levels, N application, and legume residual on grain sorghum production and stalk rot. Following alfalfa and birdsfoot trefoil, first-year sorghum yield was 7 Mg ha−1 and not affected by N fertilizer. In subsequent years, yield increases due to N were less than 20%. Sorghum yield increased at low P and K rates, especially with nitrogen (N) fertilization and was greater following birdsfoot trefoil than following alfalfa. In 1995 when fertilized with N, lodging and stalk rot severity were increased by P and reduced by K. In 1996, stalk rot severity was reduced by K fertilization. Grain sorghum, grown after legume crops, required minimal levels of P and K, especially when N fertilizer was added.