Suat Irmak’s research while affiliated with Pennsylvania State University and other places

This research investigated soybean soil water dynamics under different irrigation levels in three different soil types in the same field concurrently. Treatments imposed in each soil type were: (i) variable‐rate irrigation (VRI), (ii) fixed‐rate full irrigation (FRI‐1″ or FRI‐25.4 mm) and (iii) fixed‐rate limited irrigation (FRI‐0.75″ or FRI‐19 mm). In 2018, VRI received 75% less water than FRI‐1″ and received 49% less water than FRI‐0.75″. In 2019, VRI received 100% more irrigation than FRI‐1″ and 41% less than FRI‐0.75″. Soil water dynamics of each treatment in the same soil and between the soils exhibited substantial interannual variations. Soil type had substantial and greater impact on soil moisture dynamics than irrigation treatments. Total available water (TAW), dry spell and antecedent soil moisture were impacted to a greater extent by the spatial soil properties than irrigation treatments. The range of field capacity (FC), permanent wilting point (PWP), TAW, dry spell soil moisture and antecedent soil moisture quantified for each soil type spatially and temporally in the same research field with respect to soil moisture dynamics and impacts on irrigation requirements for different irrigation management strategies provide a beneficial scope of understanding the effects of these spatially variable soil properties on water management. The research also provides substantial evidence in terms of the critical importance of detailed quantification, analyses and understanding of the soil properties that must be considered for successful implementation of VRI technology.

Soybean growth, yield, crop evapotranspiration (ETc) and crop water use efficiency (CWUE or crop water productivity, CWP) under different irrigation levels in three different soil types in the same field were investigated concurrently. Treatments in each soil type were: (i) variable rate irrigation (VRI), (ii) fixed rate full irrigation (FR‐1″) and (iii) fixed rate limited irrigation (FR‐0.75″). There was not enough evidence suggesting the superiority of VRI over FRI‐1″ or FRI‐0.75″ in terms of improving yield or CWUE. Leaf area index (LAI) and plant height were stronger functions of soil types than irrigation treatments. Growing season cumulative grass‐reference evapotranspiration (ETo) and cumulative precipitation were 629 and 489 mm, respectively, in 2018; and 589 and 551 mm, respectively, in 2019. Variations in yield among irrigation treatments for both seasons were not significant ( p > 0.05). Soil type, rather than irrigation treatments, explained variation in yield with statistical significance ( p < 0.05). Soil types had substantial impact on ETc and CWUE. Since spatial variability in soil properties has a profound impact on soybean growth, yield, ETc and CWUE, soil variability in horizontal and vertical domain must be considered for developing accurate management zones and prescriptions for VRI, and for in‐season VRI, FRI and limited irrigation management for successful and effective operations.

Highlights NUE response to N addition is dependent on N source (fertilizer, manure, and biological fixation). Random forest models captured 71% and 47% NUE variance for CONUS and global croplands. Contribution from biological N fixation was most important for explaining NUE variance, followed by manure and fertilizer contributions. ABSTRACT. Nitrogen use efficiency (NUE) is a useful indicator of the tradeoffs among cropland harvest nitrogen (N) and total N fertilization. Total N fertilization can be fulfilled by different sources depending on local availability, livestock production, land use and crop distribution, and economics, all of which change drastically in space and time. While NUE assesses crop harvest N response to total N fertilization, it typically does not distinguish between N fertilization sources, and thus little is known on how varying contributions from diverse N inputs impact NUE achieved in a region and year. Here, we use long-term (1961–2020) N budgets combined with random forest modeling to address this knowledge gap for global croplands, with a finer spatial emphasis on conterminous United States (CONUS) croplands. Random forest models using fractional fertilization contributions (F fert , F manure , and F bnf for synthetic fertilizers, livestock manure, and biological N fixation, respectively) and captured 71% and 47% of space-time variance in NUE for CONUS and global croplands, respectively. F bnf was the most important predictor for explaining variance in county/country-year NUE, followed by F manure , and F fert . Contributions from each of the input sources exerted distinct controls on NUE through its observed ranges and these controls were visualized using partial dependence plots for NUE. The models establish that regions and years where a higher proportion of total N fertilization is met by biological N fixation (relative to fertilizers and manure) have higher NUE. Overall, our findings improve understanding of how NUE may be optimized by managing diverse N sources with the aim of meeting economic and sustainability goals. Keywords: Chemical fertilizers, Livestock, Nitrogen cycle, Nutrient budgets, Nutrients.

Highlights Crop N removal response to N inputs shows diminishing N removal beyond 163.08 kg ha-1. N inputs at which diminishing returns are observed have increased. N inputs at which diminishing returns are observed are specific to crop belts. Proportion of counties that show N inputs exceeding the optimal level has increased. ABSTRACT. The response of nitrogen (N) removal by crops to an increase in fertilization strongly determines the profitability and sustainability of agricultural systems and informs nutrient management decisions at the producer level. These response functions are analyzed for agronomic and economic optima achieved at field scales for evaluating production, economic, and environmental goals. However, such assessments are lacking for entire regional agroecosystems to allow understanding of the response of N removal collectively across all crops grown during the year (N removal ) to total N fertilization (i.e., all manageable N sources, N in ) historically. Here, we address this knowledge gap by leveraging a large-scale N budget and statistical techniques to characterize space-time variability and trends in historical (1987–2016) county-level N removal , N in , and nitrogen use efficiency (NUE) across the conterminous U.S. (CONUS). We intend to evaluate crop belt-specific characteristics of diminished returns in N removal to N in response and change over time. N in , N removal , and NUE were subject to drastic spatial variation in long-term mean values, interannual variability, and long-term change, which were quantified and mapped to understand their spatiotemporal distributions. Pooled across all counties and years, N removal shows diminished returns when N in reached 163 kg ha ⁻¹ (N in, bp ). Upon quantifying and analyzing year-specific diminished returns, we found that N in, bp has increased during 1987–2016, and so has the NUE achieved prior to attaining diminished returns. The proportion of counties (6%–22%) where N in exceeds N in, bp also increased, and counties that repeatedly demonstrated such exceedance during 1987–2016 were identified. Values of N in,bp are specific to crop belts within the U.S., the majority of which also show increased N in, bp over time. Specifically, barley, beans, and sugarbeets (198 kg ha ⁻¹ ), and alfalfa and barley (190 kg ha ⁻¹ ) belts showed notably greater N in,bp relative to the national mean (163 kg ha ⁻¹ ), while N in,bp for corn grain and soy belts was similar to the national mean. Overall, these findings represent a comprehensive assessment of how systems-level N removal across U.S. agriculture has historically responded to change in N in , a prerequisite for guiding mitigation and adaptation policy and efforts. Keywords: Fertilizer, Manure, Nitrogen cycle, Nitrogen use efficiency, Yield.

Volunteer corn ( Zea mays L.) is a competitive weed in corn-based cropping systems. Scientific literature does not exist about the water use of volunteer corn grown in different crops and irrigation systems. The objectives of this study were to characterize the growth and evapotranspiration (ET a ) of volunteer corn in corn, soybean [ Glycine max (L). Merr.], and sorghum [ Sorghum bicolor (L.) Moench] under center-pivot irrigation (CPI) and subsurface drip irrigation (SDI) systems. Field experiments were conducted in south-central Nebraska in 2021 and 2022. Soil moisture sensors were installed at depths of 0 to 0.30, 0.30 to 0.60, and 0.60 to 0.90 m to track soil water balance and quantify seasonal total ET a . Corn was the most competitive, as volunteer corn had the lowest biomass, leaf area, and plant height compared with the fallow. Soybean was the least competitive with volunteer corn, as the plant height, biomass, and leaf area of volunteer corn in soybean were similar to fallow at 15, 30, 45, and 60 d after transplanting (DATr). Averaged across crop treatments, irrigation type did not affect volunteer corn growth at 15 to 45 DATr. Soil water depletion and ET a were similar across crop treatments with and without volunteer corn, as water was not a limiting factor in this study. The ET a of volunteer corn was the highest in soybean (623 mm), followed by sorghum (622 mm), and corn (617 mm) under CPI. The SDI had higher irrigation efficiency, because without affecting crop yield, it had 3%, 6%, and 8% lower ET a in soybean (605 mm), sorghum (585 mm), and corn (571 mm), respectively. Although soil water use did not differ with volunteer corn infestation, a soybean yield loss of 27% was observed, which suggests that volunteer corn may not compete for moisture under fully irrigated conditions; however, it can impact the crop yield potential due to competition for factors other than soil moisture.

In South Korea, performance of irrigation systems can be improved through hardware changes, such as canal linings and the installation of control structures, as well as through operational improvements, such as proper and timely operation, and improved communication between water supply agencies and water users. Improving irrigation water delivery performance through canal networks is one of the most economically essential options in meeting growing water demands and sustaining the productivity of irrigated agriculture. In this study, for the purpose of evaluating the efficient use of water resources in agricultural productions and operations, we analyzed the distribution of amount of water for each irrigated area and irrigation efficiency using a hydraulic-hydrological model, EPA-SWMM (United States Environmental Protection Agency Storm Water Management Model). In addition, we assessed agricultural water supply and water supply vulnerability using irrigation efficiency indicators. As a result of the agricultural water distribution simulation, the canals located in the upstream showed a high irrigation efficiency of more than 60%, and the canals located in the downstream showed a low irrigation efficiency of less than 50%. Based on the results, the critical areas can be successfully identified where water is scarce in the irrigation area and monitoring the spatio-temporal agricultural water distribution can be more effectively realized.

Sunflower ( Helianthus annuus L.) is moderately tolerant to salt and water stress, but its production can still be significantly and adversely affected by increases in these stressors as a result of the negative impacts of climate change on agricultural soil and crop productivity. The morphological and productivity (dry head weight, dry root weight, dry shoot weight, head diameter, whole seed weight, crude protein content, crude oil content, palmitic acid, stearic acid, oleic acid, linoleic acid, eicosanoic acid, 11‐eicosenoic acid, homo‐gamma‐linolenic w6 acid, lignoceric acid and plant height) responses of modern sunflower germplasms to different levels of salt and drought stress under greenhouse and field conditions were investigated and analysed. Six germplasms were evaluated under three salt concentrations (0, 150 and 250 mM), and two germplasms were evaluated for drought response under three irrigation levels. Significant differences in the response of sunflower germplasms to water and salinity were detected. The same germplasms exhibited significant differences in response to water and salinity between the treatments, which also varied significantly between the germplasms for the same treatment. The irrigation level significantly influenced the amount of oil but not the crude protein or fatty acid composition. The results and information of this research can aid in selecting and improving sunflower productivity under adverse (i.e. saline and drought) conditions.