Development and Application of a Performance and Operational Feasibility Guide to Facilitate Adoption of Soil Moisture Sensors

Soil moisture sensors can be effective and promising decision-making tools for diverse applications and audiences, including agricultural managers, irrigation practitioners, and researchers. Nevertheless, there exists immense adoption potential in the United States, with only 1.2 in 10 farms nationally using soil moisture sensors to decide when to irrigate. This number is much lower in the global scale. Increased adoption is likely hindered by lack of scientific support in need assessment, selection, suitability and use of these sensors. Here, through extensive field research, we address the operational feasibility of soil moisture sensors, an aspect which has been overlooked in the past, and integrate it with their performance accuracy, in order to develop a quantitative framework to guide users in the selection of best-suited sensors for varying applications. These evaluations were conducted for nine commercially available sensors under silt loam and loamy sand soils in irrigated cropland and rainfed grassland for two different installation orientations [sensing component parallel (horizontal) and perpendicular (vertical) to the ground surface] typically used. All the sensors were assessed for their aptness in terms of cost, ease of operation, convenience of telemetry, and performance accuracy. Best sensors under each soil condition, sensor orientation, and user applications (research versus agricultural production) were identified. The step-by-step guide presented here will serve as an unprecedented and holistic adoption-assisting resource and can be extended to other sensors as well

Modeling of reaction-diffusion transport into a core-shell geometry

Fickian diffusion into a core-shell geometry is modeled. The interior core mimics pancreatic Langerhan islets and the exterior shell acts as inert protection. The consumption of oxygen diffusing into the cells is approximated using Michaelis-Menten kinetics. The problem is transformed to dimensionless units and solved numerically. Two regimes are identified, one that is diffusion limited and the other consumption limited. A regression is fit that describes the concentration at the center of the cells as a function of the relevant physical parameters. It is determined that, in a cell culture environment, the cells will remain viable as long as the islet has a radius of around $142 \mu m$ or less and the encapsulating shell has a radius of less than approximately $283 \mu m$. When the islet is on the order of $100 \mu m$ it is possible for the cells to remain viable in environments with as little as $4.6\times10^{-2} mol/m^{-3}$ $O_2$. These results indicate such an encapsulation scheme may be used to prepare artificial pancreas to treat diabetes

Long-Term Patterns of Air Temperatures, Daily Temperature Range, Precipitation, Grass-Reference Evapotranspiration and Aridity Index in the Usa Great Plains: Part I. Spatial Trends

Due to their substantial spatio-temporal behavior, long-term quantification and analyses of important hydrological variables are essential for practical applications in water resources planning, evaluating the water use of agricultural crop production and quantifying crop evapotranspiration patterns and irrigation management vs. hydrologic balance relationships. Observed data at over 800 sites across the Great Plains of USA, comprising of 9 states and 2,307,410 km2 of surface area, which is about 30% of the terrestrial area of the USA, were used to quantify and map large-scale and long-term (1968-2013) spatial trends of air temperatures, daily temperature range (DTR), precipitation, grass-reference evapotranspiration (ETo) and aridity index (AI) at monthly, growing season and annual time steps. Air temperatures had a strong north to south increasing trend, with annual average varying from –1 to 24°C, and growing season average temperature varying from 8 to 30°C. DTR gradually decreased from western to eastern parts of the region, with a regional annual and growing season averages of 14.25°C and 14.79°C, respectively. Precipitation had a gradual shift towards higher magnitudes from west to east, with the average annual and growing season (May-September) precipitation ranging from 163 to 1,486 mm and from 98 to 746 mm, respectively. ETo had a southwest-northeast increasing trend, with regional annual and growing season averages of 1,297 mm and 823 mm, respectively. AI increased from west to east, indicating higher humidity (less arid) towards the east, with regional annual and growing season averages of 0.49 and 0.44, respectively. The spatial datasets and maps for these important climate variables can serve as valuable background for climate change and hydrologic studies in the Great Plains region. Through identification of priority areas from the developed maps, efforts of the concerned personnel and agencies and resources can be diverted towards development of holistic strategies to address water supply and demand challenges under changing climate. These strategies can consist of, but not limited to, advancing water, crop and soil management, and genetic improvements and their relationships with the climatic variables on large scales

Use of time domain reflectometry for continuous monitoring of nitrate-nitrogen in soil and water

Nitrate-Nitrogen (NO3-N) losses to ground and surface water are an environmental and agronomic concern in modern crop production systems in the Central Great Plains. Monitoring techniques for nitrogen use in agricultural production are needed to increase crop yield, optimize nitrogen use, and reduce NO3-N leaching. Time domain reflectometry (TDR) could potentially be calibrated to continuously measure NO3-N in soil and water. The objectives of this study were to: (1) evaluate the effect of different factors affecting the response of the bulk electrical conductivity (ECb) sensed by TDR, (2) compare the sensitivity and differences between vertically-installed and horizontally-installed probes for measuring NO3-N leaching in the soil profile, and (3) evaluate the feasibility of using TDR to measure changes in NO3-N concentration in an irrigated agricultural soil. Studies were conducted in the laboratory and in the field at the University of Nebraska West Central Research and Extension Center in North Platte, Nebraska. Temperature of the medium (Ts), solute concentration, TDR cable length, and volumetric soil water content (0v) all influenced and were linearly related to the bulk electrical conductivity (ECb) sensed by the TDR probes. In the field, measured soil NO3-N correlated well with values estimated using TDR measurements of ECb, corrected for changes in 0v and Ts. These results indicated that TDR, if properly calibrated for a particular soil, could be used to continuously monitor NO3-N in soil, and should also be well-suited for monitoring NO3-N in groundwater and surface water. It is, however, important to perform the calibration over a long enough period of time to include the expected range of 0v, Ts, and NO3-N values to obtain adequate accuracy

Maize response to coupled irrigation and nitrogen fertilization under center pivot, subsurface drip and surface (furrow) irrigation: Growth, development and productivity

Water availability and water quality problems negatively impact agricultural productivity due to improper nitrogen (N) and irrigation management, which can also negatively affect environmental services. Coupled irrigation and N management practices must be developed and practiced for alleviating these challenges. Investigating crop growth and development and yield response to coupled irrigation and N management under different irrigation methods can aid in developing optimum agronomic management practices to enhance crop production efficiency. Field experiments were conducted in 2016 and 2017 growing seasons to measure and compare maize (Zea mays L.) grain yield, leaf area index (LAI), plant height (and their relationships), and stem diameter under different N application timing treatments and traditional N application under different irrigation methods [center pivot (CP), subsurface drip irrigation (SDI), and furrow irrigation (FI)]. The irrigation levels were full irrigation treatment (FIT or 100%), 80% of FIT, 60% of FIT, and rainfed conditions (RFT) coupled with fertigation application timing treatments. The N treatments were: (i) traditional (TN) with spring pre-plant application, (ii) non-traditional-1 (NT-1) with three pre-season and in-season N applications, and (iii) nontraditional-2 (NT-2) with four pre- and in-season N applications. Grain yield, LAI, and plant height were significantly (p \u3c 0.05) altered by increasing irrigation levels for the traditional N and non-traditional N treatments for the given irrigation method as well between the irrigation methods for the same treatment. The irrigation method had a substantial influence on LAI, and both CP and SDI had 24% higher averaged LAI than FI across traditional N treatments. The highest grain yields were observed under NT-1 and NT-2 at FIT across the irrigation methods. The highest grain yields of 17.3, 16.8 and 15.2 Mg ha-1 were observed in 100% NT-1-CP, 100%-NT-1-SDI, and 100% T-FI in the 2016 growing season, respectively; and 17.8, 16.7 and 14 Mg ha-1 were observed in 100% NT-1-CP, 100%-NT-2-SDI, and 100% T-FI in the 2017 growing season, respectively. The traditional N treatment showed significantly (p \u3c 0.05) higher yield under CP than FI (8.1% and 25.5% higher under CP in 2016 and 2017, respectively). SDI had 8.1% and 23% higher yield than FI in 2016 and 2017 seasons, respectively. NT-1 and NT-2 treatments had significantly higher (p \u3c 0.05) grain yields than traditional N treatment under CP and SDI; and NT-1 and NT-2 yields were significantly higher (p \u3c 0.05) under CP than SDI. There was no significant difference (p \u3e 0.05) in yield between NT-1 and NT-2. However, the TN-1 yielded 4.3% higher under CP than in SDI method. NT-1 can be an effective N management practice coupled with 80% of FIT irrigation level under CP and SDI. Results and analyses presented here can provide guidance to growers and their advisors to assess maize productivity under different irrigation and N management strategies under different irrigation methods in the soil, climatic and management practices similar to those presented in this research

TIME-DOMAIN AND FREQUENCY-DOMAIN REFLECTOMETRY TYPE SOIL MOISTURE SENSOR PERFORMANCE AND SOIL TEMPERATURE EFFECTS IN FINE- AND COARSE-TEXTURED SOILS

The performances of six time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR) type soil moisture sensors were investigated for measuring volumetric soil-water content (θv) in two different soil types. Soil-specific calibration equations were developed for each sensor using calibrated neutron probe-measured θv. Sensors were also investigated for their performance response in measuring θv to changes in soil temperature. The performance of all sensors was significantly different (P\u3c0.05) than the neutron probe-measured θv, with the same sensor also exhibiting variation between soils. In the silt loam soil, the 5TE sensor had the lowest root mean squared error (RMSE) of 0.041 m3/m3, indicating the best performance among all sensors investigated. The performance ranking of the other sensors from high performance to low was: TDR300 (High Clay Mode), CS616 (H) and 10HS, SM150, TDR300 (Standard Mode), and CS616 (V) (H: horizontal installation and V: vertical installation). In the loamy sand, the CS616 (H) performed best with an RMSE of 0.014 m3/m3 and the performance ranking of other sensors was: 5TE, CS616 (V), TDR300 (S), SM150, and 10HS. When θv was near or above field capacity, the performance error of most sensors increased. Most sensors exhibited a linear response to increase in soil temperature. Most sensors exhibited substantial sensitivity to changes in soil temperature and the θv response of the same sensor to high vs. normal soil temperatures differed significantly between the soils. All sensors underestimated θv in high temperature range in both soils. The ranking order of the magnitude of change in θv in response to 1°C increase in soil temperature (from the lowest to the greatest impact of soil temperature on sensor performance) in silt loam soil was: SM150, 5TE, TDR300 (S), 10HS, CS620, CS616 (H), and CS616 (V). The ranking order from lower to higher sensitivity to soil temperature changes in loamy sand was: 10HS, CS616 (H), 5TE, CS616 (V), SM150, and TDR300 (S). When the data from all sensors and soils are pooled, the overall average of change in θv for a 1°C increase in soil temperature was 0.21 m3/m3 in silt loam soil and -0.052 m3/m3 in loamy sand. When all TDR- and FDR-type sensors were pooled separately for both soils, the average change in θv for a 1°C increase in soil temperature for the TDR- and FDR-type sensors was 0.1918 and -0.0273 m3/m3, respectively, indicating that overall TDR-type sensors are more sensitive to soil temperature changes than FDR-type sensors when measuring θv

Standardized ASCE Penman-Monteith: Impact of sum-of-hourly vs. 24-hour timestep computations at reference weather station sites

ABSTRACT. The standardized ASCE Penman-Monteith (ASCE-PM) model was used to estimate grass-reference evapotran-spiration (ETo) over a range of climates at seven locations based on hourly and 24 h weather data. Hourly ETo computations were summed over 24 h periods and reported as sum-of-hourly (SOH). The SOH ASCE-PM ETo values (ETo,h,ASCE) were compared with the 24 h timestep ASCE-PM ETo values (ETo,d) and SOH ETo values using the FAO Paper 56 Penman-Monteith (FAO56-PM) method (ETo,h,FAO). The ETo,h,ASCE values were used as the basis for comparison. The ETo,d estimated higher than ETo,h,ASCE at all locations except one, and agreement between the computational timesteps was best in humid regions. The greatest differences between ETo,d and ETo,h,ASCE were in locations where strong, dry, hot winds cause advective increases in ETo. Three locations showed considerable signs of advection. Some of the differences between the timesteps was attributed to uncertainties in predicting soil heat flux and to the difficulty of ETo,d to effectively account for abrupt diurnal changes in wind speed, air temperature, and vapor pressure deficit. The ETo,h,FAO values correlated well with ETo,h,ASCE values (r2> 0.997), but estimated lower than ETo,h,ASCE at all locations by 5 % to 8%. This was due to the impact of higher surface resistance during daytime periods. Summing the ETo values over a weekly, monthly, or annual basis generally reduced the differences between ETo,d and ETo,h,ASCE. Summing the ETo,d values over multiple days and longer periods for peak ETo months resulted in inconsistent differences between the two timesteps. The results suggest a potential improvement in accuracy when using the standardized ASCE-PM procedure applied hourly rather than daily. The hourly application helps to account for abrupt changes in atmospheric conditions on ETo estimation in advective and other environments when hourly climate data are available

Variability Analyses of Alfalfa-Reference to Grass-Reference Evapotranspiration Ratios in Growing and Dormant Seasons

Alfalfa-reference evapotranspiration (ETr) values sometimes need to be converted to grass-reference ET (ETo), or vice versa, to enable crop coefficients developed for one reference surface to be used with the other. However, guidelines to make these conversions are lacking. The objectives of this study were to: (1) develop ETr to ETo ratios (Kr values) for different climatic regions for the growing season and nongrowing (dormant) seasons; and (2) determine the seasonal behavior of Kr values between the locations and in the same location for different seasons. Monthly average Kr values from daily values were developed for Bushland, (Tex.), Clay Center, (Neb.), Davis, (Calif.), Gainesville, (Fla.), Phoenix (Ariz.), and Rockport, (Mo.) for the calendar year and for the growing season (May– September). ETr and ETo values that were used to determine Kr values were calculated by several methods. Methods included the standardized American Society of Civil Engineers Penman–Monteith (ASCE-PM), Food and Agriculture Organization Paper 56 (FAO56) equation (68), 1972 and 1982 Kimberly-Penman, 1963 Jensen-Haise, and the High Plains Regional Climate Center (HPRCC) Penman. The Kr values determined by the same and different methods exhibited substantial variations among locations. For example, the Kr values developed with the ASCE-PM method in July were 1.38, 1.27, 1.32, 1.11, 1.28, and 1.19, for Bushland, Clay Center, Davis, Gainesville, Phoenix, and Rockport, respectively. The variability in the Kr values among locations justifies the need for developing local Kr values because the values did not appear to be transferable among locations. In general, variations in Kr values were less for the growing season than for the calendar year. Average standard deviation between years was maximum 0.13 for the calendar year and maximum 0.10 for the growing season. The ASCE-PM Kr values had less variability among locations than those obtained with other methods. The FAO56 procedure Kr values had higher variability among locations, especially for areas with low relative humidity and high wind speed. The 1972 Kim-Pen method resulted in the closest Kr values compared with the ASCE-PM method at all locations. Some of the methods, including the ASCE-PM, produced potentially unrealistically high Kr values (e.g., 1.78, 1.80) during the nongrowing season, which could be due to instabilities and uncertainties that exist when estimating ETr and ETo in dormant season since the hypothetical reference conditions are usually not met during this period in most locations. Because simultaneous and direct measurements of the ETr and ETo values rarely exist, it appears that the approach of ETr to ETo ratios calculated with the ASCE-PM method is currently the best approach available to derive Kr values for locations where these measurements are not available. The Kr values developed in this study can be useful for making conversions from ETr to ETo, or vice versa, to enable using crop coefficients developed for one reference surface with the other to determine actual crop water use for locations, with similar climatic characteristics of this study, when locally measured Kr values are not available

Yield response of corn to deficit irrigation in a semiarid climate

Irrigation water supplies are decreasing in many areas of the US Great Plains, which is requiring many farmers to consider deficit-irrigating corn (Zea mays L.) or growing crops like winter wheat (Triticum aestivum L.) that require less water, but that are less profitable. The objectives of this study were to: (1) quantify the yield response of corn to deficit irrigation, and (2) determine which of several seasonal water variables correlated best to corn yield in a semiarid climate. Eight (T1-T8) and nine (T1-T9) deficit-irrigated treatments (including dryland), were compared in 2003 and 2004 in North Platte, Nebraska. The actual seasonal crop evapotranspiration (ETd) (calculated with procedures in FAO-56) for the different treatments was 37-79% in 2003 and 63-91% in 2004 compared with the seasonal crop evapotranspiration when water is not limited (ETw). Quantitative relationships between grain yield and several seasonal water variables were developed. Water variables included, irrigation (I), total water (W ) rain + irrigation (WR+1), evaporation (E), crop evapotranspiration (ETd) ; crop transpiration (Td), and the ratios of ETd and Td to evapotranspiration and transpiration when water is not limited (ETw and Tw). Both years, yield increased linearly with seasonal irrigation, but the relationship varied from year to year. Combining data from both years, ETd had the best correlation to grain yield (yield = 0.028ETd-5.04; R2 = 0.95), and the water variables could be ranked from higher to lower R 2 when related to grain yield as: ET d(R2=0.95) > Td(R2=0.93) > ETd/ETw(R2=0.90) = Td/Tw(R2=0.90) > Wall(R2=0.89) > E(R2 =0.75) > WR+I(R2=0.65) > I(R2=0.06). Crop water productivity (CWP) (yield per unit ETd) linearly increased with ETd/ETW (R2 = 0.75), which suggests that trying to increase CWP by deficit-irrigating corn is not a good strategy under the conditions of this study