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Smart irrigation is one application of digital agriculture that can be used to achieve improved crop yields while saving water and energy. Many variations of smart irrigation can be applied, but there is no consensus among the scientific community as to which method is the best practice. The objective of this research was to evaluate two smart irrigation methods: a soil moisture–based method using sensors and an evapotranspiration- (ET-) based technique. The selected crop was sweet corn. Growth variables (biomass, yield, harvest index, and water productivity) were compared for each of the two methods. Three irrigation regimes were applied for each method: 60%, 90%, and 120% of crop evapotranspiration (ETc) for the ET-based method, and 25%, 30%, and 35% of the total soil moisture for the soil moisture–based method. Corn sap flow was measured in response to the three treatments in the soil moisture–based experiment to measure transpiration. The results showed that the ET-based method is easier to implement with less infrastructure, and it can result in similar yields compared to the soil moisture–based method. Although the fresh yield was 16% higher using the soil moisture–based method, grain yield can be sustained with the ET-based method using 8% less water. Selection of an appropriate irrigation scheduling method should be based on marketable yield: keeping the soil water content near field capacity will result in a higher fresh yield but will not translate into more dry matter. If grain yield is the target, the ET-based method is less expensive and more farmer friendly, but care should be taken to properly estimate irrigation losses to avoid underirrigation. An evaporative stress index (determined using sap flow measurements) of 70% will cause a 22% reduction in fresh sweet corn yield but only a 7% reduction in grain yield. Transpiration peaked when the soil moisture was above 85% of the available water (i.e., at 38% in the calcareous clay soil of the experiment). [ABSTRACT FROM AUTHOR]

The curve number (CN) method is the most widely used method to estimate the depth of runoff resulting from a given depth of rainfall. However, there are still doubts about the effect of rainfall characteristics and soil moisture conditions on the method's parameters (CN, and the standard initial abstraction ratio, λ). In this study, design rainfall distributions were used along with Hortonian infiltration characteristics to calculate CN and λ values for a highly clayey soil (>80%). Prerainfall infiltration conditions were characterized by the measured initial soil moisture content, and Hortonian infiltration model was obtained from experimental infiltration test measurements. The main results show that there is no influence of initial infiltration rates on CN values, and rainfall duration generates substantial influence on CN. The CN is inversely related to rainfall depth, and λ is dependent on the initial soil moisture. Further, neither tabulated CN nor standard λ corresponds to the simulated values obtained in this case. Therefore, these findings suggest that the method's parameters should be specifically adapted to local hydrological conditions. [ABSTRACT FROM AUTHOR]

Assesses the potential of the reduced-runoff surface irrigation method for clay soils to limit tailwater runoff and evaluates its impact on crop production and soil salinity throughout an alfalfa hay production cycle in Imperial Valley, California. Background on water conservation efforts in the area; Information on related studies; Research methodology; Results and discussion; Summary and conclusions.

Determines the effect of clay crack flow on tail water quality and crack flow's contribution to salt leaching conducted on farm fields in Brawley, California. Soil sampling; Experiments conducted on each soils; Sampling of surface water.

Although widely used for field measurements of soil moisture, problems continue with the use of the neutron probe in clay soils comprised of over 40% clay fractions, and in the determination of the intensity of field sampling necessary to characterize a site. We examine issues associated with field practice and calibration, data analysis and estimation of variance, and error in soil moisture measurements for silty clay soils in the Imperial Valley, California, using large calibration data sets from several different layouts of neutron access tubes. Our analysis indicates that for field calibrations: (1) bulk density corrections of the count ratio data do not necessarily improve the standard errors of the water content measurements; (2) soil sampling for calibration within the access tube hole at the time of tube installation results in smaller measurement errors; (3) calibrations improve as the average soil moisture of the profile at the time of the original sampling decreases; and (4) field-wide calibrations improve, and the sampling intensity required to characterize soil moisture content decreases with an increasing soil depth. We also address aspects of the neutron probe use associated with soil salinity and polyvinyl chloride (PVC) access tubing (chloride interference), inclusion of shallow sampling data in calibrations, and instrument, calibration, and spatially related standard variances affecting field measurements. [ABSTRACT FROM AUTHOR]

The aim of this study was to calibrate the Diviner 2000 capacitance probe in the field and in the laboratory. Field calibration was carried out on an agro-forestry farm with soil of colluvial origin with two textural horizons, clay loam overlying clay. The same soil was used for laboratory calibration at the Universidad de Chile. Prior to calibration, the Diviner 2000 probe was normalized to obtain the scaled, or standardized, frequency (SF). For each method of calibration, three sets of soil moisture conditions were generated: dry, moist and saturated, with two replicates per set. The soil was evaluated with the probe at two depths per horizon, and the volumetric water content () was immediately determined gravimetrically in situ at each depth. To calibrate the probe, the values for the samples were compared with the SF values recorded by the probe and the coefficient of determination was determined through regression analysis. A nonlinear correlation was found between the SF measured by the probe and the values obtained through gravimetry for each horizon and method of calibration, with adjustment to a potential function with a high coefficient of determination (field: ; laboratory: ). The manufacturer's calibration equation proved to be quite precise in laboratory conditions, but in field conditions it underestimated the water content of both clay loam and clay soil. [ABSTRACT FROM AUTHOR]