Abstract Lettuce ( Lactuca sativa L.) is a high-value crop for irrigation districts in the low deserts of the USA Southwest. To ensure maximal crop quality, negligible soil salinity stress, minimal ...nutrient loss and reduced pathogen susceptibility, lettuce irrigation must meet, but not exceed, crop water use requirements. However, lettuce crop water use information is outdated in this region: prior studies were conducted at least four decades ago (1960–1980) and do not represent current varieties, management practices, and climate. To address this shortcoming, 12 commercial sites in Yuma, Arizona, USA were evaluated between 2016 and 2020 to update lettuce water use requirements and crop coefficients. The study measured crop evapotranspiration (ET c ) using eddy covariance observations at eight iceberg and four romaine sites, where planting dates varied throughout the fall. Observed ET c and remote sensing data were used to model the daily soil water balance and derive crop coefficients: single (K c ), basal (K cb ), and soil evaporation (K e ). The analysis was supported by lettuce crop height estimates and fractional vegetative cover (f c ) via remote sensing. Days to maturity averaged 75 ± 15 and 89 ± 12 days for romaine and iceberg, respectively, where season lengths increased as planting dates progressed from early fall to late winter. Average planting date for romaine sites was about 20 days earlier than average iceberg sites. When growing intervals are cast in heat units, dependence on crop type and time of planting was reduced. Average cumulative growing-degree-day and enhanced-degree-day metrics were 1133 ± 87 and 754 ± 48 °C-days, respectively. Seasonal lettuce ET c averaged 278 ± 24 mm. Cumulative irrigation applied, plus precipitation, averaged 355 ± 88 mm. Lettuce K c for sites varied from 0.90 ± 0.13 to 1.19 ± 0.11 and K cb from 0.20 ± 0.05 to 1.01 ± 0.11 for the initial and mid-season growth stages, respectively. These updates will help growers improve their irrigation efficiency for lettuce and provide important documentation needed by water managers.
Field tests were conducted to obtain irrigation evaluation and solute transport data. The data were used to calibrate and validate an advection-dispersion model for furrow irrigation. The empirical ...infiltration equation and roughness parameters were estimated from the evaluation data. The inflow rate was measured with a volumetric meter and a flume and resulted in different average inflow rates. Hydraulic simulation results proved nearly as accurate with infiltration function estimates derived from the meter or flume data despite the difference in measured flow rate. Hence, the calibrated infiltration functions provide limited clues about possible problems with the inflow data. The choice of the infiltration equation used to fit the data (Branch versus modified Kostiakov) produced greater differences in the hydraulic modeling results. The timing and spread of the solute concentration pulses were well predicted independently of the inflow data and infiltration equation used to fit the data. However, differences between the meter and flume inflow rate were clearly manifested in the predicted peak solute concentrations. Results highlight the importance of accurate inflow measurements for parameter estimation.
•Direct-seeded guayule had the highest yield when irrigated with 75–100 % of crop ET.•Sandy loam soil gave 20–30 % higher rubber/resin yield than clay with 25 % more water.•Furrow irrigation is ...favored for direct-seeded guayule planted in clay soil.•Subsurface drip is preferred for direct-seeded guayule planted in sandy loam soil.
Crop establishment costs of guayule (Parthenium argentatum A. Gray), a perennial desert shrub that produces natural rubber, can be significantly reduced using direct seeding rather than the traditional practice of transplanting greenhouse-grown seedlings. However, information regarding the irrigation application, crop evapotranspiration (ETc), and crop coefficients (Kc) for managing direct-seeded guayule crops has not been provided. In this study, guayule was direct-seeded in Apr. 2018 in fields at two location in Arizona; Maricopa, on a sandy loam soil and Eloy, on a clay soil, and harvested 23–24 months later in 2020. At each location, five irrigation rates were applied with subsurface drip irrigation (SDI) ranging from 50 to 150 % replacement of ETc (denoted as D50 to D150 treatments), respectively. A 6th treatment using furrow irrigation at 100 % ETc replacement (F100) was included. Treatments were replicated three times. The ETc was estimated for the first 74–84 days of crop establishment and thereafter, actual ETc (ETc act) was determined weekly-biweekly for the D100 and F100 treatments using a soil water balance. The objectives were to evaluate the responses in dry biomass (DB), rubber yield (RY), and resin (ReY) yield to water application rate, develop irrigation management criteria for the two soil types, and determine the ETc and crop coefficients for the 100 % treatments.
The total irrigation applied to treatments ranged from 1830−1910 mm to 5090–5470 and averaged 3590 and 3320 mm for the 100 % SDI (D100) and furrow (F100) treatments at Maricopa and Eloy, respectively. The summed estimated ETc plus ETc act for the D100 and F100 treatments were 3663 and 3506 mm at Maricopa, respectively and 3428 and 3320 at Eloy, respectively. Average measured mid-season Kc in the 1st year varied from 1.20 to 1.26. Average measured mid-season Kc in the 2nd year were higher for D100 (≈1.30) than for F100 (≈1.23). Adjusted to the standard climate proposed in FAO56, mid-season Kc are 1.24 for D100 and 1.17 for F100 in the 2nd year. Average DB at Eloy (28.6 Mg ha−1) was not significantly higher than at Maricopa (24.0 Mg ha−1). However, RY and ReY were both significantly higher at Maricopa. At each location, rubber content was significantly higher for the F100 and the two lowest SDI rates than for other treatments. The highest mean RY and ReY were achieved with D100 at Maricopa and D75 at Eloy. These two also had significantly greater water productivity (WP; DB, RY, and ReY per unit of total water applied) than those at higher SDI rates and the F100 treatments. RY and ReY and their WP were generally higher for D100 than F100 in the sandy loam but not in the clay soil. For direct-seeded guayule in clay soils, furrow irrigation should be considered due to the lower rubber content and higher costs associated with SDI.
Deficit irrigation can maximize the water productivity (WP) of guayule and increase the percent rubber (%R) in shrubs compared to irrigation meeting full crop evapotranspiration (ETc). In this study, ...we hypothesize that certain deficit irrigation strategies that impose soil water deficits during specific periods of growth or throughout the growing season might produce higher %R and equivalent rubber yield (RY), thereby, increasing WP compared to full irrigation. Herein, growth and yield responses of direct-seeded guayule to different water deficit schemes were evaluated in an experiment on a silty clay loam soil, in a field in central Arizona using furrow irrigation. Two guayule cultivars (AZ2 and AZ6) were grown for 22.5 months (Apr. 2020-Mar. 2022) in a split-plot design, with six irrigation treatments in whole plots and cultivars in split-plots. After homogeneous irrigation for two months, irrigation treatments were begun. A control treatment was irrigated to meet full ETc. The other five treatments were irrigated with less water using various deficit irrigation strategies imposed during the two-year growing period. Measurements included plant height (h), cover fraction (fc), soil water contents, harvest of dry biomass (DB), RY, resin yield (ReY), %R, and percent resin (%Re). Total water applied (TWA) by irrigation and precipitation to treatments varied from 2780 to 1084 mm and DB varied from 20.5 to 9.1 Mg ha−1. The h and fc were significantly greater at higher irrigation levels, while they were also significantly greater in AZ6 than AZ2. The DB, RY, and ReY generally increased linearly with TWA. However, it was found that a treatment applying every other irrigation of the control resulted in statistically equivalent yields to the control, with 36% less irrigation. The %R generally decreased with TWA, while %Re did not change. However, DB, %R, and %Re were significantly greater for AZ2 than AZ6, as were RY, ReY, and WP. Among the deficit treatments evaluated, every other irrigation offers the best strategy to significantly increase guayule WP without causing a yield penalty.
•Guayule plant height and cover were significantly higher at higher irrigation rates.•Rubber content decreased with irrigation, while resin content was not affected.•Biomass, rubber and resin contents were significantly higher for AZ2 than AZ6.•Among deficit tactics, every other irrigation was the best-high water productivity.
Guayule (Parthenium argentatum, A. Gray), a perennial desert shrub, produces high-quality natural rubber and is targeted as a domestic natural rubber source in the U.S. While commercialization ...efforts for guayule are on-going, crop management requires plant growth monitoring, irrigation requirement assessment, and final yield estimation. Such assistance for guayule management could be provided with remote sensing (RS) data. In this study, field and RS data, collected via drones, from a 2-year guayule irrigation experiment conducted at Maricopa, Arizona were evaluated. In-season field measurements included fractional canopy cover (fc), basal (Kcb) and single (Kc) crop coefficients, and final yields of dry biomass (DB), rubber (RY), and resin (ReY). The objectives of this paper were to compare vegetations indices from MS data (NDVI) and RGB data (triangular greenness index, TGI); and derive linear prediction models for estimating fc, Kcb, Kc, and yield as functions of the MS and RGB indices. The NDVI and TGI showed similar seasonal trends and were correlated at a coefficient of determination (r2) of 0.52 and a root mean square error (RMSE) of 0.11. The prediction of measured fc as a linear function of NDVI (r2 = 0.90) was better than by TGI (r2 = 0.50). In contrast to TGI, the measured fc was highly correlated with estimated fc based on RGB image evaluation (r2 = 0.96). Linear models of Kcb and Kc, developed over the two years of guayule growth, had similar r2 values vs NDVI (r2 = 0.46 and 0.41, respectively) and vs TGI (r2 = 0.48 and 0.40, respectively). Final DB, RY, and ReY were predicted by both NDVI (r2 = 0.75, 0.53, and 0.70, respectively) and TGI (r2 = 0.72, 0.48, and 0.65, respectively). The RS-based models enable estimation of irrigation requirements and yields in guayule production fields in the U.S.
•Prediction of guayule cover was better by NDVI than an RGB index.•Data extracted from RGB imagery can be used to estimate canopy cover.•Guayule crop coefficients were effectively modeled using NDVI and the RGB index.•Final biomass and rubber yields can be predicted by both NDVI and the RGB index.
Understanding guayule’s response to environmental factors, such as location, soil type, drought stress, and seasonal growth variation is critical for irrigation management to maximize and estimate ...rubber and resin accumulation throughout the growing seasons. A study was conducted at two sites with different soil types (sandy loam soil at Maricopa, AZ and a clay soil at Eloy, AZ) to compare plant growth and rubber accumulation among different irrigation treatments during a two-year growing season. The above- and below-ground biomass, biomass growth, rubber/resin content, and rubber/resin accumulation were measured every other month from establishment to final harvest in well-watered treatments, which received 100% replacement of crop evapotranspiration (ETc) and irrigated with subsurface drip and furrow (denoted as D100 and F100, respectively), and compared to reduced irrigation treatments (D50 and F50), which received 50% replacement of ETc. Drip irrigation with high water input (D100) decreased root mass partition, but leaf, stem, and flower partitions were not significantly affected by irrigation treatment. Biomass yield was higher in the well-watered treatments as expected, while rubber and resin content were lower, indicating rubber and resin dilution by higher biomass. For all treatments, rubber and resin yield increased linearly over the two-year growing season. However, the rates of increase were different among the irrigation treatments. The D100 treatment had a higher rubber yield increase rate compared to F100 and D50 in sandy loam soil at Maricopa, while the D100 treatment had the lowest increase rate compared to the F100, F50, and D50 treatments in clay soil at Eloy. Top branches of guayule plants in the D100 treatment at Eloy lodged in the second year and likely contributed to lower rubber content and rubber yield in the treatment. The drip irrigation treatments D50 and D100 had higher water productivity for rubber yield at Maricopa. However, the D50 and F50 treatment had the highest water productivity for guayule rubber yield, while the D100 treatment had the lowest due to lower rubber content at Eloy. Root rubber content was 31–39% lower than stem at the two locations. This study indicates that rubber biosynthesis occurred in guayule year-round and that it is possible in clay soils to reduce irrigation without a significant loss in rubber yield.
•Reduced irrigation decreased guayule biomass yield, but increased rubber content.•Rubber yield increased linearly, indicating rubber was biosynthesized year-round.•Rubber content in guayule root was 31–39% lower than in stem.
•Olive transpiration measured in a sub-humid climate exhibited similar seasonal patterns as those reported for a Mediterranean climate.•The basal crop coefficients measured in a temperate sub-humid ...climate were of similar magnitude as those reported for arid and semi-arid climates.•The linear model developed between the Kcb and canopy light interception based on two years data explained 66% of the variation in the Kcb.
Young non-bearing olive trees were grown in drainage lysimeters and their water consumption was measured over two consecutive yearly-experimental periods to analyze the effect ofseasonal variations on the basal crop coefficient (Kcb). Micro-lysimeter measurements were used to quantify soil evaporation (Es) and Es was subtracted from evapotranspiration (ETc) to determine transpiration. Monthly mean (Kcb) were determined as (ETc-Es)/ETo, where ETo is the FAO-PM grass-reference evapotranspiration, calculated from locally measured weather data. The observed Kcb value at mid-season, 0.38, was obtained in the fall months, with 41% of canopy cover. The mid-season Kcb when adjusted to the FAO-56 standard climate was 0.43. Seasonal patterns of Kcb are presented and the Kcb value during the mid-season growth-stage was found to be similar to those described in the literature for Mediterranean climates. Variation of the basal crop coefficient was satisfactorily explained by measured canopy light interception (FIR) and a linear regression model is presented for Kcb as a function of FIR.
The application of plant nutrients with irrigation water is an efficient and cost-effective method for fertilizer application to enhance crop production and reduce or eliminate potential ...environmental problems related to conventional application methods. In this study, a combined overland water flow and solute transport model for analysis and management of surface fertigation/chemigation is presented. Water flow is predicted with the well-known Saint-Venant's equations using a control volume of moving cells, while solute transport is modeled with the advection-dispersion equation. The 1D transport equation was solved using a Crank-Nicholson finite-difference scheme. Four, large-scale, field experiments were conducted on blocked-end and free draining furrows to calibrate and verify the proposed model. The results showed that application of solute during the entire irrigation event, or during the second half of the irrigation for blocked end conditions with appropriate inflow rates, produced higher solute uniformity than application of solute during the first half of the irrigation event. Measured fertilizer distribution uniformity of the low quarter ranged from 21 to 76% while fertilizer distribution uniformity of the low half values varied between 62 to 87%. The model was subsequently applied to the experimental data; results showed good agreement with all field data. Water balance errors for the different experiments varied from 0.004 to 1.8%, whereas fertilizer mass balance errors ranged from 1.2 to 3.6%. A sensitivity analysis was also performed to assess the effects of longitudinal dispersivity parameter on overland solute concentrations. A value of 10 cm for dispersivity provided a reasonable fit to the experimental data.
Because of field-scale heterogeneity in soil hydraulic and solute transport properties, relatively large-scale experiments are now increasingly believed to be critical to better understand and ...predict the movement of water and dissolved solutes under field conditions. In this study, five field experiments were conducted on short blocked-end furrows to assess the effects of irrigation water level on water flow and solute transport in furrows. Three experiments were carried out, each of the same duration but with different amounts of water and solutes resulting from 6, 10, and 14 cm furrow water depths, designated as low, moderate, and high water levels, respectively. Two more experiments were performed with the same amounts of applied water and solute and, consequently, different durations, on furrows with depths of 6 and 10 cm of water. Results show that both the water level and the duration play an important role in transporting and distributing water and solutes in the soil profile. A positive correlation was found between water level and infiltrated amount of water or solute. Irrigation/solute application amounts increased with decreasing water level. Water and solutes were both distributed almost vertically (one-dimensionally) for the low water level and short application treatments, while they moved much more two-dimensionally with low and moderate water depths but longer application times. Irrigation with the 14 cm water level and short application time improved the distribution of water and solutes within the soil profiles, while also causing relatively less deep percolation of water and solutes as compared to low and moderate water levels and relatively long duration times.
Atmospheric CO^sub 2^ concentration continues to rise. It is important, therefore, to determine what acclimatory changes will occur within the photosynthetic apparatus of wheat (Triticum aestivum L. ...cv. Yecora Rojo) grown in a future high-CO^sub 2^ world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO^sub 2^ concentration of ambient air 370 μmol (CO^sub 2^) mol^sup -1^; Control and air enriched to 200 μmol (CO^sub 2^) mol^sup -1^ above ambient using a Free-Air CO^sub 2^ Enrichment (FACE) apparatus (main plot). A High (35 g m^sup -2^) or Low (7 and 1.5 g m^sup -2^ for 1996 and 1997, respectfully) level of N was applied to each half of the main CO^sub 2^ treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (g ^sub s^) by 30% at mid-morning (2 h prior to solar noon), 36% at midday (solar noon) and 27% at mid-afternoon (2.5 h after solar noon), whereas under Low-N, g ^sub s^ was reduced by as much as 31% at mid-morning, 44% at midday and 28% at mid-afternoon compared with Control. But, no significant CO^sub 2^×N interaction effects occurred. Across seasons and growth stages, daily accumulation of carbon (A') was 27% greater in FACE than Control. High-N increased A' by 18% compared with Low-N. In contrast to results for g ^sub s^, however, significant CO^sub 2^×N interaction effects occurred because FACE increased A' by 30% at High-N, but by only 23% at Low-N. FACE enhanced the seasonal accumulation of carbon (A'') by 29% during 1996 (moderate N-stress), but by only 21% during 1997 (severe N-stress). These results support the premise that in a future high-CO^sub 2^ world an acclimatory (down-regulation) response in the photosynthetic apparatus of field-grown wheat is anticipated. They also demonstrate, however, that the stimulatory effect of a rise in atmospheric CO^sub 2^ on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.PUBLICATION ABSTRACT
