Overhead Sprinkler Irrigation Research Articles

The Influence of Sprinkler and Drip Irrigation on the Incidence and Severity of Bacterial Disease in Onions Grown in Northeast California

Overhead sprinkler irrigation and its effect on leaf wetness are often referenced as a key factor for bacterial disease spread in onions grown in arid climates. A study was conducted in 2021 and 2022 in Tulelake, California, to compare the incidence and severity of bacterial disease under sprinkler and drip irrigation. The experiment was a split-plot randomized complete block design with drip and solid-set sprinkler irrigation as the main plot treatments and inoculation and no inoculation with plant-pathogenic bacteria as the split-plot treatments. The entire study area was irrigated with solid-set sprinklers from planting until the five-leaf stage to facilitate uniform onion germination and chemigation of herbicides for weed control. After the five-leaf stage, irrigation treatments were imposed for the remainder of the growing season. Total irrigation water amount and irrigation frequency were similar for both irrigation methods. Foliar disease severity and the incidence of bulb rot were 170 and 186% higher, respectively, for solid-set sprinkler compared with drip irrigation. Leaf wetness within the plant canopy during onion bulbing was on average 36% higher in the solid-set sprinkler compared with drip irrigation treatment, whereas relative humidity and temperature were similar between irrigation methods. Drip irrigation maintained lower soil water tension and increased average bulb size by 9% compared with solid-set sprinkler irrigation. This study confirms historical observations that overhead irrigation can extend leaf wetness and increase bacterial disease in onions in arid production areas and highlights the potential benefits of the adoption of drip irrigation.

Effects of drip irrigation and cultivation methods on establishment of seeded tall fescue

AbstractSubsurface drip irrigation (SDI) may save water but its effectiveness in establishing seeded turfgrass across different soil types and climates requires further investigation. This study was conducted in fine‐textured soils near Manhattan, KS. Our objectives were to investigate establishment of seeded tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] using: (a) SDI, aboveground drip irrigation (AGD), and overhead sprinkler irrigation (OH); and (b) core aeration vs. verticutting for seedbed preparation. Irrigation was applied daily at 150% reference evapotranspiration (ETo) as follows: OH, three times (3×) daily at 50% ETo per irrigation; AGD, 3× daily at 50% ETo per irrigation; SDI, one time (1×), two times (2×), and 3× daily at 150, 75, and 50% ETo per irrigation, respectively. Additional frequencies/amounts were included with SDI because it was unknown how soil hydraulic conductivity would affect uniformity of surface wetting and seed germination. Establishment was evaluated with green cover (GC), visual turfgrass quality (TQ), and normalized difference vegetation index (NDVI). Establishment was faster with SDI than AGD or OH, and similar between AGD and OH. By the end of the 1st month after seeding, GC and NDVI were up to 25 and 15% greater, respectively, in SDI than AGD and OH. In SDI, establishment was fastest when water was applied 2× vs. 3× or 1× d–1. Cultivation effects were negligible, indicating seedbed preparation with either method is appropriate as long as depths of cultivation and driplines are considered to avoid SDI damage. Results indicate seeded tall fescue turfgrass can be established with SDI in fine‐textured soils in a transition zone climate.

Establishing seeded tall fescue with covers and drip irrigation methods

AbstractThe use of covers may improve the establishment of seeded turfgrass but their use in combination with drip irrigation techniques has not been evaluated. In this study, repeated twice in the spring of 2020 near Manhattan, KS, we investigated the effects of two cover types and three irrigation methods on the establishment of seeded tall fescue turfgrass [Schedonorus arundinaceus (Schreb.) Dumort.]. Turfgrass cover types included (a) polyester mesh, (b) a straw blanket, and (c) no cover as a control. Irrigation treatments were (a) subsurface drip irrigation, (b) aboveground drip irrigation, and (c) overhead sprinkler irrigation (control). Measurements of green cover, ground and drone‐based normalized difference vegetation indices, and visual turfgrass quality ratings indicated that establishment was improved with both cover types compared with uncovered plots, in the order polyester > straw > uncovered in both trials, but polyester and straw became similar over time. The soil surface temperature averaged higher in polyester (14 °C) than in straw (9.5 °C) and uncovered (8.6 °C) plots during the first 12 d after seeding when the covers were installed. The results indicate that covers improved the spring establishment of seeded, cool‐season turfgrass in a fine‐textured soil and in a U.S. transition zone climate by mitigating low temperature extremes and reducing erosion during rainfall. Establishment was similar between drip (subsurface and aboveground) and sprinkler‐irrigated treatments, but the use of protective covers is recommended when establishing turfgrass from seed.

Erratum for “Which active optical sensor vegetation index is best for nitrogen assessment in irrigated cotton?”, by Bronson et al., Agron. J. 112:2205–2218

AbstractUse of active optical sensors (AOS) in nitrogen (N) management of row crops continues to grow. Since the first studies in the mid‐1990s, several commercial AOS are now available. Typically, canopy reflectance in red and near infrared (NIR) bands are used to calculate the normalized difference vegetation index (NDVI). More recently, commercially available AOS include a third, red‐edge band that allows the calculation of additional vegetation indices (VIs). We present two studies of five site‐years of N management studies in Maricopa, AZ on a Casa Grande sandy loam with cotton (Gossypium hirsutum L.). The 2014‐2015 study was conducted under an overhead sprinkler irrigation system (OSI), and the 2016‐2018 study was in subsurface drip irrigation (SDI). The study objective was to compare the ability of 12 different VIs to detect N deficiency among N treatments from shortly after emergence to mid‐bloom. In the OSI study, which showed delayed, small N treatment effects, the normalized difference red edge index (NDRE) and the chlorophyll index using red edge (CIRE) detected N deficiency in zero‐N and in reduced N‐reflectance‐based plots 7‐23 days before other VIs did. With SDI, the choice of VI was less critical as several VIs could distinguish N deficiency in zero‐N and in reflectance plots. The commonly used NDVI red (NDVIR) only detected N deficiency in reflectance plots in one of five site‐years. In conclusion, we recommend the use of AOS with NIR and red‐edge bands and the calculation of NDRE or CIRE to guide AOS‐based in‐season N management of irrigated cotton.

Revising petiole nitrate sufficiency/deficiency guidelines for irrigated cotton in the Desert Southwest

AbstractPetiole nitrate‐nitrogen (NO3–N) sampling and testing remains a popular in‐season nitrogen (N) management practice in the western United States for cotton (Gossypium hirsutum L.). However, the present guidelines used by Arizona are greater than 35 yr old and are in need of updating. The objectives of this study were to relate in‐season petiole NO3 levels with lint yields and N deficiencies and to revise the former critical deficiency level guidelines by growth stage. Petioles were sampled between first square and peak bloom in nine site‐years of cotton N management field trials in Maricopa and Safford, AZ, from 2014 to 2018. Irrigation type in Maricopa was overhead sprinkler irrigation (OSI) (2014–2015) and subsurface drip irrigation (SDI) (2016–2018). In Safford (2014–2017), surface irrigation (SI) was used. Petiole NO3 in SDI was dramatically lower than with SI or OSI, mostly in the deficient range. Lower lint yields in zero‐N treatments compared with pre‐plant soil NO3 test–based reference treatments occurred in eight site‐years (Safford 2016 crop lost to late hailstorm) and were considered N deficient. Critical petiole NO3–N levels from 1984 were revised downward 1 g N kg−1 because several N‐fertilized treatment means of petiole NO3 were in that range and did not exhibit an N rate–related yield depression. Sampling cotton plants for petiole NO3 analysis should start within 1 wk of first bloom. Petiole NO3 dynamics and critical levels in SDI cotton required further study.

Impacts of Effects of Deficit Irrigation Strategy on Water Use Efficiency and Yield in Cotton under Different Irrigation Systems

Irrigated cotton (Gossypium hirsutum L.) growers in the Murray-Darling Basin (MDB) of Australia, are challenged by limited water availability. This modelling-study aimed to determine if deficit irrigation (DI) practices can potentially improve water use efficiency (WUE) for furrow irrigation (FI), overhead sprinkler irrigation (OSI) and subsurface drip irrigation (SDI) systems. We validated the Agricultural Production System sIMulator (APSIM) against observed cotton lint yield and crop biomass accumulation for different management practices. The model achieved concordance correlation coefficients of 0.93 and 0.82 against observed cotton crop biomass accumulation and lint yields, respectively. The model was then applied to evaluate the impacts of different levels of DI on lint yield, WUE across cotton growing locations in the MDB (Goondiwindi, Moree, Narrabri, and Warren), during the period from 1977 to 2017. The different levels of DI for the FI system were no irrigation, full irrigation (TF) and irrigated one out of four, one out of three, one out of two, two out of three and two out of four TF events. For the OSI and SDI systems, DI levels were no irrigation, TF, 20% of TF, 40% of TF, 60% of TF and 80% of TF. Lint yield was maximised under the OSI and SDI systems for most locations by applying 80% of TF. However; modelling identified that WUE was maximised at 60% of full irrigation for OSI and SDI systems. These results suggest there are significant gains in agronomic performance to be gained through the application of DI practices with these systems. For FI, DI had no benefit in terms of increasing yield, while DI showed marginal gains in terms of WUE in some situations. This result is due to the greater exposure to periodic water deficit stress that occurred when DI practices were applied by an FI system. The results suggest that in the northern MDB, water savings could be realised for cotton production under both OSI and SDI systems if DI were adopted to a limited extent, depending on location and irrigation system.

Changes in sandy soil hydro‐physical properties as function of biochar and biogas slurry amendments

AbstractRaising a sandy soil's ability to retain more water is an important strategy to manage sandy soils. Combined application of biochar and slurry was hypothesized to be an appropriate strategy for improving soil hydro‐physical properties. A two‐season field trial was conducted by cultivating peanut (Arachis hypogaea L.) on a sandy soil under permanent overhead sprinkler irrigation. Rice straw biochar at 0, 10, 20 and 30 Mg ha−1 and biogas slurry at 0, 5, 10 and 15 Mg ha−1 were applied. Results indicated that all biogas slurry rates were more effective than biochar on improving all investigated parameters apart from infiltration rate and hydraulic conductivity which were higher with 30 Mg ha−1 of biochar than with 15 Mg ha−1 of slurry. Soil bulk density (g m−3) decreased significantly from 1.76 for the control to record 1.72 and 1.62 under biochar and slurry, respectively. Soil moisture contents at different tensions were the highest under the maximum combination rates, while biochar singly gave lower contents than slurry. The combined effect of 10 and 15 Mg ha−1 biochar and slurry, respectively, surpassed their individual effects. With strong coefficients of determination (R2 ranges from 0.88 to 0.98) and identical curves of estimated and predicted variables, it is possible to have accurate predictions for the changes in soil hydro‐physical properties linked with different combinations of biochar and biogas slurry.

Evaporation Losses and Evapotranspiration Dynamics in Overhead Sprinkler Irrigation

AbstractA comprehensive review of evaporation losses and evapotranspiration (ET) dynamics in sprinkler irrigation revealed substantial differences in the magnitudes of the different components of e...

Which active optical sensor vegetation index is best for nitrogen assessment in irrigated cotton?

AbstractUse of active optical sensors (AOS) in nitrogen (N) management of row crops continues to grow. Since the first studies in the mid‐1990s, several commercial AOS are now available. Typically, canopy reflectance in red and near infrared (NIR) bands are used to calculate the normalized difference vegetation index (NDVI). More recently, commercially available AOS include a third, red‐edge band that allows the calculation of additional vegetation indices (VIs). We present two studies of five site‐years of N management studies in Maricopa, AZ, on a Casa Grande sandy loam with cotton (Gossypium hirsutum L.). The 2014–2015 study was conducted under an overhead sprinkler irrigation system (OSI), and the 2016–2018 study was in subsurface drip irrigation (SDI). The study objective was to compare the ability of 12 different VIs to detect N deficiency among N treatments from shortly after emergence to mid‐bloom. In the OSI study, which showed delayed, small N treatment effects, NDRE and the chlorophyll index using amber (CIRE) detected N deficiency in zero‐N and in reduced N‐reflectance‐based plots 7–23 d before other VIs did. With SDI, the choice of VI was less critical as several VIs could distinguish N deficiency in zero‐N and in reflectance plots. The commonly used NDVI red (NDVIR) only detected N deficiency in reflectance plots in one of five site‐years. In conclusion, we recommend the use of AOS with NIR and red‐edge bands and the calculation of NDRE or CIRE to guide AOS‐based in‐season N management of irrigated cotton.

Effect of Deficit Irrigation on Nitrogen Uptake of Sunflower in the Low Desert Region of California

Nitrogen (N) accounts for more than 80% of the total mineral nutrients absorbed by plants and it is the most widely limiting element for crop production, particularly under water deficit conditions. For a comprehensive understanding of sunflower Helianthus annuus N uptake under deficit irrigation conditions, experimental and numerical simulation studies were conducted for full (100% ETC) and deficit (65% ETC) irrigation practices under the semi-arid conditions of the Imperial Valley, California, USA. Plants were established with overhead sprinkler irrigation before transitioning to subsurface drip irrigation (SDI). Based on pre-plant soil N testing, 39 kg ha−1 of N and 78 kg ha−1 of P were applied as a pre-plant dry fertilizer in the form of monoammonium phosphate (MAP) and an additional application of 33 kg ha−1 of N from urea ammonium nitrate (UAN-32) liquid fertilizer was made during the growing season. Soil samples at 15-cm depth increments to 1.2 m (8 layers, 15 cm each) were collected prior to planting and at three additional time points from two locations each in the full and deficit irrigation treatments. We used HYDRUS/2D for the simulation in this study and the model was calibrated for the soil moisture parameters (θs and θr), the rate constant factors of nitrification (the sensitive parameter) in the liquid and solid states (μw,3, and μs,3). The HYDRUS model predicted cumulative root water uptake fluxes of 533 mm and 337 mm for the 100% ETC and 65% ETC, respectively. The simulated cumulative drainage depths were 23.7 mm and 20.4 mm for the 100% ETC and 65% ETC which represented only 4% and 5% of the applied irrigation water, respectively. The soil wetting profile after SDI irrigation was mostly around emitters for the last four SDI irrigation events, while the maximum values of soil moisture in the top 30 cm of the soil profile were 0.262 cm3 cm−3 and 0.129 cm3 cm−3 for 100% ETC and 65% ETC, respectively. The 16.5 kg ha−1 (NH2)2CO (50% of the total N) that was applied during the growing season was completely hydrolyzed to NH4+ within 7 days of application, while 4.36 mg cm−1 cumulative decay was achieved by the end of the 98-day growing season. We found that 86% of NH4+ (74.25 mg cm−1) was nitrified to NO3− while 14% remained in the top 50 cm of the soil profile. The denitrification and free drainage of NO3− were similar for 100% ETC and 65% ETC, and the maximum nitrate was drained during the sprinkler irrigation period. By the end of the growing season, 30.8 mg cm−1 of nitrate was denitrified to N2 and the reduction of nitrate plant uptake was 17.1% for the deficit irrigation section as compared to the fully irrigated side (19.44 mg cm−1 vs. 16.12 mg cm−1). This reduction in N uptake due to deficit irrigation on sunflower could help farmers conserve resources by reducing the amount of fertilizer required if deficit irrigation practices are implemented due to the limited availability of irrigation water.

Overhead sprinkler irrigation affects pollinators and pollination in pumpkin (Cucurbita maxima)

Cucurbits are monoecious plants and most of them depend on pollinators for fruit set. However, studies suggest that pumpkin and squash fields are pollination deficient. Pollinator limitation, suboptimal flower sex ratio, and exploitative competition between invasive ants and bees are a few major suggested reasons for this. Pumpkin flowers have a corolla cup and secrete nectar throughout anthesis, which make them attractive to bees. In south India, honey bee (Apis cerana) is the major pollinator of pumpkin flowers. Like pollinators, water is also a limiting factor for growth and production of flowers in pumpkin. It has been suggested to use overhead sprinklers to irrigate and fertilize pumpkin fields. We hypothesized that the sprinkler affects the visitation characteristics of foraging bees in flowers and pollination, and so, we performed an experiment to test this. For this reason, we recorded pollinator visits on staminate and pistillate flowers for 15 min and poured water in the flower cups and examined the water retention time and the visitation characteristics of pollinators in both staminate and pistillate flowers, and fruit set in pistillate flowers. Water remained inside the staminate and pistillate flower cups until the flower senescence. Honey bees entered and foraged nectar/pollen in flowers during the waterless condition. In water-filled flowers, honey bees hovered around or landed only on the corolla and did not forage floral resources or contact the reproductive parts. As a consequence, none of the water-filled flowers developed fruits. Therefore, the overhead sprinkler irrigation, despite cover a large area effectively, may not be an appropriate irrigation method for pumpkin during flowering period.

Nitrogen Fertilizer and Irrigation Effects on Seed Yield and Oil in Camelina

Core Ideas A 2‐yr field study in Maricopa, AZ, under an overhead sprinkler irrigation system determined the effects of 10 water levels (irrigation fraction 0.5–1.1) and five N fertilizer rates (38–150 kg N ha−1) on seed yield, seed oil, and N use efficiency.Recovery efficiency of N fertilizer by camelina ranged from 12 to 72% for high to low N fertilizer rates, respectively.Oil content of seed was maximum at 40%, and decreased with N rate but increased with water level. Interest is growing in camelina (Camelina sativa L. Crantz) as a biofuel feedstock. However, there has been little camelina research in irrigated arid systems. A 2‐yr field study in Maricopa, AZ, under an overhead sprinkler irrigation system determined the effects of 10 water levels (irrigation fraction 0.5–1.1) and five N fertilizer rates (38–150 kg N ha−1) on seed yield, seed oil content, and N use efficiency. Cultivar Robinson was planted in December 2012 and 2013. Nitrogen fertilizer (urea ammonium nitrate) was applied in three split applications. Irrigation amounts were from 125 to 380 mm, and in‐season rain was 70 and 50 mm, in 2013 and 2014, respectively. Camelina seed yields were maximum at water level 7 (irrigation fraction 0.93) in 2013 at 1800 kg ha−1. Maximum seed yields were 1600 kg ha−1 at water level 6 (irrigation fraction 0.83) in 2014. These highest seed yields were achieved with 150 kg N ha−1 in both years. Oil content (maximum 41%) decreased with N rate but increased with water level. Seed N increased with N rate but decreased with irrigation level. Recovery efficiency of N fertilizer by camelina ranged from 12 to 72%. The results indicate that good high‐oil camelina yields can be produced in the southwestern United States with 320 to 380 mm irrigation plus rain and N fertilizer rates of 150 kg N ha−1.

Rice yield and relationships to soil properties for production using overhead sprinkler irrigation without soil submergence

Production of irrigated rice (Oryza sativa L.) without conventional soil submergence may increase water use efficiency but risk a decline in rice yield. Spatial variability in rice yield and relationships among yield and soil properties were examined across a 3.3-ha experimental site after uniform crop management. The site was initially consolidated from small, previously puddled parcels of land into eight laser-leveled plots across a 2.1-m elevation gradient in the Philippines. Six crops of rice in rotation with three crops of mungbean (Vigna radiata (L.) R. Wilczek) were then grown from January 2012 to March 2015. The four rice crops in the dry season (crops 1, 2, 4, and 6) were irrigated using an overhead sprinkler system to maintain soil water potential greater than −10 kPa without soil submergence. Soil was puddled and flooded with irrigation for only rice crop 5 grown in the wet season. Mean rice yield with full fertilization was 6.1 Mg ha−1 for crop 2 but only 3.6 Mg ha−1 for crop 6. Yield for rice crop 6 ranged from 1.6 to 5.4 Mg ha−1 across 36 locations in the 3.3-ha site. Rice yield for crop 6 was inversely related to soil bulk density (r = −0.72 and −0.80, P < 0.001), log10 saturated hydraulic conductivity (Ksat) (r = −0.71, P < 0.001), and sand content (r = −0.63, P < 0.001). Yield was directly related to water-filled pore space of soil (r = 0.61, P < 0.001). Field locations with large downward water movement and the correspondingly most aerobic soil conditions were most prone to low rice yields and large yield decline. Rice yield was directly related to anaerobic N mineralization (r = 0.72, P < 0.001) and soil ammonium-N (r = 0.54, P < 0.001) at 16 days after transplanting and to indigenous N supply (r = 0.83, P < 0.001), as determined from rice yield without application of fertilizer N. These relationships suggested lower net N mineralization at locations with the most aerobic soil conditions, as determined by water-filled pore space. Rice yield was, however, not limited by insufficient fertilizer N. Anaerobic N mineralization and indigenous N supply were unrelated to optimum fertilizer N rate calculated from yield gain with fertilizer N, which was determined at 36 locations using paired plots with and without added N. The long rainy season and clayey soil at the site limited triple-cropping systems to two rice crops and only one non-rice crop per year. In such environments where crop rotation is not an option to prevent yield decline for rice grown without soil submergence, periodic soil submergence to increase anaerobic soil conditions would be required to sustain rice yield. Our study suggested that soil bulk density and Ksat, which can increase for successive rice crops grown without puddling and soil submergence, could serve as indicators of field locations prone to yield decline from factors other than water-deficit stress and requiring a period of soil submergence to sustain large rice yields.

Sprinkler Irrigation Is Effective in Reducing Nitrous Oxide Emissions from a Potato Field in an Arid Region: A Two-Year Field Experiment

In arid and semi-arid regions, water-saving irrigation is the primary mode of local agricultural production. Since the chemical fertilizer is the principal source of nitrous oxide (N2O) emissions, we present results from a two-year (2016–2017) field experiment on a potato field to verify the general influence of water-saving irrigation on N2O emissions. A split-plot experiment was established with two irrigation systems and two fertilizer treatments, which give a total of four treatments. Two different irrigation systems were investigated: (i) flood irrigation with nitrogen fertilizer (NF-FI) combined with a control without any fertilizer (C-FI) and (ii) overhead sprinkler irrigation with a nitrogen fertilizer (NF-SI) accompanied with a control without any fertilizer (C-SI). The N2O emissions of the fertilizer treatment were greater than those of the control under each irrigation system. In plots where the fertilizers were applied, using overhead sprinkler irrigation reduced the average cumulative N2O emissions between 40.72% and 59.65% compared with flood irrigation. This was mainly due to the lower amount of water applied and the lower availability of NO3−-N and NH4+-N of soil associated with an overhead sprinkler irrigation. This work shows that the overhead sprinkler irrigation is an effective strategy to use to save water and mitigate emissions of the atmospheric pollutants N2O in comparison to flood irrigation.

Cotton Response to Variable Nitrogen Rate Fertigation through an Overhead Irrigation System

Recent increases in irrigated hectares in the Southeastern US have enabled growers to obtain higher yields through applying nutrients through irrigation water. Therefore, many growers apply nutrients through irrigation systems, known as fertigation. Currently, there are no practical decision-making tools available for variable-rate application of nitrogen (N) through overhead sprinkler irrigation systems. Therefore, field tests were conducted on cotton (Gossypium hirsutum L.) during the 2016 and 2017 growing seasons to 1) adapt the Clemson sensor-based N recommendation algorithms from a single side-dress application to multiple applications through an overhead irrigation system; and 2) to compare sensor-based VRFS with conventional nutrient management methods in terms of N use efficiency (NUE) and crop responses on three soil types. Two seasons of testing Clemson N prediction algorithms to apply multiple applications of N were very promising. The multiple applications of N compared to the grower’s conventional methods (even though less N was applied) had no impact on yields in either growing season. There was no difference in cotton yields between 101 and 135 kg/ha N applications in either management zone. Also, there were no differences in yield between sensor-based, multiple N applications and conventional N management techniques. In relation to comparisons of the sensor methods only applying N in three or four applications, statistically increased yields compared to single or split applications in 2016. Applying N in four applications, statistically increased yields compared to single, split or triple applications in 2017. When the sensor-based methods were compared to the grower’s conventional methods averaged over four treatments, the sensor-based N applications reduced fertilizer requirement by 69% in 2016 and 57% in 2017 compared to grower’s conventional methods. When comparing N rates among the four sensor-based methods (three or four) applications, increased N rates by 22 kg/ha in 2016 and 26 kg/ha in 2017 compared to single or split applications but increased the cotton lint yields by 272 and 139 kg/ha, for 2016 and 2017, respectively.

Drip and Overhead Sprinkler Irrigation in Blueberry as Cultural Control for Drosophila suzukii (Diptera: Drosophilidae) in Northwestern United States.

Overhead sprinkler compared to drip irrigation in cropping systems can result in increased relative humidity (RH) and decreased temperature within the plant canopy. Such conditions may also result in a more favorable microclimate for pests. Drosophila suzukii Matsumura is an invasive agricultural pest of berries in America and Europe. Drosophila suzukii is susceptible to high temperatures and low RH, thus its survival may be affected by different irrigation methods. We tested how drip and overhead sprinkler irrigation in blueberries influenced temperature and RH. Furthermore, we determined how these environmental factors affected adult emergence rates from larvae within fruit or pupae outside of fruit. RH was higher in overhead sprinkler compared to drip irrigation treatments, but there was no difference in temperatures. Although there were no differences in fly emergence from larvae between irrigation treatments, more flies emerged from pupae in overhead sprinkler compared to drip irrigation treatments. This is likely because larvae developing inside fruit are protected from desiccation, while pupae were exposed to lower RH. Regardless of irrigation method, temperatures remained above 30°C for longer periods and RH was lower above as opposed to below the mulch. Fewer D. suzukii larvae and pupae consequently survived above the mulch than below the mulch. When assessing natural infestation, we found similar numbers of D. suzukii flies emerging from blueberries collected on drip and sprinkler rows. Irrigation management can be coupled with other cultural control methods that ensure that pupae remain exposed on low RH surfaces, where they are more likely to succumb to desiccation.

Integrated cultural practices for whitefly management in organic tomato

AbstractThe whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a serious pest among the diverse insect fauna of the tomato crop, especially when cultivated in organic systems. The feeding behaviour of B. tabaci is responsible for direct damage to tomato plants and for the transmission of several viruses, such as begomoviruses. The objective of this study was to evaluate the effect of integrating the cultural practices of intercropping and irrigation systems on B. tabaci abundance and the incidence of begomovirus in organic tomato systems. Field experiments were performed in the dry season for 2 years when B. tabaci abundance and begomovirus incidence were compared in tomato crops planted either in monoculture or intercropped with coriander and irrigated by overhead sprinklers or by a drip irrigation system. Tomato plants intercropped with coriander and irrigated by overhead sprinklers showed the lowest levels of B. tabaci colonization by adult and nymph densities. Most likely, the coriander plants produced visual and olfactory barriers for insect host plant selection, and the overhead sprinkler irrigation physically interfered with the movement and establishment of the insects. The combined effect of intercropping and sprinkler irrigation made tomato plants less suitable for B. tabaci establishment. Moreover, tomatoes intercropped with coriander and irrigated by sprinkler irrigation also reduced the incidence of begomovirus‐infected plants. In summary, integrating tomato–coriander intercropping and sprinkler irrigation can help manage B. tabaci and associated viruses in organic tomato crops.

Residual Activity of ACCase-Inhibiting Herbicides on Monocot Crops and Weeds

AbstractField experiments were conducted in 2014 and 2015 in Fayetteville, Arkansas, to evaluate the residual activity of acetyl-CoA carboxylase (ACCase)–inhibiting herbicides for monocot crop injury and weed control. Conventional rice, quizalofop-resistant rice, grain sorghum, and corn crops were evaluated for tolerance to soil applications of six herbicides (quizalofop at 80 and 160 g ai ha–1, clethodim at 68 and 136 g ai ha–1, fenoxaprop at 122 g ai ha–1, cyhalofop at 313 g ai ha–1, fluazifop at 210 and 420 g ai ha–1, and sethoxydim at 140 and 280 g ai ha–1). Overhead sprinkler irrigation of 1.3 cm was applied immediately after treatment to half of the plots, and the crops planted into the treated plots at 0, 7, and 14 d after herbicide treatment. In 2014, injury from herbicide treatments increased with activation for all crops evaluated, except for quizalofop-resistant rice. At 14 d after treatment (DAT) in 2014, corn and grain sorghum were injured 19% and 20%, respectively, from the higher rate of sethoxydim with irrigation activation averaged over plant-back dates. Conventional rice was injured 13% by the higher rate of fluazifop in 2014. Quizalofop-resistant rice was injured no more than 4% by any of the graminicides evaluated in either year. In 2015, a rainfall event occurred within 24 h of initiating the experiment; thus, there were no differences between activation via irrigation or by rainfall. However, as in 2014, grain sorghum and corn were injured 16% and 13%, respectively, by the higher rate of sethoxydim, averaged over plant-back dates. All herbicides provided little residual control of grass weeds, mainly broadleaf signalgrass and barnyardgrass. These findings indicate the need to continue allowing a plant-back interval to rice following a graminicide application, unless quizalofop-resistant rice is to be planted. The plant-back interval will vary by graminicide and the amount of moisture received following the application.

Nitrogen Management Affects Nitrous Oxide Emissions under Varying Cotton Irrigation Systems in the Desert Southwest, USA.

Irrigation of food and fiber crops worldwide continues to increase. Nitrogen (N) from fertilizers is a major source of the potent greenhouse gas nitrous oxide (NO) in irrigated cropping systems. Nitrous oxide emissions data are scarce for crops in the arid western United States. The objective of these studies was to assess the effect of N fertilizer management on NO emissions from furrow-irrigated, overhead sprinkler-irrigated, and subsurface drip-irrigated cotton ( L.) in Maricopa, AZ, on Trix and Casa Grande sandy clay loam soils. Soil test- and canopy-reflectance-based N fertilizer management were compared. In the furrow- and overhead sprinkler-irrigated fields, we also tested the enhanced efficiency N fertilizer additive Agrotain Plus as a NO mitigation tool. Nitrogen fertilizer rates as liquid urea ammonium nitrate ranged from 0 to 233 kg N ha. Two applications of N fertilizer were made with furrow irrigation, three applications under overhead sprinkler irrigation, and 24 fertigations with subsurface drip irrigation. Emissions were measured weekly from May through August with 1-L vented chambers. NO emissions were not agronomically significant, but increased as much as 16-fold following N fertilizer addition compared to zero-N controls. Emission factors ranged from 0.10 to 0.54% of added N fertilizer emitted as NO-N with furrow irrigation, 0.15 to 1.1% with overhead sprinkler irrigation, and <0.1% with subsurface drip irrigation. The reduction of NO emissions due to addition of Agrotain Plus to urea ammonium nitrate was inconsistent. This study provides unique data on NO emissions in arid-land irrigated cotton and illustrates the advantage of subsurface drip irrigation as a low NO source system.

Improving Nitrogen Fertilizer Use Efficiency in Surface‐ and Overhead Sprinkler‐Irrigated Cotton in the Desert Southwest

Core Ideas Nitrogen use efficiency is low in surface‐irrigated cotton. Canopy reflectance can guide in‐season N management. Deep percolation of rain and irrigation is associated with nitrate leaching. Nitrogen fertilizer use efficiency (NUE) is low in surface‐irrigated cotton (Gossypium hirsutum L.), especially when adding N to irrigation water. A NO3 soil‐test algorithm was compared with canopy reflectance‐based N management with surface‐ overhead sprinkler‐irrigation in central Arizona. The surface irrigation studies also compared fertigation of N fertilizer with knifing‐in of N and the addition of a urease and nitrification inhibitor (Agrotain Plus, Koch Agronomic Services, Wichita, KS) to urea ammonium nitrate (UAN). Cotton lint and seed yields responded positively to N fertilizer in all four site‐years. Recovery efficiency (RE) of N at low N fertilizer rates (60 to 76 kg N ha–1) ranged from 21 to 61% with surface irrigation and from 81 to 97% with overhead sprinkler irrigation. Deep percolation below 1.8 m was 4 to 11% of applied surface irrigations and rain, but was undetectable in the overhead sprinkler. Leaching of NO3 was apparently the largest N loss pathway in the surface‐irrigated system. Fertigating UAN into surface irrigation resulted in similar lint yields and RE as knifing UAN. Use of Agrotain Plus with UAN gave similar yields and RE as using UAN alone. Reflectance‐based N management using normalized difference vegetation index‐amber (NDVIA) saved 50% of N fertilizer of the full soil‐test based dose without a yield reduction in three of four site‐ years. Nitrogen fertilizer was over‐prescribed with the soil‐test‐based treatment. This may have been due to not accounting for N mineralization, which the reflectance method indirectly measures.