Center Pivot Sprinkler Irrigation Research Articles

Evaluation of three irrigation application systems for watermelon production in the Texas High Plains

AbstractAbout 90% of the Texas High Plains area depends on the water supply from the Ogallala aquifer. The decline of the Ogallala water table raises a concern for the sustainability of producing the traditional irrigated field crops due to their high water demand. Thus, diversifying cropping systems may be a solution. However, about 70% of the irrigated cropland uses center pivots that may negatively impact specialty crop quality. Thus, a 3‐year experiment was conducted to assess the potential of using mobile drip irrigation (MDI) to produce fresh watermelon compared to center pivot sprinkler irrigation using low‐elevation spray application (LESA), and surface drip irrigation with plastic mulch (DI). The study evaluated the effects of irrigation systems on crop yield, fruit quality, physiological responses, water use efficiency (WUE), and irrigation use efficiency (IUE). On average, plants under MDI had higher yields (106 Mg ha−1) than those under DI (70 Mg ha−1) and LESA (68 Mg ha−1). Plants under MDI and DI also had more fruits per plant (1.9) than those under LESA (1.4). The higher yield was associated with higher biomass and photosynthetic function. In general, fruit quality was not affected by irrigation system. In addition, plants under MDI system showed a higher WUE and IUE, and less water stress than those under LESA and DI systems. Results of this study suggest that irrigating under an MDI system is a good alternative for growers in the Texas High Plains that aim to diversify their cropping system with high‐value vegetable crops such as watermelon (Citrullus lanatus).

The irrigation efficiency trap: rational farm-scale decisions can lead to poor hydrologic outcomes at the basin scale

Agricultural irrigation practices have changed through time as technology has enabled more efficient conveyance and application. In some agricultural regions, irrigation can contribute to incidental aquifer recharge important for groundwater return flows to streams. The Henrys Fork Snake River, Idaho (United States) overlies a portion of the Eastern Snake Plain Aquifer, where irrigated agriculture has occurred for over a century. Using irrigator interviews, aerial and satellite imagery, and statistical streamflow analysis, we document the impact of farm-scale decisions on basin-scale hydrology. Motivated to improve economic efficiency, irrigators began converting from surface to center-pivot sprinkler irrigation in the 1950s, with rapid adoption of center-pivot sprinklers through 2000. Between 1978–2000 and 2001–2022, annual surface-water diversion decreased by 311 Mm3 (23%) and annual return flow to the river decreased by 299 Mm3 over the same period. Some reaches that gained water during 1978–2000 lost water to the aquifer during the later period. We use an interdisciplinary approach to demonstrate how individual farm-scale improvements in irrigation efficiency can cumulatively affect hydrology at the landscape scale and alter groundwater-surface water relationships. Return flows are an important part of basin hydrology in irrigated landscapes and we discuss how managed and incidental aquifer recharge can be implemented to recover return flows to rivers.

Calculation of Evaporation Losses for Center Pivot Sprinkler Irrigation Systems Type (Lindsay) by Effect of Timer Percentage of Speed and the Increase of Sprayer Nozzles from Soil Surface

The experiment was conducted during summer season (July, August, September) 2019 in some field in Anbar governorate, Saqlawiya city, Gisaba area to calculate water losses by evaporation through water depths by calculating the discharges that come from nozzles and water depths to collect in side cans while calculating uniformity coefficient above soil surface. The results showed that the increase of spray nozzles in soil surface at 1.0m gave the lowest depths from evaporated water by changing the timer speed percent; where it was 0.18mm 100% speed, while increased to 3.39mm at 20% speed compared 0.66mm at 100% speed till 5.91mm at 20% speed when expanding the sprayer nozzles to 1.50m from soil surface. The 100% speed gave low percentage of losses (1.79%) and the high percentage was obtained at 20% speed (33.70%) at 1.0m height, which is better that height of 1.50m in rationalizing water in order to irrigate new areas that water was not enough for. this is due to variation in the height of spray nozzles above the ground, as well as variations in temperature and wind speed steadfastly speed up the system.

Importance of flood irrigation for foraging colonial waterbirds

AbstractFor a colonial‐nesting bird, like the white‐faced ibis (Plegadis chihi), the landscape surrounding the breeding colony can be important. White‐faced ibis must rely on areas outside their breeding colony for foraging, but this part of their life history has received little attention, and the management of this landscape even less so. To address this knowledge gap, we conducted road‐based driving surveys and a randomly selected, spatially balanced sample survey of agricultural fields within a 22‐km radius of the 2 largest white‐faced ibis breeding colonies in Idaho, USA: Market Lake Wildlife Management Area and Mud Lake Wildlife Management Area. Our study took place in 2012 and the primary objective was to quantify patterns of foraging habitat use of this marsh‐nesting species, particularly associations with specific irrigation practices and crop types. We documented the majority of foraging birds in flood‐irrigated and wheel‐line sprinkler‐irrigated agricultural fields (76%) and natural wetlands (13%), which were limited in our study area (3% of land cover). Even though 70% of the agricultural landscape included center pivot sprinkler irrigation, only 11% of foraging observations came from this irrigation type. Most agricultural fields (>85%) used by foraging ibis were flood‐irrigated and all had standing water or recent moisture at the time of use. Though ibis used many crop types when foraging in flooded agricultural fields, ibis use of alfalfa (58%) was greater than availability (38%). We also observed distinct distribution patterns around the 2 breeding colonies. Whereas birds foraged in all directions around Mud Lake (~80%) within a 12‐km radius from the colony, we observed over half of birds around Market Lake foraging within 12–22 km, and almost exclusively to the south and southeast of the colony, reflecting the distribution of flood‐irrigated agriculture in the area. The most common foraging distance (12–22 km) around Market Lake is greater than found in existing literature, suggesting that the foraging habitat is limited within 12 km of the colony and that the birds may need to travel farther to find adequate foraging habitat. Flood‐irrigated agriculture and natural wetlands provide foraging habitats for white‐faced ibis in eastern Idaho and should be considered in future management and conservation of wetland birds.

Effect of boron on the yield of wheat (Triticum aestivum L.) under center pivot sprinkler irrigation system in the West Desert of Iraq

Two field experiments were conducted under field conditions under a sprinkler irrigation system in the West desert of Iraq, Al-Qaim Area, 400 km west of Baghdad. Underground water was used as a source of irrigation water to study the effect of different rates and different times of boron application on wheat cv. Ibaa99. RCBD with five treatments and three replications was used in this study. Boron dose was 2 kg/ha for soil application method and 0.30 kg/ha for foliar application method. Boron treatments were: 0 (control T1), 2 kg B ha-1 at sowing time (T2), 2 kg B ha-1 at 30 days after sowing (T3), 0.3 kg B ha-1 foliar application at 60 days after sowing (T4) and 0.3 kg B ha-1 for foliar application at 90 days after sowing (T5). Most boron treatments gave a significant increase as compared with control in morphological, physiological and productivity characters of wheat crop. The results revealed that B application treatment at 30 days after sowing time increased significantly the 1000 grains weight (17.6%) while T5 treatment increased significantly the chlorophyll content (12.41%) over control. In most cases, B application treatment at 60 days after sowing time showed the best results and increased significantly the plant height (5.24%), leaf area (9.18%), number of grains spike-1 (30.9 %), number of spike m-2 (18.8%), spike length (65.6%), Grains yield (34.6%) over control. There was evidence that the best dose of boron was 0.3 kg B ha-1 and the best time of B application to the foliage was at 60 days after sowing.

Response of Canopy Leaf Area Index and Architecture of Tropical Rainforests in Sri Lanka to Climatic Variation along an Altitudinal Gradient

Ground mulching can affect the availability of nitrogen to a common bean crop depending on the C/N relationship. The objective of this paper was to study the response of the crop grown after corn to nitrogen application rates and time, under no-tillage. The study was conducted at the ‘Embrapa-Arroz e Feijao’ experimental station, located in the municipality of Santo Antonio de Goias, GO, Brazil, in 1999 and 2000. The soil of the experimental site was Oxisol and experiments were conducted during the dry season using center pivot sprinkler irrigation. The experiment was conducted in a randomized complete block design, with four replications. The common bean cultivar used was Apore. All treatments received 120 kg/ha of N during the crop cycle, with split applications or not, in different doses twenty days before sowing, at sowing, and at topdressing. The treatments were: T1 (0-0-120 kg/ha), T2 (0-17,5-102,5 kg/ha), T3 (0-40-80 kg/ha), T4 (0-60-60 kg/ha), T5 (0-80-40 kg/ha), T6 (0-120-0 kg/ha), T7 (40-40-40 kg/ha), T8 (0-17,5-102,5 kg/ha), and T9 (0-60-60 kg/ha). In the last two treatments, the corn mulch was chopped. Common bean under no-tillage needed a higher nitrogen dose at sowing in relation to conventional tillage. In the no-tillage system, the appropriate rate of N at sowing was 60kg/ha. When the N rate was higher than 60kg/ha, grain yield decreased. The same N split application rate produced higher yield when the corn mulch was chopped. KEY-WORDS: Phaseolus vulgaris ; N split application; mulch.

A DEVELOPED EXPERT SYSTEM FOR CENTER PIVOT IRRIGATION SYSTE MANAGEMENT UNDER NEWLY RECLAIMED SOILS OF EGYPT

Accurately estimation of actual crop evapotranspiration (ETa) as a parameter of irrigation scheduling is very critical for efficient use of limited irrigation water resources. The objectives of this study were to (1) build, verify and validate an expert system for managing on-farm irrigation water of some soils under Egyptian conditions, (2) study the effect of coefficient of uniformity (CU) and distribution uniformity for center pivot irrigation system, (3) study the effect of the precise estimation of daily actual crop evapotranspiration (ETa) on maximizing yield and improved water use efficiency. A rule-based program named CPISM-ES (Center Pivot Irrigation System Management- Expert System) was codes and compiled using python-3.7.2 language. The program was verified using ready-to-use software programs (cropwat-8 and climwat 2) for estimating the daily reference evapotranspiration and a spreadsheet named the (FAO56Ax8.xls) introduced by FAO-56 for estimating the irrigation water management parameters. It also was validated by carrying out a field experiment at site :- El Salhyia (11.2 m above sea level, 30,35°N,30,26°E), was obtained from several different sources. The irrigation expert system aims to provide the farmers by the irrigation expertise to determine the exact water needed at exact time according to the crop requirements and the environmental factors which effect factors. The experiment included the following factors: a) obtaining climatic data from a weather station b) estimation crop evapotranspiration c) coefficient of uniformity (CU) and distribution uniformity for center pivot irrigation system.the Center pivot sprinkler irrigation system is used in El Salhyia to irrigate potato. Center pivot system in consist of 8 towers. Lengths of the towers 56 m and numbers of sprinklers are different from one tower. 1- The estimation of actual crop evapotranspiration (ETa) using crop coefficient. 2- The seasonal cumulative ETa estimated by single-kc approach of El Salhyia (1875 m3/f/season). 3- Yield: the highest of crop potatoes for El Salhyia (16.2 Ton/F). 4- Water use efficiency: the maximum value of water use efficiency for El Salhyia (0.8 kg m-3) .

Differences in soil evaporation between row and interrow positions in furrowed agricultural fields

AbstractAlthough large‐scale center pivot sprinkler irrigation has replaced surface irrigation in many locations, the agricultural practice of growing crops in furrows remains common. Still, how the presence of elevated soil rows under sprinkler irrigation influences evaporation losses remains unclear, even while quantifying nonproductive water losses becomes increasingly important for informing new water conservation and irrigation strategies. In this study at the Hermiston Agricultural Research and Extension Center in Hermiston, OR, soil evaporation from the row and interrow positions within potato (Solanum tuberosum L.) fields of contrasting irrigation timing (daytime vs. nighttime) was estimated based on hydrogen and oxygen isotope ratios. Samples collected throughout the 2016 growing season were analyzed and used to calculate soil evaporation (E) losses relative to applied irrigation (I). On average, row positions were more enriched in heavy isotopes than interrow positions, indicating that the evaporated fraction of applied irrigation (E/I) depends on the position. Within the day‐irrigated field, the estimated (mean ± standard deviation) E/I ratios determined from both stable isotopes for May, July, and September were 18 ± 8%, 10 ± 3%, and 19 ± 5% for row and 15 ± 6%, 7 ± 2%, and 12 ± 4% for interrow samples. Within the night‐irrigated field during these same months, the E/I ratios were 13 ± 12%, 16 ± 7%, and 13 ± 5% for row and 12 ± 7%, 9 ± 2%, and 6 ± 2% for interrow samples, respectively. For these fields, these results reveal that there is more evaporation from row, as compared with interrow, positions. Therefore, management practices for water conservation should account for larger nonproductive evaporation from within rows in order to minimize evaporative losses.

Identification of Gaps and Remedies for Center Pivot Sprinkler Irrigation System in North-West Ethiopia

The study was carried out to study on identification of performance gaps for improvement of center pivot sprinkler system in the Tigray region of Northwest Ethiopia. The objective of the study was to identify center pivot sprinkler irrigation system gaps and suggest remedial measures for improvement of the center pivot sprinkler irrigation system. The methods used for gap Identification were observation, Interview, measurement, and using design document. Center pivot sprinkler gaps identification study revealed that Excess runoff due to leaky boots and higher application depth, absence of regular checkup for emitting devices, and improper scheduling were dominant gaps and Making functional an Automatic control system, regular checkup and maintenance of emitting accessories and proper scheduling could minimize the identified problems and finally the irrigation efficiency would be amended.

Evaluating the Irrigation Practice of Center Pivot Sprinkler Irrigation System at Hiwot Agricultural Mechanization, Ethiopia

Irrigation practice evaluation of center pivot sprinkler irrigation system at Hiwot Agricultural Mechanization farm, North/west Ethiopia was conducted. The aim of the study was evaluating the existing center pivot irrigation practice in terms of irrigation scheduling. Measuring flow rate of center pivot machines for existing irrigation practice and Crop water requirement based scheduling was used to evaluate the system. The highest value of crop water requirement at location m6, m7 and m12 was 5.24 mm/day in September at mid-stage and for location m4 and m8 in October at mid-stage equal to 4.99 mm/day. Whereas, the lowest crop water requirement at location m6, m7 and m12 was 2.52 mm/day in July at the initial stage which was and for location m4 and m8 in august at initial stage equal to 2.08 mm/day. The actual flow rate of center pivot machines varies from 0.7l/s for m7 to a maximum of 1l/s for m4 whereas estimated crop water requirement flow rate varies from 0.6l/s for m6 to a maximum of 0.8l/s for m4. The study also revealed that the actual flow rate of the nozzles was excess. Therefore improvement of center pivot sprinkler irrigation system can be amended by using proper irrigation scheduling and by introducing an automatic control system.

Moving Spray-Plate Center-Pivot Sprinkler Rating Index for Assessing Runoff Potential

Numerous moving spray-plate center-pivot sprinklers are commercially available providing a range of drop size distributions and wetted diameters. A means to quantitatively compare sprinkler choices in regards to maximizing infiltration and minimizing runoff is currently lacking. The objective of this study was to develop a soil independent quantitative runoff potential index to facilitate selection of sprinklers for center-pivot sprinkler irrigation systems. Drop sizes, velocities and water application rates of numerous moving spray-plate sprinklers were measured in the laboratory over a range of flow rates and operating pressures. The proposed sprinkler runoff index is based on application rates of kinetic energy and water computed by overlapping specific power and water application profiles of sprinklers equally spaced 3 m along a center-pivot lateral. Results show that substantial differences in runoff potential exist between sprinkler choices and several sprinklers can have similar runoff potential index values. In some cases, equivalent potential runoff index values were obtained with compensating differences in specific power and application rate. The proposed sprinkler runoff index provides a new and unique approach for evaluating moving spray-plate sprinklers in regards to runoff potential and provides an effective means for comparing sprinkler choices by identifying sprinklers with large drops and relatively small wetted diameters.

Economic Comparison of Subsurface Drip and Center Pivot Sprinkler Irrigation Using Spreadsheet Software

<abstract> <b><sc>Abstract. </sc></b>Static, single-time economic comparisons of subsurface drip irrigation and center pivot sprinkler irrigation systems for corn production are useful but do not accommodate broad changes in economic assumptions. An economic comparison decision tool was formulated in MS-Excel to allow producers and other interested parties to easily perform their own comparisons using their current individual assumptions or the latest suggestions from K-State Research and Extension. Tabular and graphical sensitivity results are provided on key economic factors including field size, SDI system cost and longevity, corn yield and selling price. The economic competitiveness of SDI systems increases with SDI longevity and overall corn yields and selling prices and also for smaller and irregular-shaped fields where center pivot sprinkler costs per unit area greatly increase.

Nitrogen metabolism in coffee plants in response to nitrogen supply by fertigation

Coffee plants require high application rates of nitrogen (N) to produce coffee beans. However, information regarding plant N uptake and assimilation under intensive high-technology cultivation systems is scarce, a situation which restrains the maximizing productivity with minimal N rates. The aim of this study was to evaluate N assimilation enzymes such as nitrate reductase (EC 1.6.6.1), glutamine synthetase (EC 6.3.1.2), urease (EC 3.5.1.5), and N compounds of coffee plants during a phenological cycle in response to N applied by fertigation. Our study was carried out with 7-year-old trees of Coffea arabica L., under a center pivot sprinkler irrigation and fertigation system, with five N rates (0, 200, 400, 600, and 800 kg ha−1) applied to the coffee field. The results of the present study suggest that both N metabolism enzymes, and the content of nitrate and ammonium in coffee were directly related to the phenological cycle. The N fertigation rates are correlated with the N and amino acid contente. Nitrate reductase and urease showed higher activities before anthesis and during grain filling. Glutamine synthetase showed highest activities during rapid grain expansion. The data also indicate that there is merit in gaining greater understanding of N metabolism in coffee plants grown under high-intensive systems. There is therefore merit in conducting further research on how monitoring the N assimilation enzymes might be used to improve fertilizer management of coffee in commercial orchards.

DETERMINING LARGE SCALE ACTUAL EVAPOTRANSPIRATION USING AGRO¬METEOROLOGICAL AND REMOTE SENSING DATA IN THE NORTHWEST OF SAO PAULO STATE, BRAZIL

The best irrigation management depends on accurate estimation of reference evapotranspiration (ET0) and then selection of the appropriate crop coefficient for each phenological stage. However, the evaluation of water productivity on a large scale can be done by using actual evapotranspiration (ETa), determined by coupling agrometeorological and remote sensing data. This paper describes methodologies used for estimating ETa for 20 centerpivots using three different approaches: the traditional FAO crop coefficient (Kc) method and two remote sensing algorithms, one called SEBAL and other named TEIXEIRA. The methods were applied to one Landsat 5 Thematic Mapper image acquired in July 2010 over the Northwest portion of the Sao Paulo State, Brazil. The corn, bean and sugar cane crops are grown under center pivot sprinkler irrigation. ET0 was calculated by the Penman-Monteith method with data from one automated weather station close to the study site. The results showed that for the crops at effective full cover, SEBAL and TEIXEIRA’s methods agreed well comparing with the traditional method. However, both remote sensing methods overestimated ETa according to the degree of exposed soil, with the TEIXEIRA method presenting closer ETa values with those resulted from the traditional FAO Kc method. This study showed that remote sensing algorithms can be useful tools for monitoring and establishing realistic Kc values to further determine ETa on a large scale. However, several images during the growing seasons must be used to establish the necessary adjustments to the traditional FAO crop coefficient method.

First Report of Bacterial Panicle Blight of Rice Caused by Burkholderia glumae in South Africa.

In April 2013, upright, straw-colored panicles were observed in rice (Oryza sativa L.) fields with center pivot sprinkler irrigation at Ukulima farm in Limpopo Province, South Africa. Affected panicles contained florets that initially exhibited discoloration ranging from light green to light brown on the basal portion of the glumes and later developed a reddish-brown margin separating this area from the rest of the glume that became straw-colored. The stems of infected florets remained green. Affected grains were partially filled or aborted, causing panicles to remain upright. These symptoms appeared on approximately 25% of the rice plants of the varieties Presidio and WAB56-104. A gram-negative, rod-shaped bacterium was isolated consistently from symptomatic panicles. These strains produced circular, smooth-margined, convex colonies on King's B medium (KB) with a yellowish-green, diffusible non-fluorescent pigment. Four strains, two from each of the two varieties, were selected for physiological, molecular, and pathogenicity assays. These strains grew on nutrient-broth yeast (NBY) agar at 40°C and in NBY amended with 3% NaCl. They utilized acetate, adonitol, and citrate, and were positive for gelatin hydrolysis, but negative for oxidase and arginine dihydrolase. These morphological and physiological data indicate that the characteristics of these strains were similar to those of Burkholderia glumae. The strains were further verified using B. glumae-specific PCR method (2). In a greenhouse, 12 panicles each of Presidio and WAB56-104 were spray-inoculated at the flowering stage with a bacterial suspension (108 CFU/ml) of each strain generated from cultures grown on KB at 30°C for 24 h. Twelve panicles of each variety treated in the same way with sterile water served as controls. After inoculation, treated panicles were covered with transparent polyethylene bags and maintained in the greenhouse with temperatures ranging from 24 to 35°C. After 2 days, the polyethylene bags were removed. Symptoms similar to those observed in the field developed on all the panicles inoculated with each strain by 10 days of inoculation. No symptoms were observed on the control panicles. Bacteria with the same morphological and cultural characteristics of B. glumae were consistently re-isolated from diseased panicles. All eight randomly selected, re-isolated strains were confirmed to be B. glumae based on the B. glumae-specific PCR and physiological assays described above. This pathogenicity experiment was repeated once with similar results. This is the first report of bacterial panicle blight of rice caused by B. glumae in South Africa. Overhead sprinkler irrigation appeared to promote the development and spread of the disease. Since the bacterium is seedborne (3) and there are no acceptable levels of resistance available in commercial varieties, bacterial panicle blight poses a threat to rice production. This bacterium was first described in Japan as the causing agent of grain rot and seedling rot on rice grown under flood irrigation conditions (1). Bacterial panicle blight caused by B. glumae has since been reported in China, Korea, Latin America, the Philippines, and the United States (2).

Discussion of “Role of Transpiration Reduction during Center-Pivot Sprinkler Irrigation in Application Efficiency” by Yenny Urrego-Pereira, José Cavero, Eva T. Medina, and Antonio Martínez-Cob

Discussion of “Role of Transpiration Reduction during Center-Pivot Sprinkler Irrigation in Application Efficiency” by Yenny Urrego-Pereira, José Cavero, Eva T. Medina, and Antonio Martínez-Cob

Role of Transpiration Reduction during Center-Pivot Sprinkler Irrigation in Application Efficiency

AbstractThe magnitude and duration of corn transpiration reduction during center-pivot sprinkler irrigation was analyzed on a commercial plot. The irrigation event was defined as the period during which the pivot arm was passing over the transect AC and water droplets were moistening the plants (moist treatment). Corn transpiration rates were measured at three spots of that transect and simultaneously at another spot (dry treatment) located approximately 270 m east from the transect AC. Corn transpiration rates for the moist treatment location were reduced by 30–36% compared to the dry treatment location during the irrigation event. After irrigation, the transpiration reduction lasted for 1.8–2.6 h, and ranged from 22–29%. The gross wind drift and evaporation losses ranged from 10–13% of the applied water, whereas the net interception losses were 2% of the applied water. Considering the observed corn transpiration reduction during and after the irrigation, the net sprinkler evaporation losses ranged from ...

Microclimatic and physiological changes under a center pivot system irrigating maize

The microclimatic (air temperature and vapor pressure deficit (VPD)) and physiological (canopy temperature and plant transpiration) changes due to center pivot sprinkler irrigation were monitored at a commercial plot of maize (Zea mays L.). Two treatments were considered: (a) moist, measurements taken at three spots on a transect when the pivot was running over it; (b) dry, measurements taken simultaneously at a fourth spot D, 270m apart. A total of 34 irrigation events were monitored, seven of which included plant transpiration measurements. For the transpiration-measured irrigation events, significant (P=0.05) reductions in the monitored variables for the moist treatment were observed for 0.6–2.1h before, during and 0.5–2.4h after the irrigation. The average decreases for the phase during were 1.8–2.1°C for air temperature, 0.53–0.61kPa for VPD, 3.1–3.8°C for canopy temperature, and 0.22–0.28mmh−1 (30–36%) for transpiration. Lower reductions were found for the phases before and after. The duration of the microclimatic changes decreased as the distance from the center of the pivot increased (from 3.9 to 2.2h), but the duration of the physiological changes was similar in the different pivot arm portions (≈4h). Microclimatic and physiological changes were higher in drier and warmer days. Transpiration reduction due to irrigation was higher as closer to the center of the pivot and represented 5–7% of the applied water. The estimated reduction of ET represented 1.5–1.8% of the applied water. The reduction of transpiration and ET is positive because it represents a reduction in irrigation requirements.The decrease in maize canopy temperature could be positive or negative depending on its effect on photosynthesis.

Initial Drop Velocity in a Fixed Spray Plate Sprinkler

Ballistic simulation has been successfully applied to impact sprinklers. However, ballistic simulation of center pivot sprinkler irrigation has been limited by the difficulty in estimating the initial drop velocity vector in fixed and rotating spray plate sprinklers. Initial velocity is severely affected by the impact of the jet on the sprinkler deflecting plate (or plates). In this work, experimental techniques based on drop photography have been used to obtain the droplet velocity and angle in the vicinity of a fixed spray plate sprinkler by using three different nozzle diameters. Furthermore, simulation techniques based on the inverse solution of drop trajectory were combined to determine the initial velocity vector and energy loss at the spray. Our analysis suggests that the ballistic model can be used to simulate drop inverse trajectory in these sprinklers, although the ballistic model can benefit from 5 to 10% effective drag-force screening. The ratio of initial drop velocity to jet velocity was between 0.67 and 0.82, whereas the kinetic energy losses in the spray sprinklers amounted to 33–55%.

DEPIVOT: A model for center-pivot design and evaluation

Center-pivot sprinkler irrigation became very popular. Hence, aimed at farmers advising, the simulation model DEPIVOT has been developed with the objective of design new systems or changes in systems in operation. The software consists of a simulation package developed in Visual Basic and data base in Access. The model comprises five main sub-models for: (a) computation of the gross irrigation requirements; (b) sizing of the lateral pipe spans through the hydraulics computation of the friction losses and respective operative simulation considering to the effects of topography and the possible requirements of an end gun; (c) selecting a sprinklers package with computation of pressure and discharge at each outlet and including the consideration of pressure regulators; (d) verification of the sprinklers package through estimation of runoff potential by comparing application and infiltration rates at selected locations along the lateral; and (e) estimating the expected uniformity performance indicators when in operation. The user verifies if performance is within target values set at start and may develop and compare alternative sprinkler packages until appropriate conditions are obtained. When the model is used for evaluation of systems under operation using data collected in farmers’ fields performance indicators are computed and, responding to farmers’ needs, the model may be used to design changes in the existing systems and to improve management. This paper describes the model and shows examples of applications to select a sprinkler package and assess the respective runoff potential.