Center Pivot Irrigation System Research Articles

IRRIGATION, DEEP TILLAGE, AND NITROGEN MANAGEMENT FOR A CORN–SOYBEAN ROTATION

Of the numerous factors affecting crop yield, the major factor for corn and soybean in the southeastern CoastalPlain appears to be available soil water. Inadequate rainfall and soil compaction, which limits root exploration of stored soilwater, exacerbate this problem. Potential solutions, though costly and energy intensive, include irrigation and annual deeptillage. Sometimes, doing both provides additive yield increases for corn. The objectives of this study were: (1) to prove asitespecific irrigation system, and (2) to test the separate and combined effects of irrigation, tillage, Nfertilizer, and croprotation on corn and soybean yield. A centerpivot irrigation system that had been modified to allow variablerate water andnutrient applications to 100m 2 plots within the system was used to manage an experiment with cornsoybean rotation,irrigation, deep tillage, and Nfertilizer treatments during 19951998. The modified centerpivot system satisfactorilyapplied water and N fertilizer to the treatment areas, and reliability of the control system improved during this experiment.Irrigation increased corn yield all years (8% to 135%) and soybean yield three of four years (26% to 31%). Deep tillageincreased yield in only two years, for corn (4% to 6%). For these soil and weather conditions, irrigation increased corn andsoybean yields more consistently than deep tillage. The sitespecific irrigation facility performed as expected and shouldprovide the research infrastructure to answer many longstanding questions about irrigated cropping systems in thesoutheastern Coastal Plain.

Modeling Water Distribution for Irrigation Machine with Small Spray Nozzles

A model and computer program were developed to calculate water application depth and uniformity coefficient for small spray nozzles mounted on a center-pivot irrigation system. The program requires...

A Case Study of the Beneficial Reuse of Treated Groundwater

AbstractThe future disposal of treated groundwater at the former Nebraska Ordnance Plant (NOP) Superfund site has been a topic of interest to the local property owners, the U.S. Army Corps of Engineers, and the local regulatory agencies. The Record of Decision for the site includes the extraction, treatment, and disposal of almost 3,000 gpm of groundwater with an estimated restoration time period exceeding 100 years. Interest from property owners and the Nebraska agency charged with regulating groundwater supply prompted the Corps of Engineers to consider several strategies for beneficially reusing the treated water. Alternatives included the establishment of a rural water district or local distribution system; delivery of the water to the municipal supply system of Lincoln, Nebraska, andsol;or other nearby municipalities; and consideration of innovative remedial technologies to reduce the quantity of treated water requiring disposal. The selected disposal plan consists of providing treated groundwater to interested parties for agricultural use with excess treated groundwater discharged to two streams. Multiple feasibility studies were generated, public input was solicited, and interagency agreements were executed during the course of the project. The remediation project is currently being constructed, and at least one property owner has constructed a new center‐pivot irrigation system to use the treated groundwater. © 2001 John Wiley & Sons.

SOIL–SAMPLING ISSUES FOR PRECISION MANAGEMENT OF CROP PRODUCTION

A study to examine soil–sampling issues for adequate representation of soil property variation in precision agriculture was conducted on a 26–ha farm growing cotton under a center–pivot irrigation system. Proper sampling depth, appropriate representation of field variability and laboratory–to–laboratory variances were examined. Sampling depth significantly affected soil sample test results of phosphorous and pH when comparing sample depths of 7.5 and 15 cm, while potassium levels were not significantly affected. The field was divided into a grid of 31 points and seven management zones. Recommended application of phosphate, potash and lime were substantially different when comparing zone and grid, field delineation. When soil sample test results from two laboratories were compared, there was a significant difference in measured potassium, phosphorous, and pH levels. Each laboratory also used different criteria for developing recommended rates to meet yield goals. Consequently, laboratory choice, depth of soil sample, and field delineation all affected the resulting recommended application rates and could result in poor precision management decisions. Cotton yields were measured with a yield monitor and used to compare yield goals to application rates. There was not an evident correlation between additional fertilizer and increased yield. It was suggested that variable yield goals might also be an efficient way of utilizing the field strengths when making application recommendations.

Assessing insecticide drift during and after center-pivot chemigation to corn using glass plates and gauze pads.

Insecticide application to corn through center-pivot irrigation systems (chemigation) is a common practice. According to Kohl et al. (1987), drift during and subsequent to chemigation may be a potential problem. Published data are available on pesticide drift from conventional applications (Bode et al. 1976; Byass and Lake 1977; Draper et al. 1981; Draper and Street 1981; Nordby and Skuterud 1975; Smith et al. 1982; Threadgill and Smith 1975; Ware et al. 1969, 1969, 1970; Yates et al. 1974). However, paucity of data exist regarding insecticide drift from chemigation (Byers et al. 1993). This study was undertaken to: a) measure drift using gauze pads and glass plates during and subsequent to chemigation of chlorpyrifos, permethrin, and carbaryl to corn; and b) estimate potential human exposure from drifted insecticides.

Estimativa do volume máximo de calda para aplicação foliar de produtos químicos na cultura de milho

Com o objetivo de estimar o volume de água por hectare retido na folhagem da cultura de milho para fins de quimigação (alvo folha), é proposto um modelo, tendo sido conduzido um experimento em que foi avaliada a interceptação de água pela parte aérea das plantas de milho sob diferentes lâminas de irrigação aplicadas via pivô central. Foi semeado um híbrido de milho, em três densidades, obtendo-se assim três arranjos espaciais diferentes. As avaliações foram realizadas em 3 estádios fenológicos: i) 4-5 folhas; ii) 8 folhas e iii) 14 folhas. A quantidade de água retida nas folhas das plantas foi estimada subtraindo à massa total da planta medida após a passagem do pivô, a massa de matéria seca e a água constitutiva das plantas. Para a análise estatística dos resultados, utilizou-se um delineamento experimental em parcelas subdivididas no tempo, com quatro repetições. O tratamento principal foi a população de plantas e o subtratamento a data de amostragem. A área foliar foi avaliada em cada amostragem. A fenologia e o desenvolvimento relativo da cultura foram avaliados periodicamente. Os resultados permitiram verificar que o modelo proposto é utilizável.

Evaluating an Automated Irrigation Control System for Site-Specific Herbigation1

Site-specific herbigation using a linear-move irrigation system equipped with an automated irrigation control system was evaluated in a series of field trials conducted at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. In the first study, the experimental area was divided into site-specific management zones that were randomly assigned herbigation treatments of metolachlor at 0, 1.8, 2.7, or 3.6 kg ai/ha. In a second study, site-specific herbigation treatments of metribuzin at 0, 0.28, 0.42, or 0.56 kg ai/ha were applied. The tests covered a range in system flow rate from 29 to 90% of maximum design flow. Average metolachlor rates applied were within 1, 2, and 4% of the target 1.8, 2.7, and 3.6 kg/ha rates, respectively, and average metribuzin rates were on target at the 0.28 kg/ha rate and within 5 and 2% of the 0.42 and 0.56 kg/ha target rates, respectively. In a third study, potato (Solanum tuberosum) fields were divided into management zones, and low, medium, or high populations of Indian mustard (Brassica juncea) and foxtail millet (Setaria italica) were seeded in each zone. Different rates of a metolachlor plus metribuzin mixture were herbigated in each zone—higher rates in zones with high populations and lower rates in zones with low populations. Weed control was excellent in all zones. Results suggest good potential for site-specific herbigation when linear-move or center-pivot irrigation systems are equipped with the automated irrigation control system.Nomenclature: Metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5-(4H)-one; Indian mustard, Brassica juncea (L.) Czern. et Coss. #3 BRSJU ‘Common Brown’; foxtail millet, Setaria italica (L.) Beauv. # SETIT; potato, Solanum tuberosum L. ‘Russet Burbank’ # SOLTU.Additional index words: Chemigation, herbicide application, precision agriculture, variable-rate application technology, Chenopodium album, Amaranthus retroflexus, AMARE, CHEAL.Abbreviations: CV, coefficient of variation; DF, dry flowable; EC, emulsifiable concentrate.

Methyl isothiocyanate volatilization from fields treated with metam-sodium

Emission of methyl isothiocyanate (MITC) from fields treated with metam-sodium (sodium N-methyldithiocarbamate) is a potential environmental and human safety hazard. Concentrations of MITC at three heights above four arable fields were measured following the application of metam-sodium at a rate of 480 litre ha−1 (166 kg AI ha−1). Two of these fields were treated by injection into a center-pivot irrigation system (chemigation), while in the other two fields the fumigant was applied through injection directly into the soil. Generally, higher MITC air concentrations were observed above chemigated than above injected fields. Maximum MITC air concentrations were 11.2 and 7.4 µg m−3 recorded 10 cm above ground 6–8 h following application and the minimum concentrations were 0.7 and 0.2 µg m−3 observed at 200 cm 30–35 h after application above chemigated and injected fields, respectively. The estimated MITC respiratory exposure a worker might encounter during the re-entry period ranged between 1.37 and 0.03 mg day−1 in chemigated fields and between 0.35 and 0.02 mg day−1 in the injected fields. These results suggest that application of the fumigant through injection reduced MITC volatilization losses in comparison with the chemigation method, thus posing a relatively lower risk of exposure to MITC emissions. © 2000 Society of Chemical Industry

CENTER PIVOT IRRIGATION MANAGEMENT OPTIMIZATION OF DRY BEANS IN HUMID AREAS

During the spring growing season, periods of drought can cause a significant reduction in dry bean yield inBrazil. Therefore, irrigation is applied to reduce the risks associated with the variability in weather conditions. Thecommon irrigation system in Brazil is a center pivot system. Irrigation managers usually operate a center pivot irrigationsystem in such a way that it requires more than one day to complete the irrigation of an entire field. In general, cropmodel simulations assume that irrigation of an entire field is completed in one day. This article presents modificationmade in the CROPGRO simulation model to provide irrigation managers with decision support information that isequivalent to their local conditions. The modified model takes into account the number of days that a center pivotirrigation system requires to complete one revolution. Different management regimes for three different water capacitycenter pivot systems were evaluated for dry bean as a function of net return for the State of Parana, Brazil. Themanagement regimes that were evaluated included the completion of the center pivot revolution in either one, two or threedays. Six different irrigation thresholds were applied, ranging from 40 to 90% of the remaining available soil watercontent, and three different commodity prices were analyzed. The center pivot system that showed the highest net returnwas the system that applied 6 mm/day. The irrigation management regime that resulted in the highest net return was toirrigate the entire field in one day (the highest frequency possible), when the soil water content in the top 30 cm of theprofile dropped below 70 or 80% of available soil water, depending on the commodity price. Future research is needed toevaluate different weather conditions and soil types to make these modifications in the CROPGRO simulation model morewidely applicable.

Computer control system for spatially varied water and chemical application studies with continuous-move irrigation systems

A microcomputer driven open-loop digital control system for implementing spatially variable water and chemical application from center pivot and linear-move irrigation systems is described. The control system is comprised of readily available commercial components and provides an effective means of implementing variable rate water and chemical application in crop production studies for evaluating potential benefits. The control system was implemented on a three-span 100 m linear-move irrigation system and on a 39-ha commercial center pivot irrigation system. Water and chemical application were monitored to document control system performance. The results show that spatially varied water and chemical application was achieved with the same accuracy as that of conventional uniform application. This paper provides details on the control system hardware and software and documents field performance.

Variabilidade espacial de micronutrientes em solo sob pivô central no sul do Estado de Mato Grosso

Este estudo foi desenvolvido para identificar, caracterizar e comparar a estrutura da dependência espacial dos micronutrientes boro, cobre, ferro, manganês e zinco solúveis em um Latossolo Vermelho-Escuro sob pivô central após 14 anos de uso intensivo, no sul do Estado de Mato Grosso. O esquema de amostragem consistiu de coletas de 132 amostras com espaçamento regular de 167 m, especialmente idealizado para determinar a variabilidade espacial em distância de até 1 m. Com exceção do zinco, o uso intensivo propiciou um aumento significativo nas concentrações desses nutrientes na camada mais afetada pelo manejo (0-20 cm), mesmo assim insuficientes para atingir o nível crítico estabelecido para a região. Cerca de 95% das amostras de boro, 75% das amostras de cobre, 95% das amostras de manganês e 1,5% das amostras de zinco apresentaram valores abaixo do nível crítico, distribuídos diferentemente pelos quadrantes, o que mostra que as práticas de fertilização e/ou as operações de preparo de solo não foram eficientes na distribuição e homogeneização dos fertilizantes.

Fungicide Application for Late Blight Management: A Boom Attached to a Center Pivot Irrigation System.

Chlorothalonil was applied to commercial potato fields of cvs. Russet Norkotah and Russert Burbank in replicated trials through either a center-pivot irrigation system or a spray-boom-attached-to-the-pivot system. Water rates were 26,192 and 675 liters/ha for the center pivot and attached boom, respectively. Three crop canopy levels were sampled within 2 h and again after 6 days following fungicide applications made at 7-day intervals. Efficacy of the two application methods was tested by inoculation of individual excised leaves with an isolate of strain US-1 or US-8 of Phytophthora infestans and by chemical residue analysis. Severity of late blight did not differ between the two fungicide application methods 2 h after application but, after 6 days, disease severity was significantly less on leaves where chlorothalonil was applied by the attached boom. Fungicide residues were three times higher on leaves where chlorothalonil was applied by the attached boom than with the center-pivot system. Significantly more disease occurred on fungicide-treated and non-treated leaves inoculated with the US-8 than the US-1 strain. Severity of late blight on inoculated leaves was inversely related to the amount of chlorothalonil residue on leaves.

Transformation of Landownership and Land Use in the Sandhills of Southwest Kansas

The adoption and diffusion of center pivot irrigation systems transformed the traditional landscape of the High Plains. While Finney County in southwest Kansas has been known as one of the most advanced irrigation districts of the High Plains, vast sandhills on the right bank of the Arkansas River remained extensive cattle pasture until center pivot irrigation systems had completely changed the farming landscape during the 1970s. The new irrigation technology and feed crop cultivation combined to develop the feedlot and beef packing industries in the region. This paper examines the transformation process of landownership and land use in the sandhills of Finney County with special reference to the diffusion of center pivot irrigation systems.Cattle industry began in the Garden City area in the late nineteenth century, and large landholdings and extensive cattle raising continued to dominate the sandhills up to the 1960s. Large landholdings with over 10, 000 acres included Brown, Cowgill, Burnside, Douglas, and Jones ranches. They purchased calves from ranchers of the western states, raised them on the natural pasture, and shipped them to the corn belt for finishing. Some ranchers specialized in breeding high quality beef cattle, and others took care of the calves born in the local farms from spring through fall. The region, blessed with ground water and natural pasture, was also known as winter refuge for animals.Land register maps and aerial photos reveal substantial changes which took place in the sandhills during the 1970s. Large feedlot companies and agribusinesses came to own large tracts of land by purchasing traditional cattle ranches, while descendants of homesteaders also participated in the irrigation development. Gigot Irrigation Co. first demonstrated the effectiveness of center pivot irrigation systems in developing additional sandhills land which they purchased, while acting as a sales agent of the Valley brand irrigation systems. The company sold 600 sets of center pivot irrigation systems annually in two boom years of 1972 and 1973, while the company's average annual sales amounted to around 200 sets in the following years. Thus, the rich ground water resources of Ogalalla aquifer were exploited. The rapid process of adopting the new technology transformed the traditional barrens into the fertile farming regions irrigated by big circles.Large land holders are typically found in the sandhills. Circle Land and Cattle Inc. owned by Gigot families manage more than 20, 000 acres. Brookover Feedyards, which started cattle feeding in the early 1950s just northwest of Garden City, expanded their business in the sandhills by introducing center pivot irrigation systems, developing subdivisions, and managing golf courses. IBP, a beef packing company operating the world's largest packing plant just west of Garden City, and Tim Dewey Farms and Cattle Co. also started irrigation farming by purchasing land in the sandhills. Corn and alfalfa are the two major irrigation crops, which are consumed locally at large feedlots. Because of these developments since the 1970s, lowering the water table of the Ogalalla aquifer is considered a serious problem in order to sustain the highly water consuming farming of the sandhills.

アメリカ合衆国ハイプレーンズにおける潅がい化と農業地域の変化 カンザス州南西部の事例

In the High Plains regions of the United States, once called the Great American Desert, productive farming regions were formed due to the introduction of center pivot irrigation systems since the 1960s. Finney county of Southwest Kansas, our study area, is one of the most productive farming regions in the High Plains, where irrigation has a long history. While windmills were built to take advantage of shallow ground water in the late nineteenth century, surface water became diverted from the Arkansas River by constructing irrigtion ditches beginning in the 1880s. Ditch irrigation was further promoted by the construction of sugar factory in Garden City in 1906 and the subsequent sugar beet cultivation mainly on the High Plains tablelands of the left bank of the Arkansas. On the other hand, introduction of turbine pumps and the use of inexpensive natural gas pumped from the underlying Hugoton gas field combined to promote the development of ground water irrigation from the 1940s.The most striking in the history of the High Plains is the invention and introduction of the center pivot irrigation system. The Gigots introduced a valley brand system of center pivot irrigation in 1963 in order to improve their farmland in the sandhill, and their success triggered the application of the new irrigation technology. The early 1970s were boom years in Garden City and its vicinity when the Gigot Irrigation soled 600 systems annually. The sandhills on the right bank of the Arkansas, where rolling topography, infertile soils, and excessive drainage defied intensive use of land and therefore remained the barrens, were most efectively transformed into the landscape dominated by big circles. On the left bank, center pivot systems were introduced in the dry land farming districts on the talbelands, while they are gradually replacing traditional ditch and groundwater irrigation. Such a transformation process is well documented by the distribution of wells and the aerial photo analyses. Due to these irrigation developments, production of feed crops expanded such as maize, alfalfa, sorghum, and soy beans.The development of irrigation and feed crop production is key to understand the subsequent phases of regional changes, including feedlot and beef packing industries, population composition and dynamics, and undergroud water management. It is necessary to closely examine these geographic features in order to understand the sustainability of the High Plains regions.

Alternating Furrow Irrigation of Peppermint (Mentha piperita)

Furrow irrigation of peppermint (Mentha piperita L.) has certain benefits over sprinkler irrigation, but usually wastes irrigation water. Alternate-furrow irrigation allows frequent application of small amounts of water, which is an advantage over conventional furrow irrigation. In a variation of alternate-furrow irrigation, alternating-furrow irrigation, every other furrow is irrigated at the first irrigation, and the remainder at the second, then this procedure is repeated throughout the season. It is a low-cost, low-energy alternative to sprinkler and center pivot irrigation systems. Our objective was to compare yield and water use of alternating-furrow irrigation with those of conventional every-furrow irrigation for peppermint. Field experiments in 1992 and 1993 indicated that the soil water content was adequate under both irrigation treatments, and the water savings for alternating-furrow irrigation were attributed to less runoff and less evaporation from the soil surface. There was no difference in yield between the systems, although alternating-furrow irrigation required about half of the water applied with the conventional treatment. One limitation of alternating-furrow irrigation occurred near the end of the growing season, when the plants lodged, partially dammed the furrow streams, and made timely furrow advance difficult. This problem was resolved by irrigating every furrow after lodging occurred.

Desempenho e uniformidade da distribuição de água de um pivô central

O objetivo deste experimento foi avaliar as características de desempenho de um equipamento de irrigação pivô central, de baixa pressão, bem como determinar a uniformidade de distribuição de água, tanto abaixo como acima da superfície do solo. Para a avaliação do desempenho do sistema utilizaram-se os coeficientes de uniformidade de Christiansen (CUC) e de distribuição (CUD), calculados a partir de dados da precipitação dos aspersores. O pivô central foi ensaiado nas velocidades de 25%, 50%, 75% e 100% da velocidade máxima de deslocamento do equipamento. Utilizou-se quatro linhas de coletores, uniformemente espaçados. Os valores encontrados do CUC e o CUD foram superiores ao mínimo recomendado para a cultura do milho, confirmando o bom desempenho do pivô central. Em todas as profundidades do solo estudadas os coeficientes de uniformidade foram superiores aos obtidos acima do solo, ocorrendo um aumento nos valores dos coeficientes de uniformidade abaixo da superfície do solo com o tempo.

SUPERVISORY CONTROL AND DATAACQUISITION SYSTEM FOR SITE-SPECIFIC CENTER PIVOT IRRIGATION

A distributed control and data acquisition network was developed for implementing variable rate water application to irregularly shaped areas under a center pivot irrigation system. The control network was designed to meet system requirements for variable rate irrigation. The control network utilizes power line carrier technology for communicating over the three-phase 480 VAC center pivot power cable and multiple network nodes in a master-slave configuration distributed along the center pivot lateral. The network was implemented on a commercial 392 m (1285 ft) center pivot system and field tested during the 1996 irrigation season. The supervisory control and data acquisition network was used to withhold water from non-cropped areas of the field and minimize system operating pressure according to distributed pressure measurements by controlling the speed of the water supply pump using a 111 kVA variable speed motor controller. A description of the control network hardware, software, system implementation, and preliminary operational performance are presented.

ハイプレーンズにおけるフィードロットの展開と牛肉加工業の垂直的統合 カンザス州南西部を中心にして

The High Plains regions of the western United States, once called the Great AmericanDesert, recently emerged as a center of beef production. This paper examines the development process of cattle feedlots and beef packing plants and the vertical integration attained by major agribusinesses in southwestern Kansas.The Arkansas River valley in southwestern Kansas has retained optimal conditions forcattle fattening since the late nineteenth century. Prior to the advent of irrigation farming, cattle were grazed on native grassland and stubbles of wheat and milo (grain sorghum), while the region was an important winter refuge to which cattle were brought from other grazing areas. The beet sugar factory operated in Garden City during the first half of the twentieth century also provided cattle with excellent feed.Cattle finishing began with farmer feedlots where grain growers fattened their cattle, depending on subsistent feed harvested within their farms. The number of feedlots increased from the late 1960s through 1980 as the plentiful ground water resources of the Ogallala Aquifer were exploited using center pivot irrigation systems, and feed crop production increased rapidly. Although the majority of farmer feedlots went out of business with a return to grain farming by the 1980s due to unstable beef prices, the number of commercial feedlots, owned and operated by agribusiness firms and depending entirely on purchased feed, increased. The total number of feedlots decreased after 1980, while the sizes of feedlots expanded and their integration proceeded. Some commercial feedlots developed into corporate custom feedlots by expanding feeding capacity and diversifying business operations.The development of cattle feeding in the High Plains promoted a locational shift ofAmerican beef packing industry. It was traditionally found in and around large cities adjacent to stockyards. Large packers, such as IBP, originated in the Corn Belt to take advantage of feed supplies and to secure easy access to feedlots, began to establish new packing plants in the High Plains. Monfort and Excell, two other major beef packers, also expanded their beef packing operations in the High Plains by either initiating or purchasing beef packing plants. New developments in marketing such as refrigerated boxed meat also promoted such locational shifts. Four major beef packers of IBP, Monfort, Excell, and National Beef Packing have major packing plants in southwestern Kansas.Major grain companies have been playing an important role in the development of vertically integrated grain-cattle-beef business. A subsidiary of Cargill, Inc. operates seven large feedlots, and Excell also belongs to this grain company. Continental Grain, another major grain company, operates the largest feedlot in the United States. Thus, southwestern Kansas is characterized by the beef industry where feed production, cattle fattening at feedlots, and beef packing are effectively integrated on the abundant ground water resources of Ogallala Aquifer.

EVALUATION OF LESA TECHNOLOGY IN A SASKATCHEWAN ENVIRONMENT

The need for high energy input is one of the primary limitations to developing the sustainability of centre pivot irrigation. The purpose of the project described in this paper was to evaluate Saskatchewan performance data for Low Elevation Spray Application (LESA) irrigation technology. A centre pivot irrigation system equipped with standard impact nozzles was modified by the addition of drop tubes and Low Drift Nozzles (LDN). The application efficiency for the impact and LDN nozzles showed that both had a decreasing trend with increasing wind speeds, but the low drift nozzles had a better efficiency at all wind speeds. The application efficiency for the high pressure nozzles ranged from 69%–86% and the low drift nozzles from 74%–98%: an 8% difference in application efficiency for the LESA technology. The energy consumed by the two systems indicated that both systems had increased energy consumption with increased wind speed, but the low pressure LESA system used on average one half the energy required by the medium pressure impact system to deliver the same amount of water (0.107 kWh/m3 as compared to 0.057 kWh/m3).

MODIFIED CENTER PIVOT SYSTEM FOR PRECISION MANAGEMENT OF WATER AND NUTRIENTS

Spatial yields since 1985 in a corn-wheat-soybean rotation at Florence, S.C., show little correlation of yielddata with expected yields for soil map units. Research suggests that spatial yield variability for the southeastern CoastalPlain may be caused primarily by water relations. This causes difficulties in scheduling irrigation for conventional centerpivot irrigation systems, which are not capable of applying variable depths of water to small areas of variation within thetotal system. Thus, the objectives of this work were to design and construct a site-specific center pivot irrigation systemthat could independently apply variable rates of water and chemicals to 100-m2 areas within the irrigation system. Acommercial center pivot system was modified by adding three 9.1-m manifolds in each of 13 segments along the truss.Nozzles were spaced 1.5 m apart along each manifold, and both manifolds and nozzles were sized to provide 1x, 2x, and4x nominal application rate at a given tower speed. All combinations of the three manifolds provided up to 7x nominaldepth, which was 12.7 mm, in 1.8-mm increments when the outer tower traveled at 50% of full speed. A programmable,computer-controlled management system was installed near the pivot on the moving portion of the center pivot system.This controller obtained the position from the center pivot controller via a radio frequency modem and switched on theappropriate valves to obtain the application rate for a specific area. During 1995 and 1996, the system applied water andN fertilizer in a fixed-boundary field experiment. Measurements and observations of water and N application uniformitieswere acceptable; however, more extensive evaluation will be required before definitive conclusions can be reachedregarding N application. Surface temperatures measured with an integral infrared thermometer system producedencouraging results that may be useful in management of water and nutrients. Using experience gained with this system,a second commercial center pivot system is being modified for site-specific water, nutrient, and pesticide management ona field with soil variation (irregular boundaries) typical of the Coastal Plain.