Maricopa Agricultural Center Research Articles

Data from the Arizona (Free-Air CO2 Enrichment) Experiments on Cotton at Ample and Limiting Levels of Water Supply and Nitrogen Fertilization and at various Plant Densities

Several cotton experiments have been conducted at the University of Arizona's Maricopa Agricultural Center from which datasets have been obtained documenting cotton responses to elevated CO2 concentrations, water supply, nitrogen fertilizer, and planting density. In particular, these experiments included FACE (free-air CO2 enrichment; CO2, water; 10 treatment-years), AgIIS (Agricultural Irrigation Imaging System, pronounced Ag Eyes; nitrogen fertilizer, water supply; 4 treatment-years), and FISE (FAO-56 Irrigation Scheduling Experiments; irrigation scheduling method, planting density, nitrogen fertilizer; 24 treatment-years). Besides achieving the experimental objectives of determining cotton's response to the several variables, as well as testing remote sensing techniques, the comprehensive datasets are suitable for validating plant growth models because they include weather, soils, management, growth, yield and other data.

Effects of harvest date and growth stage on triticale forages in the southwest USA: kinetics of in vitro disappearance of fiber and dry matter.

Recently, there has been interest in including triticale (X Triticosecale Wittmack) within forage programs in the southwest USA. Our objectives were to evaluate in vitro disappearance kinetics of neutral detergent fiber (NDF) and dry matter (DM) for cultivars identified during 2019 as positively or negatively deviant from typical cultivars, based specifically on regressions of 48-h in vitro disappearance of NDF on growth stage (GRST). All NDF analyses included the use of heat-stable α-amylase and sodium sulfite, as well as correction for residual ash (asNDFom). Seven triticale cultivars were established on December 18, 2019 at the University of Arizona Maricopa Agricultural Center, located near Maricopa, AZ. Forage plots were arranged in a randomized complete block design with three complete blocks (replications), and then harvested on seven dates the following late-winter and spring (February 26, March 17, April 1, April 14, April 28, May 12, and May 26). Based on a linear model, GRST was highly variable among cultivars on March 17 (44 ± 10.6), April 1 (57 ± 12.1), April 14 (67 ± 8.9), and April 28 (79 ± 7.2) compared with other harvest dates (SD ≤ 1.7). For concentrations of asNDFom, all cultivars exhibited linear (P ≤ 0.042) and quadratic (P < 0.001) polynomial contrasts in response to harvest date, and all cultivars except Merlin Max (P ≥ 0.063) exhibited at least one additional cubic or quartic effect (P ≤ 0.015). A contributing factor to the unique response by Merlin Max was the numerically greater maximum canopy height (145 ± 9.8cm) compared with the mean of all cultivars (107 ± 17.7cm), which also was associated with greater percentages of stem, as well as reduced percentages of DM partitioned within the grain head. Regressions of asNDFom disappearance after 30- or 48-h incubations on GRST indicated this was an effective independent variable (R2 ≥ 0.927), and responses were most often linear in nature. Generally, relationships for DM disappearance were quadratic, ostensibly due to the complicating effect of grain fill, but GRST was again an effective predictor variable with R2 statistics ≥ 0.852 for 12 of 14 combinations of cultivar and incubation time. Predicted percentages of digestible DM attributed to asNDFom disappearance were ≥50.3% through the fully flowered stage of growth, but digestible contributions from nonfiber components following the onset of grain fill profoundly affected overall DM digestibility among cultivars harvested at later GRST.

Moment Analysis for Modeling Soil Water Distribution in Furrow Irrigation: Variable vs. Constant Ponding Depths

Despite increasing use of pressurized irrigation methods, most irrigation projects worldwide still involve surface systems. Accurate estimation of the amount of infiltrating water and its spatial distribution in the soil is of great importance in the design and management of furrow irrigation systems. Moment analysis has previously been applied to describe the subsurface water distribution using input data from numerical simulations rather than field measured data, and assuming a constant ponding depth in the furrow. A field experiment was conducted in a blocked-end level furrow at Maricopa Agricultural Center, Arizona, USA, to study the effect of time-variable ponding depths on soil water distribution and the resulting wetting bulb under real conditions in the field using moment analysis. The simulated volumetric soil water contents run with variable and constant (average) ponding depths using HYDRUS 2D/3D were almost identical, and both compared favorably with the field data. Hence, only the simulated soil water contents with variable ponding depths were used to calculate the moments. It was concluded that the fluctuating flow depth had no significant influence on the resulting time-evolving ellipses. This was related to the negligible 10-cm variation in ponding depths compared to the high negative matric potential of the unsaturated soil.

Long-term simulations of site-specific irrigation management for Arizona cotton production

Engineering technologies for site-specific irrigation management (SSIM) have already been developed for applications in precision irrigation. However, further studies are needed to identify scenarios where SSIM leads to better agronomic outcomes than conventional uniform irrigation management (CUIM). The objective was to conduct a long-term simulation study to compare SSIM and CUIM given spatial soil variability at the Maricopa Agricultural Center (MAC) in Arizona. More than 500 surface soil samples were collected across a 730-ha area of the MAC from 1984 to 1987. A more detailed soil data set was more recently obtained across a 5.9-ha area at a MAC location designated for SSIM studies. Ordinary kriging was used for spatial interpolation of soil hydraulic properties within $$10\,\hbox {m} \times 10\,\hbox {m}$$ zones across the MAC, and 11 field parcels with an area of approximately 60 ha were delineated on the MAC quarter sections. Using an agroecosystem model, simulations of cotton production at the zone level with a 30-year weather record were conducted using a field-tested algorithm to optimize irrigation schedules for SSIM and CUIM. Long-term seed cotton yield, irrigation requirements, water use efficiency, and marginal net return for SSIM and CUIM strategies were often not different ($$p>0.05$$). Differences in seed cotton yield and irrigation requirements among the tested irrigation strategies were less than 11% and 6%, respectively, and within the typical range of model error. Most soils on the MAC have enough available water holding capacity to sustain cotton production at full potential with weekly CUIM, and advantages of SSIM were not consistently demonstrated by the simulations.

Lint Yield Compensatory Response to Main Stem Node Removal in Upland Cotton (Gossypium hirsutum)

AbstractHail storm damage to the cotton (Gossypium hirsutum L.) plants can destroy vegetative and reproductive structures, modify canopy architecture and impact lint yield. Field studies were conducted at University of Arizona Maricopa Agricultural Center in 2011, 2012 and 2013 to examine cotton plant architecture changes and compensatory growth in response to removal treatments of uppermost nodes on main stem (terminal bud removal, 2 node removal and 4 node removal) as simulation of hail damage at the node 2, 4, 8, 12, 16 and 24 growth stages. Main stem node removal caused significant decrease in leaf area and biomass, especially at early growth stages. However, significant lint yield reduction only occurred by removing 2 nodes at the node 4 stage and removing 4 nodes at the node 8 stage in 2011, removing terminal bud at the node 12 stage in 2012 and removing terminal bud, 2 nodes and 4 nodes at the node 8 stage in 2013. The lint yield reduction did not exceed 13 % in all three growing seasons. Yield loss due to main stem node removal was mainly compensated by increased boll number on the vegetative branches at early growth stages and on fruiting branches at late growth stages. Yield compensation from vegetative branches increased with number of main stem nodes removed. This study suggests that the cotton crop has a strong compensatory ability to plant structure damage due to its indeterminate growth and longer growing season in the region.

Comparison of traditional and ET-based irrigation scheduling of surface-irrigated cotton in the arid southwestern USA

The use of irrigation scheduling tools to produce cotton under-surface irrigation in the arid southwestern USA is minimal. In the State of Arizona, where traditional irrigation scheduling is the norm, producers use an average of 1460mm annually to grow a cotton crop. The purpose of this paper was to determine whether or not the use of ET-based irrigation scheduling methods could improve lint yield and irrigation water use productivity over traditional cotton border irrigation scheduling practices in the region. A field study with four irrigation scheduling treatments replicated in 4 blocks was conducted for two cotton seasons (2009 and 2011) in 16, 12-m×168-m cotton borders at the Maricopa Agricultural Center (MAC), in Arizona, USA. Remotely-sensed vegetation indices (VI) were used to estimate basal crop coefficients (Kcb) at 40, 4-m×8-m zones within borders for two treatments, denoted as VI_A and VI_B, whereas a single Kcb curve was applied to all zones in borders for a third treatment (FAO). Daily ETc for these three treatments was estimated using FAO-56 dual crop coefficient procedures with local weather data and irrigation scheduling for the three treatments were based on soil water balance predictions of soil water depletion (SWD). For the VI_A and FAO treatments, irrigations were given when predicted SWD of all 160 zones in the treatment averaged 45% of total available water (TAW). For the VI_B treatment, irrigations were given when 5% of the 160 zones in the treatment were predicted to be at 65% SWD. A fourth treatment (MAC) represented the traditional irrigation scheduling treatment and was scheduled solely by the MAC farm irrigation manager using only experience as a guide. The study showed that the lint yields attained under the MAC farm manager’s irrigation scheduling equaled or exceeded the yields for the three ET-based irrigation scheduling treatments. Although the MAC irrigation scheduling resulted in somewhat higher irrigation input than for the other treatments, the MAC treatment maintained or exceeded the irrigation water productivity attained for other treatments that had lower irrigation inputs. A major conclusion of the study was that present-day irrigation water use for cotton in surface-irrigated fields could be substantially reduced. When compared to Arizona state cotton averages, any of the four treatments presented in the study could potentially offer methods to significantly reduce cotton irrigation water use while maintaining or increasing current lint yields levels.

Evaluation of CSM-CROPGRO-Cotton for Simulating Effects of Management and Climate Change on Cotton Growth and Evapotranspiration in an Arid Environment

<abstract> <bold><sc>Abstract.</sc></bold> Originally developed for simulating soybean growth and development, the CROPGRO model was recently re-parameterized for cotton. However, further efforts are necessary to evaluate the model’s performance against field measurements for new environments and management options. The objective of this study was to evaluate CSM-CROPGRO-Cotton using data from five cotton experiments conducted at the Maricopa Agricultural Center in Maricopa, Arizona. The field experiments tested ambient atmospheric carbon dioxide (CO₂) versus free-air CO₂ enrichment (FACE) over two growing seasons (1990 and 1991), two irrigation levels and two nitrogen fertilization levels for one growing season (1999), and three planting densities and two nitrogen fertilization levels with optimum irrigation for two growing seasons (2002 and 2003). The model was calibrated by adjusting cultivar and soil parameters for the most optimal or standard treatment of each field trial, and the model’s responses to suboptimal irrigation, suboptimal nitrogen fertilization, nonstandard planting density, and CO₂ enrichment were evaluated. Modifications to the model’s evapotranspiration (ET) routines were required for more realistic ET simulations in the arid conditions of central Arizona because default approaches underestimated seasonal ET up to 157 mm (15% of mean values). Data quality and availability among the field trials were highly variable, but the combination of data sets from multiple field investigations permitted a more thorough model evaluation. Simulations of leaf area index, canopy weight, canopy height, and canopy width responded appropriately compared to measurements from experimental treatments, although some experiments did not impose enough treatment variability to elicit substantial model responses. Simulation results for densely planted cotton were particularly deficient as compared to other experimental treatments. The model simulated seed cotton yield with root mean squared errors ranging from 105 to 1107 kg ha^-1 (3% to 28% of mean values), and total seasonal ET was simulated with root mean squared errors ranging from 12 to 42 mm (1% to 5% of mean values). Seed cotton yield and ET variability due to the imposed experimental treatments were simulated appropriately (p < 0.05), independent of the year-to-year variability due to seasonal factors. Modification of the ET routines permitted maximum simulated crop coefficients ranging from 1.31 to 1.35, which were more realistic than that required for default ET methods in the model. Overall, the evaluation demonstrated appropriate model responses to water deficit, nitrogen deficit, planting density, and CO₂ enrichment. Potential opportunities for further model improvement include the estimation of crop responses to high planting densities, the simulation of cotton maturity and defoliation events, and the calculation of canopy temperature as part of a complete energy balance algorithm.

Plant architecture influences growth and yield response of upland cotton to population density

Plant architectural characteristics directly affect inter-plant interactions and cotton crop management. Field studies were conducted in the 2010 and 2011 growing seasons at the University of Arizona Maricopa Agricultural Center to investigate the influence of plant architecture on the crop growth, biomass partitioning, and lint yield response of upland cotton to population density under irrigated desert conditions. Two cotton varieties of contrasting architecture, a tall stature columnar type, Delta and Pine 164B2RF (DP164), and a short stature bush type, Stoneville 4498B2F (ST4498), were evaluated under three plant population densities: low density (LD, 57,300–66,500 plantsha−1), medium density (MD, 77,300–109,800 plantsha−1), and high density (HD, 126,700–146,000 plantsha−1). While high population densities significantly increased plant height of both varieties at early growth stages, plant height at late growth stages were not significantly different. High plant population reduced main stem node number of both varieties. However, the effect was more pronounced with ST4498 where the HD treatment had 2.9 and 2.5 nodes less than the LD treatments in 2010 and 2011, respectively. Plant population affected the height to node ratio of DP164 more than ST4498. The taller, columnar type DP164 partitioned more biomass into stems than the bush type ST4498 at all three plant populations. The LD treatment significantly reduced cotton growth and yield of DP164 in 2010. This study suggests the existence of differences in responses to plant population density among upland cotton varieties, attributable to canopy architecture. Additionally, results indicate that shorter bush type varieties might have higher growth plasticity and thus accommodate a broader range of plant densities than taller stature columnar type varieties.

Thermal Infrared Emissivity Dependence on Soil Moisture in Field Conditions

An accurate estimate of land surface temperature, which is a key parameter in surface energy balance models, requires knowledge of surface emissivity. Emissivity dependence on soil water content has been already reported and modeled under controlled conditions at the laboratory. This paper completes and extends that previous work by providing emissivity measurements under field conditions without elimination of impurities, local heterogeneities, or soil cracks appearing in the drying process. The multispectral radiometer CE312-2, with five narrow bands and a broad band in the 8-13-μm range, was used, and surface emissivity values were determined through a temperature-emissivity separation algorithm. A bare soil plot of 10 ×17 m2 was selected for this study in the framework of a camelina 2010 experiment. This experiment was carried out during March and April 2010 at The University of Arizona Maricopa Agricultural Center in central Arizona, USA. The soil plot was flood irrigated every two to three days and left to dry. Field emissivity measurements were collected under cloud-free skies, around noon, for different values of soil water content. Soil samples were collected to estimate the soil moisture (SM) using the gravimetric method. An overall increase of emissivity with SM was obtained in all channels. However, when wetted soils subsequently dried, the final minimum emissivity was greater than the initial minimum emissivity. This hysteresis could be due to cavity effects produced by soil cracks not originally present. Thus, the deterioration of soil surface tends to reduce the emissivity spectral contrast. Soil-specific and general relationships obtained by Mira et al. were tested and compared with the field measurements. Field emissivities agree within 2% with the modeled values for all bands under noncracked surface conditions, whereas differences reach 5% in the 8-9- μm range when cracks are present.

Determining optimum harvest time for guayule latex and biomass

Guayule ( Parthenium argentatum Gray) is a perennial shrub native to the Chihuahuan Desert of Northern Mexico and the Big Bend area of southwest Texas. One of the most valuable products from guayule is its hypoallergenic latex. However, little research has been done on the optimum harvest time for latex concentration and yield. The objective of this study was to determine the optimum harvest time during the growth cycle for latex content, plant biomass, and latex yield of guayule. Treatments consisted of three guayule lines (11591, AZ3, and G7-11TC) harvested every other month for 2 years. Plants were transplanted on 4 April 1995 at the University of Arizona Maricopa Agricultural Center, Maricopa, Arizona. Harvesting began in March 1998 and continued every other month through January 2000. Samples were analyzed for latex concentration and total biomass. Latex yields were calculated as the product of the latex concentration times the dry plant biomass. The experimental design was a randomized complete block with four replications. Results varied among lines and harvest dates. There appears to be enough differences among lines that planting lines selected for different optimum harvest dates would allow growers to spread the optimum harvest time throughout most of the year. This would also benefit processors by allowing them to reduce their production costs by spreading the harvest over several months instead of only a few months. More research must be done to determine whether specific environmental factors can be associated with the optimum harvest time and line specific harvesting guides such as growing degree days or other methods for determining optimum harvest date can be utilized in guayule.

Post-harvest storage effects on guayule latex, rubber, and resin contents and yields

Guayule is a new crop being commercialized for hypoallergenic latex production. Because natural processes that occur in the plant following harvest, notably dehydration, result in rapid loss of latex and immediate processing of guayule shrub for latex on a commercial scale is not feasible, storage conditions that maintain latex concentration and yield need to be established. The objective of this study was to determine the effects of different storage conditions on the extractable latex, total rubber, resin, and guayulin A and B contents, and extractable latex, total rubber, and resin yields in harvested guayule shrub. The experiment was established using plants transplanted into the field at the University of Arizona Maricopa Agricultural Center, Maricopa, AZ, USA, on 22 March 2001. A randomized complete block design with four replications was used. Two germplasm lines (11591 and AZ-2) were used for this experiment. Twenty plants of each line were harvested six times (November 2002, March 2003, July 2003, November 2003, March 2004, and July 2004) from each field plot. Two plants of each line were randomly assigned to each of 10 storage treatment combinations reflecting wet, dry, or wet alternated with dry conditions prior to chipping for latex extraction. Extractable latex content, total rubber content, resin content, and guayulin A and B contents were determined after storage and compared with freshly harvested shrub. Plant biomass, latex yield, rubber yield, and resin yield were also determined and compared with fresh harvested shrub. AZ-2 was significantly lower in latex, rubber, and guayulin A content than 11591, and significantly higher in biomass, latex yield, rubber yield, resin content, resin yield, and guayulin B content. The results from this study show that moist storage of harvested shrub prior to dry chipping allows a higher yield of latex. Storing the shrub under moist conditions may allow more flexible harvesting and processing schedules, by limiting post-harvest latex losses and increasing the time interval between harvesting and processing.

EVALUATION OF ADDED NITROGEN INTERACTION EFFECTS ON RECOVERY EFFICIENCY IN IRRIGATED COTTON

Studies were conducted in 1997 and 1999 at the University of Arizona Maricopa Agricultural Center to evaluate the added nitrogen (N) interaction or 'priming effect' on the determination of N recovery efficiencies (NRE) in Upland cotton (Gossypium hirsutum L.). Overall growth patterns of the crop were significantly different between the two years. In 1997, the crop experienced a favorable balance between reproductive and vegetative growth. The NRE estimates were 34.7% and 34.7% for Treatment 1 (recommended fertilizer N rate, 168 kg N ha -1 (RecN)) and 25.2% and 26.0% for Treatment 2 (twice recommended fertilizer N rate, 336 kg N ha (RecN 2x)) for the difference and isotopic dilution technique, respectively. In 1999, however, the crop experienced very poor fruit load and vigorous vegetative growth. This resulted in a crop that produced much more vegetative dry matter at the expense of reproductive dry matter (yield). Higher NRE estimates were observed using the difference technique (50.8% and 40.5% for RecN and RecN 2x, respectively) when compared with the isotopic dilution technique (32.3% and 35.2% for RecN and RecN 2x, respectively). Higher amounts of soil N taken up by the plant were also observed in 1999 when compared with those in 1997. The results presented from these studies indicate that plant uptake of indigenous soil N was much higher in 1999 than in 1997, which is evidence of an added N interaction. However, this increase does not seem to have been stimulated by the addition of fertilizer N but rather the increased vegetative growth and root exploration that occurred in 1999.

Post-harvest storage effects on guayule latex quality from agronomic trials

Current guayule commercialization efforts are based upon the production of hypoallergenic latex. The objective of this study was to determine how latex yield and quality are affected by post-harvest plant storage in order to provide flexibility in the harvesting, chipping, and processing steps for guayule latex. The experiments were conducted on two lines (11591 and AZ-2) at the University of Arizona Maricopa Agricultural Center, from March 2001, through December 2004. Weight-average molecular weight of guayule latex increased as the plants aged from 1.7 to 2.7 years. Guayule latex quality was affected by shrub storage conditions, and addition of moisture extended the storage time for guayule shrub without negatively impacting molecular weight for both varieties. However, under extreme conditions, for example, high temperatures and extended dry storage times, polymer molecular weight reduction of up to 30% occurred.

Water use and crop coefficient of subsurface drip-irrigated lettuce in Central Arizona

A two year field study (1996/97 and 1997/98 growing seasons) was carried out at the Maricopa Agricultural Center (33º04'07" N; 111º57'18" W) of the University of Arizona, USA, to investigate the water use and to derive Kc's for subsurface drip-irrigated head lettuce grown in small weighable lysimeters. Measurement periods ranged from 480 to 1100 ºC-day (96/97) and from 439 to 1098 ºC-day (97/98). These intervals corresponded essentially to the second half of the crop cycle which amounted to a 1100 ºC-day, on average. The lysimeters were weighed periodically and the computation of the water balance revealed an average water use of 117 mm. Basal crop Kc was expressed as a function of cumulative growing degree days following a multiple linear regression procedure in which the data were fitted with a Fourier sine series model with up to six coefficients. Two-year Kc curves were obtained based on the Hargreaves, FAO Penman and FAO Penman-Monteith equations and compared to the AZSCHED (AriZona SCHEDuling) irrigation package. Predicted Kc peaked 0.88, 0.80 and 0.81 with the Hargreaves, FAO Penman, FAO Penman-Monteith equations, respectively, in the range of 1000 to 1050 ºC-day, in contrast to AZSCHED which predicted the peak Kc to be 1.01 at 1150 ºC-day.

Planting date effects on flowering, seed yield, and oil content of rape and crambe cultivars

Both crambe ( Crambe abyssinicia, Hochst) and rape ( Brassica napus L. and Brassica rapus L.) are cool season crops, thus they may have potential as irrigated, winter rotational crops in the low deserts of the southwestern United States and northern Mexico. Currently, no information is available on the effects of fall planting date on the production of these crops. The objectives of this study were (1) to determine the effects of fall planting date on flowering patterns, seed yield, and oil content of crambe and two species of rape, and (2) to determine the suitability of rape and crambe as rotational crops for the low deserts of the southwestern United States. Nine cultivars of rape and one cultivar of crambe were planted at the Maricopa Agricultural Center on three dates in November and December of 1995 and four dates from October through December of 1997 on a variable Mohall sandy loam soil (fine-loamy, mixed hyperthermic, Typic Haplargid). Five of the rape cultivars were B. napus types and the remaining four were B. rapus. One was an industrial rape (R-500) and the other eight were Canola types. Seed yield, oil concentration, and seed weight were determined. In 1996, the percent of plants flowering was observed visually on a periodic basis. In 1998, detailed imaging of flowering was done periodically using a digital camera. Planting date affected water application by controlling the length of the growing season. Our plants were taller, oil content was higher, seed weights were comparable, days to flowering were more than doubled, and seed yields were lower than plants from spring plantings in the Northern Great Plains. In both years of the study, the highest yields were obtained when rape and crambe were planted in November, which would fit well with cotton harvest dates. Lodging was a serious problem in rape. Crambe was sensitive to frost and could fail in some years. Only R-500 matured early enough to be used in rotation with current cotton cultivars. In addition to the onset of flowering, the automated method for estimating flowering was able to detect differences between Brassica species and cultivars and to measure the duration of flowering. Each species had a distinctive flowering pattern. Planting dates also affected the pattern and efficiency of flowering. Reproductive efficiency appeared to change with planting date and in general, October and November planting dates produced seed with higher oil content and seed weights than December planting dates.

Simulation of Large-Scale Field Infiltration Experiments Using a Hierarchy of Models Based on Public, Generic, and Site Data

Comparative simulations of a large-scale field infiltration experiment at the Maricopa Agricultural Center (MAC) near Phoenix, AZ, were conducted using a hierarchy of models based on public, generic, and site data joined with pedotransfer functions and an inverse procedure. Our purpose was to investigate the ability of simple models and relatively inexpensive data to reproduce and predict reliably the time evolution of water content profiles in nine 10-m-deep neutron monitoring boreholes at the site. By relying solely on public sources of information one might conclude that soil at the MAC site is uniform to a depth of 16 m, with a water table at about 22 m. Upon collecting soil samples at the site, we learned the soils are layered and laterally discontinuous, with a perched water table at about 13 m. To identify the least level of complexity required to simulate infiltration at the MAC, we compared models that consider one- and two-dimensional flow in a uniform soil, a soil consisting of uniform layers, and a stratified soil with laterally distinct zones. There is a paucity of hydraulic characterization data for the site. To investigate the feasibility of obtaining hydraulic parameter estimates for the models on the basis of soil type, we ascribed uniform properties to each layer or zone using mean values of three generic databases. To improve these estimates, we ascribed variable soil hydraulic properties to individual soil samples using regression and neural network pedotransfer functions based on soil type and bulk density; we then used them to obtain Bayesian updates of mean hydraulic properties in each layer or zone. We used the various models and mean parameter estimates to simulate water contents during one of several infiltration experiments at the MAC. None of the results compared well with measured water contents, although one set of generic mean parameter values yielded much better results than the other two. Estimating parameters using pedotransfer functions and Bayesian updating does not lead to improved simulations. Only when the parameters are estimated by means of an inverse procedure does one notice a significant improvement in model fit. We compared and ranked the various models and parameter estimates using likelihood-based model discrimination criteria and confirmed our choice of best model by successfully simulating flow during an earlier infiltration experiment.

Simulation of Large‐Scale Field Infiltration Experiments Using a Hierarchy of Models Based on Public, Generic, and Site Data

Comparative simulations of a large‐scale field infiltration experiment at the Maricopa Agricultural Center (MAC) near Phoenix, AZ, were conducted using a hierarchy of models based on public, generic, and site data joined with pedotransfer functions and an inverse procedure. Our purpose was to investigate the ability of simple models and relatively inexpensive data to reproduce and predict reliably the time evolution of water content profiles in nine 10‐m‐deep neutron monitoring boreholes at the site. By relying solely on public sources of information one might conclude that soil at the MAC site is uniform to a depth of 16 m, with a water table at about 22 m. Upon collecting soil samples at the site, we learned the soils are layered and laterally discontinuous, with a perched water table at about 13 m. To identify the least level of complexity required to simulate infiltration at the MAC, we compared models that consider one‐ and two‐dimensional flow in a uniform soil, a soil consisting of uniform layers, and a stratified soil with laterally distinct zones. There is a paucity of hydraulic characterization data for the site. To investigate the feasibility of obtaining hydraulic parameter estimates for the models on the basis of soil type, we ascribed uniform properties to each layer or zone using mean values of three generic databases. To improve these estimates, we ascribed variable soil hydraulic properties to individual soil samples using regression and neural network pedotransfer functions based on soil type and bulk density; we then used them to obtain Bayesian updates of mean hydraulic properties in each layer or zone. We used the various models and mean parameter estimates to simulate water contents during one of several infiltration experiments at the MAC. None of the results compared well with measured water contents, although one set of generic mean parameter values yielded much better results than the other two. Estimating parameters using pedotransfer functions and Bayesian updating does not lead to improved simulations. Only when the parameters are estimated by means of an inverse procedure does one notice a significant improvement in model fit. We compared and ranked the various models and parameter estimates using likelihood‐based model discrimination criteria and confirmed our choice of best model by successfully simulating flow during an earlier infiltration experiment.

Flowering and seed yield of lesquerella as affected by nitrogen fertilization and seeding rate

The lesquerolic acid in lesquerella seed can be used in industrial applications such as greases, cosmetics, polishes, inks, and coatings. Successful commercialization of lesquerella will depend on the development of improved cultural practices. Lesquerella flowers are bright yellow and are prominently displayed. As a result, many cultural practices could be tied to flowering in a qualitative way. A new method of estimating flowers such as those of lesquerella using digital images has been developed that is rapid, not labor intensive, and can be automated. The purpose of this study was to determine the effects of nitrogen fertilizer and plant density on flowering of lesquerella and to develop relationships between seed yield and flowering. The lesquerella crop was planted on 15 October 1997, at the Maricopa Agricultural Center, approximately 40 km south of Phoenix, Arizona on a variable Mohall sandy loam (fine-loamy, mixed hyperthermic, Typic Haplargid). The experimental design was a complete factorial of three fertilizer rates and four seeding rates. Ammonium sulfate at rates of 0, 60 and 120 kg of N ha −1 was applied at flowering on 18 March 1998. Digital images of the plots were taken periodically from 19 March 1998 to 4 June 1998 using a color digital camera. Images were acquired between 1030 and 1300 h MST. In this experiment, the crop did not respond to seeding rate. Flowers present at initial bloom could be used to estimate stand establishment. The early flowers did not contribute much to final yield, but flowers present in the first 3 weeks of May were a good predictor of yield. Flowering increased with N additions and noticeable peaks in flowering occurred after irrigations. The new method was verified as a viable method for estimating flower number. The method of flower estimation should also be useful for plant breeders for selection of earlier maturing lines, which would increase the potential for use of lesquerella in rotational systems.

Early results on the characterization of the Terra MODIS spatial response

A project to characterize the Moderate Resolution-Imaging Spectroradiometer (MODIS) spatial response (SR) using preflight Modulation Transfer Function (MTF) validation data and on-orbit imagery is described, and the results from the analyses are presented. The preflight validation data are used to estimate the optical blurring parameters to complete a system MTF model for MODIS bands 1 and 2. The model and data indicate that the prelaunch MTF is higher for band 2 than for band 1. The on-orbit imagery is used in a two-image MTF estimation technique to characterize the on-orbit MTF for MODIS bands 1 and 2. Three data sets coincident with MODIS collects are used, Landsat-7 ETM+ imagery of Maricopa Agricultural Center, Arizona, on September 26, 2000 and May 24, 2001 and ASTER imagery of Mono Lake, CA, on September 29, 2000. The on-orbit MTFs obtained to date are consistent with prelaunch validation MTF measurements in the cross-track direction, but are less than prelaunch MTFs in the in-track direction. Further analysis is in progress to confirm these results.

Registration of Five Extra-Long Staple Cotton Germplasm Lines Possessing Superior Fiber Length and Strength

Crop ScienceVolume 42, Issue 3 p. 988-988 Registration of Germplasm Registration of Five Extra-Long Staple Cotton Germplasm Lines Possessing Superior Fiber Length and Strength R.G. Percy, Corresponding Author R.G. Percy [email protected] USDA-ARS, Maricopa Agricultural Center, 37860 W. Smith-Enke Road, Maricopa, AZ, 85239Corresponding author ([email protected])Search for more papers by this author R.G. Percy, Corresponding Author R.G. Percy [email protected] USDA-ARS, Maricopa Agricultural Center, 37860 W. Smith-Enke Road, Maricopa, AZ, 85239Corresponding author ([email protected])Search for more papers by this author First published: 01 May 2002 https://doi.org/10.2135/cropsci2002.9880Citations: 4 Registration by CSSA. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume42, Issue3May–June 2002Pages 988-988 RelatedInformation