Peak Bloom Research Articles

순차적인 최적화 기법에 의한 생물계절모형 모수추정 방식 개선

Accurate prediction of peak bloom dates (PBD) of flowering cherry trees is critical for organizing local cherry festivals and other associated cultural and economic activities. A two-step phenology model is commonly used for predicting flowering time depending on local temperatures as a result of two consecutive steps followed by chill and heat accumulations. However, an extensive computation requirement for parameter estimation has been a limitation for its practical use. We propose a sequential parameterization method by exploiting previously unused records of development stages. With an extra constraint formed by heat accumulation between two intervening stages, each parameter can then be solved sequentially in much shorter time than the brute-force method. The result was found to be almost identical to the previous solution known for cherry trees (Prunus × yedoensis) in the Tidal Basin, Washington D.C.

A large-scale field study examining effects of exposure to clothianidin seed-treated canola on honey bee colony health, development, and overwintering success.

In summer 2012, we initiated a large-scale field experiment in southern Ontario, Canada, to determine whether exposure to clothianidin seed-treated canola (oil seed rape) has any adverse impacts on honey bees. Colonies were placed in clothianidin seed-treated or control canola fields during bloom, and thereafter were moved to an apiary with no surrounding crops grown from seeds treated with neonicotinoids. Colony weight gain, honey production, pest incidence, bee mortality, number of adults, and amount of sealed brood were assessed in each colony throughout summer and autumn. Samples of honey, beeswax, pollen, and nectar were regularly collected, and samples were analyzed for clothianidin residues. Several of these endpoints were also measured in spring 2013. Overall, colonies were vigorous during and after the exposure period, and we found no effects of exposure to clothianidin seed-treated canola on any endpoint measures. Bees foraged heavily on the test fields during peak bloom and residue analysis indicated that honey bees were exposed to low levels (0.5–2 ppb) of clothianidin in pollen. Low levels of clothianidin were detected in a few pollen samples collected toward the end of the bloom from control hives, illustrating the difficulty of conducting a perfectly controlled field study with free-ranging honey bees in agricultural landscapes. Overwintering success did not differ significantly between treatment and control hives, and was similar to overwintering colony loss rates reported for the winter of 2012–2013 for beekeepers in Ontario and Canada. Our results suggest that exposure to canola grown from seed treated with clothianidin poses low risk to honey bees.

Potential drivers of sinking particle's size spectra and vertical flux of particulate organic carbon (POC): Turbulence, phytoplankton, and zooplankton

AbstractPhytoplankton spring blooms in temperate and high‐latitude shelf seas are commonly associated with an enhanced particulate organic carbon (POC) export of aggregates from the euphotic zone. In contrast, a postbloom situation is usually linked to a predominant POC retention, where small cells (<10 μm) and strong grazing pressure prevail. This study aimed to examine impacts of turbulence, phytoplankton, bloom stage, and zooplankton abundance on the sinking particles' size spectra and POC flux to improve the understanding of the downward flux mechanisms in the upper 100 m. We deployed sediment traps, partly modified with gel jars, at four depths along a stratification and phytoplankton bloom gradient in the Barents Sea, an Arctic shelf sea. The highest POC export (60 m: 923 mg C m−2 d−1) was found in deep‐mixed, postbloom Atlantic influenced waters, despite the high grazer abundance (12,000 individuals m−3). Particle size spectra indicated that this flux was dominated by particles of 0.05–1.00 mm equivalent spherical diameter (ESDimage) with a POC:volume ratio matching copepod fecal pellets. Large particles (0.5–2.8 mm ESDimage) dominated the flux at a stratified, late peak bloom station in Arctic Waters and a stratified, late bloom situation at the Polar Front, but with lower POC:volume ratio and POC flux (60 m: <823 mg C m−2 d−1). Accordingly, a high POC flux at the base of the euphotic zone is not necessarily driven by large phytoplankton aggregates, but can also occur during a postbloom situation in form of small fecal pellet fragments with high POC content.

Chromophoric dissolved organic matter (CDOM) in first-year sea ice in the western Canadian Arctic

We monitored the spatiotemporal progression of chromophoric dissolved organic matter (CDOM) in first-year sea ice in the western Canadian Arctic between mid-March and early July 2008. CDOM abundance in bottom ice, as quantified by absorption coefficient at 325nm, aCDOM(325), showed a positive, linear relationship with the concentration of chlorophyll a, being low at the start of ice algal accumulation, highly enriched during the peak bloom and early post-bloom, and depleted again during sea ice melting. Vertical profiles of CDOM in early and late spring were typically characterized by slight to moderate elevations at both the surface and bottom and rather constancy within the interior ice. In the ice algae-thriving mid-spring, L-type profiles prevailed due to extremely high CDOM in the lowermost 10-cm layer. Bottom-layer CDOM in landfast ice (aCDOM(325): 15.8m−1) more than doubled that in drift ice (aCDOM(325): 6.6m−1). CDOM in the ice cover, except the bottom layer, was generally lower than or similar to that in the under-ice surface water. Salinity accounted for 58% of the CDOM variability in drift ice having minimal terrestrial and ice algal signatures. CDOM absorption spectra of algae-rich bottom ice samples exhibited ultraviolet (UV) absorption shoulders attributable to mycosporine-like amino acids (MAAs). These compounds were readily photodegradable by solar UV radiation. Our results suggest that 1) inclusion of organic solutes and in situ biological production are the dominant processes controlling the distribution of CDOM in sea ice in the study area, 2) biological production in bottom ice is a minor source of CDOM to the underlying surface water; 3) CDOM plays a critical role in shielding sympagic organisms in bottom ice against UV radiation; 4) the MAAs are effective photoprotectants only under low-UV conditions.

Impact of multispecies diatom bloom on plankton community structure in Sundarban mangrove wetland, India

A multispecies bloom caused by the centric diatoms, viz. Coscinodiscus radiatus, Chaetoceros lorenzianus and the pennate diatom Thalassiothrix frauenfeldii was investigated in the context of its impact on phytoplankton and microzooplankton (the loricate ciliate tintinnids) in the coastal regions of Sagar Island, the western part of Sundarban mangrove wetland, India. Both number (15–18 species) and cell densities (12.3×103cellsl−1 to 11.4×105cellsl−1) of phytoplankton species increased during peak bloom phase, exhibiting moderately high species diversity (H′=2.86), richness (R′=6.38) and evenness (E′=0.80). The diatom bloom, which existed for a week, had a negative impact on the tintinnid community in terms of drastic changes in species diversity index (1.09–0.004) and population density (582.5×103 to 50×103indm−3). The bloom is suggested to have been driven by the aquaculture activities and river effluents resulting high nutrient concentrations in this region. An attempt has been made to correlate the satellite remote sensing-derived information to the bloom conditions. MODIS-Aqua derived chlorophyll maps have been interpreted.

Insect Visitors and Pollination Ecology of Spalding's Catchfly (Silene spaldingii) in the Zumwalt Prairie of Northeastern Oregon

ABSTRACT: Silene spaldingii S. Watson (Spalding's catchfly) is a threatened wildflower that relies on insect-mediated pollination. However, its pollination ecology is not well understood, particularly in the Zumwalt Prairie of northeastern Oregon, which contains the largest known S. spaldingii population. Our objectives were to: (1) describe the principal insect visitors to S. spaldingii in the Zumwalt Prairie, (2) quantify the available pool of pollinators in the area, and (3) determine whether the visitation rate to individual plants is associated with the density of S. spaldingii at the patch scale, as predicted by the resource concentration hypothesis, and/or by the density and composition of non-S. spaldingii blooming plants, as predicted by the facilitation and competition hypotheses. We recorded insect visits to S. spaldingii during peak bloom at 30 patches and characterized the local bee community using blue vane traps. We quantified the patch-scale density of S. spaldingii and the composition and...

Timing of Episodic Drought Can Be Critical in Cotton

Episodes of drought stress in upland cotton (Gossypium hirsutum L.) can be detrimental to vegetative growth, yield characteristics, and fiber quality, depending on the specific growth stage drought occurs. Growth, yield, fiber quality, and boll distribution were compared among four cotton cultivars subjected to four growth‐stage specific drought periods that were repeated in three studies over 2 yr in West Texas. Drought timings occurred at pinhead square, early bloom, and two periods of stress during peak bloom. Both years of the study were hot and dry, with minimal rainfall during the episodic drought treatments. Yield was not significantly different among cultivars, nor was there a significant cultivar × irrigation interaction related to cotton yield. However, there were differential effects on fiber quality among cultivars subjected to the different episodic drought timings. Drought stress during squaring resulted in significantly shorter plants with fewer nodes; however, yield was comparable to the highest yields among the other drought stress treatments, and fiber quality parameters were significantly improved compared to all other treatments except full irrigation. The early flowering growth stage was the most sensitive to drought stress and produced the lowest yields, the lowest fruit retention, and poor fiber quality. Drought events at peak bloom resulted in similar yield losses to those at squaring, but poorer fiber quality. This information may be crucial for producers who either have competing demands for water resources or who want to maximize profits or resources after the occurrence of a drought episode.

Expression of a xanthine permease and phosphate transporter in cultures and field populations of the harmful alga Aureococcus anophagefferens: tracking nutritional deficiency during brown tides.

Targeted gene expression using quantitative reverse transcription polymerase chain reaction (qRT-PCR) was employed to track patterns in the expression of genes indicative of nitrogen or phosphorus deficiency in the brown tide-forming alga Aureococcus anophagefferens. During culture experiments, a xanthine/uracil/vitamin C permease (XUV) was upregulated ∼20-fold under nitrogen-deficient conditions relative to a nitrogen-replete control and rapidly returned to nitrogen-replete levels after nitrogen-deficient cells were resupplied with nitrate or ammonium. It was not responsive to phosphorus deficiency. Expression of an inorganic phosphate transporter (PTA3) was enriched ∼10-fold under phosphorus-deficient conditions relative to a phosphorus-replete control, and this signal was rapidly lost upon phosphate resupply. PTA3 was not upregulated by nitrogen deficiency. Natural A. anophagefferens populations from a dense brown tide that occurred in Long Island, NY, in 2009 were assayed for XUV and PTA3 expression and compared with nutrient concentrations over the peak of a bloom. Patterns in XUV expression were consistent with nitrogen-replete growth, never reaching the values observed in N-deficient cultures. PTA3 expression was highest prior to peak bloom stages, reaching expression levels within the range of P-deficient cultures. These data highlight the value of molecular-level assessments of nutrient deficiency and suggest that phosphorus deficiency could play a role in the dynamics of destructive A. anophagefferens blooms.

Plant Growth Stage-Specific Injury and Economic Injury Level for Verde Plant Bug, <I>Creontiades signatus</I> (Hemiptera: Miridae), on Cotton: Effect of Bloom Period of Infestation

Verde plant bugs, Creontiades signatus Distant (Hemiptera: Miridae), were released onto caged cotton, Cossypium hirsutum L., for a 1-wk period to characterize the effects of insect density and bloom period of infestation on cotton injury and yield in 2011 and 2012, Corpus Christi, TX. When plants were infested during early bloom (10-11 nodes above first white flower), a linear decline in fruit retention and boll load and a linear increase in boll injury were detected as verde plant bug infestation levels increased from an average of 0.5 to 4 bugs per plant. Lint and seed yield per plant showed a corresponding decline. Fruit retention, boll load, and yield were not affected on plants infested 1 wk later at peak bloom (8-9 nodes above first white flower), even though boll injury increased as infestation levels increased. Second-year testing verified boll injury but not yield loss, when infestations occurred at peak bloom. Incidence of cotton boll rot, known to be associated with verde plant bug feeding, was low to modest (< 1% [2012] to 12% [2011] of bolls with disease symptoms), and drought stress persisted throughout the study. Caging effect was minimal: a 10% fruit retention decline was associated with caging, and the effect was not detectable in the other measurements. Overall, reduced fruit retention and boll load caused by verde plant bug were important contributors to yield decline, damage potential was greatest during the early bloom period of infestation, and a simple linear response best described the yield response-insect density relationship at early bloom. Confirmation that cotton after peak bloom was less prone to verde plant bug injury and an early bloom-specific economic injury level were key findings that can improve integrated pest management decision-making for dryland cotton, at least under low-rainfall growing conditions.

Biodiversity ensures plant–pollinator phenological synchrony against climate change

Climate change has the potential to alter the phenological synchrony between interacting mutualists, such as plants and their pollinators. However, high levels of biodiversity might buffer the negative effects of species-specific phenological shifts and maintain synchrony at the community level, as predicted by the biodiversity insurance hypothesis. Here, we explore how biodiversity might enhance and stabilise phenological synchrony between a valuable crop, apple and its native pollinators. We combine 46 years of data on apple flowering phenology with historical records of bee pollinators over the same period. When the key apple pollinators are considered altogether, we found extensive synchrony between bee activity and apple peak bloom due to complementarity among bee species' activity periods, and also a stable trend over time due to differential responses to warming climate among bee species. A simulation model confirms that high biodiversity levels can ensure plant-pollinator phenological synchrony and thus pollination function.

Assimilation of Diazotrophic Nitrogen into Pelagic Food Webs

The fate of diazotrophic nitrogen (ND) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that ND fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable ND (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, ND can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable ND (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which ND was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of ND by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of ND from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of ND to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-ND pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that ND can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes underlying the propagation of ND through pelagic food webs.

Ethephon Improved Pigmentation but Had No Effect on Cayenne Pepper Fruit Yield in Southern New Mexico

In the desert southwest of the United States, cayenne pepper (Capsicum annuum L.) is an important crop. It is used in the production of hot sauce mash, the precursor to many hot sauces. Because hand harvest is currently required to accommodate staggered crop development, more uniform maturity is desired to facilitate mechanical harvest to decrease labor costs. This study was performed over 3 years (2009–11) and in two locations in southern New Mexico, resulting in five unique year/location scenarios (environments). Four timings of ethephon (0.56 kg a.i./ha) spray applications were evaluated for their potential to increase red cayenne cv. Mesilla yields and percentage of red pods. If yield increases and pigmentation improvements occur, ethephon may facilitate a once-over mechanical harvest. Ethephon was applied once at four key cayenne growth stages based on heat units accumulated after planting (HUAP): 1400 HUAP (late June to early July), 1800 HUAP (mid-July), 2800 HUAP (late August to early September), and 3100 HUAP (mid- to late September). Application timings corresponded to early bloom, peak bloom, late physiological maturity of plants, and preharvest, respectively. A non-sprayed control was also included. Fresh red, green, and non-marketable pod weights were recorded for each treatment in a once-over simulated machine harvest in October and analyzed for statistical differences. Mid- to late-season (2800–3100 HUAP) ethephon treatments significantly decreased undesirable green pod yield and, therefore, increased red pod percentage in four of five environments. Although a red pod yield increase was only observed in one environment (a drip-irrigated plot in 2010), there were no negative impacts on red pod yield in any environment resulting from ethephon application. In addition, pepper quality (yield of unmarketable pods) was not significantly reduced by ethephon. Previous work has focused on increasing red pod yields with mixed results. The results show that ethephon may synchronize cayenne pepper red fruit maturity necessary for mechanical harvest and reduce the labor involved in removing green pods before processing.

Fertilizer 15N Accumulation, Recovery and Distribution in Cotton Plant as Affected by N Rate and Split

N fertilization of 300 kg N ha−1 is normally applied to cotton crops in three splits: pre-plant application (PPA, 30%), first bloom application (FBA, 40%) and peak bloom application (PBA, 30%) in the Yangtze River Valley China. However, low fertilizer N plant recovery (NPR) (30-35%) causes problems such as cotton yield stagnation even in higher N rate, low profit margin of cotton production and fertilizer release to the environment. Therefore, it is questioned: Are these three splits the same significance to cotton N uptake and distribution? An outdoor pot trial was conducted with five N rates and 15N labeled urea to determine the recovery and distribution of 15N from different splits in cotton (Gossypium hirsutum L. cv. Huazamian H318) plant. The results showed that, cotton plant absorbed fertilizer 15N during the whole growing period, the majority during flowering for 18-20 d regardless of N rates (150-600 kg ha−1). Fertilizer 15N proportion to the total N accumulated in cotton plant increased with N rates, and it was the highest in reproductive organs (88% averaged across N rates) among all the plant parts. FBA had the highest NPR (70%), the lowest fertilizer N lose (FNL, 19%), and the highest contribution to the fertilizer 15N proportion to the total N (46%) in cotton plant, whereas PPA had the reverse effect. It suggests that FBA should be the most important split for N absorption and yield formation comparatively and allocating more fertilizer N for late application from PPA should improve the benefit from fertilizer.

Chytrid epidemics may increase genetic diversity of a diatom spring-bloom

Contrary to expectation, populations of clonal organisms are often genetically highly diverse. In phytoplankton, this diversity is maintained throughout periods of high population growth (that is, blooms), even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes. Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms. Here, we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure. The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure, whereas the within group dispersion did not change under low parasite pressure. Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts.

Using Remote Sensing and Soil Physical Properties for Predicting The Spatial Distribution of Cotton Lint Yield

This field crop research study addresses the potential of image based remote sensing to provide spatially and temporally distributed information on timely basis for site-specific cotton crop management. Universal applicability of site specific crop management is hampered by lack of timely distributed and economically feasible information on soils and crop conditions in the field and their interaction. The objectives of this study were to demonstrate (1) how site-specific lint yield and associated soil physical properties in a cotton (Gossypium hirsutum L.) production field are related to changes in NDVI across the growing season, and (2) when multispectral images should be collected to optimize the cost and efficiency of remote sensing as a tool for site-specific management of the cotton crop. Temporal multispectral images data acquired comprised 10 dates (1998) and 17 dates (1999) during growing seasons, respectively with analysis focused on 24 areas of interest (AOI) (each 2 x 8 m) located in two transects on a 162-ha farm field. Along each transect, soil textural classification ranged from sandy loam to silt loam. At an early growth stage [~300-600 degree days (DDs) after emergence], low NDVI and plant density were associated with soils having low saturated hydraulic conductivity (ks) and characterized as drainage ways. Among the AOI’s, maximal NDVI was reached at approximately 1565 DD in 1998 and 1350 DD in 1999. A strong range of Pearson correlation (r2=0.65 – 0.83) between lint yield and NDVI during flowering stage (~800-1500 DDs) supports the utility of NDVI maps for site-specific application. However, values for NDVI did not correlate well with lint yields beyond 1500 DDs [fruit (boll) opening stage] and decreased sharply on sites with sandy soil texture. Visual separation of seasonal trends in the NDVI vs. DD relationship was also related to sandy soil vs. silt loam soil texture and seasonal rainfall difference between years. Based on the statistical relationship between NDVI vs. DD it was concluded that acquisition of a single imagery during peak bloom period would be sufficient for predicting the spatial distribution of lint yield and will also be economically feasible. Results of this study indicate that spatial variability in soil physical properties induced variability in crop growth and yield. Similar methodology could be adopted for site-specific management of other crops

Soil Testing and Plant Analysis Relationships for Irrigated Chile Production

In a field study of irrigated chile (Capsicum annum L.) production in southeastern Arizona and southwestern New Mexico from 2008 through 2009, soil and tissue test samples were analyzed for a spectrum of plant nutrients at 16 different sites, including nitrogen (N), phosphorus (P), potassium (K), zinc (Zn), iron (Fe), and boron (B). The objectives were to evaluate soil and tissue nutrient testing procedures and to establish basic soil and plant tissue-testing guidelines and recommendations with respect to yield potentials. Soil samples were collected before planting. Plant tissue samples from plots at all sites were collected at the following four stages of growth: first bloom (FB), early bloom (EB), peak bloom (PB), and physiological maturity (PM). Fertilizer and nutrient inputs were monitored, managed, and recorded within current extension guidelines for irrigated chiles. Results for soil and tissue analyses were compared to yield results. The results provide estimates for baselines, which can be tested through subsequent calibration experiments to establish recommendations for critical soil- and tissue-test values. Absolute minimum soil-test nutrient values were identified as 10 parts per million (ppm) P, 110 ppm K, 0.3 ppm Zn, 2.0 ppm Fe, and 0.25 ppm B. Absolute minimum FB leaf tissue test values were 0.2% P, 4.5% K, 10 ppm Zn, 80 ppm Fe, and 30 ppm B. Complete data sets for leaf and petiole tissue-test values for all stages of growth were collected. These soil-test and plant nutrient values will be evaluated in subsequent experiments to better define fertilizer nutrient inputs and to gain better nutrient-management efficiencies in irrigated chile production systems.

Changes in N:P stoichiometry influence taxonomic composition and nutritional quality of phytoplankton in the Peruvian upwelling

Inorganic dissolved macronutrient (nitrogen, N, and phosphorus, P) supply to surface waters in the eastern tropical South Pacific is influenced by expanding oxygen minimum zones, since N loss occurs due to microbial processes under anoxic conditions while P is increasingly released from the shelf sediments. To investigate the impact of decreasing N:P supply ratios in the Peruvian Upwelling, we conducted nutrient manipulation experiments using a shipboard mesocosm setup with a natural phytoplankton community. In a first experiment, either N or P or no nutrients were added with mesozooplankton present or absent. In a second experiment, initial nutrient concentrations were adjusted to four N:P ratios ranging from 2.5 to 16 using two “high N” and two “high P” levels in combination (i.e., +N, +P, +N and P, no addition). Over six and seven days, respectively, microalgal biomass development as well as nutrient uptake was monitored. Phytoplankton biomass strongly responded to N addition, in both mesozooplankton-grazed and not grazed treatments. The developing diatom bloom in the “high N” exceeded that in the “low N” treatments by a factor of two. No modulation of the total biomass by P-addition was observed, however, species-specific responses were more variable. Notably, some organisms were able to benefit from low N:P fertilization ratios, especially Heterosigma sp. and Phaeocystis globosa which are notorious for forming blooms that are toxic or inadequate for mesozooplankton nutrition. After the decline of the diatom bloom, the relative contribution of unsaturated fatty acid to the lipid content of seston was positively correlated to diatom biomass in the peak bloom, indicating that positive effects of diatom blooms on food quality of the protist community to higher trophic levels remain even after the phytoplankton biomass was incorporated by grazers. Our results indicate an overall N-limitation of the system, especially in the case of dominating diatoms, which were able to immediately utilize the available nitrate (within two days) and develop a biomass maximum within three days of incubation. After the decline of diatom biomass, detection of the cyanobacterial marker pigment aphanizophyll indicated the occurrence of diazotrophs, especially in those enclosures initially provided with high N supply. This was surprising, as diazotrophs are thought to play a role in compensating to some extent the N deficit above OMZs in the succession of phytoplankton after an upwelling event.

Sampling Strategies for Square and Boll-Feeding Plant Bugs (Hemiptera: Miridae) Occurring on Cotton

Sampling methods for square and boll-feeding plant bugs (Hemiptera: Miridae) occurring on cotton, Gossypium hirsutum L., were compared with the intent to assess if one approach was viable for two species occurring from early-season squaring to late bloom in 25 fields located along the coastal cotton growing region of south Texas. Cotton fleaphopper, Pseudatomoscelis seriatus (Reuter), damages squares early-season and dominated collections using five sampling methods (approximately 99% of insects collected). A major species composition shift occurred beginning at peak bloom in coastal fields, when verde plant bug, Creontiades signatus Distant, represented 55-65% of collections. Significantly more cotton fleahoppers were captured by experienced samplers with the beat bucket and sweep net than with the other methods (30-100% more). There were more than twice as many verde plant bugs captured by experienced and inexperienced samplers with the beat bucket and sweep net than captured with the KISS and visual methods. Using a beat bucket or sweep net reduced sampling time compared with the visual method for the experienced samplers. For both species, comparing regressions of beat bucket-based counts to counts from the traditional visual method across nine cultivar and water regime combinations resulted in only one combination differing from the rest, suggesting broad applicability and ability to translate established visual-based economic thresholds to beat bucket-based thresholds. In a first look at sample size considerations, 40 plants (four 10-plant samples) per field site was no more variable than variation associated with larger sample sizes. Overall, the beat bucket is much more effective in sampling for cotton fleahopper and verde plant bug than the traditional visual method, it is more suited to cotton fleahopper sampling early-season when plants are small, it transitions well to sample for verde plant bug during bloom, and it performs well under a variety of soil moisture conditions and cultivar selections.

Use of Nitrogen Calibration Ramps and Canopy Reflectance on Farmers' Irrigated Cotton Fields

Nitrogen is the main nutrient limiting irrigated cotton (Gossypium hirsutum L.) production in the southwestern United States. Canopy spectral reflectance may assess the need for in‐season N in irrigated cotton and guide N fertilizer applications. However, calibration of remote sensing indices such as normalized difference vegetative index (NDVI) to the crop's need for N fertilizer is difficult. Well‐fertilized reference strips or plots reference NDVI data in the crop area of interest but can result in rank growth and reduced lint yields. Recently, Oklahoma State University developed a calibration procedure of using multiple, sequential, N rate calibration plots, or a ramp approach for wheat (Triticum aestivum L.) and corn (Zea mays L.). We tested this approach in irrigated cotton fields in Lubbock County, Texas, in 2008 and 2009. The main objective of this research was to test a calibration ramp approach to determining optimum in‐season N fertilizer rates in irrigated cotton in West Texas. Near infrared, red, and amber reflectance was measured with active spectroradiometers at 1 m above the canopy. Wide ranges in soil type and irrigation amounts influenced NDVI much more than N fertilizer rate. Normalized difference vegetative index at mid‐bloom and at peak bloom were positively related to N fertilizer rate in only one ramp in each year. These two ramp‐years also had significant N fertilizer rate response in lint yield. Ramps that did not have mid‐ or peak bloom NDVI responses to N rate, likewise had no lint yield response to N rate. In both low irrigation‐ low N input and in high irrigation‐high N input farms, in‐season NDVI correctly predicted lint yield response to N fertilizer rate.

Association of Spectral Reflectance Indices with Plant Growth and Lint Yield in Upland Cotton

ABSTRACTCanopy reflectance plays an increasingly important role in crop management and yield prediction at large scale. The relationship of four spectral reflectance indices with cotton (Gossypium hirsutum L.) biomass, leaf area index (LAI), and crop yield were investigated using three cotton varieties and five N rates in the irrigated low desert in Arizona during the 2009 and 2010 growing seasons. Biomass, LAI, and canopy reflectance indices (normalized difference vegetation index [NDVI], simple ratio [SR], near‐infrared index [NIR], and ratio vegetation index [RVI]) were determined at different growth stages. The commonly used NDVI and the other three canopy reflectance indices explained over 87% variation in cotton biomass (all R2 &gt; 0.87) and LAI (R2 &gt; 0.93). Indices SR, NIR, and RVI all had higher coefficients of determination (R2) compared to NDVI because these indices were not saturated at late growth stages. There was no significant relationship between lint yield and the spectral indices measured at early growth stages. However, the spectral indices determined at peak bloom showed significant correlations with lint yield. Indices SR, NIR, and RVI explained 56, 60, and 58% of variations in cotton lint yield, respectively, while NDVI only explained 47% of variation in lint yield. This study suggests canopy reflectance indices can be used to predict cotton lint yield at peak bloom and the accuracy of yield prediction can be significantly improved when SR, NIR, and RVI are used.