Sap Nitrate Research Articles

CHLORIDE CHANNEL-b mediates vacuolar nitrate efflux to improve low nitrogen adaptation in Arabidopsis.

The vacuole is an important organelle for nitrate storage, and the reuse of vacuolar nitrate under nitrate starvation helps plants adapt to low-nitrate environments. CHLORIDE CHANNEL-b (CLC-b) in the vacuolar membrane is a nitrate transporter; however, its regulation and effects on nitrate efflux have not been established. Here, we evaluated CLC-b expression and its effects on physiological parameters under low nitrate conditions. CLC-b expression increased significantly in the roots of wild-type Arabidopsis (Arabidopsis thaliana) Col-0 under nitrate starvation. Under low nitrate, clcb mutants showed reductions in chlorophyll content and xylem sap nitrate concentration, shoot/root nitrate ratios, shoot/root total N ratios, and biomass. CLC-b-overexpression yielded opposite phenotypes and increased nitrogen use efficiency. CLC-b mutants showed elevated chlorate tolerance and an increased proportion of vacuolar nitrate relative to the total protoplast nitrate content as compared to the wild type. Yeast 1-hybrid, EMSA, and chromatin immunoprecipitation (ChIP) experiments showed that HRS1 HOMOLOG2 (HHO2), the expression of which is downregulated under low nitrate, binds directly to the promoter of CLC-b. clcb/hho2 double mutants and HHO2-overexpressing clcb plants had similar phenotypes under low nitrate to those of clcb single mutants. Thus, CLC-b mediates vacuolar nitrate efflux and is negatively regulated by HHO2, providing a theoretical basis for improving plant adaptability to low nitrate.

Comparison of SPAD-based leaf greenness and paralleled petiole sap nitrate concentrations for monitoring potato vine nitrogen status

Comparison of SPAD-based leaf greenness and paralleled petiole sap nitrate concentrations for monitoring potato vine nitrogen status

Topdress strategies and remote sensing for nitrogen management in processing carrots

AbstractImproved nitrogen (N) fertilizer management strategies are required to optimize yield and quality in processing carrots (Daucus carota L.) while minimizing risks of N loss. A 2‐year field study was conducted in commercial carrot fields near Hesperia and Pentwater, MI, USA, to investigate the effects of N fertilizer rate (29, 67, 135, and 202 kg ha−1 N), topdress N frequency (single vs. three split applications), and timing of split N applications on carrot production and N utilization. In addition, the potential for remote sensing‐based vegetation indices (VIs) to guide in‐season N topdress decisions was evaluated relative to conventional methods including petiole sap nitrate testing. Both carrot root yield and shoot biomass increased with greater N rates but did not plateau. Split‐applied topdress N and timing of topdress applications did not affect yield. However, greater N rates, single front‐loaded applications, and both earlier and later than typical topdress timings exhibited potential to increase N loss depending on the year. While VIs explained at most 66% and 29% of the variation in yield in 2019 and 2020, respectively, the indices consistently explained greater variation compared to petiole sap nitrate (6%), shoot N concentration (8%), and carrot root (10%) and shoot (14%) weights. Hypothetical N topdress decisions made using VI‐based sufficiency indices recommended N 26% less often than petiole sap nitrate, but more research is needed to evaluate reference and threshold selections. Despite labor and technological tradeoffs, remote sensing may increase accuracy, resolution, and scalability of N decision support in processing carrot production.

Using processed fertilizers or composted poultry manure results in similar yields but contrasting nutrient budgets in organic cabbage production

Certified organic farmers who grow mixed vegetables often rely on composted manure as their primary nutrient source to build soil organic matter and long-term fertility, but this can result in excessive phosphorus inputs relative to processed organic fertilizers. We established a two-year experiment to compare two certified organic fertilizers − 13-0-0 (derived from hydrolyzed feather meal, meat meal, and blood meal) and 10-2-8 (same components as 13-0-0 in addition to bone meal and sulfate of potash) – and composted chicken manure added to provide 112 kg plant-available N ha−1 in organic cabbage production of Northern Florida. Crown diameter was highest with processed fertilizers in both years, whereas SPAD readings were highest with 13-0-0 in 2020. In both years, sap nitrate measured during the growing season was generally higher with processed fertilizers relative to the composted manure treatment. Marketable yield was highest with processed fertilizers for both years and nutrient concentrations at harvest were similar among treatments, except for nitrogen concentrations that were highest with 10-2-8 in 2021. Nutrient export generally followed differences in yields and was comparable for processed fertilizers and composted manure. Using composted manure resulted in large nutrient surpluses, as opposed to smaller surpluses for 10-2-8 and deficits of phosphorus and potassium for 13-0-0. Our results confirm that poultry manure composted directly onsite can result in comparable organic cabbage yields relative to processed fertilizers, although this resulted in important phosphorus surpluses when applied to meet crop N demand.

Evaluation of real-time nutrient analysis of fertilized raspberry using petiole sap.

The time delay in receiving conventional tissue nutrient analysis results caused red raspberry (Rubus idaeus L.) growers to be interested in rapid sap tests to provide real-time results to guide immediate nutrient management practices. However, sap analysis has never been conducted in raspberry. The present work aimed to evaluate the relationship of petiole sap nitrate (NO3–), potassium (K+), and calcium (Ca2+) concentrations measured using compact ion meters and leaf tissue total nitrogen (TN), potassium (K), and calcium (Ca) concentrations measured using conventional tissue nutrient analysis. The relationship of petiole sap NO3– and leaf tissue TN concentrations with plant growth and production variables was also explored. Fertilizer treatments of urea were surface applied to raised beds of established “Meeker” floricane red raspberry plots at control, low, medium, and high rates (0, 34, 67, and 101 kg N ha–1, respectively) in 2019 and 2020. The experiment was arranged in a randomized complete block design with three replications. Whole leaves were collected from representative primocanes in mid- and late- July and August 2019 and 2020 (i.e., four sampling time points per year). At each sampling time point, a subsample of leaves was used for petiole sap analyses of NO3–, K+, and Ca2+ concentrations using compact ion meters, and conventional tissue testing of leaf tissue TN, K, and Ca concentrations, respectively. There were no interactions between N fertilizer rate and year nor between N fertilizer rate and sampling time. No significant differences were found due to N fertilizer rate for petiole sap NO3–, K+, Ca2+ nor leaf tissue TN, K, Ca concentrations. However, significant year and sampling time effects occurred in measured petiole sap and leaf tissue nutrient concentrations. Overall, the correlations between petiole sap NO3– and leaf tissue TN, petiole sap Ca2+ and leaf tissue Ca, petiole sap K+ and leaf tissue K concentrations were non-strong and inconsistent. Future research is warranted as the interpretation of correlations between raspberry petiole sap and leaf tissue nutrient concentrations were inconclusive.

Why is phloem sap nitrate kept low?

Since the first description of phloem sap composition nearly 60 years ago, it is generally assumed that phloem sap does not contain nitrate and that there is little or no backflow of nitrate from shoots to roots. While it is true that nitrate can occasionally be absent from phloem sap, there is now substantial evidence that phloem can carry nitrate and furthermore, transporters involved in nitrate redistribution to shoot sink organs and roots have been found. This raises the question of why nitrate may or may not be present in phloem sap, why its concentration is generally kept low, and whether plant shoot-root nutrient cycling also involves nitrate. We propose here that phloem sap nitrate is not only an essential component of plant nutritional signaling but also contributes to physical properties of phloem sap and as such, its concentration must be controlled to ensure proper coordination of plant development and nutrient transport. This article is protected by copyright. All rights reserved.

Petiole sap nitrate concentration to assess crop nitrogen status of greenhouse sweet pepper

Vegetable production requires improved nitrogen (N) management practices. Monitoring petiole sap nitrate concentration ([NO3−–N]) is a simple and cheap method to evaluate crop N status. The sensitivity of petiole sap [NO3−–N] to assess crop N status of sweet pepper was evaluated. Three sweet pepper crops were grown in different cropping seasons, each with an autumn-winter growing period. The crops commenced in 2014, 2016, and 2017. Combined fertigation and drip irrigation frequently applied (every 1–4 days) complete nutrient solution throughout each crop. The crops were grown in a greenhouse in soil. Five N treatments as N concentrations were applied throughout each crop: N1 (2.0–2.4 mmol L−1); N2 (5.3–6.2 mmol L−1); N3 (9.7–12.6 mmol L−1); N4 (13.1–16.1 mmol L−1); N5 (16.7–20.0 mmol L−1). These corresponded to very deficient, deficient, conventional, excessive and very excessive N supply. Petiole sap [NO3−–N] was determined every 1–2 weeks and related to Nitrogen Nutrition Index (NNI), which was used as an indicator of crop N status. For each of the N treatments in each crop, petiole sap [NO3−–N] was relatively constant throughout the crop. The relationship between petiole sap [NO3−–N] and NNI, for pooled data from the three pepper crops, was described by (a) the polynomial equation NNI=−1.10E−07×Sap2+0.000473×Sap+0.5514 with an R2 of 0.84, and (b) the segmented linear equations NNI=0.00034×Sap+0.572 and NNI = 1.04, with an R2 of 0.83. Sufficiency values for maximum growth of sweet pepper were obtained by (a) solving the polynomial equation for NNI = 1.0, and (b) using the intercept value of the horizontal line of the segmented linear regression. The corresponding sufficiency values for the duration of a complete crop cycle were 1441 and 1367 mg NO3−–N L−1, respectively. A sufficiency value of 1400 mg NO3−–N L−1 was rounded-off and suggested for the duration of a complete crop cycle of greenhouse-grown sweet pepper in SE Spain. The relationships between petiole sap [NO3−–N] and NNI, and the derived sufficiency values for the flowering and early fruit growth, and harvest phenological stages were similar to those determined for the entire crop. Petiole sap [NO3−–N] is a sensitive and effective method to monitor crop N status of sweet pepper.

Development of Nitrogen Fertilizer Topdressing Model for Winter Wheat Based on Critical Nitrogen Dilution Curve

Critical nitrogen (Nc) dilution curve and its extended N nutrient index (NNI) in previous study was only be applied to wheat for N status diagnosis. This research improved this model and further established the N topdressing model which can be quantify the N topdressing rate when NNI < 1. To facilitate the estimate of the Nc concentration, the determination of basal stem tissue sap nitrate (Nit) concentration as a rapid and operational way was used to characterize N status in this study. The results revealed that N dilution curve in this study specific to winter wheat could be used to establish the N nutrition status. There was significantly positive relationship between the Nit concentration and whole plant N concentration at each growth stage. Moreover, the Nit concentration linearly and positively correlated to the N fertilizer application rate, then deducing the N fertilizer topdressing rate per 100 Nit unit, which finally established the N fertilizer topdressing model: N topdressing rate = (critical Nit − actual Nit) × N topdressing rate per 100 Nit unit. The N dilution curve-based model will offer technical support for managing the precise application of N during the growth period of wheat crops.

Relationships between petiol sap nitrate with nitrogen content of soil and plant in protected cucumber cultivation

Ülkemiz örtüaltı sebze yetiştiriciliğinde hıyar üretimi domatesten sonra ikinci sırada yer almaktadır. Gübreleme her türlü bitkisel üretimde olduğu gibi hıyar yetiştiriciliğinde de verim ve kalite üzerine önemli düzeyde etkilidir. Bitkinin beslenme durumunun hızlı bir şekilde belirlenip gerekli önlemlerin alınması, özellikle serada yapılan üretim faaliyetinde önemlidir. Hızlı ve kolay bir metot olarak petiol özsuyu NO3-N’u miktarının belirlenerek bitkinin azotla beslenme durumunun tespitinde kullanımı son yıllarda ilgi görmektedir. Bu araştırma serada yetiştirilen hıyarın azotla beslenme durumunun tespitinde kullanılmak üzere petiol özsuyu NO3-N’u içeriği ile toprak ve bitkinin farklı azot bileşikleri arasındaki ilişkileri belirlemek amacıyla yürütülmüştür. Denemede, bitki (petiol özsuyu, yaprak) ve toprak örnekleri ilk çiçeklenme ve hasat dönemi olmak üzere iki farklı dönemde alınmıştır. Petiol özsuyu örneklerinde NO3-N miktarını belirlemek için iki farklı hızlı test tekniği; seçici iyon metre ve test şeritleri kullanılmıştır. Ayrıca standart metotlarla yaprak örneklerinde NO3-N’u ve toplam azot, toprak örneklerinde ise organik madde, NO3-N’u ve toplam N değerleri belirlenmiştir. Her iki örnek alma döneminde elde edilen değerler birlikte incelendiğinde; seçici iyon metreyle ölçülen petiol özsuyu NO3-N’u ile yaprağın toplam N ve NO3-N’u içeriği yanında toprak NO3-N’u arasında önemli düzeyde ilişki olduğu belirlenmiştir. Petiol özsuyunda test şeritleri ile belirlenen NO3-N’u ile sadece toprak NO3-N’u arasındaki önemli ilişki her iki dönemde ortaya çıkmıştır. Seçici iyon metreyle ölçülen petiol özsuyu nitrat konsantrasyonu ile yaprak toplam azotu arasındaki ilişkinin her iki dönemde de önemli düzeyde gerçekleşmesi, bitkinin N ile beslenme durumunun belirlenmesinde hızlı test tekniklerinin hıyar yetiştirilen sera koşullarında kullanılabileceğinin göstergesi olarak değerlendirilebilir.

Foliar N Concentration and Reflectance Meters to Guide N Fertilization for Anthracnose Management of Annual Bluegrass Putting Green Turf

Site‐specific management using objective assays to determine N requirement based on canopy reflectance could improve current recommendations for cultural control of anthracnose (Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman). The objectives of this study were to determine the relationships among foliar sap nitrate–nitrogen (NO3–N) concentrations, canopy reflectance indices (normalized difference vegetation index [NDVI] and chlorophyll index [CI]), foliar total N concentrations, and N rate on anthracnose severity in annual bluegrass (ABG), Poa annua L. f. reptans (Hausskn) T. Koyama. A 2‐yr field study was conducted on ABG putting green turf in Storrs, CT. Nitrogen treatments were applied as urea at 0.0 to 36.8 kg ha−1 every 14 d in spring and summer of 2011 to 2012. Anthracnose severity declined linearly with increasing biweekly N rate from 0 kg ha−1 up to the estimated critical level of 12.8 kg ha−1. A minimum critical foliar N concentration of 33.5 g kg−1 maintained anthracnose at ≤32% plot area. Canopy reflectance indices were correlated with foliar N concentration. Anthracnose severity decreased linearly as relative NDVI and relative CI increased. Maintaining relative NDVI between 0.94 to 0.98 through N fertility alone would provide a ∼76 to 93% probability of maintaining ≤32% turf area infested, or relative CI range of 0.73 to 0.93 had the same result ∼40 to 98% of the time.

Effect of Water Recirculation Duration and Shading on Lettuce ( Lactuca sativa ) Growth and Leaf Nitrate Content in a Commercial Aquaponic System

Two experiments were conducted to evaluate the effects of three water recirculating duration (daytime (07.00h to18.00h); nighttime (18.00h to 07.00h); and 24 hours control) and shading (30%, 60% and no shading control), respectively, on growth and sap's nitrate content of lettuce in a commercial aquaponic system integrated with red tilapia culture. First experiment showed that water recirculating time did not affect the lettuce growth, thus offering the possibility to increase aquaponics profitability by reducing the operational cost. The second experiment revealed that shading affected nitrate content in the sap of the leaf midribs, but it remained in range specified by EU regulations in all treatments. The highest lettuce growth was observed at the rate of 30% shading whereas 60% shading gave the lowest growth (P<0.05). (Resume d'auteur)

Natural abundance (δ¹⁵N) indicates shifts in nitrogen relations of woody taxa along a savanna-woodland continental rainfall gradient.

Water and nitrogen (N) interact to influence soil N cycling and plant N acquisition. We studied indices of soil N availability and acquisition by woody plant taxa with distinct nutritional specialisations along a north Australian rainfall gradient from monsoonal savanna (1,600-1,300 mm annual rainfall) to semi-arid woodland (600-250 mm). Aridity resulted in increased 'openness' of N cycling, indicated by increasing δ(15)N(soil) and nitrate:ammonium ratios, as plant communities transitioned from N to water limitation. In this context, we tested the hypothesis that δ(15)N(root) xylem sap provides a more direct measure of plant N acquisition than δ(15)N(foliage). We found highly variable offsets between δ(15)N(foliage) and δ(15)N(root) xylem sap, both between taxa at a single site (1.3-3.4 ‰) and within taxa across sites (0.8-3.4 ‰). As a result, δ(15)N(foliage) overlapped between N-fixing Acacia and non-fixing Eucalyptus/Corymbia and could not be used to reliably identify biological N fixation (BNF). However, Acacia δ(15)N(root) xylem sap indicated a decline in BNF with aridity corroborated by absence of root nodules and increasing xylem sap nitrate concentrations and consistent with shifting resource limitation. Acacia dominance at arid sites may be attributed to flexibility in N acquisition rather than BNF capacity. δ(15)N(root) xylem sap showed no evidence of shifting N acquisition in non-mycorrhizal Hakea/Grevillea and indicated only minor shifts in Eucalyptus/Corymbia consistent with enrichment of δ(15)N(soil) and/or decreasing mycorrhizal colonisation with aridity. We propose that δ(15)N(root) xylem sap is a more direct indicator of N source than δ(15)N(foliage), with calibration required before it could be applied to quantify BNF.

SAP NITRATE IN FROZEN-THAWED AND REFRIGERATED STEMS OF AMARANTHUS TRICOLOR IS INDICATIVE OF NITROGEN FERTILIZER SUPPLY

Amaranthus tricolor is a potential accumulator of nitrate but nutrient sufficiency guidelines have not been developed for this vegetable. We investigated whether the shoot stem of A. tricolor is a suitable index for crop nitrate status, and whether freezing the stem, which aids sap extraction, would render it unsuitable for the analysis of nitrate and other nutrients. We grew A. tricolor at two nitrogen (N) rates (100 and 200 mg L−1 as nitrate-N) and established that sap nitrate from both fresh and frozen-thawed stems did not differ but was significantly increased by additional N fertilizer. Shoot growth was correspondingly higher with additional N. Therefore, the stem is a suitable index for crop nitrate. Boron (B), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na) and sulfur (S) were significantly affected by frozen storage but potassium (K), phosphorus (P) and zinc (Zn) were not. A single sufficiency guideline is possible for these nutrients, for use with both fresh and frozen-thawed stem sap.

Organic Fertilization Programs for Greenhouse Fresh-cut Basil and Spearmint in a Soilless Media Trough System

Greenhouse experiments were conducted in 2005 and 2006 near Live Oak, FL, to develop fertilization programs for fresh-cut ‘Nufar’ basil (Ocimum basilicum) and spearmint (Mentha spicata) in troughs with soilless media using inputs compliant with the U.S. Department of Agriculture's National Organic Program (NOP). Four NOP-compliant fertilizer treatments were evaluated in comparison with a conventional control. Treatments and their analyses in nitrogen (N), phosphorus (P), and potassium (K) contents are as follows: conventional hydroponic nutrient solution [HNS (150 ppm N, 50 ppm P, and 200 ppm K)], granular poultry (GP) litter (4N–0.9P–2.5K), granular composite [GC (4N–0.9P–3.3K)], granular meal [GM (8N–2.2P–4.1K)], and GM plus a sidedress application of 5N–0.9P–1.7K fish emulsion (GM + FE). Electrical conductivity (EC) of the media, fresh petiole sap nitrate (NO3-N) and K concentrations, dried whole leaf NO3-N, P, and K concentrations, and yield and postharvest quality of harvested herbs were evaluated in response to the treatments. Basil yield was similar with HNS (340 g/plant) and GP (325 g/plant) in 2005 and greatest with HNS (417 g/plant) in 2006. Spearmint yield was similar with all treatments in 2005. In 2006, spearmint yields were similar with the HNS and GP yields (172 and 189 g/plant, respectively) and greater than the yields with the remaining treatments. In both years and crops, media EC values were generally greater with the GC than with the GP, GM, and GM + FE treatments but not in all cases and ranged from 1.77 to 0.55 dS·m−1 during the experiments. Furthermore, HNS media EC values were consistently equal to or lower than the GP media EC values except with EC measurements on 106 days after transplanting in both crops in 2005. Petiole NO3-N and K results were variable among crops and years, but provided valuable insight into the EC and yield data. We expected EC, petiole NO3-N, and petiole K to be consistently higher with HNS than with organic treatments, but they were not, indicating a reasonable synchrony of nutrient availability and crop demand among the organic treatments. The postharvest quality of both basil and spearmint was excellent with all treatments with few exceptions.

Diagnosis of N nutrient status of corn using digital image processing technique

基于6个不同水平的氮肥田间试验, 采用数码相机获取夏玉米6叶期和10叶期的冠层图像, 分析了不同供氮水平下夏玉米冠层图像色彩参数指标与施氮量、叶片SPAD值、植株硝酸盐浓度、植株全氮含量、0~90 cm土壤硝态氮含量之间的关系。结果表明: 在6叶期, 玉米冠层数字图像色彩参数指标B/(R+G+B)、G/B、R/B、B/L均与施氮量、叶片SPAD值、植株硝酸盐浓度、植株全氮含量、0~90 cm土壤硝态氮含量存在极显著的线性相关关系, 其中B/(R+G+B)与各营养参数的相关关系最好, 其次是B/L。因此, 运用数字图像技术进行玉米的氮素营养诊断是可行的。夏玉米6叶期冠层图像色彩参数指标与上述营养参数间的相关性明显高于10叶期, 可作为应用数字图像技术进行氮素营养诊断的关键时期, 而蓝光标准化值[B/(R+G+B)]是进行夏玉米氮素营养诊断的最佳冠层图像色彩参数指标。

Nitrate uptake, xylem NO3- flux, and nitrate assimilation in cowpea exposed to salinity

This work was carried out to evaluate what is the nitrate acquisition stage (nitrate uptake, xylem nitrate flux or assimilatory reduction) most influenced by the presence of NaCl in cowpea. Twelve day-old seedlings were treated with 50 mM of NaCl in nutrient solution during four days and measurements carried out under two contrasting environmental conditions: typical day (full sun) and completely cloudy day (cloudiness). The salinity affected more intensely the xylem sap flux and nitrate flux than transpiration. Plants treated with NaCl showed a strong decrease in both nitrate uptake rate and leaf nitrate reductase activity as in the full sun as in cloudy day. Transpiration was reduced by the cloudiness while xylem sap flux and nitrate flux remained unchanged, in both salt-treated and control. Moreover, nitrate uptake and nitrate reductase activity were less affected by cloudiness than the transpiration. In addition, NaCl negatively affected nitrate accumulation in roots, stems and leaves while the cloudiness affected only the leaf nitrate accumulation, both in control and stressed plants. Salinity affects more negatively the nitrate xylem flux, as compared with the nitrate uptake and nitrate assimilatory reduction in cowpea leaves.

Potato Crop Nitrogen Status Assessment to Improve N Fertilization Management and Efficiency: Past–Present–Future

Improving nitrogen use efficiency is important for the potato crop, because of its relatively low ability to take up available soil mineral nitrogen (N). Splitting of N fertilizer application is a suitable approach to better match N need and supply. In-season crop N monitoring methods are therefore required to support such strategies. This paper deals with the state of the art and potential development of characteristics, use and implementation of well known and more recent methods aimed to assess in-season potato Crop Nitrogen Status (CNS). A short overview of this concept is given for the potato crop. The most important and available methods for CNS assessment are evaluated for their accuracy, precision, sensitivity, sensibility and feasibility. These are: the petiole sap nitrate concentration test; the leaf chlorophyll concentration measurement using a hand-held chlorophyll meter; the measurement of crop light reflectance through a hand-held radiometer using passive sensors. More recent methods still under investigation based on near, ground-based, air-borne or space-borne remote sensing are discussed for their scientific and practical interest in the near future. The current and potential use and implementation of these methods into decision support systems for potato N fertilization management aimed at improving the potato crop nitrogen use efficiency are analysed by: comparing relative and raw data; establishing threshold values of CNS; and combining or integrating the CNS values into models dedicated to N recommendation or to crop growth simulation.

Using High-Resolution Satellite Imaging to Evaluate Nitrogen Status of Winter Wheat

ABSTRACT Nitrogen (N) applications often increase crop yields significantly, but N needs vary spatially across fields and landscapes. The color of the wheat plant is sensitive to N status and may provide a means to accurately predict N fertilizer rates matching spatial variability. Previous researches have reported that remote sensing may contribute to N management decisions by collecting spatially dense information. The objective of this study was to determine the feasibility of using high-resolution satellite imaging for evaluating N status of winter wheat in the North China Plain. High-resolution images from a QuickBird satellite were taken on April 1, 2002 at booting stage of wheat with multi-spectral wavelengths (blue, green, red, and near-infrared). Correlation analyses indicated that all the broadband indices derived from the satellite images correlated well with sap nitrate concentration, SPAD readings, total N concentration, and aboveground biomass. The individual band reflectance values R, G, B correlated well with sap nitrate concentration, SPAD readings, total N concentration, and aboveground biomass. These results demonstrated the potential of using new generation high-resolution satellite imaging for large area wheat N status diagnosis.

Establishment of Critical Sap and Soil Nitrate Concentrations using a Cardy Nitrate Meter for Two Carrot Cultivars Grown on Organic and Mineral Soil

Nitrate (NO3 −) meters have been used effectively for crop nitrogen (N) management in many crops, including corn and cabbage. The use of a Cardy NO3 − meter to assess the N status of the carrot crop could improve the utilization of applied N, but critical NO3‐N concentrations are required. Two carrot cultivars were grown on mineral and organic soils over 3 years at five N application rates to establish critical sap and soil NO3‐N concentrations and to identify the effects of soil type and cultivar. Although a yield response to N application occurred on mineral soil in 2 of 3 years, consistent critical sap NO3‐N concentrations could not be established because of variability among years, cultivars, and soil types. Critical soil nitrate concentrations were highly variable, but values of 31 to 36 mg · L−1 NO3‐N could be established for the early sampling date to 30 cm deep. Sap NO3‐N concentrations cannot be used alone for N analysis of carrots, but early‐season soil NO3‐N assessment could be useful in adjusting N‐fertilization practices.

Optimum Nitrogen Fertilization of Winter Wheat Based on Color Digital Camera Images

Site‐specific nitrogen (N) fertilizer management based on soil Nmin (soil mineral N) and the plant N status (sap nitrate analysis and chlorophyll meter (SPAD) reading test) has been shown to be effective in decreasing excessive N inputs for winter wheat in the North China Plain, but the multiple sampling of soil and plants in individual fields is too time‐consuming and costly for producers and farmers. In this study, a color digital camera was used to capture wheat canopy images at a specific growth stage to assess N needs. Treatments included a farmer's N treatment (typical farmer practice), an optimum N treatment (N application based on soil–plant testing), and four treatments without N (one to four cropping seasons without any N fertilizer input). Digital images were analyzed to get red, green, and blue color‐band intensities for each treatment. Normalized intensities of the red, green, and blue color bands were well correlated with soil Nmin, SPAD readings, sap nitrate concentration, and total N concentration of winter wheat. This research indicated the potential of using a digital camera as a tool combined with an improved Nmin method to make N fertilizer recommendations for larger fields.