Sap NO3 Research Articles

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.

Suitable fertilization depth can improve the water productivity and maize yield by regulating development of the root system

An undeveloped root system generally leads to low water utilization efficiency and decreases the yield in spring maize (Zea mays L.). Little is known about whether changing the fertilization depth can optimize the root distribution to improve the water productivity and maize yield. During 2019 and 2020, we conducted a field experiment with spring maize and applied the fertilizer at different soil depths of 0.05 m (D5), 0.15 m (D15), 0.25 m (D25), and 0.35 m (D35) to clarify the regulatory effects of the fertilization depth on the root distribution, water productivity at the biomass level (WPb), and maize yield formation. Compared with D5, D25 significantly increased the root length density of the vertical roots, inter-row roots, and within-row roots in the 0–1.0 m soil depth by 18%, 14%, and 24%, respectively, and the root surface area density increased by 39%, 17%, and 22%. Compared with D5, D25 significantly increased the soil water consumption by 28 mm during the maize jointing to silking stage and reduced the soil water content in the 0.4–1.4 m soil depth at the maize silking stage. D25 and D15 also significantly increased the root sap production rate and NO3–-N and NH4+-N concentrations in the root sap compared with D5 and D35 after the maize silking stage. The N uptake and nitrogen use efficiency under D25 were 17% and 39% higher, respectively, compared with D5. The water productivity at the grain yield and biomass level, biomass, and maize yield values under D25 were 23.5 kg ha–1 mm–1, 45.7 kg ha–1 mm–1, 24320 kg ha–1, and 12477 kg ha–1, respectively, which were 10%, 12%, 13%, and 14% higher compared with D5. The different fertilization depths explained 91%, 86%, and 66% of the variations in the maize yield, N uptake, and total evapotranspiration, respectively. Therefore, deep fertilization at a suitable soil depth regulated the distribution of the root system, which improved the capability of soil water and nitrogen utilization, and eventually increased the water productivity and maize yield. The most effective fertilizer depth was 0.25 m and it can be used as an effective water and fertilizer management strategy for the sustainable development of maize.

THE EFFECT OF POULTRY, CATTLE AND SWINE MANURE APPLICATIONS TO SOIL ON LETTUCE YIELD AND QUALITY AND GROUND WATER CONTAMINATION POTENTIAL

This study investigated the effect that poultry, cattle, swine manures, and artificial fertilizer have on the yield and quality of lettuce (Lactucasativa L.). The ground water contamination potential of these fertilizers when applied to calcareous soil was also studied. Lettuce plants were cultivated in pots containing soil amended with either of the fertilizers together with a no-fertilizer control. The amount of fertilizer applied to soil was in line with that used by the lettuce growers in Malta. The experiment, including 20 replicates for each treatment, was set up in a greenhouse and the crop height, width, fresh and dry mass, root length, sap NO3 - and K + , and heavy metal content were monitored. The drain water from the pots was analysed periodically for NO3 - content and salinity. The best crop performance was obtained from poultry manure followed by swine manure, cattle manure and artificial fertilizer. Yield from the control soil was poor and also resulted in a crop containing the highest NO3 - concentration in the sap. No significant difference was found in sap NO3 - concentration in plants grown in soil amended with the fertilizers. The heavy metal content concentration in the plants was not significantly different except for Ni, Mn and Cu. The highest NO3 - leaching was shown in the soil amended with manure, especially with that from poultry. Crops grown on cattle manure showed the highest variation in crop mass and also the lowest yield-to-ground water NO3 - contamination potential ratio.

Guiding fall fertilization of cool‐season turfgrass lawns with verdure tissue‐N tests

AbstractObjective tests are not widely used to guide fall N fertilization of turfgrasses, and N is applied at predetermined rates regardless of plant‐N status. This study was conducted across 3 yr in Connecticut to determine if fall verdure concentrations of total N, dry‐tissue extractable nitrate (NO3)–N, and fresh sap NO3–N could guide fall N fertilization for a mixed‐species, cool‐season turfgrass lawn. Field experiments were set out with varying fall N rates and verdure samples were collected weekly in October and November. Verdure tissue‐N test concentrations in response to N rates were analyzed with polynomial (quadratic or cubic) and linear‐response and plateau (LRP) models. Models were significant (P < .0001) for all tissue concentrations in response to N rates and estimates were comparable between models. When referenced to expected responses from the commonly recommended fall N rates of 24.5, 49, and 98 kg ha−1, there would be no need for N fertilizer when concentrations of fall verdure total N are ≥22, ≥25, and ≥30 g kg−1; dry‐tissue extractable NO3–N are ≥119, ≥193, and ≥840 mg kg−1; and fresh sap NO3–N are ≥94, ≥115, and ≥171 mg L−1, respectively. Variability of the verdure tissue‐N tests was no greater than most routine soil and tissue tests currently used to monitor nutrient status in turfgrasses. The results suggest that verdure tissue‐N tests have potential in guiding fall N fertilization of cool‐season turfgrass lawns.

Isotopic composition and concentration of total nitrogen and nitrate in xylem sap under near steady-state hydroponics.

After root uptake, nitrate is effluxed back to the medium, assimilated locally, or translocated to shoots. Rooted black cottonwood (Populus trichocarpa) scions were supplied with a NO3- -based (0.5 mM) nutrient medium of known isotopic composition (δ15 N), and xylem sap was collected by pressure bombing. To establish a sampling protocol, sap was collected from lower and upper stem sections at 0.1-0.2 MPa above the balancing pressure, and after increasing the pressure by a further 0.5 MPa. Xylem sap from upper stem sections was partially diluted at higher pressure. Further analysis was restricted to sap obtained from intact shoots at low pressure. Total-, NO3- -N and, by difference, organic-N concentrations ranged from 6.1-11.0, 1.2-2.4, and 4.6-9.4 mM, while discrimination relative to the nutrient medium was -6.3 to 0.5‰, -23.3 to -11.5‰ and - 1.3 to 4.9‰, respectively. There was diurnal variation in δ15 N of total- and organic-N, but not NO3- . The difference in δ15 N between xylem NO3- and organic-N suggests that discrimination by nitrate reductase is near 25.1 ± 1.6‰. When this value was used in an isotope mass balance model, the predicted xylem sap NO3- -N to total-N ratio closely matched direct measurement.

Nitrate Transport Rate in the Xylem of Tomato Plants Grafted onto a Vigorous Rootstock

Vigorous interspecific rootstocks increase nitrogen (N) uptake in tomato plants but limited information is available on xylem transport rate. Non-grafted and self-grafted tomato plants cv. Attiya and plants grafted onto an interspecific hybrid, Kaiser, were grown under growth chamber conditions and subjected to two light levels, 400 or 800 µmol PAR m−2 s−1. Plant water uptake, xylem sap NO3− content, and stem hydraulic conductance (ks) were measured after two weeks of growth. Xylem vessel number and diameter were evaluated in cross-sectional stem cuts and the theoretical xylem hydraulic conductance (kh) was calculated. Only the light level modified the xylem NO3− content. Grafting reduced ks by 84% in comparison to non-grafted plants. The water uptake rate and xylem sap NO3− content were 4.02 ± 0.66 g H2O kg−1 DW h−1 and 12.78 ± 1.16 mM, respectively, across all grafting treatments. The rootstock has a higher kh because the vessel diameter is 79.3 ± 14.4 µm while in non-grafted plants it is 62.0 ± 10.1 µm. Nitrate concentration and transport rate changes accordingly to the plant’s growth rate. The vigorous rootstock relies on larger vessels to supply the required amounts of N.

Impact of Low and Moderate Salinity Water on Plant Performance of Leafy Vegetables in a Recirculating NFT System

Two greenhouse experiments were conducted to examine the growth and mineral nutrition of four leafy vegetables in a nutrient film technique (NFT) system with water with low to moderate salinity. In Expt. 1, a nutrient solution was prepared using reverse osmosis (RO) water and treatments consisted of supplementing with RO water, tap water, or nutrient solution. In Expt. 2, nutrient solution was prepared using three different water sources (treatments), namely, RO water, tap water, or tap water, plus sodium chloride (NaCl), and supplementing solution was prepared using the same three water sources at one third strength. For both of the experiments, seeds of pac choi ‘Tokyo Bekana’, ‘Mei Qing Choi’, and ‘Rosie’ (Brassica rapa var. chinensis) and leaf lettuce ‘Tropicana’ (Lactuca sativa) were sown and were grown in a growth chamber. Two weeks after sowing, seedlings were transplanted to the NFT systems. Expt. 1 was conducted from 19 April to 19 May 2016 and Expt. 2 from 6 September to 12 October 2016. In Expt. 1, nitrate (NO3−) and phosphorus (P) levels in the tanks decreased, and potassium (K+) levels reached almost zero at the end of the experiment when supplemented with RO or tap water. However, calcium (Ca2+), magnesium (Mg2+), and sulfate (SO42−) either did not decrease or increased over time. Supplementing water type did not affect the growth of leaf lettuce and ‘Mei Qing Choi’ pac choi; however, fresh weight of ‘Rosie’ pac choi and both fresh and dry weight of ‘Tokyo Bekana’ pac choi were reduced when supplemented with RO water. Leaf sap NO3− was reduced in ‘Tokyo Bekana’ pac choi, but not in other varieties, when supplemented with RO or tap water. Leaf sap K+ decreased in ‘Tokyo Bekana’, but not in other varieties. The supplementing water type did not impact leaf sap Ca2+, regardless of vegetable varieties. In Expt. 2, NO3− in all of the treatments, P in RO water, and K+ in RO or tap water decreased in the last week of the experiment. Other macronutrients did not change substantially over time. The addition of NaCl significantly reduced the growth of all the vegetables. ‘Tropicana’ leaf lettuce was the least tolerant to NaCl, followed by ‘Rosie’ pac choi. Water source did not affect leaf Ca2+, K+, P, SO42−, and Mg2+ except for ‘Tokyo Bekana’ where NaCl addition decreased Ca2+ and Mg2+. Our results indicated that the tested leafy vegetables differed in response to various types of water used as supplementing or as source water. N, P, and especially K, should be supplemented in the late stage of the experiment, while replacing the whole tank nutrient solution is only necessary when Na+ and/Cl− build up to harmful levels.

ASSESSING NITROGEN NUTRITIONAL STATUS, BIOMASS AND YIELD OF COTTON WITH NDVI, SPAD AND PETIOLE SAP NITRATE CONCENTRATION

SUMMARYCanopy normalized difference vegetation index (NDVI), soil plant analysis development (SPAD) reading and petiole sap NO3−‒N concentration are increasingly used as quick and non-destructive methods to monitor plant N nutrition and growth status and predict yield of crops. However, little information is available on the comparisons of these three methods in assessing N nutrition, growth and yield for cotton (Gossypium hirsutum L.). Four N rates (0, 34, 67 and 101 kg N ha−1) under two cover conditions [no cover crop and hairy vetch (Vicia villosa) crop] in a 33-year long-term field trial were used to evaluate how canopy NDVI, SPAD reading (related to chlorophyll content) and petiole sap NO3−‒N concentration (conventional method) are able to assess N nutrition and plant biomass and predict yield for cotton. Canopy NDVI and SPAD readings responded less sensitively to N rates than petiole sap NO3−‒N. The responses of NDVI and SPAD reading to N rates were generally reduced due to the winter cover crop with hairy vetch. Significant and positive correlations existed mostly among NDVI, SPAD reading, and petiole sap NO3−‒N concentration. Canopy NDVI during mid-bloom to late bloom and SPAD reading during early bloom to late bloom were effective alternative methods for assessing cotton N nutrition status. The SPAD reading at late bloom was an effective parameter to estimate cotton biomass. The NDVI at early square and SPAD reading during early square to mid-bloom were effective for cotton yield prediction.

Stomatal closure of Pelargonium × hortorum in response to soil water deficit is associated with decreased leaf water potential only under rapid soil drying.

Soil water deficits applied at different rates and for different durations can decrease both stomatal conductance (gs ) and leaf water potential (Ψleaf ). Understanding the physiological mechanisms regulating these responses is important in sustainable irrigation scheduling. Glasshouse-grown, containerized Pelargonium × hortorum BullsEye plants were irrigated either daily at various fractions of plant evapotranspiration (100, 75 and 50% ET) for 20 days or irrigation was withheld for 4 days. Xylem sap was collected and gs and Ψleaf were measured on days 15 and 20, and on days 16-19 for the respective treatments. Xylem sap pH and NO3 (-) and Ca(2+) concentrations did not differ between irrigation treatments. Xylem abscisic acid (ABA) concentrations ([ABA]xyl ) increased within 24 h of irrigation being withheld whilst gs and Ψleaf decreased. Supplying irrigation at a fraction of daily ET produced a similar relationship between [ABA]xyl and gs , but did not change Ψleaf . Treatment differences occurred independently of whether Ψleaf was measured in whole leaves with a pressure chamber, or in the lamina with a thermocouple psychrometer. Plants that were irrigated daily showed lower [ABA]xyl than plants from which irrigation was withheld, even at comparable soil moisture content. This implies that regular re-watering attenuates ABA signaling due to maintenance of soil moisture in the upper soil levels. Crucially, detached leaves supplied with synthetic ABA showed a similar relationship between [ABA]xyl and gs as intact plants, suggesting that stomatal closure of P. hortorum in response to soil water deficit is primarily an ABA-induced response, independent of changes in Ψleaf .

Inter-relationships of cotton plant height, canopy width, ground cover and plant nitrogen status indicators

Petiole-NO3, leaf N and chlorophyll (SPAD) meter readings are good in-season indicators of the N status of the uppermost part of cotton (Gossypium hirsutum L.) plants. Petiole-NO3, particularly is widely used in the USA as an in-season plant N test that guides N fertilizer recommendations in cotton. However, these N status indicators do not take account of plant biomass, canopy width or percent cover. The objectives of this study were to assess the effect of N fertilizer rates on the commonly used indicators of plant N status; leaf N, petiole sap NO3 and chlorophyll meter (SPAD) readings and the plant growth measurements; plant height, canopy width, and percent ground cover, and determine to inter-correlations among the them. Irrigated field studies were conducted at Lubbock, TX USA in 2010 and 2011, New Deal, TX in 2010, and at Halfway, TX in 2011. Zero-N and a full N fertilizer rate of 134, 101, and 112kgNha−1 were used at Lubbock, New Deal, and Halfway, respectively. The 2010 cotton growing season in West Texas was much wetter than average, and the 2011 season was much drier than normal. As a result, plant height, canopy width, and ground cover were greater in the 2010 sites than in 2011. The effects of N fertilizer were greatest for the two cultivars in subsurface drip irrigation (SDI) at New Deal in 2010 for all three N status indicators, and for the three plant growth measures compared to the other site-years. Correlation analysis indicated that among the three plant N indicators, leaf N was the most sensitive to plant parameters. These effects were positive in 2010 and negative in the 2011 dry year. Petiole NO3 was the plant N indicator that was the most insensitive to plant growth, but the marked seasonal decline pattern reduces its usefulness for late-season N management.

Nitrogen metabolism and translocation in soybean plants subjected to root oxygen deficiency

Although nitrate (NO3(-)) but not ammonium (NH4(+)) improves plant tolerance to oxygen deficiency, the mechanisms involved in this phenomenon are just beginning to be understood. By using gas chromatography-mass spectrometry, we investigated the metabolic fate of (15)NO3(-) and (15)NH4(+) in soybean plants (Glycine max L. Merril cv. IAC-23) subjected to root hypoxia. This stress reduced the uptake of (15)NO3(-) and (15)NH4(+) from the medium and decreased the overall assimilation of these nitrogen sources into amino acids in roots and leaves. Root (15)NO3(-) assimilation was more affected by hypoxia than that of (15)NH4(+), resulting in enhanced nitrite and nitric oxide release in the solution. However, (15)NO3(-) was translocated in substantial amounts by xylem sap and considerable (15)NO3(-) assimilation into amino acids also occurred in the leaves, both under hypoxia and normoxia. By contrast, (15)NH4(+) assimilation occurred predominantly in roots, resulting in accumulation of mainly (15)N-alanine in this tissue during hypoxia. Analysis of lactate levels suggested higher fermentation in roots from NH4(+)-treated plants compared to the NO3(-) treatment. Thus, foliar NO3(-) assimilation may be relevant to plant tolerance to oxygen deficiency, since it would economize energy expenditure by hypoxic roots. Additionally, the involvement of nitric oxide synthesis from nitrite in the beneficial effect of NO3(-) is discussed.

Basal Stem Nitrate Tests for Irrigated Malting Barley

Nitrogen fertilizer use is essential for optimizing yield of irrigated malting barley (Hordeum vulgare L.) but must be managed carefully to achieve optimum grain protein concentrations demanded by the malting industry. Development of tissue tests, applicable for growing conditions in the desert Southwest, would be of benefit to growers for optimizing yield and grain protein of irrigated malting barley. Field experiments were conducted with two cultivars of malting barley [Morex (six row) and Crystal (two row)] under irrigated conditions in southern Arizona. The objectives were to (i) determine yield and grain protein response to N applications, (ii) determine the relationship between lower‐stem tissue and sap NO3–N, and (iii) develop lower‐stem and sap NO3 test guidelines for N management in malting barley. Yields ≥90% of maximum relative yield and grain protein concentrations acceptable for malting were achieved at N rates (kg ha−1) of 242 to 269 (1997–1998) and 205 to 269 (1998–1999) for Morex and 162 to 178 (1997–1998) and 166 to 181 (1998–1999) for Crystal. Stem and sap NO3–N were significantly correlated in both cultivars, with r2 values of 0.72 in Morex and 0.82 in Crystal. We propose that, to achieve acceptable grain yield and protein, lower‐stem sap NO3–N in malting barley should be no less than 300, 180, and 120 mg L−1 and dry stem tissue NO3–N should be no less than 3000, 1000, and 800 mg kg−1 at Feekes growth stages 3, 7, and 10, respectively.

Basal Stem Nitrate Tests for Irrigated Malting Barley

Nitrogen fertilizer use is essential for optimizing yield of irrigated malting barley (Hordeum vulgare L.) but must be managed carefully to achieve optimum grain protein concentrations demanded by the malting industry. Development of tissue tests, applicable for growing conditions in the desert Southwest, would be of benefit to growers for optimizing yield and grain protein of irrigated malting barley. Field experiments were conducted with two cultivars of malting barley [Morex (six row) and Crystal (two row)] under irrigated conditions in southern Arizona. The objectives were to (i) determine yield and grain protein response to N applications, (ii) determine the relationship between lower-stem tissue and sap NO3–N, and (iii) develop lower-stem and sap NO3 test guidelines for N management in malting barley. Yields ≥90% of maximum relative yield and grain protein concentrations acceptable for malting were achieved at N rates (kg ha−1) of 242 to 269 (1997–1998) and 205 to 269 (1998–1999) for Morex and 162 to 178 (1997–1998) and 166 to 181 (1998–1999) for Crystal. Stem and sap NO3–N were significantly correlated in both cultivars, with r2 values of 0.72 in Morex and 0.82 in Crystal. We propose that, to achieve acceptable grain yield and protein, lower-stem sap NO3–N in malting barley should be no less than 300, 180, and 120 mg L−1 and dry stem tissue NO3–N should be no less than 3000, 1000, and 800 mg kg−1 at Feekes growth stages 3, 7, and 10, respectively.

Petiole Sap Nitrate and Leaf Nitrogen Critical Values in Melon Plants Grown in Unheated Greenhouse and Field Conditions#

Two experiments with melon plants were carried out with similar procedures; one in unheated greenhouse and another in field conditions to establish petiole sap NO3 − and leaf N critical values. Each experiment consisted of four randomized blocks containing five plots. Different Nitrogen (N) rates (0, 75, 150, 300, and 450 kg ha−1) as urea were placed in furrows (30%) before seedling transplanting and the remaining 70% were trickle‐applied through the plant cycle. Petiole sap NO3 − (NS) and leaf N (NT) concentrations were determined in the 5th leaf from the apex sampled at 25 (first fruit set) and 52 DAT (second fruit set). Both NS and NT at the first and second sampling were increased with increasing N applications in both greenhouse and field. There was a high correlation between NS and NT. NS and NT critical values were higher in plants grown in greenhouse than in the field being more accentuated at the first than at the second sampling. In greenhouse, at the first melon fruit set, the petiole sap NO3 −, and the 5th leaf from the apex N concentrations should be 5360 mg L−1 and 4.38 day kg−1, respectively, or slightly lower at the second fruit set and under field conditions. #Project supported with scholarship by CNPq.

USE OF INNOVATIVE TOOLS TO INCREASE NITROGEN USE EFFICIENCY AND PROTECT ENVIRONMENTAL QUALITY IN CROP ROTATIONS

Cropping systems grown over sandy coarse soils are susceptible to nutrient leaching due to local thunderstorms and irrigation. Additionally, erosion can contribute to removal of nutrients, soil organic matter, and fine particles. Balancing nutrients for these systems while protecting water and soil quality requires best management practices (BMPs). Crop rotations with deeper rooted small grains and winter cover crops reduced potential losses of fine particles, soil organic matter, nitrogen, and other nutrients due to wind erosion and protected soil and water quality. The cropping system N status can be monitored by assessing chlorophyll, sap NO3 −-N concentrations and N indexes of the canopy. The Nitrogen Leaching Economic Analysis Package (NLEAP) model simulated residual soil NO3 −-N and soil water and showed that there is potential to use precision farming to improve NUE. Simulations of the system showed that BMPs increased NUE and that NO3 −-N can potentially be removed from the shallow underground water table protecting water quality. These results show that with the application of models, and tools to monitor the N status of the aboveground canopy, such as chlorophyl readings, sap NO3 −-N concentrations, N indices, and other new technologies such as precision farming and remote sensing, nutrient use efficiency in the new millennium will be significantly increased, environmental quality will be conserved, and product quality will be improved at the farm level for the benefit of producers, processors and consumers.

411 Effect of Compost and Mineral Fertilizer Applications on the Sensory Quality of Basil (Ocimum basilicum L.)

The sensory quality of fresh basil (cv. Sweet Italian) was evaluated to determine if compost or mineral fertilizer applications affected flavor and aroma intensity. The four treatments, arranged in a randomized complete-block design with three replications, were: compost applied at 50 t·ha–1; compost applied at 200 t·ha–1; mineral N applied at 110 kg·ha–1; and a control receiving no amendment. Leaves from the first four nodes of young shoots were used in the evaluation. Twelve trained panel members scored samples of three leaves from each treatment for aroma and flavor intensity using a linear scale, converted to a scale of 1–10 where 1 = much less intense than a reference sample (control), and 10 = much more intense than the reference. No significant difference between treatments was found in flavor intensity. Significant difference between treatments in aroma intensity was found. Aroma scores were highest in samples from the compost and synthetic fertilizer treatments, and lowest in those from the control. Scores for aroma from the compost and synthetic fertilizer treatments were similar to each other. Aroma intensity increased with increased rate of compost application. No significant correlation was found between aroma intensity and plant tissue N content, sap NO3– levels, or yield.

Changes in growth and nitrogen assimilation in barley seedlings under cadmium stress

Barley (Hordeum vulgare L. cv. Martin) plants grown in solution culture, were exposed to increasing cadmium (Cd) concentration (0, 5, 10, 25, 50, and 100 μM) for a duration of 12 days. The sequence of important biochemical steps of nitrate (NO3) assimilation were studied in roots and shoots as a function of external Cd concentration. Cadmium uptake in roots and shoots increased gradually with Cd concentration in the medium. This Cd accumulation lowered substantially root and shoot biomass. The nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NiR, EC 1.6.6.4) activities declined under Cd stress. Concurrently, tissue NO3 contents and xylem sap NO3 concentration were also decreased in Cd‐treated plants. These results suggest that Cd could exert an inhibitory effect on the assimilatory NO3 reducing system (NR and NiR) through a restriction of NO3 availability in the tissues. We therefore examined, in short‐term experiments (12 h), the impact of Cd on NO3 uptake and the two reductases in nitrogen (N)‐starved plants that were pretreated or not with Cd. It was found that Cd induced inhibition of both NO3 uptake and activities of NR and NiR, during NO3 induction period. The possible mechanisms of Cd action on NO3 uptake are proposed. Further, in Cd‐grown plants, the glutamine synthetase (GS, EC 6.3.1.2) showed a decreasing activity both in shoots and roots. However, increasing external Cd concentration resulted in a marked enhancement of glutamate dehydrogenase (NADH‐GDH, EC 1.4.1.2) activity, coupled with elevated levels of ammonium (NH4 in tissues. On the other hand, the total protein content in Cd‐treated plants declined with a progressive and substantial increase of protease activity in the tissues. These findings indicate that under Cd stress the usual pathway of NH4 assimilation (glutamine synthetase/glutamate synthase) can switch to an alternative one (glutamate dehydrogenase). The changes in all parameters investigated were concentration‐dependent and more marked in roots than shoots. The regulation of N absorption and assimilation by Cd in relation to growth and adaptation to stress conditions are discussed.

Sap analysis for diagnosis of nitrate accumulation in cereal forages1

Development of a quantitative, preharvest quiektest for NO3 levels in cereal forages would improve crop management options to avoid NO3 toxicity in livestock. Our objective was to determine if concentrations of NO3 in sap expressed from oat (Avenasativa) and barley (Hordeum vulgare) are correlated with those in dry tissue of simultaneously harvested hay, and to test the reliability of the Cardy portable NO3 meter for sap analysis in these species. In 1993, whole plant samples were gathered from plots fertilized with variable nitrogen (N) rates at four environments in Montana, and were analyzed for NO3 concentration in lower‐internode sap and in whole plant dry matter. In 1994 and 1995, the study was repeated at two environments. The sampling technique included three subsamples from each plot for sap analysis, followed immediately by harvest of the entire plot for hay, and further subsampling for dry matter NO3 analysis after drying. Linear correlations between dry matter and sap NO3 concentrations were found across species at each environment in 1993 with r values of 0.64 to 0.81. No relationship was established for oat at one environment. Locations differed in the coefficient of correlation, indicating environmental influences on the relationship and/ or variability due to sampling technique. In 1994 and 1995, each species fit a separate linear correlation across site‐years with r values of 0.89 (oat) and 0.87 (barley). The consistency across site‐years (1994–1995) indicates that the variability in preliminary results was overcome with sampling technique. We propose a quantitative quiektest for NO3 levels in cereal forages using conditional predictions of dry matter NO3 based on observed values of sap NO3. Since sap NO3 readings with the Cardy portable nitrate meter were well correlated (r=0.93) with Accumet ISE readings across critical ranges, quiektest procedures are practical.

Calibration of a petiole sap nitrate test for irrigated ‘russet Burbank’ potato

Portable electrodes for rapid quantitative determination of nitrate‐N (NO3‐N) in plant sap have recently been developed, thus enabling a quick assessment of the crop nitrogen (N) status. The intent of this study was to provide diagnostic criteria necessary for the interpretation of petiole sap NO3‐N concentrations for potato (Solanum tuberosum L.). Specific objectives were to characterize the relationship between potato petiole sap NO3‐N concentration and petiole NO3‐N determined by conventional dry weight analysis, and to establish NO3‐N sufficiency ranges (NSR) for irrigated potatoes based on sap analyses associated with maximum and 85–95% of maximum yield. A four‐year experiment was conducted on a loamy sand soil (Udic haploboroll) at the Sand Plain Research Farm, Becker, Minn. Ten treatments consisting of various rates and times of N application were evaluated. Recently matured leaves were collected every 10 to 14 days, and petioles were split for sap NO3 and dry tissue NO3 analysis. Two portable NO3 electrodes, the Cardy and Hach meters, designed for quick tests, and a fixed laboratory method, the Wescan, were used to determine sap NO3‐N concentrations. Dry petiole NO3‐N and petiole sap NO3‐N were linearly and significantly related, with regression coefficients r2=0.91, 0.92, and 0.93 for the Cardy, Hach, and Wescan methods, respectively. Nitrate‐N sufficiency ranges determined with the Cardy were 50 mg L‐1 higher than those determined with the Hach. During the vegetative/tuber initiation stage (15–30 days after emergence), NSR were 1350–1450, and 1300–1400 mg L‐1 for the Cardy and Hach, respectively. As the season progressed, the NSR decreased. During the tuber bulking period (30–75 days after emergence), NSR were 600–1350 mg L‐1 for the Cardy and 550–1300 mg L‐1 for the Hach. At maturity, NSR were less than 600 and 550 mg L‐1 for the same respective electrodes. Petiole sap NO3‐N determined by either the Cardy or Hach methods can be a quick and useful tool to assess potato N status.

Kinetics of soil‐plant nitrate relations in potato and peppermint: A model for derivative diagnosis

Abstract Suitable plant diagnostic procedures for nitrogen (N) management in high input crops such as potato (Solanum tuberosum) and peppermint (Piper mentha) should be derivative [measuring instantaneous nitrogen (N) uptake] rather than integrative (total accumulation) and should reflect concurrent soil N availability. Analyses for dry matter or sap nitrate (NO3) in potato petioles or peppermint stems are proposed as derivative procedures, but the plant‐soil NO3 relations of these analyses are not well understood. Our objectives were to test the validity of these derivative plant diagnoses as measures of concurrent uptake against the Michaelis‐Menten model of saturation kinetics. Periodic measures of dry matter and sap NO3 in potato petioles and peppermint stems were taken from field experiments with various rates and timings of N fertilizer, and regressed against concurrent soil NO3 (0–30 cm) by nonlinear least squares fit to the model: V = (Vmax · SN)/(Ks + SN) where: V = potato petiole or peppermint s...