Sap Nitrate Research Articles

Nitrogen application rates for greenhouse tomato based on real-time diagnosis of petiole sap: Effects of soil nitrate contents before cultivation

(pp. 825–831) This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L−1. For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg−1 dry soil or higher in the 0–30 cm layer; 38 kg ha−1 of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg−1 dry soil; 75 kg ha−1 of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg−1 dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L−1 from early harvest time to topping time under these conditions.

Use of Digital Camera to Assess Nitrogen Status of Winter Wheat in the Northern China Plain

The most widely used methods to assess the nitrogen (N) status of winter wheat (Triticum aestivum L.) are the determination of plant total N by combustion, the testing of nitrate in the leaf tissue and the use of SPAD readings. However, due to their labor requirements or high costs these methods can hardly be applied to the huge wheat growing areas of the Northern China Plain. This study therefore examined an alternative method to measure the N status of wheat by using a digital camera to record the visible green light reflected from the plant canopy. The experiment was conducted near Beijing in a multi-factorial field trial with three levels of N. The intensity of green light reflected from the wheat canopy was compared to the total N concentration, to the nitrate concentration of the basal stem, and to the SPAD readings of leaves. The results show significant inverse relationships between greenness intensity, canopy total N, and SPAD readings at booting and flowering. At booting, sap nitrate <2000 mg L−1 was inversely related to greenness intensity and to sap nitrate concentration in the basal stem. At sap nitrate ˜2000 mg L−1, the greenness intensity reached a plateau. At booting and flowering, significant inverse relationships between greenness intensity and shoot biomass were found. The results show the potential of the new method to assess the N status of winter wheat.

Low-altitude aerial photography for optimum N fertilization of winter wheat on the North China Plain

Previous research has shown that site-specific nitrogen (N) fertilizer recommendations based on an assessment of a soil’s N supply (mineral N testing) and the crop’s N status (sap nitrate analysis) can help to decrease excessive N inputs for winter wheat on the North China Plain. However, the costs to derive such recommendations based on multiple sampling of a single field hamper the use of this approach at the on-farm level. In this study low-altitude aerial true-color photographs were used to examine the relationship between image-derived reflectance values and soil–plant data in an on-station experiment. Treatments comprised a conventional N treatment (typical farmers’ practice), an optimum N treatment (N application based on soil–plant testing) and six treatments without N (one to six cropping seasons without any N fertilizer input). Normalized intensities of the red, green and blue color bands on the photographs were highly correlated with total N concentrations, SPAD readings and stem sap nitrate of winter wheat. The results indicate the potential of aerial photography to determine in combination with on site soil–plant testing the optimum N fertilizer rate for larger fields and to thereby decrease the costs for N need assessments.

Comparison of Laboratory and Quick‐Test Methods for Forage Nitrate

Nitrate contained in forage may pose performance and health risks to ruminants. With timely and accurate assessment of forage nitrate levels, steps to reduce the risks of excessive nitrate intake by livestock can be applied. Traditionally, plant nitrate is measured in the laboratory from finely ground oven‐dried tissue, which is slower than nitrate quick‐test assays of plant sap. However, use of plant sap nitrate requires calibration to nitrate in dried samples. Winter wheat forage (Triticum aestivum L.) collected at jointing and heading from fields fertilized with 56 to 235 kg N ha−1 was used to compare a laboratory flow injection analysis (FIA) method (Cu‐Cd reduction column) with nontraditional laboratory microplate (M‐NaR) and field‐test (F‐NaR) enzyme linked kits (nitrate reductase, E.C. 1.6.6.1), and two hand‐held quick‐test nitrate assays using a card mounted ion specific electrode (ISE‐card) and test strip reflectance meter (TSR). Hot‐water extracts of oven‐dried samples and fresh samples macerated in propanol solution with a high‐speed hand‐held blender were prepared. Compared with FIA, mean differences in tissue nitrate were nearly always greater (13–66%, P = 0.05) with the other methods. For dried samples, these differences were due partially to extract interferences that suppressed detection of nitrate with FIA and falsely elevated nitrate detection with the ISE‐card. Interferences caused only a slight underestimation of forage nitrate with TSR, and were nearly absent with the M‐NaR assay. The ISE‐card was the most variable and deviated the most from the FIA. Nitrate extraction over a nearly four‐fold range was 18% less from fresh than oven‐dried tissue. The quick‐test consumable cost per nitrate assay was similar for F‐NaR and TSR methods, but the TSR was easier to use. Because a hand‐held meter is not required with F‐NaR, initial startup cost can be reduced. Both TSR and F‐NaR performed well for quick‐tests of tissue nitrate.

Rapid Determination of Nitrogen Status in Pansy

Two experiments were conducted with pansy (Viola ×wittrockiana Gams `Bingo Yello') to determine the relationship between foliar nitrogen (% of dry weight) (FN) and either sap nitrate concentration (SN) in petioles or SPAD readings of foliage. FN was highly correlated to SN throughout both experiments (r = 0.80 to 0.91). FN was poorly correlated to SPAD readings early in both experiments (r = 0.54 to 0.65), but more highly correlated later when visual symptoms of N deficiency were apparent (r = 0.84 to 0.90). SN determined with the Cardy sap nitrate meter was a reliable predictor of FN in pansy, while SPAD readings were only reliable after symptoms of N deficiency were visually evident. FN can be predicted with SN using the following equation: log(SN) = 0.47*FN + 1.6 [r2 = 0.80, n = 132]. Growers and landscape professionals can use SN readings to predict FN levels in pansy, and thus rapidly and accurately diagnose the N status of their crop.

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.

Rapid Determination of Nitrogen Status in Annual Vinca

Abstract Three experiments were conducted to develop a method for rapid determination of nitrogen (N) status in ‘Pacifica White’ vinca (Catharanthus roseus (L.) G. Don). In experiment 1, N was applied to potted vinca at 40, 80, 120, or 160 ppm N to produce plants ranging from N deficient to N sufficient. Data were collected 14, 28, and 42 days after treatment (DAT) and included flower number, growth index [(height + width + width) ÷ 3], and from recently matured foliage the following parameters: SPAD-502 readings, petiole sap nitrate (SN) concentration, and total-N (percent of dry weight) (FN). Experiment 2 was similar with the exception that N rates applied were 30, 60, 90, 120, 150, or 180 ppm N, and data were collected 14, 29, and 42 DAT. In experiment 3, N was applied at 0, 90, or 180 ppm N and data were collected 0, 4, 7, 10, and 14 DAT. In experiments 1 and 2, SPAD readings were poorly correlated to FN (correlation coefficients ranged from 0.35 to 0.88) and the relationship between FN and SPAD readings changed at different collection dates. Petiole sap nitrate concentration determined by a Cardy nitrate meter was highly correlated throughout the three experiments. Above 380 ppm SN, the relationship between FN and SN was determined to be: SN/1000 = 2.3 × FN-4.8 (r2 = 0.73, n = 104). In experiment 3, FN and SN readings were able to detect N deficiency in vinca by 4 DAT, despite lack of visual symptoms until 14 DAT. SPAD readings were not suitable for predicting FN and plant N status. SN was a reliable predictor of FN and thus could be used to rapidly determine plant N status.

USE OF PETIOLAR SAP NITRATE FOR ASSESSING NITROGEN STATUS OF IRRIGATED BRUSSELS SPROUT CROPS

ABSTRACT Four field experiments were carried out during 1992/93 (sites 1 and 2) and 1993/94 (sites 3 and 4) to assess the effects of nitrogen (N), at rates up to 600 kg N ha−1 on sap nitrate concentrations in petioles of the youngest fully expanded leaves (P-YFEL) of Brussels sprouts (Brassica oleracea L. var. gemmifera). The experiments were located in commercial plantings in the Mount Lofty Ranges of South Australia. Plant samples were collected at 2–4 week intervals from 4 to 28 weeks after the plants were transplanted. Temporal variation and the effect on sap nitrate concentration of sampling leaves next in age to the index leaf (YFEL−1 to YFEL+2), were also studied. Nitrate concentrations in the sap of P-YFEL showed poor sensitivity to variations in side-dressed N fertilizer and the magnitude of the changes varied between sites and sampling time. For example, at 12 weeks after transplanting, sap nitrate concentrations varied by less than 2,000 mg L−1 over the range of N applied. Nitrate concentrations in petioles also varied with the age of the leaf sampled. Nitrate concentrations in petioles sampled at 4, 6, 8, and 10 weeks after transplanting increased with leaf age. Linear and quadratic models were used to study the relationships between sap nitrate concentration in P-YFEL sampled during the period 4 to 24 weeks after transplanting and yield response to applied N. Significant relationships were only found at site 2, 8 weeks after transplanting, R2=0.98; site 3 at 18 weeks, R2=0.87 and site 4 at 8 and 10 weeks, R2=0.93 and 0.87, respectively. Based on lack of sensitivity (as indicated by the narrow range in petiolar sap nitrate concentrations in response to variations in N supply), temporal variation (changes in petiolar sap nitrate concentrations during the season) and the lack of consistent relationships between sap nitrate concentrations and yield response, we concluded that sap nitrate concentration is not a useful indicator of plant N status and yield response of Brussels sprouts.

Role of xylem sap nitrate in the regulation of nitrate reductase gene expression in leaves of barley (Hordeum vulgare L.) seedlings

The role of xylem sap nitrate in the regulation of nitrate reductase (NR) in leaves was investigated in barley (Hordeum vulgare L.) seedlings. Upon the exposure of barley roots to nitrate at concentrations ranging from 0.1 to 5 mm, rapid accumulation of NADH-specific NR mRNA was observed in both leaves and roots. In the same treatment, the concentration of xylem sap nitrate also rapidly increased during the early feeding period and reached a steady state at concentration ranging from 15 to 50 mm. Patterns of NR mRNA accumulation in leaves were closely linked with the increase in the nitrate concentration in the xylem sap, but not with the amount of nitrate stored in the leaf tissues. High levels of NR mRNA in intact leaves were observed only when the xylem sap nitrate reached mm levels. Supply of different concentrations of nitrate to detached leaves also indicated that mm levels of nitrate supplied through the xylem were required for adequate accumulation of NR mRNA in leaves. When nitrate-grown seedlings were transferred to a nitrate-free medium, a parallel decline in both the concentration of xylem sap nitrate and NR mRNA level was observed, while the nitrate concentrations in leaf tissues remained constant. These results indicate that continuous supply of mm levels of nitrate through the xylem is important for maintaining the high levels of NR mRNA in barley leaves.

Influence of nitrogen fertilization on yield, hollow stem incidence and sap nitrate concentration in broccoli

This study, spanning 2 yr at two different sites, compared the effects of nitrogen fertilization on broccoli yield and quality in relation to the influence of site and production season. This research also evaluated the potential use of measuring nitrate in petiole extracts to determine broccoli nitrogen requirements when making a second fertilizer application 5 wk after transplant. Treatments consisted of factorial combinations of three nitrogen fertilization rates at transplant (Nmin, 50-Nmin and 100-Nmin kg N ha–1, where Nmin was the soil nitrate concentration) and four nitrogen fertilization rates 5 wk after transplant (0, 50, 100 and 150 kg N ha–1). The marketable yield of broccoli increased with the rate of nitrogen application. Hollow stem incidence showed the same trend as yield, and was greatest when high levels of nitrogen were applied 5 wk after transplant. Interactions between the 5-wk nitrogen application and production year, as well as growing site were significant. The nitrate content of the sap was measured immediately before the 5-wk nitrogen application and 2 wk later. The nitrate concentration measured at 5 wk increased with transplant nitrogen, as did the concentration measured at 7 wk. Nitrate concentration at 7 wk increased curvilinearly with the 5-wk fertilizer application rates. Sap analysis provided clear evidence of the effect of nitrogen application rates, but Environment precluded determination of an absolute threshold of nitrate sufficiency in the sap. Key words: Brassica oleracea L. var. Italica, split application, quality, environment

647 Effects of Nitrogen Application Rates on Leachate Nitrogen Concentrations and Leatherleaf Fern Establishment

One of the most difficult times to balance crop nitrogen (N) requirements with concerns about nitrate-N leaching occurs during crop establishment, when root systems are poorly developed and not widely distributed in the growing medium. This dilemma can be exacerbated when producing a slow-growing plant such as leatherleaf fern (Rumohra adiantiformis [Forst.] Ching) on sandy soils in shadehouses in areas with significant rainfall. Rhizomes were planted in 36 drainage lysimeters containing Tavares fine sand located in a shadehouse. Nitrogen fertilizer was applied at nine rates using liquid and/or controlled-release fertilizer. Nitrogen application rates were varied as the rhizomes became established and spread into unplanted areas of the lysimeters. Irrigation and rainfall were monitored and the amount of water not lost to evapotranspiration was determined. Nitrogen (ammoniacal, nitrate/nitrite, total Kjeldahl) concentrations in leachate collected below the rootzone were determined. Stipe sap nitrate and frond total Kjeldahl nitrogen (TKN) were determined to try to develop a production monitoring technique. Initially, only leachate samples from controlled-release fertilizer plots treated at 21 and 42 kg of N/ha per year and liquid fertilizer at 28 kg of N/ha per year were consistently below the maximum contamination level (MCL) of 10 mg·L–1. As the fern became established, leachate nitrate/nitrite-N concentrations from higher N application rate treatments also remained below the MCL. Leachate N concentrations decreased as rainfall increased. Fern growth increased with increasing N application rate. Stipe sap nitrate-N and frond TKN concentrations were not well-correlated during establishment.

Determination of Nitrogen Status in Winter Wheat by Measuring Basal Stem Tissue Sap Nitrate Concentration

The aim of this study was to assess a quick-test method determining nitrate in basal stem tissue sap for the prediction of nitrogen status in winter wheat (Triticum aestivum L.). The nitrate content in plant stem tissue sap collected at Zadoks growth stages GS 31 and GS 49 of winter wheat in 11 annual field trials in south-east Norway in the years 1993-96 was measured with Merckoquant test strips with a Nitracheck Meter. Relationships between NO3 - concentrations and final yields were good within individual trials, but when the results from all trials were pooled, the NO3 - concentration was a poor predictor of final yields. This study suggests that the critical nitrate values required in plant stem sap for sufficient grain protein content for bread-baking quality are 4000 ppm NO3 - at GS 31 and 2000 ppm at GS 49 in situations with a single N application in the spring. In situations with split N applications (25 kg N ha-1 at GS 31 and 25 kg N ha-1 at GS 49 in addition to spring application), 1000 and 500 ppm were found to be the critical values at GS 31 and 49, respectively. Because of the large between-site and between-year variability, this study does not indicate that the method can be recommended for extended practical use.

深夜照明と培養液からのＮＯ３｀−´除去が水耕ホウレンソウの生育と葉の汁液中ＮＯ３｀−´濃度に及ぼす影響

The effects of supplemental night lighting and nitrate exclusion in the nutrient solution on the growth, nitrate concentration, and nitrate reductase activity (NRA) in the leaf of spinach plants grown under NFT and natural light in the greenhouse were studied. When the plants became of marketable size, they were grown in a nutrient solution without nitrate and exposed to artificial lighting of different light intensities and qualities from 23 : 00 to 6 : 00 1. Two days after treatments, top fresh weight was not affected by nitrate exclusion, whereas 7 days after treatments, plant growth was markedly reduced by nitrate exclusion. However, supplemental night lighting after nitrate exclusion on the subsequent growth of spinach were ineffective. 2. After nitrate exclusion, sap nitrate concentrations of leaf blades and petioles under supplemental night lighting decreased more rapidly than that without the treatment. The decrease of sap nitrate concentrations was unaffected with light quality. However, light intensities affected markedly, and the sap nitrate concentrations of leaf blade at two days after treatment were 1, 059, 799, 612 and 531 ppm under 0 (without lighting), 50, 150 and 250 m mol m-2s-1 (PPFD), respectively. 3. NRA of the plants with supplemental night lighting was higher than that without lighting.

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.

A petiole sap nitrate test for broccoli

Nitrogen (N) status of vegetable crops is often monitored by analysis of dried plant tissues. However, dry tissue analysis often causes a significant delay between sampling and analysis. This study was conducted to examine the accuracy of a portable nitrate meter for determining petiole sap nitrate (NO3) contents, and the relationship between NO3‐N concentration in fresh petiole sap and in dried petiole tissue of broccoli grown in southern Arizona during the 1993–94 and 1994–95 winter growing seasons. Experiments were factorial combinations of three irrigation rates and four N rates, both ranging from deficient to excessive. Petioles were sampled throughout each season, and split for sap and dry tissue analysis. A linear correlation was obtained between the two measurements in both seasons, with no consistent effect due to irrigation treatment or crop maturity. The regression coefficients did not differ among seasons. Therefore, a combined regression equation: Y=343+0.047X (r2 = 0.799) was derived, in which Y=NO3‐N (mg/L) in fresh petiole sap, and X=NO3‐N (mg/kg) in dried petioles. These results suggest that the sap test can be a valuable and rapid technique to predict N needs of broccoli. Differences between the two methods are likely due to interferences in fresh petiole sap and slight differences in pools of extracted NO3.

Sink‐stimulated photosynthesis and sink‐dependent increase in nitrate uptake: nitrogen and carbon relations of the parasitic association Cuscuta reflexa–Ricinus communis

ABSTRACT Ricinus communis L. was grown under limiting N supply in quartz sand culture, fed with 0.2, 1 or 5 mol m−3 NO3−, or in liquid culture with 0.022, 0.05 or 0.5 mol m−3 NO3−. Some of the plants were infected with Cuscuta reflexa Roxb. As occurred for the host, dry matter production and growth of C. reflexa were severely depressed with decreasing N supply to the host. When parasitized by C. reflexa, the shoot and root dry weight of Ricinus was diminished at all levels of N nutrition, but the total dry weight of host plus parasite was almost the same as that of uninfected Ricinus. In contrast to the situation in Lupinus albus (Jeschke et al. 1994b), infection by Cuscuta resulted in increased tissue N levels in the host and the N content of the system Ricinus plus C. reflexa was the same or even somewhat larger than that of uninfected plants. This indicated a sink‐dependent stimulation of nitrate uptake. As a result of decreased root weights, nitrate uptake g−1 FW was stimulated by 80, 60 or only 40% at 0.2, 1 or 5 mol m−3 nitrate supply. Increased nitrate uptake was reflected, particularly at low N supply, in xylem transport; xylem sap nitrate concentrations were substantially elevated, while those of amino acids were decreased in parasitized plants. This indicated an inhibition of nitrate assimilation in roots of parasitized plants under limiting N supply. Besides these effects on N relations, C. reflexa induced a substantial sink‐dependent stimulation of net photosynthesis in host leaves and a concomitant increase in stomatal opening and transpiration. This stimulation depended on the relative sink size induced by Cuscuta, on nitrogen nutrition and on leaf age, indicating that delayed senescence of leaves contributes to the overall effects of Cuscuta on its host. The Cuscuta‐induced inhibition of nitrate assimilation in the roots and the increase in nitrate uptake suggest that nitrate reduction was shifted towards the leaves in the presence of C. reflexa. The stimulating effects of C. reflexa in the Ricinus‐Cuscuta association are compared with the strongly inhibitory effects occurring in the tripartite association L. albus–Rhizobium–Cuscuta reflexa.

Nitrogen Management of Drip-iIrrigated Peppers

Inadequate N can reduce growth and yield, but excess N can be uneconomical and environmentally harmful. Our objective was to investigate the potential for using fertigation and on-farm plant-nutrient monitoring to improve the efficiency of N fertilizer use by bell peppers (Capsicum annuum L.). Two N fertilizer treatments were compared: 1) all N applied preplant and 2) one-third of the N applied preplant and the remainder injected into the drip-irrigation lines throughout the growing season. Total application rates were N at 118 kg·ha–1 for both treatments. Data were collected for total yield, marketable yield, and fruit size. Leaf and petiole samples were collected every 2 weeks and were used to monitor plant N status throughout the growing season. A Horiba/Cardy nitrate meter was used to measure nitrate concentrations in freshly-pressed petiole sap. A SPAD chlorophyll meter was used to measure leaf chlorophyll content and give an indirect measure of leaf N concentrations. Subsamples of leaves and petioles also were saved for conventional laboratory analyses. Whole (aboveground) plant samples were collected every 2 weeks, analyzed, and used to calculate differences in N accumulation. Suction cup samplers were installed at the 24-in soil depth and water samples collected every 1 to 2 weeks for nitrate analysis. Except for early in the growing season, petiole sap nitrate and leaf chlorophyll were higher in the fertigation treatment. Plant dry matter and total N accumulation also were much larger, but fertigation did not increase yield. Nitrate leaching was greater early in the season with 100% preplant N, but later in the season it was greater with fertigation. Data suggested that adequate plant N, reduced nitrate leaching, and equivalent yields are possible with fertigation at reduced N-rates compared to 100% preplant fertilizer applications.

Factors affecting potato petiole sap nitrate tests

Abstract Many factors can affect the nitrate‐nitrogen concentration of potato petioles. They include but are not limited to the following: N‐fertilizer applications, mineralizable soil N, time of sampling, position of the petiole on the plant, age of the plant, potato cultivar, time of the day when plants are sampled, and the environmental conditions prior to sampling. A better understanding of these factors should lead to an improved sap test. Five irrigated potato studies were conducted between 1991 and 1993 to evaluate this variability. Sap nitrate‐N concentration was found to be closely associated with N‐fertilizer rates and soil mineralizable N. Sap nitrate levels were usually highest early in the season and declined with the age of the plant. The decline with time can be interrupted or delayed by in‐season N applications. Although the sap nitrate level among six different cultivars and diurnal sampling periods was found to be statistically significant, the differences were relatively small. By caref...

Comparison of Specific Electrode Techniques for Measuring Bell Pepper Petiole Sap Nitrate Concentration

Sap nitrate was determined with the ion-selective electrodes, HACH combination nitrate electrode, and the CARDY nitrate meter on pepper petioles over five sample dates (n = 160). The electrode values were compared to the Cd reduction method performed on a Lachat automated ion analyzer with flow injection analysis. Thirty petioles were collected from plots of each of several N rate studies and the sap expressed by a hand-held garlic press. Correlation among the techniques were similar (r &gt; 0.9), but the CARDY meter constantly read 100 to 175 ppm higher than the HACH. Across all dates the standard deviation of the difference, compared with the Cd reduction, for the HACH = 16 ppm, while for the CARDY it was 50. While the CARDY meter is easier to use and has fewer steps, the HACH electrode values were closer to the true readings and less erratic. One must use care when interpreting nitrate sufficiency value ranges with different quick-test techniques.

Comparison of Specific Electrode Techniques for Measuring Bell Pepper Petiole Sap Nitrate Concentration

Sap nitrate was determined with the ion-selective electrodes, HACH combination nitrate electrode, and the CARDY nitrate meter on pepper petioles over five sample dates (n = 160). The electrode values were compared to the Cd reduction method performed on a Lachat automated ion analyzer with flow injection analysis. Thirty petioles were collected from plots of each of several N rate studies and the sap expressed by a hand-held garlic press. Correlation among the techniques were similar (r &gt; 0.9), but the CARDY meter constantly read 100 to 175 ppm higher than the HACH. Across all dates the standard deviation of the difference, compared with the Cd reduction, for the HACH = 16 ppm, while for the CARDY it was 50. While the CARDY meter is easier to use and has fewer steps, the HACH electrode values were closer to the true readings and less erratic. One must use care when interpreting nitrate sufficiency value ranges with different quick-test techniques.