Diagnosing nitrogen fertilization requirements of cereals in less than 30 seconds

Abstract

Stems of barley and wheat plants of wide range in nutritional status were analysed for sap NO₃ concentration at the tillering stage using both “Merckoquant”; nitrate test strips and a specific‐ion nitrate electrode. Even though the “Merckoquanf'test strips used in this study did not give precise NO₃ readings they were found to be a satisfactory method for determining the NO₃ content of stems of cereals, and can be used in situ by farmers to predict the necessity of N fertilization for maximum grain yield. If the NO₃ sensitive area on the test strip is coloured to match the standard 500 ppm NO₃ colour in less than 30 seconds, after the application of sap, this is an indication of adequate N nutrition. If the 500 ppm NO₃ colour standard is reached between 30 to 60 seconds, then this is an indication of intermediate N nutrition and fertilization is recommended only under favorable weather conditions. If colour development of the test strip for the 500 ppm N0₃ standard takes more than 60 seconds, or the colour developed does not reach this standard, this is an indication of deficient N nutrition. Therefore, the use of the “Merchoquant”; test strips offers a useful tool in deciding if N fertilization of small‐grain cereals is needed.     

On‐farm monitoring of soil and crop nitrogen status by nitrate‐selective electrode

Abstract

Nitrate‐nitrogen concentration in fresh petiole sap, as measured by a portable, battery‐operated, nitrate‐selective electrode, was highly correlated with NO₃‐N concentration in dry petiole tissue of broccoli [Brassica oleracea L. (Italica group), r² = 0.84], celery [Apium graveolens L. var. dulce (Mill.) Pers., r² = 0.88], lettuce (Lacluca saliva L., r² = 0.77), pepper (Capsicum annuum var. annuum L., r² = 0.89), tomato (Lycopersicon esculentum Mill., r² = 0.83), and watermelon [Citrulius lanatus (Thunb.) Matsum. & Nakai, r² = 0.88]. This relationship was linear over a wide range of NO₃‐N values and was generally unaffected by site, crop, cultivar, or growth stage, provided that petiole tissue analyzed was from recently matured leaves. Sap was analyzed directly without dilution or filtration. The slope of the regression equation differed widely among crops. Selective electrode analysis of NO₃‐N concentration of soil solution samples obtained by suction lysimetry was also highly correlated with conventional laboratory technique (r² = 0.87). The nitrate‐selective electrode appeared to be a useful tool for on‐farm monitoring of soil and crop N status.     

Monitoring sap nitrate in vegetable crops: Comparison of test strips with electrode methods,and effects of time of day and leaf position

Abstract

A field crop of 3‐month old cabbages was sampled every 2 h from 0600 h until 2000 h. At each sampling, an upper, middle and lower leaf were taken from four plants, and their petiole nitrate status measured by three methods (a) “Merckoquant”; test strips (b) specific ion electrode on a fresh macerated extract and (c) the same electrode on an extract of oven dry tissue. All three methods led to similar conclusions: a. there were very big differences in concentration with leaf position, the middle leaf having the highest;

b. there were large concentration differences between plants, especially for the lower leaves;

c. the effect of time of day was not significant.

The test strips are capable of giving satisfactory results provided that sufficient plants are sampled, but values thus obtained for sap may be lower than for macerated fresh tissue, especially at the low end of the concentration range.     

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.     

A quick test procedure for soil nitrate‐nitrogen

Abstract

A procedure for extraction and measurement of nitrate‐nitrogen (NO₃‐N) in soil is described. Extracting solution [0.025M Al₂(SO₄)₃] and field‐moist soil are measured volumetrically, with NO₃‐N concentration measured by nitrate‐sensitive colorometric test strips or nitrate‐selective electrode. Across a range of soil texture, moisture content, and NO₃‐N concentration, the procedure was well correlated with conventional laboratory analysis of 2N KC1 soil extracts (r² = 0.94). This quick test procedure is proposed as an on‐farm monitoring technique to improve N management.     

A quick‐test procedure for soil and plant tissue nitrates using test strips and a hand‐held reflectometer

Abstract

Development of a nitrate quick‐test for use by fanners or field consultants would likely encourage the use of plant tissue and soil nitrate tests as a means to improve nitrogen management. To evaluate a quick‐test method, nitrate concentrations in plant tissue and soils were measured using commercially available nitrate test strips and a hand‐held reflectometer. The results were compared with those obtained with standard laboratory methods. Test strip accuracy and precision and reflectometer precision were determined over a 10 day period using standard KNO₃solutions and colored paper strips. Coefficients of variation ranged from 22.4 to 9.5 percent for the test strips and from 3.5 to 1.6 percent for the reflectometer. Quick‐test results were highly correlated with laboratory results for both plant tissue nitrate (r=0.87) and soil nitrate (r=0.98) concentrations. Results indicated that test strips provide a rapid, reasonably accurate and precise method to determine nitrate concentrations in both soil and plant material     

Evaluating the Validity of a Nitrate Quick Test in Different Chinese Soils

Because laboratory tests are expensive and time-consuming and may not be available to farmers, soil nitrate quick tests are required for optimal nitrogen management strategies in China to increase nitrogen use effciency and to reduce nitrogen losses. A total of 328 soil samples were collected at different soil depths from 225 sites in China, which covered a wide range of climatic and geographic regions, soil types, croplands and soil textures, to evaluate the suitability of a quick reflectometer test method for analysing soil NO-3-N in a wide range of soil NO-3 concentrations, soil types and cropping systems in China, mainly by comparison of soil NO-3-N assessed by a quick-test method (a reflectometer) and a standard laboratory method, i.e., high-performance liquid chromatography (HPLC). The reflectometer showed excellent agreement with the laboratory HPLC method with regard to soil nitrate contents for all analysed soil samples. The linear regression had slopes of 1 ± 0.08 and intercepts of ±1.38 mg NO-3-N L-1 among different soil types and croplands. Compared with the 1:1 lines, the regression analysis for each soil type showed statistically significant but small differences in slope; the relative difference between the values measured using the two analytical systems varied from -8% to 6%, and there were no differences in intercept except for paddy soil. The reflectometer showed adequate, statistically significant precision in determining soil nitrate contents, and it could therefore be directly used instead of the laboratory methods for soil NO-3-N measurement in China.     

Field measurement of soil nitrate concentrations

Abstract

Information on the nitrate concentration of soil at the time of sowing crops is useful in estimating the optimal amount of fertilizer nitrogen (N). A field measurement of soil nitrate overcomes the delay and cost of laboratory analysis. The accuracy of Merckoquant test strips used with a hand‐held Nitrachek reflectometer was tested with a wide range of soil samples. We have found that the system gave accurate results provided two precautions were taken. First, samples should be compared with standard solutions analyzed at the same temperature, because the method was found to be temperature dependent. Second, the extractant should be 0.5M K₂SO₄ or water, since the usual soil extractant, KCl, interferes with the analysis. The use of water for extraction reduces the cost of analysis and makes it feasible to analyze kilogram amounts of soil, thereby reducing the error of subsampling. We report a procedure which minimizes the time of extraction and hence the chance of denitrification, by filtering the suspension of soil in water through a 0.8‐mm filter attached to a syringe.     

Ion chromatography in nutrient depletion studies: Measurement of very low nitrate concentrations

Abstract

Determination of the extent to which plants can deplete nitrate from nutrient solutions (C_min) has been hindered in the past by insufficiently sensitive assay techniques. Now ion chromatography on a Dionex AS4A column can be used to separate and quantitate as little as 5 pmoles nitrate (a sensitivity of 0.02 + 0.005 μM NO₃ ^‐[0.3 ppb NO₃ ^‐N]) in nutrient medium containing other anions in more than 10⁵molar excess. To obtain this precision in actual depletion experiments, however, certain important precautions must be observed, including the avoidance of membrane filters with interfering extractables, i.e. all types tested. Under these conditions, other components of the medium do not interfere, nor apparently do root exudates. The sensitivity and absence of interference is compared with that of existing methods for nitrate estimation (nitrate electrode, salicylate, phenoldisulfonate, nitrate reductase/ nitrite diazotization, and ultraviolet absorption, alone, or coupled with high pressure liquid chromatography). The technique is used to demonstrate that pumpkins (Cucurbita moschataPoir.) growing in nutrient solutions can deplete nitrate at least to 0.16 μM, a concentration probably not measurable by any non‐chromatographic method, and measurable accurately at present only by the ion chromatography technique described here. Chloride uptake, and efflux, has also been measured simultaneously from the same chromatography profiles     

Extraction of soil‐available phosphate,nitrate, and sulphate ions using ion exchange membranes and determination by ion exchange chromatography

Abstract

In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H₂PO₄ ^‐), nitrate (NO₃ ^‐), and sulfate (SO₄ ^2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha^‐1 as triple superphosphate. The efficacy of the IEM was high (85% for SO₄ ^2‐, and 92% for H₂PO₄ ^‐ and NO₃ ^‐). Statistically significant correlations were obtained between the H₂PO₄ ^‐ extracted by IEM and the H₂PO₄ ^‐ obtained by the Bray P1 procedure (r²=0.936) and with the H₂PO₄ ^‐ extracted using Saunders and Williams (1955) procedure (r²=0.370). The correlation obtained between the amount of NO₃ ^‐ extracted with IEM and that obtained using 2M potassium chloride (KCl) was also highly significant (r²=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the concentrations of soil available H₂PO₄ ^‐, NO₃ ^‐, and SO₄ ^2‐ ions, which are of great plant nutrition interest. Phosphorus extractable with IEM yielded a close relationship with biomass production and could be used for determining the P requirement of these forest trees.     

Sap analysis for diagnosis of nitrate accumulation in cereal forages

Abstract

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.     

Quick nitrate test for hybrid sudangrass and pearlmillet Hays

Abstract

Hybrid sudangrass and pearlmillet are noted as having a high potential for accumulating nitrate (NO₃) and poisoning cattle. Hay samples can be accurately tested for NO₃ content in the laboratory, however, this may take considerable time for farmers to obtain their results. This study was conducted to evaluate applicability of a quick Nitrate Meter for in‐field testing of forage NO₃ in the plant sap and to study the effects of nitrogen (N) fertilization on forage NO₃ accumulation. Nitrate readings taken from the sap were highly correlated with those using the conventional laboratory method (R²=0.85–0.95 for hybrid sudangrass and 0.91–0.94 for pearlmillet). Nitrate concentrations varied with plant height, growing stages, locations in the test plots, N rates and sources, and environmental conditions. Nitrate concentrations in the whole plant decreased with plant height and plant maturity. Higher NO₃ levels were correlated with higher rates of N fertilizers. Nitrate accumulation was also enhanced by drought stress. The quick NO₃test method is easy to use and usually takes less than 20 minutes to obtain results. This methodology allows increased management flexibility for farmers who use warm‐season annual grasses in their production systems.     

Jahreszeitliche Veränderung der NO3−-Konzentrationen im Xylemsaft des unteren Stammteiles von Buchen (Fagus sylvatica L.)

Seasonal variation of NO₃^? concentration in xylem sap of the lower trunk part of beeches (Fagus sylvatica L.) From October 1988 to October 1989 five beech trees from a 35-year-old and a 42-year-old stand were felled in 14 day intervals. Xylem sap was extracted from the lower 100 cm of the trunk by means of liquid displacement. In general there was an increase of NO₃^? xylem sap concentrations in summer. Higher xylem sap nitrate concentrations were accompanied by an almost equal but opposite pH decrease. It is assumed that the rapid surge in NO₃^? concentration of the xylem sap was due to summer acidification pushes in the forest soil.     

Study on ammonium tolerance of cucumber plants

The influence of N form on xylem exudate and the guttation fluid concentration in cucumber plants was studied under greenhouse conditions. Plants were hydroponically grown with three NO₃:NH₄ ratios (100:0, 80:20, and 60:40) at a constant pH of 6.0 in the nutrient solutions. Plants supplied with 60:40 NO₃:NH₄ ratio displayed a significant decrease of NO₃‐N, total‐N, organic‐P, and Mn concentrations in the xylem sap and an increase of H₂PO₄‐P, SO₄‐S, Cl, B, and Zn concentrations. Potassium and Ca uptake in these plants was slightly reduced, indicating that pH control was an important factor for cationic nutrition in cucumber plants fed with NH₄. The major ions present in the nutrient solutions are concentrated in the xylem sap, particularly for NO₃, K, Ca, and Na. The NO₃:NH₄ ratio had a small effect on the ionic levels of the guttation fluid. The concentrations of all nutrients in the guttation fluid were substantially reduced, except for Cl, showing that the leaf tissues of cucumber plants remove the excess of Cl ion. Finally, in this study, secondary effects of N source on ion uptake and release were minimized by controlling nutrient solution pH.     

Use of anion exchange membranes to assess nitrogen needs of perennial grasslands

Abstract

Anion exchange membranes (AEMs) have recently become available and have proven effective in measuring phosphorus present in soils as well as nitrate (NO₃ ^‐) under both cultivated and grassland field conditions. We have attempted to assess the ability of AEM strips to measure NO₃ ^‐ present under a perennial grassland harvested for hay three times during the growing season. In all cases, we found significant quadratic relationships between nitrogen (N) applied and NO₃ ^‐ desorbed from the AEM strips. Using both linear‐response‐and‐plateau (LRP) and quadratic‐plateau (QP) models, we found highly significant relationships to relative yield and the ability to predict a critical level (CL) of NO₃ ^‐‐N necessary to reach maximum yield during two harvest periods. The AEM strips provided a good correlation between NO₃ ^‐and N rate, and between NC₃ ^‐ and yield. Critical levels at which subsequent N would need to be applied in order to achieve maximum yield were identified. These need to be further field‐tested for consistency under differing environmental conditions.     

Detection of nitrate leaching through bypass flow using pan lysimeter,suction cup,and resin capsule

Abstract

We compared the use of mixed-bed ion exchange resin capsules (RC), suction cups (SC), pan lysimeters (PL), and subsurface drainage (DR) for the detection of nitrate movement through a clayey soil where onion (Allium cepa L.) had been cultivated over a period of seven months. At the topsoil level, solutions collected with SC showed higher concentrations of NO₃ ^? than the PL-collected samples. At 80-cm depth, however, the concentrations of NO₃ ^? were higher for the DR and PL samples than for the SC samples, suggesting that bypass or macropore flow was the primary mechanism of NO₃ ^? transport to subsurface drainage or groundwater, while solutions collected by SC mostly represented solutions inside soil aggregates. The use of the resin capsule method resulted in higher values of NO₃ ^? at 15- than at 50-cm depth initially but the trend was reversed after sufficient leaching and plant uptake. High and significant correlations were obtained between the amount of NO₃ ^? adsorbed on RC at 15-cm depth and the mean concentration of NO₃ ^? in the DR samples during the RC installation period and between the NO₃ ^? adsorbed on RC at 50-cm depth and the mean NO₃ ^? concentration of PL samples at 80-cm depth. Such results indicate that the RC method which enables the detection of nitrate transport via macropore flow is a promising technique for nitrate leaching measurements.     

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

Abstract

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.     

Evaluation of a rapid sap nitrate test for young kiwifruit vines

Abstract

A glasshouse experiment was conducted with young grafted kiwifruit plants to evaluate a rapid sap nitrate test using Merck nitrate test strips, and to establish critical values for maximum vine growth. Total N leaf concentration for these plants was also related to vine growth. Sap nitrate nitrogen was significantly related to growth of the plant expressed as unit leaf rate (ULR) over four and six week periods from the time of sampling. Total N, on the other hand, was only significantly related to the total cane length at the time of sampling but not to the ULR. Using Cate‐Nelson graphical method, the critical sap NO₃‐N value for maximum growth was established at 500–600 ppm. The critical value for total N was established at around 3.2%.     

Host-rhizobia interaction for effective inoculation: evaluation of the potential use of the ureide assay to monitor the symbiotic performance of tepary bean (Phaseolus acutifolius A. Gray)

Domesticated and wild-type tepary beans (Phaseolus acutifolius A. Gray) were grown with or without inoculation with rhizobia in pots under bacteriologically controlled conditions in a temperature-controlled glasshouse. Seeds were inoculated with a mixture of seven strains isolated from nodules collected from domesticated field-grown tepary bean in Arizona, USA, or with a commercial inoculant strain for Phaseolus vulgaris (CC511). Different degrees of plant reliance upon N₂ fixation for growth were generated by supplying the inoculated plants throughout growth with nutrients containing a range of concentrations of ¹⁵N-labeled NO₃ (0, 1, 2, 5 or 10 mM). An uninoculated treatment that received 10 mM ¹⁵N-labeled NO₃ was included to provide data for plants solely dependent upon NO₃ for growth. Six weeks after sowing, shoots were harvested for dry matter determination and subsequent ¹⁵N analysis, root-bleeding xylem sap was collected, and nodulation assessed. With regard to shoot biomass production, domesticated lines were more responsive to inoculation, but less responsive to applied N than wild types. All inoculated plants were nodulated, but the field isolates from tepary bean were more effective in N₂ fixation than strain CC511. It was concluded that tepary bean requires a specific inoculant to benefit from fixation of atmospheric N₂. Xylem sap samples were analysed for ureides (allantoin and allantoic acid), amino acid content (α-amino-N), and NO₃ concentration. The amount of ureide-N present in xylem sap was expressed as a percentage of total solute N, described as the relative abundance of ureide-N (RUN), for each N treatment and was compared to the proportion of plant N derived from N₂ fixation (%Ndfa) calculated using a ¹⁵N dilution technique. The RUN values ranged from 8% for saps collected from uninoculated plants provided with 10 mM NO₃ in the nutrient solution (%Ndfa=0) to 86-91% for nodulated plants grown in the absence of externally supplied NO₃ (%Ndfa=100). These data indicated that ureides were the principal product of N₂ fixation exported from the nodules to the shoot in xylem sap. Since RUN values were closely related to %Ndfa, it was proposed that N-solute analysis of xylem sap could provide a valuable analytical tool to monitor the symbiotic performance of tepary bean.     

Effect of External Nitrogen and Potassium Supply on Xylem Sap Composition of Sugarcane

ABSTRACT

This study was conducted to evaluate the effect of nitrogen (N) and potassium (K) availability on root exudate composition of two sugarcane cultivars known to differ with regard to their resistance to drought and salinity stress. The plants were hydroponically grown in a greenhouse and subjected to three levels of N (0.1, 1.0, and 10 mM N) and three levels of K (0.02, 0.2, and 2 mM K). Nitrogen and K stress altered the xylem sap composition. Nitrogen stress significantly reduced nitrate (NO₃ ^?), ammonium (NH₄ ⁺), calcium (Ca), magnesium (Mg), and amino acid content and increased the pH, phosphorus (P), and K content. Whereas, K stress significantly decreased pH, K, NH₄ ⁺, and amino acid content but increased Ca, Mg, and P content. Nitrogen and K stress had opposing effects on xylem sap pH and osmolality. Results indicated that sugarcane plants recycle compounds between the phloem and xylem. The results also suggested that the NO₃ ^? and K concentration of xylem sap could be effectively used to estimate the N and K status of the soil solution.