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%.     

Nitrogen rate and cultivar effects on nitrogen and nitrate concentration of sweet potato leaf tissue

Abstract

Nitrogen applications to dallisgrass grown on Olivier silt loam, an Aquic Fragiudalf, increased forage yield, forage digestibility, nutrient concentrations and nutrient contents as N rates increased to 896 kg ha^‐1. Expressing yield as a function of N application rate resulted in quadratic prediction equations that accounted for 75 to 98% of the variability in yield during five years. Eighty‐six percent of the maximum yield was obtained during the five years at 448 kg of N ha^‐1. Plant concentrations of N, Ca and Mg were increased more than concentrations of the other macronutrients as N rates increased. Plant contents of N, Ca and Mg in the forage increased 4.0, 3.2 and 3.5‐fold as N rates increased to 448 kg ha^‐1, while that of P, K and S increased 2.5 to 2.8‐fold. Residual N accumulations in the soil profile were apparent at the 896 kg ha^‐1 rate at the end of the growing seasons but were not detected the following March, indicating N losses by leaching and/or denitrification occurred at that N rate. Phosphorus applications increased forage P concentrations but did not increase forage yield nor available P levels in the surface 15 cm of soil. Maximum yields were obtained at forage P concentrations and Bray No. 2 soil P levels as low as 2.0 g kg^‐1 and 17 mg kg^‐1, respectively.     

Influence of nitrogen nutrition on nitrate levels of strawberry leaf blades and petioles

Hydroponic and field experiments were conducted to assess the optimum nitrogen (N) levels in strawberry leaves for the appropriate management of its N nutrition under field or protected cultivation. Unlike the common view that leaf petiole is the right plant organ to sample for strawberries, the study showed that the leaf blade, of the most recently fully expanded leaf, is more responsive and therefore a better indicator of the N supply changes in the strawberry plant. This was attributed to the distinctive characteristic of strawberry plants to accumulate high concentrations of nitrates in leaf blades when there is luxury consumption of N.     

Petiole and leaf nitrate studies in sunflower

Abstract

This study was conducted at two sites in Mississippi to determine whether petiole and leaf NO^‐ ₃ monitoring could be used as a management tool in making fertilizer N recommendations for sunflower (Hellanthus annuus L.). Petiole and leaf samples were taken at the four leaf stage at both sites, and later at two week intervals at Brooksville. Petiole and leaf NO^‐ ₃ at the four leaf stage was significantly influenced by rate of N application at both sites. The level of petiole and leaf NO^‐ ₃ was highly correlated with rate of N application as well as with seed yield. The concentration of NO^‐ ₃ in petioles and leaves was greatest at the four leaf stage and showed quadratic declines as the season progressed. Petiole and leaf NO^‐ ₃ showed the highest correlations with rate of N application and seed yield at the four leaf stage than at any other sampling time at Brooksville, indicating that this was the “best” period for taking petiole and leaf samples. However, analysis of petioles and leaves at the four leaf growth stage for NO^‐ ₃ may have limited potential of becoming a useful tool in making N fertilizer recommendations for sunflower. This is due to the sensitivity of both petiole and leaf NO^‐ ₃ to time of sampling and locational differences, as well as lack of information on response of sunflower to N applied after this stage of growth.     

A simplified method for determining acetic acid soluble phosphorus in plant tissue

Abstract

The proposed procedure greatly simplifies the determination of 2% HOAc soluble P in plant tissue. Extraction with Darco G 60 eliminates the need for the H₂O₂ oxidation of the extract. The use of vanadomolybdic acid as the chromogen results in a high degree of color stability eliminating the need for careful timing of the period between color development and transmission readings.     

Rapid and sensitive determination of nitrate in plant tissue using flow injection analysis

Abstract

The determination of nitrate in waters and soil extracts by the reduction of nitrate to nitrite by metallic or liquid reductants followed by the colorimetric determination of NO₂ ^‐using the Griess‐Ilosvay reaction has been automated for use with air‐segmented auto‐analyzers or flow injection techniques. However, this technique is not applicable to plant extracts as organic species in the extracts inactivate the reduction columns. The objective of this study was to develop an automated procedure that would allow the determination of NO₃ ^‐in plant extracts without the necessity of prior manual treatment. A flow injection technique was developed that successively traps and releases NO₃in an anion exchange column thereby removing pigments and other non‐ionic and cationic species that otherwise interfere with conversion of NO₃ ^‐ to NO₂ ^‐on a copperized cadmium column. This reduction step is subsequently followed by standard Griess‐Ilosvay colorimetric detection of this ion at a wavelength of 530 nm. The technique uses relatively simple and inexpensive equipment, principally a spectrophotometer equipped with a flow‐through cell and a pen recorder output, a 6‐channel peristaltic pump with accompanying tubing and a Perspex injector/commutator valve made in a laboratory workshop. The technique was found to avoid any significant interference of pigments or other organic compounds in the plant extracts, and the results compared favorably with those obtained using the manual transnitration technique. Analysis time was approximately 1.5 min per sample and could detect NO₃’ concentration as low as 0.1 ug NO₃’‐N ml/¹ in plant extracts (10 ug NO₃’‐N g‘¹of plant material).     

A simple and precise method for total chlorophyll analysis in tropical foliage plants 1

Methods currently in use for total chlorophyll analysis of plant tissue were reviewed. Storage of leaf tissue before analysis, filtration methods during analysis and extract longevity were investigated. The final procedure includes the use of leaf area cores and extraction with 100% acetone with results reported by area and oven dry weight. A simple and precise composite method was adopted.     

Evaluation of a hand held reflectometer for rapid quantitative determination of nitrate

Abstract

An inexpensive hand held reflectometer was used to estimate NO₃ concentration with Merckoquant NO₃ indicator strips. For KNO₃ solutions a fourfold improvement in precision was obtained over the visual method of colour comparison. The instrument calibration was stable over several days and not affected by temperature in the range 8–34^o C. The reflectometer showed quantitatively that increasing temperature (8–34^oC) reduced the optimal time for reading the strips from 120s to 40s. With standard NO₃ solutions a simple hyperbolic transformation of the reflectometer readings produced a linear calibration of good fit (r²=0.99). NO₃ could be estimated in different soil types within half an hour. The results agreed well with values from ion chromatography (r² =0.97, slope=1.07). Plant sap analysis was moderately precise (r² =0.92) but inaccurate and underestimated by more than 60% values obtained by ion chromatography. This discrepancy was not caused by the reflectometer but seemed to be due to factors within the plant sap that interfered with the NO₃ colour reaction in the Merckoquant strips.     

Evaluation of a rapid method for plant sap nitrate analysis

Abstract

A rapid method of analysis of nitrate in plant sap using Merck test strips was evaluated. Accuracy and precision of the strips was found to be acceptable in a test in which aqueous samples were tested by four operators. Nitrate N was measured in five vegetable crops at two stages of growth by two methods: squeezing sap from fresh petiole or stem tissue with NO3‐N determination by Merck test strip; and acetic acid extraction from dried petiole or stem tissue with NO3‐N determination by autoanalyser. The relationship between the two methods was found to be highly significant with coefficient of determination exceeding 0.82 in eight out of 10 cases (crops x sampling dates). When the strip results were corrected for moisture content the relationship with the laboratory method improved in most cases.     

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.     

The diagnosis of nitrogen deficiency in wheat by means of a critical nitrate concentration in stem bases

Abstract

Stem bases from wheat plants in a glasshouse pot experiment conducted under varying nitrogen and two water regimes, were analysed for nitrate (NO₃) concentration. The concentration of NO₃ at three stages of growth i.e. tillering, jointing and anthesis were related both to rates of applied nitrogen and to shoot dry matter yield at time of sampling. Plotted against rate of increasing nitrogen application, the response curve of NO₃ concentration in wheat stem bases was sigmoidal. The level of nitrogen application at which NO₃ began to accumulate in the plants was the supply at which plants reached maximum dry matter yield. The concentration of NO₃ at which plant yield was 90% of maximum dry matter was taken as the critical level. This concentration was around 1000 ppm NO₃‐N at all stages. Compared with plants supplied with unlimited water, plants under moderate water stress accumulated relatively more NO₃ but had a similar critical NO₃ concentration.

Maximum grain yield was obtained from plants which stayed above the critical level throughout the growing season.     

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.     

Rapid preparation of plant samples for cation analysis

Abstract

In the dry ashing of plant material for chemical analysis, the hot digestion on the steam bath of the ashed sample was replaced by the quantitative addition of dilute HCl and stirring very briefly to dissolve the ash. By waiting a few minutes for the particles to settle, there was no need to filter the solution prior to dilution with an automatic diluter and the determination of K, Na, Ca and Mg by atomic absorption spectrophotometry. The new procedure permits the handling of large batches of samples conveniently, eliminates the use of pipettes and volumetric flasks and decreases the risk of inadvertent contamination by sodium and therefore enhances accuracy. Precision was at least as good as with the standard procedure and the method is expected to be more suitable for use in conjunction with automated analytical techniques.     

A simple procedure for 15N determinations in relatively large samples by emission spectrometry

Abstract

Discharge tubes containing argon, and NH₃ separated from atmospheric N₂ by condensation in a liquid‐nitrogen—cooled trap, are used to determine ¹⁵N: ¹⁴N ratios in ammonium solutions. Reduction of NH₃ to N₂ during sample preparation is not required; the dissociation of NH₃ in the discharge tube produces sufficiently intense N₂ band spectra for the isotope analysis. The method can be readily applied to the analysis of ammonium solutions derived from Kjeldahl digests of plant material.     

Critical nitrate levels for leaf lettuce,radish, and spinach plants

Abstract

Leaf lettuce (Lactuca sativa var. crispa L.), radish (Raphanus sativus L.), and spinach (Spinacea oleracea L.) plants were grown in sand culture under variable N concentrations from 0.187 to 48.0 meq/l. The plants were harvested when those grown at 12 meq N/l had attained approximate market maturity. Growth was restricted, and symptoms of N deficiency were evident at the low levels of N. Growth was also restricted at the highest N level. Approximate critical levels for leaf lettuce, radish roots, and spinach are 2000 ppm, 5000 ppm, and 4000 ppm, nitrate‐N respectively, on a dry weight basis.     

Rapid gravimetric determination of Si in rice straw

Abstract

The Si content of rice straw is used as a measure of the Si status of rice plants, the growth and grain production of which are reduced when plant Si is low. Straw Si often is determined gravimetrically following digestion of plant tissue. A new, rapid gravimetric procedure has been developed for determining Si in rice straw. The straw is oxidized, washed free of various components, and SiO₂is developed and weighed in fritted glass Gooche crucibles. The rapid method reduces the analysis time, reduces glassware requirements, and eliminates analyte transfers.     

Rapid perchloric acid digest methods for analysis of major elements in plant tissue

Abstract

The nutrient element composition of tissue from a plant species is not fixed. Composition in the plant varies among different plant parts at the same or different physiological stages of maturity, as soil type changes, from day to day, even hour to hour on the same day due to past and current environmental conditions. These observations seem to undermine the general trend in plant tissue analysis to develop quantitative procedures that are time consuming and, therefore, foster insufficient nutrient status monitoring within and/or between different physiological stages of maturity of like or different plant parts. Therefore, until tissue sampling becomes more definitive, a digest procedure with 90–100% recovery should be more than adequate for major elemental analysis. The HClO₄ digestion procedures described here meet that requirement and take only 15 to 30 min to complete. N recovery was greater than 100% with the H₂O₂‐HClO₄ digestion procedure. However, when HNO₃ was combined with H₂O₂ and HClO₄, N was lost, although even then N volatilization occured only when digestion was extended past clearing.     

Digestion of plant tissue for analysis by ICP emission spectroscopy

Abstract

A method of digesting plant tissue samples for multi‐element analysis by inductively‐coupled plasma (ICP) emission spectroscopy was developed which does not require the use of HclO₄. A substitute oxidant, H₂O₂, eliminated the hazards associated with hot, concentrated HClO₄. Optimal conditions for pre‐digestion and digestion were investigated.

The procedure adopted consists of a pre‐digestion in concentrated HNO₃ from room temperature to 60°C in 30 min followed by digestion at 90°C for 90 min with the addition of 30% H₂O₂ Analysis of NBS standard tissue samples by the proposed method gave results in good agreement with analysis following digestion in HNO₃,‐HClO₄ and with certified values, except for Fe.     

Diurnal,shade, and hybrid effects on nitrate content of young corn stalks

Abstract

Significant correlations have been found between the nitrate concentration in young corn (Zea mays L.) stalks and available soi 1 N and relative grain yield when N availability is a yield limiting factor. To successfully use nitrate tissue testing as an indicator of the N status of plants, the effects of factors other than soil or fertilizer N on the nitrate concentration in the tested tissue must be understood. Diurnal effects on stalk nitrate content were studied in a greenhouse experiment, in which stalk samples were collected every two hours for 24 hours, and in a field study, where plants in an N‐fertilizer response experiment were sampled at sunrise and at mid‐day. A significant diurnal cycle was observed for stalk nitrate content in the greenhouse, with a peak at 0800 h and a low at 1400 h, but no diurnal effect was found in the field study, possibly due to plant stress from other environmental factors. In a second greenhouse study, stalk samples from seedlings in direct and 66% shaded natural light were collected for two consecutive days and measured for nitrate content to ascertain the consequences of sampling on overcast days. Significant accumulations of nitrate occurred in stalks of plants sampled after two consecutive days of shading. Stalk samples from three standard hybrid corn trials in central Pennsylvania were measured for nitrate content to determine if hybrid differences existed. Hybrid differences in stalk nitrate were significant in only one of the three sites studied, and the variation in that one may have been due to differences in drought tolerance as well as nitrate metabolism. The results suggest that sampling strategies should be designed to minimize the effects of irradiance level on nitrate accumulation, but that differences in nitrate accumulation among corn varieties may not be a major concern in using nitrate tissue tests to predict N availability.     

Drying method effects on extractable phosphorus levels in plant tissue

Abstract

The level of soluble tissue phosphorus (PO₄‐P) may be correlated with the plant P nutritional status, but the amount extracted depends upon dry matter losses or the amount of enzymatic or heat—induced hydrolysis of organic P compounds during sample drying.

Alfalfa (Medieago sativa L) and sugarbeet (Beta vulgaris L) plant parts grown under low and high soil P conditions, were freeze‐dried or oven‐dried at 40, 56, 70, or 100 C. Total K, P, and 0.35 N acetic‐acid‐soluble P (measured as PO ‐P) were determined. Dry matter losses were 0, 6.5, 3.6, 5.5, and 4.9 percent for the respective drying methods. The total‐P values, once corrected for dry matter losses, were not affected by the drying methods. The corrected PO₄‐P values were 0.15, 0.17, 0.16, 0.16, and 0.19 percent, while the (PO₄‐P)/P values were 0.63, 0.69, 0.67, 0.68, and 0.78 for each of the respective drying methods.

The potential utility of extractable PO₄‐P in describing the plants’ P nutritional status will depend upon rigorous sampledrying techniques. Freeze‐drying was the most satisfactory method tested, since it resulted in the least dry‐matter loss and least organic P hydrolysis.