A rapid petiole sap nitrate‐nitrogen test for potatoes

Abstract

A rapid test for measuring petiole sap nitrate‐N in potatoes was developed using a pH/ISE meter equipped with a nitrate‐ion specific electrode. Nitrate‐N measurements were made on fresh sap that was diluted with a solution of 0.075M Al₂(SO₄)₃‐18H₂O and 0.02M H₃BO₃. The sap nitrate‐N concentration, as determined by the rapid test, was highly correlated (r = 0.91, P<0.01) with dry matter nitrate‐N. Because of the non‐clogging design properties of the electrode used, this test procedure produced rapid and reliable results with good instrument stability and long electrode life. The chemicals used for this test are relatively non‐hazardous and the required tools can be assembled into a small portable kit. When properly calibrated, this test will provide added impetus to growers to rely on tissue analysis for corrective in‐season nitrogen (N) fertilization of potatoes.     

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     

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.     

Site specific soil‐test interpretation for snapbean

Abstract

Phosphorus (P) and potassium (K) requirements of snap bean (Phaseolus vulgaris L.) in North Florida are not well defined in the literature. Response of a bush type snap bean to P and K was determined in a 2‐year test at NFREC, Quincy. The resulting data were used in site specific soil‐test interpretations. Residual soil‐P levels were 7, 11, 29, and 66 mg/kg the first yr and 7, 12, 21, and 42 mg/kg the second yr, no fertilizer K was added either yr. Residual soil‐K was 26, 60, and 73 mg/kg the first yr. Fertilizer K was added the second yr at 0,95, and 190 kg/ha. Soil samples were collected from each plot near the beginning of each growing season for determination of soil‐test P and K levels. Soil type was Norfolk loamy fine sand (fine loamy, siliceous, thermic, Typic Kandiudult). Maximum nutrient levels required for snap bean were: soil‐test P 30 mg/kg and soil‐test K 80 mg/kg. Soil‐test interpretations for P were: low <15 mg/kg, medium 15 to 30 mg/kg, and high >30 mg/kg. Potassium soil‐test interpretations were low <40 mg/kg, medium 40 to 80 mg/kg, and high >80 mg/kg.     

Soil sample bag effects on pre‐sidedress soil nitrate test concentrations

Abstract

Most soil testing laboratories require soil samples collected for the pre‐sidedress soil nitrate test (PSNT) to be dried before shipment. Shipment of field‐moist samples would make it easier to use the test. The objective of this study was to measure the effect of bag type on changes in soil nitrate in samples collected for the PSNT. Soil samples were collected from the surface foot of soil when corn (Zea mays L.) plants were 15‐ to 30‐cm tall. Four fields with a history of manure applications were sampled. The bulk sample was subsampled in the field and the subsamples were kept cool during transport to the laboratory and were immediately air dried after arrival at the laboratory. Field‐moist subsamples from each bulk sample were placed into either cloth bags or plastic‐lined paper bags after arrival at the laboratory. Four replications of the subsamples were incubated at 30°C for 1, 2, 3, and 4 days. After removal from the incubator, the subsamples were immediately spread to air dry. The soils incubated in the plastic‐lined paper bags did not significantly increase in nitrate after one day of incubation. There was a significant increase, however, in nitrate each day after the second, third and fourth day of incubation. The soils incubated in the cloth bags did not significantly increase in nitrate until the fourth day of incubation. The average increase in nitrate‐N concentration in the cloth bags between day 3 and day 4 was 1.5 mg kg L^‐1soil. The results suggest that cloth bags could be used to ship field‐moist soil samples for the PSNT without significant changes in soil nitrate concentrations.     

Relationships between nitrogen rate,plant nitrogen concentration,yield and residual soil nitrate‐nitrogen in silage corn

Abstract

Nitrogen (N) fertilizer is a key factor of yield increase but also an environmental pollution hazard. The sustainable agriculture system should have an acceptable level of productivity and profitability and an adequate environmental protection. The objectives of this study were to determine the relationships between N rate, DM yield, plant N concentration (NC) and residual soil nitrate‐nitrogen in order to improve the predicted N rate in corn (Zea mays L.) silage. The experiment was conducted over a period of three years in the province of Quebec on three soil series in a continuous corn crop sequence. Treatments consisted of six rates of N: O, 40, 80, 120, 160, and 200 kg N ha^‐1 as ammonium nitrate applied at planting: broadcast and side banded. Four optimum N rates were calculated using different models: (i) economic rate base on fertilizer and corn price using the quadratic model (E); (ii) economic rate based on fertilizer and corn price using the quadratic‐plus‐plateau model (QP); (iii) critical rate based on linear‐plus‐plateau model (P); (iv) lower than maximum rate (L) corresponding to 95% of maximum yield. The optimum plant NC at all growing stages and the N uptake at harvest were calculated depending on these N rates and yields.

The NC of whole plant at 8‐leaf stage (25–30 cm plant height) of ear leaf at tasselling and of whole plant at harvest stage, the N rate, the N uptake at harvest and the DM yield were all significantly intercorrelated and affected by soils and years, but not affected by N fertilizer application method. The DM yield was linearly and significantly related to NC of whole plant at 8‐leaf stage (rv = 0.932**). At this stage, the average NC corresponding to the optimum N rate and yield was of 3.71, 3.68, and 3.66% as calculated with E, L, and P model, respectively. Our data suggest that the NC of whole plant at 8‐leaf stage may be used to evaluate the N nutrition status of plant and the required optimum N fertilizer rate. The NC of ear leaf at tassel stage was also significantly correlated to corn yield (r = 0.994**). It may be used as an indicator to evaluate the near‐optimum N rate in the subsequent years.

The N uptake by whole above‐ground plant at harvest was quadratically related to corn yield. Data show that at high fertilizer N rate, the N uptake still increased without significantly increasing yield. The N uptake was of 176.5, 163.0, and 155.0 kg N ha^‐1 using the E, L and P rates of 146, 126, and 115 kg N applied ha^‐1, respectively. The optimum N rate and yield were affected by soil type and year, but not by the method of N fertilizer application. The yield increased rapidly up to a N rate of about 120 kg N ha^‐1 and then quite slightly to a maximum N rate of 192 kg N ha^‐1. The optimum N rate was of 115 and 126 kg N ha^‐1 using the P and L model respectively and as high as 146.8 kg N ha^‐1 using the E model. The L model, using a much smaller N rate, gave a reasonably high yield compared to E rate (12.2 and 12.5 Mg ha^‐1, respectively). The data show that a relatively much lower N rate than maximum did not proportionally diminish the yield. Thus, for a difference of 40.4% between maximum N rate and P rate a difference of only 7.4% in yield was observed. Using the L model the differences in rate and yield were of 34.4% and 4.7%, respectively. The QP model gave no significant difference compared to E model.

At harvest the residual soil NO₃‐N increased significantly with increasing N fertilizer rate in whole of the 100 cm soil profile, but mainly in the top 40 cm soil layer. The total NO₃‐N found in 0–100 cm profile at rate of 0, 120 and 200 kg applied N ha^‐1 at planting was as high as 33.7, 60.5, and 74.5 kg N ha^‐1 respectively in a light soil and 37.5, 97.5, and 145.5 kg N ha^‐1 in a heavy clay soil. The difference in NO₃‐N content in the 60–100 cm layer between different applied N rate suggests that at harvest, part of fertilizer N applied at planting was already leached below the 100 cm soil layer. Results, thus, show that reasonably high corn yields can be obtained using more adequate N fertilizer rates which avoid the overfertilization and are likely to reduce the air and ground water pollution.     

Simplified procedure for rapid,manual analysis of nitrate in soil extracts by copper‐cadmium reduction

Abstract

An inexpensive modification of the commonly used manual nitrate (NO₃)‐nitrogen (N) analysis for soil extracts is described. This procedure uses multiple reductors of copperized cadmium (Cd) wire threaded through Teflon tubing and a peristaltic pump to rapidly pass a low volume of soil extract through the reductors at a constant flow rate. In excess of 150 prepared samples can be processed daily with minimum waste generation. Efficiency of reduction is >98% and precision of analysis (coefficient of variation) for replicate standards of known NO₃‐N concentration is excellent, at <0.5% over the concentration range 0.025 to 0.2 μg NO₃‐N mL^‐1. Column life and storage characteristics are high, at >250 samples per column and one month, respectively. Column activation and regeneration in these wire type reductors are simpler and less tedious than for reductors constructed of copperized Cd granules.     

Paper test‐strips for rapid determination of nitrate tracer

Abstract

The leaching of nitrate from soil to ground and surface waters is now limited by European legislation to protect human drinking water. Much long term monitoring and short term experimentation has been undertaken using fertilisers and nitrate tracers to understand how transport occurs. A paper test‐strip technology, used in conjunction with a modern hand‐held reflectometer was tested and utilised to permit fine spatial and temporal resolution analysis of nitrate breakthrough in a large undisturbed soil block. It was found that characteristic types of breakthrough occurred in the soil block, and that a fine resolution picture of the breakthrough curve could easily be established without recourse to sample storage and laboratory analysis. The techniques proved cost effective and had the added benefit of stopping locally generated toxic waste. It is concluded that paper test‐strip technology is highly suited to monitoring research where strong concentration tracers are used.     

Use of reflectometry for determination of nitrate‐nitrogen in well water

Recurrent monitoring of water wells is necessary to ensure that nitrate‐nitrogen (NO3‐N) concentrations in groundwater do not exceed 10 mg/L, the maximum contaminant level set by the U.S. Environmental Protection Agency. Continuous chemical analysis is often a time consuming and expensive process. A recently developed ‘Reflectoquant Analysis System’, which employs reflectometry techniques, may offer a simple and accurate method for NO3‐N analysis. The objective of this study was to evaluate the ‘Reflectoquant Analysis System’ as an alternative method for determination of NO3‐N in well water. Water samples were collected from 42 wells in Oklahoma. The samples were analyzed using the ‘Reflectoquant Analysis System’, automated cadmium reduction (Griess‐Ilosvay), ion chromatography, and phenoldisulfonic acid procedures. The linear range of the ‘Reflectoquant Analysis System’ is 1.1 to 50.6 mg/L NO3‐N. Samples exceeding this range must be diluted before analysis is performed. Excluding two wells where NO3‐N was >50.6 mg/L, simple correlation was high (r > 0.91) among the four procedures evaluated. In addition, slopes and intercepts from linear regression of NO3‐N among procedures were not significantly different. Population means obtained using the four methods were very similar. For this sample of wells, the ‘Reflectoquant Analysis System’ was precise and provided NO3‐N analysis of water samples equivalent to standard methods. Other advantages of the ‘Reflectoquant Analysis System’ are short analytical times, reduced operator training period, and competitive costs compared to standard methods.     

Movement of nitrogen‐15 labeled nitrate in large undisturbed columns of poorly drained soil

Abstract

A laboratory study was conducted with large (20‐cm i.d., 110‐cm long PVC pipe) intact soil columns to determine the movement of fertilizer NO₃ ^‐ in poorly drained, conventionally tilled soil under simulated low (7.6 cm) and heavy (15.2 cm) rainfall. Soil in the columns was brought to near‐maximum water‐holding capacity (9 kPa) to simulate the typical field soil moisture regime during the spring. A constant‐level water table was imposed at the base of the column to further simulate field conditions of the Drummer silty clay loam (mixed, mesic, Typic Haplaquoll) soil used. Fertilizer was applied in solution at a rate equivalent to 168 kg N ha^‐1 as ¹⁵N‐labeled KNO₃. Water was then applied in three applications, spaced one wk apart. To minimize the movement of water along the soil‐pipe interface, a 3 mm‐wide band of air‐dried disturbed soil was packed around the core to ensure a seal along the interface. Recovery of fertilizer NO₃ ^‐‐N below the water table at the end of the 28‐d study was < 0.06% (0.1 kg N ha^‐1) and 0.5% (0.9 kg N ha^‐1) of that applied for the low and high treatments, respectively. Denitrification losses were negligible for both water treatments (≤ 1 kg N ha^‐1). Fertilizer N distribution in the columns indicated significant movement of N beyond estimated water‐displacement depths, apparently caused by preferential flow. However, the majority of the N was restricted to the upper portions of the columns. The results indicate that preferential flow of water in poorly drained, conventionally tilled soils during high rainfall periods can lead to the movement of fertilizer N to shallow ground water, but that the amounts are apparently very small.     

Sap test to determine nitrate‐nitrogen concentrations in aboveground biomass of winter cover crops

Abstract

In the San Luis Valley of south central Colorado, winter cover crops (WCC) are used to reduce soil erosion and scavenge residual soil‐N. Some San Luis Valley farmers are beginning to use WCC as a source of over‐winter or early‐spring grazing. Common WCC used by farmers, wheat (Triticum aestivum L.) and rye (Secale cereale L.) are reported to accumulate high levels of nitrate nitrogen (NO₃ ^‐‐N) in aboveground biomass that can be toxic to animals. Evaluation and calibration of a quick Cardy Meter² Sap Test (CMST) for determination of NO₃ ^‐‐N status in the field will facilitate the management of these WCC. Field and growth chamber studies were conducted to correlate the CMST with laboratory procedures and with plant and soil parameters. In field and growth chamber studies, the CMST was correlated with standard dry tissue NC₃ ^‐‐N laboratory analysis (P<.001) and with soil inorganic N content (P<.05). These field and growth chamber studies show that the CMST can be a tool in helping farmers identify fields where WCC aboveground biomass is accumulating potentially toxic levels of NO₃ ^‐‐N. Additionally, plant parameters such as nitrogen uptake, biomass, and grain yield of WCC grown under growth chamber conditions were correlated with the CMST readings conducted at the growth stage, Feekes five (P<.05). The growth chamber results suggest that if WCC are grown for grain production, the CMST can help identify the needs for additional nitrogen (N) fertilizer application at Feekes five.     

A new soil test method for the determination of plant‐available cadmium in soils

Abstract

A new soil test procedure using 1M NH₄Cl was developed for the extraction of plant‐available cadmium (Cd) from soils. Five grams of soil is weighed into a 50‐mL polyethylene vial to which 30 mL of 1M NH₄Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25°C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 μm nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH₄Cl‐extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10^‐7). In comparison with several commonly used extradants, such as ABDTPA, CaCl₂, NH₄OAc, and NH₄NO₃, the 1M NH₄Cl‐extracted Cd from soils was found to be a better index of Cd availability.     

A computer‐assisted method for CEC estimation and quality control in a routine soil‐test operation

Abstract

Cation‐exchange capacity (CEC) of 30 Alabama soils was estimated by two different methods based or routine soil‐test results consisting of soil‐water pH, Adams‐Evans buffer pH, and Mehlich‐1 extractable cations (K, Mg, and Ca), which were obtained automatically by a computerized data acquisition system. In one method, CEC was calculated by solving a quadratic equation involving soil‐water and buffer pH's; in the other, CEC was estimated as the summation of extractable cations and exchangeable acidity. The two estimated CEC's agreed well with each other and also had the same magnitude as CEC determined by the normal NaOAc, pH 8.2 method. By averaging the two calculated values, an even closer estimation of the measured CEC was found. These calculations and comparisons can be accomplished quickly and efficiently by a minicomputer via a simple FORTRAN program.

In addition, a discrepancy between the two estimated CEC's would indicate possible errors in analytical determinations and/or the inadequacy of the soil testing procedures. Therefore, an additional means for quality control in a routine soil‐test operation can be obtained by comparing the two CEC values.     

Extraction of soil nitrogen by chloroform fumigation – A new index for the evaluation of soil nitrogen supply

The N extracted after chloroform (CHCl₃) fumigation was determined as a possible index of soil N supply to plants. The relationships between extractable N following fumigation and reference indices such as total N, alkali-hydrolyzable N, N released by the Stanford short-term incubation method, and the N extracted by KCl and by CaCl₂, were measured in nine soils of differing soil N supply capacity. A highly significant correlation was achieved between the extractable N released by fumigation and the N released by the Stanford method, i.e. a short-term aerobic incubation (r = 0.87). Similarly, the correlation between extractable N by fumigation and the N uptake by ryegrass was highly statistically significant (r = 0.93). Using the N extracted following fumigation has the advantage that laboratory results are available in two days and are both reproducible and of high precision. Therefore, the N extracted following fumigation is a valid, timesaving and precise index of soil N supply capacity.     

Use of the nitrate‐specific ion electrode for the determination of nitrate nitrogen in surface and ground water

Abstract

The usefulness of the nitrate‐specific ion electrode (NE) for the determination of nitrate nitrogen (NO3‐N) in surface and ground water was determined. The NE method had several advantages that made it superior to the phenoldisulfonic acid (PDS) method in our environmental quality studies. Samples could be analyzed quickly and with a minimum of sample preparation. Sample coloration and soluble salts did not interfere with the performance of the electrode. Range of detection without dilution was much wider than by the PDS method. Also, the values obtained by the NE method, although slightly greater than those obtained by the PDS method, were satisfactory.     

Evaluation of methods for nitrogen‐15 analysis of inorganic nitrogen in soil extracts: I. Steam‐distillation methods

Abstract

A study was conducted to evaluate conventional steam‐distillation techniques for N‐isotope analysis of inorganic forms of N in soil extracts. Extracts obtained with 2 M KCl from 10 diverse soils were treated with: (i) (¹⁵NH₄)₂SO₄ and KNO₃, (ii) (NH₄)₂SO₄ and K¹⁵NO₃, or (iii) KNO₃and Na¹⁵NO₂. Steam distillations were performed sequentially to determine NH₄ ⁺‐N and NO₃ ^‐‐N, and were also carried out to determine (NO₃ ^‐ + NO₂ ^‐)‐N or (NH₄ ⁺ + NO₃ ^‐ + NO₂ ^‐)‐N; a pretreatment with sulfamic acid was used to determine NO₃ ^‐‐N in the presence of NO₂ ^‐‐N. Recovery of added N ranged from 95 to 102%. Significant isotopic contamination was observed in sequential distillation of unlabeled NO₃ ^‐‐N following labeled NH₄ ⁺‐N; otherwise, analyses for ¹⁵N were usually within 1% of the values calculated by isotope‐dilution equations.     

Simultaneous determination of soil aluminum,ammonium‐ and nitrate‐nitrogen using 1 M potassium chloride extraction

Abstract

Determination of soil aluminum (Al), ammonium‐nitrogen (NH₄‐N), and nitrate‐nitrogen (NO₃‐N) is often needed from the same soil samples for lime and fertilizer recommendations, but Al has to be extracted and quantified separately from NH₄‐N and NO₃‐N according to present methods. The objective of this study was to develop a reliable method for simultaneous analyses of soil Al, NH₄‐N and NO₃‐N using a Flow Injection Autoanalyzer. Thirty‐five soil samples from different locations with wide ranges of extractable Al, NH₄‐N and NO₃‐N were selected for this study. Aluminum, NH₄‐N and NO₃‐N were extracted by both 1 M and 2 M potassium chloride (KCl), and quantified using a LACHAT Flow Injection Autoanalyzer simultaneously and separately. One molar KCl was found to be a suitable extractant for all three compounds when compared to 2 M KCl. The 1 M KCl extract proposed could aid in decreasing the costs associated with simultaneous NH₄‐N, NO₃‐N, and Al analyses. Results of those three compounds analyzed simultaneously were not statistically different from those analyzed separately in 1 M KCl solution. This new procedure of simultaneous determination of NH₄‐N, NO₃‐N, and Al increases efficiency and reduces cost for soil test laboratories and laboratory users.     

Recovery of nitrate‐N in dry soil and plant samples by the standard,unmodified Kjeldahl procedure

Abstract

In the literature, various modifications of the standard Kjeldahl procedure for the determination of total nitrogen are used to include nitrate‐N in soil and plant samples. This study suggests that these modifications, which are usually time consuming and tedious, are not necessary in the case of dry soil samples. However, if total‐N (including nitrate‐N) is to be measured in dry plant samples then the use of one of the modifications is essential.     

Mehlich‐I soil‐test calibration for watermelon: Cu,Zn, and Mn

Abstract

Predictive soil tests were used to detect possible need for Cu, Zn, and Mn fertilizers for the optimum production of watermelons (Citrullus lanatus (Thumb.) Masf.) in north and central Florida. Predictive Mehlich‐I soil testing indicated a possible response to additions of Mn and Cu but not to additions of Zn at three locations: Gainesville, Dunnellon, and Live Oak. Results showed no total marketable yield response to selected Cu, Zn, and Mn treatments at any of the three sites. Yields for the Gainesville, Dunnellon, and Live Oak sites were 41.5, 29.0, and 38.0 Mg/ha, respectively, well above the state average watermelon yield of 19.0 Mg/ha. Tissue analyses at the Gainesville and Live Oak sites showed Cu, Zn, and Mn levels within or above suggested sufficiency ranges. This study indicates that current University of Florida interpretations for the Mehlich‐I extractant can identify sites with adequate extractable Cu, Zn, and Mn levels, thus avoiding unnecessary fertilization. At no time were University of Florida Cu, Zn, or Mn interpretations and recommendations found to be limiting for watermelon production.     

Determination of dissolved organic nitrogen using persulfate oxidation and conductimetric quantification of nitrate‐nitrogen

Abstract

Nitrogen (N) in forest soil extracts and surface waters may be dominantly in organic compounds as dissolved organic nitrogen (DON). Due to various difficulties associated with measuring total N (as TKN) by the Rjeldahl digest, this important vehicle for nutrient movement is rarely monitored. By coupling two relatively new methods and optimizing them for use in soil studies, we developed an alternative method for measuring DON. Analysis of pure compounds and field samples shows that persulfate oxidation combined with conductimetric quantification of nitrate (NO₃) provides a highly accurate measure of dissolved N content. With relatively inexpensive equipment and reagents, a single technician can digest and assay over a hundred samples a day. This rapid, simple, and accurate assay may make it possible to routinely monitor DON where it had previously been impractical. This in turn could substantially enhance understanding about the form and quantity of N involved in nutrient fluxes.