Stalk Nitrate Test Research Articles

Late-season corn stalk nitrate measurements across the US Midwest from 2006 to 2018

The late-season Corn Stalk Nitrate Test (CSNT) is a well-known tool to help evaluate the after-the-fact performance of nitrogen management. The CSNT has the unique ability to distinguish between optimal and excessive corn nitrogen status, which makes it helpful for identifying the over-application of N so that farmers can adjust their future nitrogen decisions. This paper presents a multi-year and multi-location dataset of late-season corn stalk nitrate test measurements across the US Midwest from 2006 to 2018. The dataset consists of 32,025 corn stalk nitrate measurements from 10,675 corn fields. The nitrogen form, total N rate applied, US state, year of harvest, and climatic conditions are included for each corn field. When available, previous crop, manure source, tillage, and timing of N application are also informed. We provide a detailed description of the dataset to make it usable by the scientific community. Data are published through an R package and also available at the USDA National Agricultural Library Ag Data Commons repository and through an interactive website.

Conservation tillage is compatible with manure injection in corn silage systems

AbstractAdoption of conservation tillage practices has increased over the past 30 yr in the United States. Research is needed to evaluate if reduced tillage practices are compatible with manure injection on dairy farms. Two corn (Zea mays L.) silage studies were conducted in New York to evaluate the impact of zone tillage depth and tillage intensity on early plant growth and soil nitrate‐N, corn silage productivity and quality, and nutrient uptake at harvest. Treatments included three zone tillage depths (0, 18, and 36 cm; with aerator seedbed preparation) for Study 1 (2012–2013) and three tillage intensities (no tillage, reduced tillage [aerator seedbed preparation without zone tillage], and intensified reduced tillage [aerator seedbed preparation plus zone tillage at 18‐cm depth]) for Study 2 (2014–2016). Manure was injected in the spring, and all fields had a manure and zone tillage history. Zone tillage depth did not affect early plant growth, soil nitrate‐N content at V5‐V6, corn silage yield, quality, corn stalk nitrate test (CSNT)‐N, or nutrient removal with harvest. The CSNT‐N levels exceeded 2,000 mg NO3–N kg–1, confirming sufficient N for each treatment. Study 2 showed no impact of tillage intensity on corn growth, yield, or nutritive value, and CSNT‐N levels always exceeded 2,000 mg NO3–N kg–1. These findings show that, on fields with a history of manure addition and reduced tillage, manure injection followed by planting without further seedbed preparation or zone tillage can maintain yields and quality and can conserve N while reducing soil disturbance and tillage‐associated fuel, equipment, and labor costs.

In‐Field Spatial Variability of Corn Stalk Nitrate Test Results

The corn (Zea mays L.) stalk nitrate test (CSNT) is a postharvest plant test that provides feedback on N supply vs. crop needs of a growing season. As such, test results can provide information on the need for adjustments in N management in future years. However, CSNT‐N can be variable within fields. The aim of this study was to (i) describe and relate within‐field CSNT‐N and corn silage yield spatial variability and (ii) to evaluate a yield‐based, targeted, CSNT sampling alternative. In 2013, five corn fields were grid sampled to determine the impact of sampling density on accuracy of CSNT‐N classification for the whole field. Close‐proximity variability (within a 3‐m row) was determined as well. In 2014, the study was expanded to include three additional fields with 2013 and 2014 yield data. Results showed similar means and standard deviation (SD) for close‐proximity sampling and whole‐field sampling. Thus, time and resources invested in CSNT sampling can be reduced with close‐proximity sampling. Current sampling guidelines (composite sample per field using a sampling intensity of 2.5 stalks ha−1) resulted in probabilities of estimating a field's mean CSNT‐N of 25, 32, and 72% for coefficients of variation (CV) of ±6.4, ±11, and ±22%, respectively. High‐yielding areas had more homogenous CSNT‐N values than low‐yielding areas. The analysis of corn stalks per yield zone resulted in reduced CSNT‐N spatial variability. Even intense sampling strategies for whole fields can result in interpretation errors while yield‐based CSNT sampling results in more meaningful information for N management.Core Ideas Corn stalk nitrate test results help corn growers fine‐tune N management. Within‐field corn stalk nitrate test‐N variability can lead to incorrect interpretations. Adoption of corn stalk nitrate test use can be enhanced with yield‐based field sampling. The ratio of yield and corn stalk nitrate test‐N may be helpful to identify areas with sufficient N.

Evaluating Tissue Tests to Improve Nitrogen Management in Furrow‐Irrigated Mid‐South Corn Production

An ear‐leaf N of 30 g kg−1 differentiated between N‐adequate and N‐deficient corn plants at the R1 growth stage. The optimal corn stalk nitrate concentration ranged from 170 to 1000 mg nitrate N kg−1 at maturity. Nitrogen availability was excessive when stalk nitrate concentration values were >1000 mg nitrate N kg−1. The N rate needed for 95% relative grain yield was consistently near the N rate where nitrate accumulated in the stalk. The corn stalk nitrate test (CSNT) and ear‐leaf N concentration (ELNC) are used to determine the adequacy of corn (Zea mays L.) N management programs and is used most extensively in the Midwest and northeastern United States. Information on the utility of both the CSNT and ELNC for irrigated corn produced in the mid‐South is lacking. Twenty‐four N rate trials were conducted in Arkansas between 2013 and 2016 to evaluate the utility of the ELNC and CSNT in a furrow‐irrigated corn production system. An ELNC of 30 g kg−1 has been determined to differentiate between N‐adequate and N‐deficient corn plants at the R1 growth stage. The optimal CSNT concentration ranged from 170 to 1000 mg nitrate N kg−1 at maturity, indicating that adequate N was available to the corn crop to produce near‐maximum grain yield. The N rate needed to achieve 95% relative grain yield (RGY) was consistently identified near the N rate where nitrate N began to accumulate in the corn stalk. A CSNT values of <170 mg nitrate N kg−1 was found to represent the low category, suggesting that N was limiting corn grain yield, whereas N availability was found to exceed the amount needed to maximize grain yield when CSNT values were >1000 mg nitrate N kg−1. The ELNC and CSNT can be used to adequately determine the N status of corn produced within a furrow‐irrigated mid‐South corn production system.

Long-term effects of pig slurry combined with mineral nitrogen on maize in a Mediterranean irrigated environment

Intensive pig farming generates large amounts of manure which is applied to agricultural fields as slurry. It is therefore important to know the nitrogen (N) fertilizer values and long-term environmental effects of different pig slurry application rates. We investigated the performance of sprinkler-irrigated maize crops in a Mediterranean environment with different fertilizer treatments as part of a 12-year experiment (2002–2007, 2010–2015). We compared pig slurry applied using the surface splash plate method at rates of 0, 30 and 50m3ha−1 yr−1 combined with mineral N fertilizer application rates of 0, 100 and 200kgNha−1 yr−1 as a side-dressing. The fertilizer treatments affected maize grain and biomass yields, N uptake, chlorophyll levels, soil N levels, N use efficiency (NUE) and basal stalk nitrate levels. Satisfactory average grain yields (∼13.5Mgha−1) were achieved at application rates of ∼200–300kgNha−1 with average residual soil N levels below 180kgNha−1 (0–90cm depth) and a NUE greater than 50%. However, the maximum average grain yields (∼14.5Mgha−1) required treatments providing more than 400kgNha−1yr−1 but resulted in residual soil N levels greater than 300kgNha−1 and the NUE fell below 50%. The 12-year average relative N fertilizer value of pig slurry applied at 30 and 50m3ha−1yr−1 was 51% of the mineral N value applied at side-dress, suggesting that more efficient application methods for pig slurry are required. The end of season basal stalk nitrate test was useful for the quantification of excess nitrogen, and 2.5g NO3− kg−1 was considered the maximum optimal concentration for our cropping conditions and grain yields.

Improving Sample Collection, Sample Processing, and Laboratory Analyses for Corn Stalk Nitrate Test

Core Ideas Corn stalk nitrate test results can help corn growers fine‐tune N management. Adoption of corn stalk nitrate test use can be enhanced with more practical field sampling protocols. Laboratory processing of corn stalk nitrate test samples can be simplified for reduced analytical cost. The corn (Zea mays L.) stalk nitrate test (CSNT) is a site‐specific, after‐the‐fact, diagnostic tool for N management of corn. Although considered effective, widespread adoption of CSNT is limited due to somewhat impractical sample collection, handling, and laboratory sample processing protocols. Five studies were conducted to evaluate the impact of alternative sampling, sample handling, and laboratory processing protocols on CSNT outcomes. Study 1 evaluated the effect of stalk length and position on CSNT values. In Study 2 timing of sampling or growth stage was evaluated. In Study 3 several sampling patterns within a field (samples taken within a corn row vs. perpendicular or under an angle to rows) were analyzed. Study 4 tested if (a) quartering of stalks, (b) delay in mailing of stalks to the laboratory, and (c) temperature during storage (refrigerator, freezer, room temperature) affected CSNT‐N. Laboratory grinding, extraction, and determination procedures were compared in Study 5. The results suggest that sampling protocols can be adjusted to include shorter stalk samples, taken within 5 d after silage harvest. Direction of sampling within a field did not impact CSNT‐N, eliminating the need for more labor‐intensive sampling. Also, quartering of stalks and different temperature during storage did not change CSNT‐N. Laboratories can use 2‐mm grinding, extraction with distilled water, and a nitrate specific ion electrode or flow injection analysis. We conclude that adjustments in sampling protocols and sample processing can be made, possibly increasing farmer acceptance of the test, and reducing the cost of sampling, sample processing, and laboratory analyses.

Application of the end-of-season stalk nitrate test for a high-yield maize production system in Northwestern China

ABSTRACTExcessive nitrogen application has caused serious environmental pollution under high-yield maize system in China. Our objective was to evaluate critical stalk nitrate (NO3−) levels that support high yield (>13 Mgha−1), but are not in excess. Optimal stalk NO3− concentration was determined by conducting seven nitrogen levels experiments in two high yield maize regions: Dongyang County (DY) and Wenshui County (WS). Optimal stalk NO3− concentration category range to obtain maximum yield in DY (sandy loam, higher accumulated temperature and solar radiation compared with WS) was 0.44–1.19, which similar to the criteria of US (0.70–2.0 g kg−1). While for WS (loam soil, lower accumulated temperature and solar radiation compared with DY), optimal stalk NO3− concentration category range to obtain maximum yield was 1.95–4.15, greatly higher than the US criteria. These results suggested thatit is necessary to establish matching optimal stalk NO3− category ranges for different ecological regions in China.

Using the Corn Stalk Nitrate Test under New York growing conditions

Since it was first developed, the Corn Stalk Nitrate Test (CSNT) has gained use in several parts of the U.S., and over the past three years, researchers at Cornell University have tested its performance under New York growing conditions. In this article, their research findings are summarized and interpretations provided for New York soils and growing conditions. Earn 0.5 CEUs in Nutrient Management by reading this article and taking the quiz at www.certifiedcropadviser.org/certifications/self‐study/794.

Testing the suitability of the end-of-season stalk nitrate test for summer corn (Zea mays L.) production in China

The end-of-season corn stalk nitrate test (CSNT) is a desirable indicator of N status and functions as a guide for agricultural practice and regulation of corn production. Our objectives were to evaluate the CSNT concentration of three summer corn varieties: XY335, introduced from the US; YD13, a senescent hybrid; and ZD958, a “stay-green” hybrid, under different N application rates and to validate the feasibility of using the CSNT criteria developed in the US for summer corn production in China. The response of grain yield and N uptake to N availability fit a linear-plateau model, whereas the CSNT concentration of summer corn increased linearly with increasing N availability, indicating excess N accumulated in the stalk as nitrate when luxury N consumption occurred. The CSNT concentrations among the different varieties increased in the order XY335<YD13<ZD958. The United States CSNT category range (0.70–2.0gkg−1) was suitable only for XY335, which was introduced to China from the US. For ZD958 and YD13, the optimal CSNT categories to achieve maximum grain yield were 0.9–5.36gkg−1 and 0.56–4.56gkg−1, respectively. The study results suggest that it is not necessary to adjust the US CSNT criteria for different geographical regions, but new categories may be needed for varieties that are not used in the US.

Nitrogen Requirements of First‐Year Corn following Alfalfa Were Not Altered by Fall‐Applied Manure

Although farmers in the midwestern United States often apply livestock manure when terminating alfalfa (Medicago sativa L.), there are no published reports on direct effects of fall manure application on alfalfa N credits to first‐year corn (Zea mays L.). Therefore, eight on‐farm experiments were conducted in Minnesota to test whether manure applied during alfalfa termination in fall affects the rate of fertilizer N needed for the subsequent corn crop. Manure application rates were determined by cooperating growers and N fertilizer rates were 0, 45, 90 or 179 kg N ha–1 at planting and 45 kg N ha–1 as a sidedress. At five locations, neither manure nor fertilizer N increased grain or silage yield. At three remaining locations, N fertilizer was needed to economically optimize grain (98 kg N ha–1 at two locations) or silage yield (113 kg N ha–1 at three locations), but manure did not alter the response to fertilizer N. The presidedress soil nitrate test (PSNT) predicted the need for N fertilizer to optimize grain yield 63% of the time and the basal stalk nitrate test (BSNT) identified the need for N fertilizer 75% of the time. When results of this study were combined with data from the literature, the PSNT was accurate only 55% of the time and the BSNT could not separate responsive and nonresponsive sites. These results confirm that first‐year corn following alfalfa often does not require supplemental N for maximum grain yield, and that more accurate methods are needed to predict fertilizer N response.

Probability of profitable yield response to nitrification inhibitor used with liquid swine manure on corn

Nitrification inhibitors (NI) can be used with liquid swine manure (LSM) to decrease potential NO3 losses, but knowledge specifying when and where NI can increase corn (Zea mays L.) yields is limited. Eleven on-farm evaluation trials (OET) were conducted in 2009 and 15 in 2010 to identify site-specific factors for using Instinct (an encapsulated form of nitrapyrin) with LSM in Iowa. Farmers injected LSM in the fall in at least three field-long strips with and without NI. Yield responses (YR) to NI were calculated by dividing yield monitor data into 50-m cells within each field. Hierarchical models were used to estimate predictive probabilities of profitable YR for two categories of monthly average rainfall and soil drainage. On average, NI produced no YR in relatively normal 2009 and a 0.15 Mg ha−1 YR in extremely wet 2010. The NI did not change late-season corn N status but half of corn stalk nitrate test (CSNT) samples were N deficient in 2009 and about 65 % in 2010. Fields receiving >90 cm March through August rainfall in 2010 were predicted 65 % more likely to have economic YR (>0.13 Mg ha−1) than fields receiving <90 cm rainfall. Within-field variability in YR was about four times greater than among-field variability, but within field-level factors had no significant effects on YR. The NI effects may not have lasted long enough to increase yields across all OET and predictive probabilities suggest that NI may produce profitable YR only when spring and summer rainfall exceed the long-term averages by more than 40 %.

First‐Year Corn after Alfalfa Showed No Response to Fertilizer Nitrogen under No‐Tillage

Although fertilizer N response of first‐year corn (Zea mays L.) following alfalfa (Medicago sativa L.) has been reported for more than 350 site‐years of research, N responses under no‐tillage have been reported for only 17 site‐years. To determine the rate of N fertilizer required for first‐year corn after alfalfa in no‐tillage systems, on‐farm experiments were conducted at seven locations in southern Minnesota and southwestern Wisconsin. The accuracy of the presidedress soil nitrate test (PSNT) and basal stalk nitrate test (BSNT) to identify the need for supplemental N in first‐year, no‐tillage corn also was evaluated. Across seven site‐years, no yield response to fertilizer N was observed for corn grain, cob, stover, or silage yield, confirming that alfalfa N credits can supply the entire N requirement of no‐tillage corn following alfalfa. Critical levels of PSNT used in other U.S. Corn Belt states, incorrectly predicted responses to supplemental N at all six locations where PSNT was measured (soil NO3–N concentrations were ≤18 mg kg−1), suggesting that critical levels may need to be reduced in no‐tillage corn following alfalfa. In this first report under no‐tillage conditions, the BSNT concentrations in nonfertilized corn after alfalfa were in the marginal range at two locations (between 250 and 700 mg NO3–N kg−1) and optimum or above at the other five locations, indicating that the BSNT incorrectly characterized N supply in two of seven cases.

On‐Farm Evaluations to Calibrate Tools for Estimating Late‐Season Nitrogen Status of Corn

Properly calibrated diagnostic tools are needed to evaluate the performance of different N management practices for corn (Zea mays L.). Until now, mostly controlled studies were used for such calibrations. We utilizedon‐farm evaluation studies to verify current and identify new N status categories using the corn stalk nitrate test (CSNT) andlate‐season digital aerial imagery of the corn canopy. From 2007 through 2010, producers conducted 125 trials across Iowa. Each trial had treatments of a producer's normal N rate alternated with a rate that was about one‐third lower or higher. Categorical yield response (YR), expressed as profitable and unprofitable, was related to green reflectance (GR), relative green reflectance (RGR), or CSNT sampled within nine areas in each trial. Multilevel binary logistic regressions were used to estimate the probability of receiving profitable YR for a range of CSNT, RGR, and GR values. Among the three diagnostics, RGR performed slightly better but required applying at least two N rates within producers' fields. For CSNT, the identified optimal category was almost the same as that currently recommended in Iowa (700–2000 mg NO3–N kg−1), even when corn and N prices deviated from their long‐term averages by 30%. Due to the uncertainty in N availability, however, the critical CSNT value for fall manure treatments was about 3000 mg NO3–N kg−1 higher than that for fall anhydrous NH3, spring urea–NH4NO3, or sidedress N. On‐farm studies can be used to calibratelate‐season N diagnostic tools for evaluating management practices that differ in rates, forms, and timing of N applications.

Late‐Season Corn Measurements to Assess Soil Residual Nitrate and Nitrogen Management

Evaluation of corn (Zea mays L.) N management and soil residual NO3–N late in the growing season could provide important management information for subsequent small grain crops and about potential NO3–N loss. Our objective was to evaluate the ability of several late‐season corn measurements, which have been advocated to assess N management, to identify sites with elevated soil residual NO3–N. These crop‐based measurements were collected at three reproductive phases and included normalized difference vegetative index (NDVI) at 10 site‐years and green‐leaf number and chlorophyll (SPAD) meter readings at six of these sites. The corn stalk nitrate test (CSNT) and postharvest soil residual NO3–N were measured at all sites. Four levels of N were applied, ranging from N deficient (0 or 67 kg N ha−1) to excessive (269 kg N ha−1). The CSNT was positively (p &lt; 0.001) correlated with residual NO3–N, although residual NO3–N was not always low at CSNT values &lt;2.0 g NO3–N kg−1, where drought reduced production. Drought stress was a major factor influencing excess N supply and residual soil NO3–N. Canopy measurement values at growth stages R3–R4, including NDVI, which can be measured remotely, were effective indicators of drought stress. Across sites, relative canopy readings best predicted relative grain yield when collected at R3–R4, underscoring the importance of reference strips. Use of remotely measured NDVI would allow policymakers to identify drought sites in the late summer and target them for cover crop planting, thus reducing potential winter NO3–N losses in humid regions.

Late-season digital aerial imagery and stalk nitrate testing to estimate the percentage of areas with different nitrogen status within fields

Precision agriculture technologies offer potential economic and environmental benefits from site-specific management of nitrogen (N) fertilizer and animal manure sources for corn (Zea mays L.). However, lack of knowledge and reliable methodology for developing and evaluating site-specific N fertilizer recommendations are the major obstacles for realizing these potential benefits. The objective of this study was to evaluate corn N status at the field scale and across many fields using late-season digital aerial imagery and the end-of-season corn stalk nitrate test in large-scale on-farm evaluation studies. About 30 groups of farmers, lead by agronomists and crop consultants, were formed across Iowa to evaluate different N management practices. Late-season color digital aerial imagery and digital soil maps were used to guide the collection of the corn stalk nitrate test samples within 683 cornfields in 2006, 824 fields in 2007, and 828 fields in 2008. Four areas—one from each of the three predominant soil types and one within a target-deficient area—were sampled in each field. Multilevel binary logistic regressions were used to quantify the relationship between green reflectance of the corn canopy and corn N status, expressed as deficient and sufficient (a com- bination of marginal, optimal, and excessive categories of the corn stalk nitrate test), within and across the fields. Percentages of areas within fields with deficient and sufficient N status were estimated using distributions of pixel counts of green reflectance of the corn canopy. Multiple regression analysis was used to identify factors affecting percentage-deficient area within the fields. Results showed that N management category (a combination of N form and timing of application) and early season rainfall (May, June, or cumulative from March through June) had the largest effects on percentage-deficient area. Fields with liquid swine manure applied in the fall or urea-ammonium nitrate solution applied in the spring (before planting) or urea-ammonium nitrate solution applied at sidedress had larger areas of N defi- ciency than fields with anhydrous ammonia applied in the spring. Larger early season rainfalls also increased percentage-deficient area during each year. The results of large-scale evaluations can be used to develop more accurate site-specific N recommendations based on knowledge of differences between management practices and effects of soil properties and rainfall on N status within fields. Future evaluations can identify areas that persistently have excessive N status and quantify potential N fertilizer reductions within those areas or fields.

Normalization of uncalibrated late-season digital aerial imagery for evaluating corn nitrogen status

Using uncalibrated digital aerial imagery (DAI) for diagnosing in-season nitrogen (N) status of corn (Zea mays L.) is challenging because of the dynamic nature of corn growth and the difficulty of obtaining timely imagery. Late-season DAI is more accurate for identifying areas deficient in N than early-season imagery. Even so, the quantitative use of the imagery across many fields is still limited because DAI is often not radiometrically calibrated. This study tested whether spectral characteristics of corn canopy derived from normalized uncalibrated late-season DAI could predict final corn N status. Color and near-infrared (NIR) imagery was collected in late August or early September across Iowa from 683 corn fields in 2006, 824 in 2007, and 828 fields in 2007. Four sampling areas (one within a target-deficient area) were selected within each field for conducting the end-of-season corn stalk nitrate test (CSNT). Each image was enhanced to increase the dynamic range within each field and to normalize reflectance values across all fields within a year. The reflectance values of individual bands and three vegetation indices were used to predict corn N status expressed as Deficient and Sufficient (a combination of marginal, optimal, and excessive CSNT categories) using a binary logistic regression (BLR). The green reflectance had the highest prediction rate, which was 70, 64, and 60% in 2006, 2007, and 2008, respectively. The results suggest that the normalized (enhanced) late-season uncalibrated DAI can be used to predict final corn N status in large-scale on-farm evaluation studies.

Corn Stalk Nitrate Concentration Profile

The end‐of‐season stalk nitrate test provides a method of assessing the N available to the corn (Zea mays L.) crop during the latter part of the season. This study was conducted to determine how stalk nitrate test results and interpretations are affected by sample composition. Stalks were collected from three field sites and separated into phytomers (node plus internode above), which were subdivided into three or five segments after length was measured. Nitrate‐N concentration of phytomers decreased linearly from the soil to the ear. Within a phytomer, segments also decreased acropetally (from base to apex). Node tissue NO3–N concentration did not differ from that of the internode segment immediately above the node. Weighted means were used to compute NO3–N concentration of stalk samples collected 5 cm higher (from 20 to 40 cm above the soil) or lower (from 10 to 30 cm above the soil) on the stalk than in the original method (from 15 to 35 cm above the soil). Although the three samples (10–30, 15–35, and 20–40 cm) differed in NO3–N concentration, the difference was only about 15% compared with the 25% difference in sampling position (±5 cm of 20‐cm sample length). The phytomer nearest the soil had 35 to 40% greater NO3–N concentrations than the section of stalk 15 to 35 cm above the soil. Critical values delineating yield‐limiting, adequate, and excessive N availability should be modified if stalk sections other than the standard 15 to 35 cm section are used. However, the qualitative nature of the stalk nitrate test and the range of NO3–N concentrations observed with reasonable corn cultural practices (1000×) make this test quite robust and precise definition of sample composition and critical values less necessary.

Does the crop or the soil indicate how to save nitrogen in maize production?: Reviewing the state of the art

High nitrogen (N) application rates are used by maize growers as an ‘insurance’, but may have an adverse effect on the environment. In this paper, the potential for nitrogen savings by the use of site-specific N fertilization rates is reviewed. Various tools for a more precise assessment of N requirements are available. Adjustments of N rates to the amounts of soil mineral N present shortly before planting can contribute to efficient N use, as can a deliberate delay of N dressings combined with indicator-based N supplementation after emergence. Conditions, under which these strategies are effective, are discussed. Post-emergence tests indicate whether a crop is likely to respond to sidedress N, but few tests quantify how much N should be sidedressed. Tissue tests are of less value for the support of decisions on N supplementation than indicators that are directly related to the soil or to the measurement of leaf and canopy greenness. Greenness and tissue tests are both unable to quantify excessive availability of N at early crop stages, as opposed to soil related indicators. Moreover, all crop tests generally need an on-site calibration with a reference plot. At later sampling dates, indicators can provide clues for the adjustment of N management in subsequent maize crops. The late stalk nitrate test and the post-harvest soil mineral N test appear to be the most valuable. Although indicators capable of identifying fields with an excessive N availability may save money, little attention has been paid to a cost-benefit analysis of indicator-based site-specific N management.

Evaluation of Soil and Plant Nitrogen Tests for Maize on Manured Soils of the Atlantic Coastal Plain

AbstractImproved N management programs for fertilizers and manures are needed in the Atlantic Coastal Plain because of concerns about agriculture's role in groundwater contamination with nitrate‐N. We conducted a 3‐yr study (1990–1992) at 56 locations in Delaware to evaluate the use of soil and plant N tests as components of a manure‐based N management program for maize. In Phase 1 (15 sites), a factorial design was used; main plots were either poultry manure (PM, at 4.5 Mg ha−1) applied at planting or starter fertilizer (SF, at 30 kg N ha−1) and split plots were six rates of sidedress N. Phase 2 was conducted on 41 farms and evaluated the response of maize to sidedress N (0 to 268 kg N ha−1). The pre‐sidedress soil nitrate test (PSNT) and two quicktests (the Nitrachek and Cardy meters) were used to identify N‐sufficient sites in both phases. In Phase 1, we also evaluated the effect of time and depth of PSNT sampling and two plant N tests: the leaf chlorophyll meter (LCM; 1992 only) and the late‐season stalk nitrate test. Maize response to sidedress N was rare at manured sites, and the ratio of total N added as manure and/or fertilizer to maize yield was consistently lower than the commonly used value of 17.8 kg N Mg−1 maize (1.0 pound N bushel−1 maize). Average ratios for manured and nonmanured sites in Phase 1 were 13.0 and 13.2 kg N Mg−1 maize. The PSNT effectively identified N‐sufficient or N‐deficient sites ≈70% of the time. Delaying sampling, deeper sampling, or using NH4‐N + NO3‐N instead of NO3‐N alone did not significantly improve predictive accuracy of the PSNT. The stalk nitrate test was found to be effective at identifying sites that were nonresponsive to sidedress N; our critical range was 0.7 to 2.0 g NO3‐N kg−1. The LCM results were encouraging and suggest that further research should be conducted on its use as an alternative to the PSNT. The Nitrachek meter was better correlated with laboratory measurements of soil NO3‐N (r2 = 0.87***) than the Cardy meter (r2 = 0.60***) and should be an effective means to identify N‐sufficient sites under field conditions.

Techniques for monitoring crop nitrogen status in corn

Abstract Nitrogen (N) fertilizers used in corn production contribute to the occurrence of nitrate to ground water. Tissue testing is a tool that can aid in fertilizer N management. Several tissue testing techniques were evaluated for their potential to aid in N management of irrigated corn in Nebraska. Leaf N content provided a traditional means of identifying N deficiencies in corn. Leaf N concentrations were difficult to interpret because of luxury consumption and the lack of consistent critical levels across hybrids and growth stages. Chlorophyll meters showed little sensitivity to luxury consumption and provided instantaneous results, but required an in‐field reference fertilized with extra N. Chlorophyll meter readings were highly correlated with grain yield and provided early detection of a N deficiency. The combination of chlorophyll meter data and irrigation demonstrated the merits of a “fertilization‐as‐needed”; approach to N management. The post‐harvest stalk nitrate test accurately identified s...