Nitrate Test Research Articles

Liquid Swine Manure Application to Soybean and Residual-Year Nitrogen Supply to Corn

Liquid swine (Sus scrofa domesticus) manure (LSM) is a valuable source of plant nutrients; however, information on application to soybean [Glycine max (L.) Merr.] and subsequent potential N response in residual-year corn (Zea mays L.) is lacking. Replicated on-farm trials were conducted at eight sites from 2000 to 2003 in Iowa with control, low, and high LSM application rates applied to soybean. In the following year corn, four fertilizer N (FN) rates were applied within each prior-year LSM rate. Soybean grain yield (GY) increased at 63% of sites with LSM application (mean 0.17 Mg ha−1), with no soybean GY reductions. Postsoybean harvest soil profile NO3–N increased at four sites, with mean increases across sites of 12 and 24 kg NO3–N ha−1 for the low and high LSM rates, respectively. Residual-year corn GY increased at 71% of sites from the prior-year low and high LSM rates (mean 0.6 and 1.1 Mg ha−1) that received no FN. The residual-year N supply to corn was estimated at 11% of the total LSM-N applied to soybean, the amount of postsoybean harvest profile NO3–N ha−1 increase from each LSM rate. Corn leaf relative chlorophyll meter (RCM) and end of season corn stalk NO3–N (CSNT) reflected the residual N supply, but the late spring nitrate test (LSNT) did not detect that residual N. Application of LSM to soybean can be a viable nutrient management practice; however, total-N application should be at a rate to minimize excessive residual NO3–N and carryover to future crops.

Prediction of Relative Corn Yield with Soil‐Nitrate Tests under Irrigated Mediterranean Conditions

Soil nitrate tests are a useful tool to manage corn (Zea mays L.) N fertilization under rainfed conditions, but the feasibility of using these tests under irrigated Mediterranean conditions has received little attention. The objective of this study was to determine whether the preplant nitrate test (PPNT), pre‐sidedress nitrate test (PSNT), and soil available‐N content test (PPNT or PSNT plus N fertilizer) could accurately predict relative corn yield (RY) under irrigated, high‐yielding conditions. Twenty‐one corn N‐response experiments were conducted in Northeast Spain between 1999 and 2009. The trials were flood‐ or sprinkler‐irrigated. In each trial, three to six N treatments (from 0–300 kg N ha–1) were surface‐applied to corn. Predictions of RY with the soil nitrate tests were low when the two irrigated systems were considered together (R2 < 0.43). However, the available‐N content provided moderately good predictions of RY for the sprinkler‐irrigated fields (R2 = 0.54–0.65) and poor predictions for the flood‐irrigated fields (R2 = 0.17–0.36). The critical soil available‐N content (0–30‐cm soil depth) for maximum RY was established at 193 to 209 kg NO3–N ha–1 (≈46–50 mg kg–1) for sprinkler‐irrigated corn preceded by a cereal crop. These critical available‐N values were lower when corn followed alfalfa and were greater than the critical PSNT levels reported for rainfed conditions in the Midwest and in Argentina (20–30 mg kg–1). The soil available‐N content test could be a useful tool for managing corn N fertilization under sprinkler‐irrigated Mediterranean conditions.

Resistance of anti-tuberculosis drugs among pulmonary tuberculosis patients in Yemen

Background: Tuberculosis (TB) is still a major global public health problem worldwide. The global prevalence of Mycobacterium (M tuberculosis) infection has been estimated in 32% of the world population with more than 8 million new cases diagnosed each year.
 Materials and Methods: A total of 192 M tuberculosis complex isolates were collected from patients with positive sputum smear who had been treated previously with the four main anti- tuberculosis drugs for more than two months. The isolates were identified by their colonial morphology, pigmentation, shapes on Ziehl-Neelsen smears, growth on Löwenstein-Jenson medium and biochemical tests as niacin and nitrate tests. A proportional method was used for the in vitro drug susceptibility testing.Objective: To estimate drug resistance among previously treated tuberculosis patients, focusing on multi-drug resistant strains at two time intervals (2002 and 2009) in Yemen.
 Results: Of the 192 M tuberculosis complex tested isolates, 55 (28.7%) were resistant to one or more drug; 20 (10.4%) were resistant to one drug, 13 (6.8%) to two drugs, 13 (6.8%) to three drugs and 9 (4.7%) to four drugs. Regarding the resistance to an individual drug, out of 192 tested isolates, 36 (18.7%) were resistant to rifampicin, 34 (17.7%) to isoniazid, 33 (17.2%) to ethambutol and 18 (9.4%) to streptomycin and these results were without a statistical significance. The incidence of multidrug resistance against rifampicin and isoniazid with or without other drugs was 13.5% among the tested M tuberculosis complex strains and this result was also without a statistical significance.
 Conclusion: The results of this study revealed nearly similar drug resistance patterns for the tested isolates in comparison with previous findings of 2002 and the emergence of more multi-drug resistance M tuberculosis complex strains after a time interval in Yemen.

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.

Evaluation of ammonia emissions from manure incorporated with different soil aerator configurations

The incorporation of swine manure with tillage effectively reduces ammonia (NH₃) emissions and conserves crop available nitrogen (N) but is not compatible with no-till and many other conservation tillage programs. Rolling-tine aerators potentially provide a means to enhance manure infiltration with limited disruption of the soil surface; however, the impact of the range of aerator configurations and manure placements has not been widely studied. We measured NH₃ emissions, conducted presidedress nitrate (NO₃) tests (PSNT), monitored corn (<i>Zea mays</i> L.) grain yield when swine manure was incorporated with combinations of two aerator toolbar offset angles (0° and 10°) and two manure placements (broadcast before aeration and banded behind aerator), and compared those measurements to unincorporated surface application and an unmanured control. Additional plots were established with five rates of mineral N fertilization to determine N response curve and estimate fertilizer N equivalent of the applied manure. Measurement of cumulative NH₃ emissions using a dynamic chamber method showed that offsetting the aerator toolbar by 10° reduced emissions by 65% to 75%, with both manure placements, compared to surface application. However, no consistent reductions in NH₃ emissions were observed when the toolbar was not offset. While reduction in NH₃ with the offset toolbar could conserve substantial amounts of plant available N, the soil disturbance caused by the offset tines would not be compatible with most conservation tillage programs. Presidedress NO₃ test values increased when NH₃ emissions were reduced. In 2009, both the angled and straight aerator treatments with manure banded behind the aerator resulted in significantly higher corn grain yield than all other treatments despite reductions in NH₃ emissions only when the toolbar was angled. Correlation of yield from manure application treatments with the N response curve for multiple mineral N application rates showed a greater than expected response to manure application. Yield responses are an indication that aeration has benefits in addition to N conservation. We do not recommend the rolling-tine aerator if reducing NH₃ emissions in conservation tillage is the primary goal, but future study into other yield-increasing benefits of aeration is needed.

Evaluating Nutrient Availability in Semi-arid Soils with Resin Capsules and Conventional Soil Tests, II: Field Studies

Commonly used soil analyses and resin capsules are employed to assess nutrient status in agriculture soils, but their validity in semi-arid ecosystems is unknown. Field studies with six rates of nitrogen (N) and phosphorus (P) application were established on crested wheat stands in both Rush Valley and Skull Valley, Utah. Resin capsule and conventional soil tests for nitrate (NO3)-N, ammonium (NH4)-N, and P were administered, and plant nutrient status was examined. Resin capsules were removed and replaced, and soil samples were taken every 90 d for 1 year. Concentration of P in resin capsules was not related to P rate but sodium bicarbonate (NaHCO3)-extracted P was, and resin NH4-N, resin NO3-N, potassium chloride (KCl)–extracted NO3-N and KCl-extracted NH4-N were all related to N rate. Only KCl-extracted NO3-N and NH4-N levels related to plant tissue N. Overall, traditional soil tests are more effective than resin capsules in semi-arid field conditions, but resin capsules have potential for use in N assessment.

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.

Characterization of boron tolerant bacteria isolated from a fly ash dumping site for bacterial boron remediation

Boron is an essential micronutrient for plants, but can above certain concentrations be toxic to living organisms. A major environmental concern is the removal of boron from contaminated water and fly ash. For this purpose, the samples were collected from a fly ash dumping site, Nagasaki prefecture, Japan. The chemical characteristics and heavy metal concentration of the samples were performed by X-ray fluorescent analysis and leaching test. For bacterial analysis, samples were collected in sterile plastic sheets and isolation was carried out by serial dilution method. The boron tolerant isolates that showed values of maximum inhibitory concentration toward boron ranging from 100 to 260mM level were screened. Based on 16S rRNA sequencing and phylogenetic analysis, the isolates were most closely related to the genera Bacillus, Lysinibacillus, Microbacterium and Ralstonia. The boron tolerance of these strains was also associated with resistant to several heavy metals, such as As (III), Cr (VI), Cd, Cu, Pb, Ni, Se (III) and Zn. Indeed, these strains were arsenic oxidizing bacteria confirmed by silver nitrate test. These strains exhibited their salt resistances ranging from 4 to 15% were determined in Trypticase soy agar medium. The boron tolerant strains were capable of removing 0.1-2.0 and 2.7-3.7mgl(-1) boron from the medium and fly ash at 168h. Thus, we have successfully identified the boron tolerant and removal bacteria from a fly ash dumping site for boron remediation.

Nitrogen Requirements and N Status Determination of Lettuce

As concern over NO3-N pollution of groundwater increases, California lettuce growers are under pressure to improve nitrogen (N) fertilizer efficiency. Crop growth, N uptake, and the value of soil and plant N diagnostic measures were evaluated in 24 iceberg and romaine lettuce (Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010. The reliability of presidedressing soil nitrate testing (PSNT) to identify fields in which N application could be reduced or eliminated was evaluated in 16 non-replicated strip trials and five replicated trials on commercial farms. All commercial field sites had greater than 20 mg·kg−1 residual soil NO3-N at the time of the first in-season N application. In the strip trials, plots in which the cooperating growers’ initial sidedress N application was eliminated or reduced were compared with the growers’ standard N fertilization program. In the replicated trials, the growers’ N regime was compared with treatments in which one or more N fertigation through drip irrigation was eliminated. Additionally, seasonal N rates from 11 to 336 kg·ha−1 were compared in three replicated drip-irrigated research farm trials. Seasonal N application in the strip trials was reduced by an average of 77 kg·ha−1 (73 kg·ha−1 vs. 150 kg·ha−1 for the grower N regime) with no reduction in fresh biomass produced and only a slight reduction in crop N uptake (151 kg·ha−1 vs. 156 kg·ha−1 for the grower N regime). Similarly, an average seasonal N rate reduction of 88 kg·ha−1 (96 kg·ha−1 vs. 184 kg·ha−1) was achieved in the replicated commercial trials with no biomass reduction. Seasonal N rates between 111 and 192 kg·ha−1 maximized fresh biomass in the research farm trials, which were conducted in fields with lower residual soil NO3-N than the commercial trials. Across fields, lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0.5 kg·ha−1·d−1. N uptake then increased linearly until harvest (≈9 weeks after planting), averaging ≈4 kg·ha−1·d−1 over that period. Whole plant critical N concentration (Nc, the minimum whole plant N concentration required to maximize growth) was estimated by the equation Nc (g·kg−1) = 42 − 2.8 dry mass (DM, Mg·ha−1); on that basis, critical N uptake (crop N uptake required to maintain whole plant N above Nc) in the commercial fields averaged 116 kg·ha−1 compared with the mean uptake of 145 kg·ha−1 with the grower N regime. Soil NO3-N greater than 20 mg·kg−1 was a reliable indicator that N application could be reduced or delayed. Neither leaf N nor midrib NO3-N was correlated with concurrently measured soil NO3-N and therefore of limited value in directing in-season N fertilization.

835 The Value of a Positive Nitrate Test in Routine Urine Analysis for the Diagnosis of Childhood UTI

Urinary tract infection (UTI) is one of the most common diseases in children. Its diagnosis depends mainly on urine culture. Urinalysis is used as a screening test to exclude UTI....

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.

Characterization of boron resistant and accumulating bacteria Lysinibacillus fusiformis M1, Bacillus cereus M2, Bacillus cereus M3, Bacillus pumilus M4 isolated from former mining site, Hokkaido, Japan

Boron is known to be widespread environmental contaminant that is relatively mobile in soil when compared to other metal contaminants. The present study made an attempt to isolate and characterize the boron resistant and accumulating bacteria from former mining site at Hokkaido, Japan. Four potential strains M1, M2, M3 and M4 were selected based on high degree of boron and heavy metal resistances. The morphological, biochemical and 16S rDNA sequencing analysis of mining bacteria revealed that the isolates were highly homology to Lysinibacillus fusiformis M1 (99 %), Bacillus cereus M2 (99 %), Bacillus cereus M3 (99 %) and Bacillus pumilus M4 (99 %) respectively. The strains M1, M2, M3 and M4 showed resistance to several heavy metals such as As (III), As (V) and Cr (VI), Cu, Ni, Pb and Zn. The selected strains were found to be arsenic oxidizing bacteria confirmed by Silver nitrate test. The resting and growing cells of mining bacteria were used for boron accumulation analysis. Selected strains were found to be efficiently accumulating boron concentration ranging from 0.1–2.3 mg L −1 and 1.5–4.7 mg L −1 at 24 h and 168 h, respectively. The following results conclude that the mining bacteria act as potent bioaccumulator of boron and its resistant, removal characteristic can be valuable in boron bioremediation.

Gastric ventilation: A new approach to metal phosphide fumigant ingestion

Introduction. Phosphine is absorbed rapidly across mucous membranes causing systemic poisoning including functional cellular hypoxia. Following ingestion of metal phosphides, continuous absorption of phosphine could contribute to the intractable systemic manifestations. Case report. A 16-year-old male was admitted to hospital 1-hour post-ingestion of two fresh 3 g tablets of aluminum phosphide 56%. He complained of abdominal discomfort and burning pain, thirst, nausea, and foul-odor vomitus. The silver nitrate test was positive by exhaled breath and gastric content, confirming exposure to phosphine. Initial therapy included intravenous fluids and gastric lavage with sodium bicarbonate and potassium permanganate. Hypotension, severe agitation and tachypnea prompted endotracheal intubation and treatment with gastric ventilation. This procedure involves insertion of a nasogastric tube to insufflate air into the distal part of the stomach. An orogastric tube is inserted near the gastro-esophageal junction as an inflow air tract. Ventilation was provided by blowing fresh air using an air-pump into the naso-gastric tube and phosphine contaminated air escaped via the wide-bore orogastric tube; the treatment continued for several hours. Although there was some evidence of progression of poisoning, including metabolic acidosis, arterial fibrillation, and mild gastrointestinal bleeding, the patient subsequently recovered and was discharged 6 days later with no persisting complications. This case report discusses probable benefit, availability, and simplicity of this treatment. We suggest that further clinical trials are required to confirm that this treatment improves outcomes in this highly toxic poisoning.

Nutrient Applications Reported by Farmers Compared with Performance‐Based Nutrient Management Plans

This study had two main objectives: (i) to evaluate how well farmers implemented nutrient management plans (NMPs) by comparing the farmers’ reported practices with the recommended management for manure and fertilizer; and (ii) to evaluate whether the management of manure and fertilizer had significant effects on the nutrient status of soil and corn tissue tests. The analysis relied on data from four dairy farms that had 5 to 7 yr of records at the field level. The farmers chose to apply the recommended amount of fertilizer P from 50 to 100% of the fields. The amount applied was often only 10 to 20 kg P2O5 ha−1 different from the recommended amount. The farmers applied the recommended amount of fertilizer N from 40 to 71% of the fields when the pre‐sidedress soil nitrate test (PSNT) was used for the recommendation, but only 1 to 21% of the fields received the recommended amount when the yield goal method was used. These data suggest that the farmers trusted a fertilizer recommendation developed from a soil test more than they trusted a nonsoil test recommendation. Only a small percentage of fields (3–37%) received the recommended amount of manure N and P. Variability in the amount of residual N available from previous manure applications caused great variation in the PSNT and corn stalk nitrate values (CSNT). This variation in N availability in fields indicates that a number of years of data are needed before the PSNT and the CSNT can be used to objectively evaluate the performance of an NMP.

Answer to March 2012 Photo Quiz

Answer: Cardiobacterium hominis endocarditis. All blood cultures grew Cardiobacterium hominis. The organism, which was presumptively identified on the basis of its colony morphology, its characteristic Gram stain, and the results of catalase, oxidase, indole, and nitrate tests, was confirmed as C.

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.

Evaluation of the Pre-sidedress Soil Nitrate Test in Ohio

Evaluation of the Pre-sidedress Soil Nitrate Test in Ohio

Accumulation and redistribution of residual chloride, nitrate, and soil test phosphorus in soil profiles amended with fresh and composted cattle manure containing straw or wood-chip bedding

Miller, J. J., Beasley, B. W., Drury, C. F. and Zebarth, B. J. 2011. Accumulation and redistribution of residual chloride, nitrate, and soil test phosphorus in soil profiles amended with fresh and composted cattle manure containing straw or wood-chip bedding. Can. J. Soil Sci. 91: 969–984. Limited research has compared the effect of fresh versus composted beef (Bos taurus) cattle feedlot manure containing straw or wood chips on accumulation and redistribution of residual chloride (Cl), NO3-N, and soil test P (STP) in soil profiles of the Great Plains region of North America. Barley (Hordeum vulgare L.) was grown (1999–2007) on an irrigated clay loam soil in southern Alberta where organic amendments and fertilizer were annually applied for 9 yr from 1998 to 2006. The field experiment was a factorial arrangement of two manure types (fresh versus composted feedlot manure), two bedding materials (straw versus wood-chips), and three application rates (13, 39, 77 Mg ha−1dry wt). There was also one inorganic (IN) fertilizer treatment and an unamended control. The soil profile (0–1.5 m) was sampled in the fall of 1999 to 2002, 2004, 2006, and 2007 and analyzed for residual soil NO3-N, Cl, and STP. Manure type had a significant (P≤0.05) effect on the accumulation of these chemicals, but there was an interaction with application rate (NO3-N), or with bedding and year (STP). The maximum accumulation of Cl after 9 yr was at the 0.6 to 0.9 m depth, but mean values at this depth were similar for the four organic amendments. The maximum accumulation of NO3-N after 9 yr (2007) was at the 0.3 to 0.6 m depth, and mean values at this depth were significantly greater by four- to sixfold for FM and CM with straw than wood-chips, which suggested greater N immobilization in soils with wood. Redistribution of Cl and NO3-N downward into the soil profile suggested a potential for leaching of these chemicals below the root zone. In contrast, soil test P did not accumulate below the 0.3 m depth, suggesting little potential for leaching. However, accumulation of soil test P at this depth was generally greater for the amendment treatments compared with inorganic fertilizer and was likely related to greater P applied in the amendments.

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.