Presidedress Soil Nitrate Test Research Articles

Recalibrating the Pennsylvania pre‐sidedress soil nitrate test recommendations for modern corn production

AbstractThe pre‐sidedress soil nitrate test (PSNT) was developed over 30 years ago to determine sidedress nitrogen (N) fertilizer recommendations for corn (Zea mays L.). Since the original PSNT calibrations were developed, changes in production practices such as no‐till and cover cropping and increases in corn yields and N use efficiency could affect the accuracy of PSNT recommendations. To update the PSNT recommendations in Pennsylvania and demonstrate the test's efficacy, we compiled a dataset of 32 calibration sites and 13 demonstration sites where the PSNT was conducted, and the economically optimum N rate (EONR) for corn was determined from an N fertilizer yield response curve. We recalibrated the PSNT recommendation algorithm and compared its accuracy to the original calibration. The new calibration resulted in a single long‐term manure history factor that interacted with the PSNT result to adjust the sidedress N recommendation (−5.7 kg N ha−1 [mg NO3‐N kg−1]−1). The new calibration also included a term for a mixed species cover crop, which increased the sidedress N recommendation 56.2 kg N ha−1. Finally, the coefficient that scales the N fertilizer recommendation based on yield goal decreased by 29% from the original calibration to 12.9 kg N Mg−1 grain. The new algorithm for predicting EONR reduced the error of the sidedress N recommendation by one‐half compared to the original calibration. The new PSNT calibration will allow users to accurately determine sidedress N recommendations in sites with a long‐term manure history and underscores the importance of updating soil fertility recommendation algorithms with modern data.

Do Soil Tests Help Forecast Nitrogen Response in First‐Year Corn Following Alfalfa on Fine‐Textured Soils?

Core Ideas ISNT and PSNT concentrations did not differ among alfalfa stand ages in five long‐term trials. Only PSNT concentration increased during first‐year corn in three of five long‐term trials. The PSNT was less related to soil N mineralization and more related to available N than the ISNT. The PSNT more accurately predicted corn response or nonresponse to fertilizer N than the ISNT. The product of alfalfa stand age and PSNT separated N response in 87% of 15 independent site‐years. Improved methods are needed to predict grain yield response to fertilizer N for first‐year corn (Zea mays L.) following alfalfa (Medicago sativa L.) on fine‐textured soils. Data from 21 site‐years in the North Central Region of the United States were used to determine how Illinois soil nitrogen test (ISNT) and pre‐sidedress soil nitrate test (PSNT) concentrations change during alfalfa–corn rotations and how they relate to mineralized N, available N, and grain yield response to fertilizer N in first‐year corn. In five long‐term crop rotation trials, ISNT and PSNT taken in the alfalfa phase did not change with alfalfa stand age, but PSNT concentration in first‐year corn increased with alfalfa stand age in three of five trials. Across 21 site‐years, the PSNT more accurately predicted corn response or nonresponse to fertilizer N than the ISNT (67 vs. 52% of site‐years). The interaction of PSNT with alfalfa stand age resulted in 87% accuracy when validated with 15 independent site‐years; no N response was likely in first‐year corn when the product of PSNT × stand age exceeded 42. Incubation of soil from first‐year corn showed that the ISNT explained over twice as much variation in soil nitrate‐N accumulation after 17 wk than the PSNT (30 vs. 13%). Overall, the PSNT was less related to soil N mineralization and more related to aboveground corn N uptake, total available N, and grain yield response to fertilizer N in first‐year corn than the ISNT. This research provided a simple method for predicting when N response is likely in first‐year corn after alfalfa, but further research is needed to predict the size and mineralization rate of soil N pools after alfalfa termination to estimate the economically optimum nitrogen rate when fertilizer N response is likely.

What's driving adoption of in‐season nitrogen application?

What's driving adoption of in‐season nitrogen application?

Second‐Year Corn after Alfalfa Often Requires No Fertilizer Nitrogen

Terminated alfalfa(Medicago sativaL.) often provides N to at least 2 yr of subsequent corn (Zea maysL.) crops, but the variability in fertilizer N guidelines for second‐year corn in the midwestern United States needs to be addressed. In several states, fertilizer N guidelines are the same for second‐year corn after alfalfa as they are for continuous corn, whereas other states recommend reducing fertilizer N rates to second‐year corn by 25 to 145 kg N ha−1. Experiments were conducted at 28 farms in Iowa and Minnesota to determine fertilizer N requirements of second‐year corn after alfalfa. Second‐year corn in half of the trials showed no response to fertilizer N and the economically optimum N rate (EONR) for corn grain yield in the 14 responsive trials ranged from ≤67 to 196 kg N ha−1. Furthermore, in 10 of 19 trials there was no response of grain yield to fertilizer N in both first‐ and second‐year corn. These results indicate that current university fertilizer N guidelines for second‐year corn after alfalfa often are unreliable. At the widely adopted critical concentration of 21 mg kg−1, the pre‐sidedress soil nitrate test (PSNT) correctly identified only 63% of the trials as responsive or nonresponsive to fertilizer N. When results of our experiments were combined with data from the literature, second‐year corn grain yield responded to fertilizer N 55% of the time and the PSNT remained accurate only 65% of the time, indicating that more accurate forecasting of second‐year corn N requirements is needed.

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.

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.

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.

Evaluation of the Pre-sidedress Soil Nitrate Test in Ohio

Evaluation of the Pre-sidedress Soil Nitrate Test in Ohio

Improved Nitrogen Management for Burley Tobacco Production in the United States

Burley tobacco (Nicotiana tabacumL.) has historically been fertilized with nitrogen rates ranging from 150 to 250 kg N/ha. The objectives of the this study were to: (i) evaluate the response of burley tobacco to N fertilization; (ii) determine if split N applications increase burley tobacco yields; and (iii) evaluate a modified pre-sidedress soil nitrate test (PSNT) as a tool for N management in burley tobacco. Nitrogen rates included: 0, 67, 135, 202, and 270 kg N/ha preplant in combination with 0 and 67 kg/ha N sidedress. In 2008, the 270 kg N/ha rate was dropped and the variety TN 90LC was added to the study. Modified pre-sidedress nitrate test (PSNT) samples were taken to a depth of 15 cm prior to sidedress N applications. Analysis of variance was used to analyze burley tobacco yield response to preplant and sidedress N applications and polynomial regression was used to analyze PSNT levels and preplant N rates. Optimal yields were reached with 135 kg N/ha. Pre-sidedress nitrate test levels in 2008 predicted yields more precisely than in 2007 due to higher precipitation at experimental sites. The information from the study indicates that burley tobacco yields were maintained at lower N rates than traditional N applications rates.

Clover and Manure Management Strategies for Overcoming the Wheat Residue Antagonism of No-Till Corn

Wheat (Triticum aestivum L.) crop residue can negatively affect the growth and development of no-till corn (Zea mays L.). The objective of this study was to determine whether nitrogen management practices including legume cover crops and manure applications used in conjunction with a pre-sidedress soil nitrate test (PSNT) could be used to overcome the observed wheat residue antagonism of no-till corn growth and development. A PSNT nitrogen strategy was effective in maintaining no-till corn grain yield in wheat residue systems equivalent to no-till corn grain yield in no-wheat residue systems in 4 of 6 site years. Similar results were obtained for PSNT plus clover cover crop and PSNT plus manure plus clover cover crop nitrogen management systems. Utilization of a PSNT with manure application equalized no-till corn grain yield in high wheat residue treatments with no-till corn grain yield in treatments without wheat residue in all site years. This can be a recommended practice in the Michigan eco-region.

Contribution of Anaerobically Mineralized Nitrogen to the Reliability of Planting or Presidedress Soil Nitrogen Test in Maize

The objective of this work was to evaluate if soil mineralizable N under anaerobic conditions (Nan) improves the reliability of preplant soil nitrate test (PPNT) and presidedress soil nitrate test (PSNT). The study was conducted under no‐tillage (NT) in the southeastern Buenos Aires province, Argentina, in 26 site‐years. In some site‐years treatments were fixed N rates (0, 70, 140, and 210 kg ha−1 or 0, 60, 120, 180, and 240 kg ha−1) applied at planting, whereas in others site‐years N rates were determined by adding N to lead targets of N supply up to 120, 160, and 200 kg N ha−1. When sites were not separated by Nan, relative yield (RY) correlated with PPNT (r2 = 0.37) and reliability of PPNT did not increase when sites were separated by low (<48 mg kg−1) and high Nan (>48 mg kg−1). A high relationship between RY and PSNT (r2 = 0.56) was determined. However, when sites were separated by Nan, reliability of PSNT increased, mainly for sites with low Nan (r2 = 0.68 and 0.44 for sites with low and high Nan, respectively). Critical PSNT values for 94% of RY were 75 and 90 kg N ha−1 for sites with high and low Nan, respectively. The results show that PSNT was a better diagnostic method for maize (Zea mays L.) than PPNT. However, the separation of sites by its N mineralization capacity increased reliability of PSNT by indicating a lower N requirement to reach 94% of RY, decreasing the risk of overfertilization, an important feature from economical and environmental standpoints.

Presidedress Soil Nitrogen Test for No‐Tillage Maize at Different Row Spacing

A presidedress soil nitrate test (PSNT) can be used to evaluate preplant N applications as a complementary method to N budget in maize (Zea mays L.) under different management practices. Narrow rows have shown increased N accumulation and recovery efficiency by maize, and therefore soil NO3−–N critical concentration (CC) for maximum yield could be lower than in conventional row spacing. An experiment was performed at Balcarce (Argentina) in 1996–1997, 1999–2000, and 2000–2001 to evaluate the PSNT for irrigated no‐till (NT) maize with different row spacings (70, 52, and 35 cm) and N rates (0, 90, 140, and 180 kg N ha−1). Soil samples were collected to a 30‐cm and 30‐ to 60‐cm depth when maize was at the six‐leaf stage (V6). Grain yield was significantly increased by narrow rows mainly at low N availability. Relative yield was highly associated (r2 = 0.73 and 0.68) with soil NO3−–N concentration (0–30 cm) at V6 for conventional and narrow rows, respectively. Soil NO3−–N concentration for maximum yield (95%) was greater for conventional row spacing (22 mg kg−1) compared with narrow rows (17 mg kg−1). The reliability of the PSNT (r2) did not improve when sampling was done up to a 60‐cm depth. These results confirm the hypothesis that the NO3−–N CC determined for the PSNT is lower for maize crops growing in narrow rows than conventional row spacing. Narrow rows maize is a simple management practice that could contribute to enhancing system sustainability.

Potential Long‐Term Benefits of No‐Tillage and Organic Cropping Systems for Grain Production and Soil Improvement

There have been few comparisons of the performance of no‐tillage cropping systems vs. organic farming systems, particularly on erodible, droughty soils where reduced‐tillage systems are recommended. In particular, there is skepticism whether organic farming can improve soils as well as conventional no‐tillage systems because of the requirement for tillage associated with many organic farming operations. A 9‐yr comparison of selected minimum‐tillage strategies for grain production of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) was conducted on a sloping, droughty site in Beltsville, MD, from 1994 to 2002. Four systems were compared: (i) a standard mid‐Atlantic no‐tillage system (NT) with recommended herbicide and N inputs, (ii) a cover crop‐based no‐tillage system (CC) including hairy vetch (Vicia villosa Roth) before corn, and rye (Secale cereale L.) before soybean, with reduced herbicide and N inputs, (iii) a no‐tillage crownvetch (Coronilla varia L.) living mulch system (CV) with recommended herbicide and N inputs, and (iv) a chisel‐plow based organic system (OR) with cover crops and manure for nutrients and postplanting cultivation for weed control. After 9 yr, competition with corn by weeds in OR and by the crownvetch living mulch in CV was unacceptable, particularly in dry years. On average, corn yields were 28 and 12% lower in OR and CV, respectively, than in the standard NT, whereas corn yields in CC and NT were similar. Despite the use of tillage, soil combustible C and N concentrations were higher at all depth intervals to 30 cm in OR compared with that in all other systems. A uniformity trial was conducted from 2003 to 2005 with corn grown according to the NT system on all plots. Yield of corn grown on plots with a 9‐yr history of OR and CV were 18 and 19% higher, respectively, than those with a history of NT whereas there was no difference between corn yield of plots with a history of NT and CC. Three tests of N availability (corn yield loss in subplots with no N applied in 2003–2005, presidedress soil nitrate test, and corn ear leaf N) all confirmed that there was more N available to corn in OR and CV than in NT. These results suggest that OR can provide greater long‐term soil benefits than conventional NT, despite the use of tillage in OR. However, these benefits may not be realized because of difficulty controlling weeds in OR.

Evaluation of LEACHMN for simulating seasonal changes in plant available nitrogen across a variable landscape

A model that accurately simulates the seasonal variation in nitrogen (N) dynamics may represent an important additional tool in N management. The objectives of this study were to evaluate whether seasonal changes in the amount of N that becomes available to a maize crop in a variable landscape can be simulated with LEACHMN and, in particular, to assess the potential value of LEACHMN in estimating N available at the time of the presidedress soil nitrate test (PSNT). Soil mineral N (SMN) and shoot N were measured biweekly over seven growing seasons in corn (Zea Mays L.) grown under conventional tillage in a variable landscape in Southern Ontario, Canada. The model was calibrated using data from 2002 and 2003 from each of five positions in the landscape and then evaluated using data from the 1997–2001 growing seasons. Although the model under-estimated SMN and over-estimated shoot N, the model was more successful in simulating the sum, defined as plant available N (PAN). Simulations of PAN were best at the summit and shoulder positions. The agreement between measured and simulated PAN were poorest early in the season. Although the accuracy of PAN simulations late in the growing season indicates this model has potential value in N management decisions, the errors in simulating SMN early in the season suggest adjustments are required before it can be used, along with other tools, as a substitute for the PSNT in cool humid environments. Key words: Soil mineral N, Plant available N, variable landscapes, LEACHMN

Effect of Winter Wheat Crop Residue on No‐Till Corn Growth and Development

Two established methods for increasing the sustainability of production agricultural cropping systems are (i) increasing crop residue levels by reducing tillage and (ii) including a winter annual crop in the rotation. A wide range of crop yield responses have been reported for no‐till systems adopted to a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. However, little research has been done in the Northern Corn Belt on no‐till corn following winter wheat (Triticum aestivum L.). The objective of this study was to evaluate the effect of winter wheat crop residue on the growth and development of no‐till corn. The experimental design was a randomized complete block. Treatments consisted of no‐till systems with three levels of winter wheat residue [no wheat residue (NWR), wheat root residue only (WRR), and wheat root and shoot residue (WRSR)]. Data were collected in 2003, 2004, and 2005. Measurements included plant emergence, plant height, time of tasseling (VT stage), chlorophyll content, presidedress soil nitrate test (PSNT) soil nitrate levels, soil moisture and temperature, corn grain yield, grain moisture, and grain test weight of corn at harvest. In all years, the presence of winter wheat residue above and below ground decreased soil temperature, increased soil moisture, and decreased chlorophyll content in corn leaves and plant height in the early stages of corn development. The VT stage of corn was delayed for about 1 wk in residue systems. Winter wheat residue decreased the amount of plant available N and increased grain moisture and test weight of corn grain at harvest. Emergence and population of corn in 2003 and 2005 were reduced in residue systems. The use of a PSNT‐based N application rate was successful in maintaining corn grain yield in wheat residue systems with corn grain yield in NWR systems in 2003 and 2004 despite wheat residue antagonism of corn growth and development. In 2005, corn grain yield in wheat residue treatments was less than in NWR treatments, but was equal to PSNT target yields.

Pre‐Sidedress Nitrate Test and Other Crop‐Based Indicators for Fresh Market and Processing Sweet Corn

Commercial sweet corn (Zea mays L.) production requires significant quantities of fertilizer N, leading to inefficient N use and negative environmental impact. A field experiment was conducted for 4 yr (2001–2004) in Ottawa, Canada, to assess and compare presidedress soil nitrate test (PSNT) with some crop‐based measurements (canopy reflectance, leaf chlorophyll and plant total N) for improved N management. A fresh market sweet corn (FMSC, hybrid ‘Temptation’) grown from 2001 to 2003, and a processing sweet corn (PSC, hybrid ‘Hollywood’) from 2002 to 2004, both received five fertilizer N rates (0, 50, 100, 150, and 200 kg N ha−1). Soil samples taken from the V4 to V8 growth stages were analyzed for NO3−–N. Leaf chlorophyll content (SPAD) and canopy reflectance were also measured for FMSC at the same time. All N treatments affected the number of marketable ears, kernel dry weight and total biomass production. However, in most cases, there was no difference between N treatments from 100 to 200 kg ha−1. The PSNT NO3−–N increased linearly with the fertilizer N rates, and there were significant positive correlations between PSNT at V4 to V6 and the number of marketable ears. It was evident that PSNT, plant N concentration at V6, SPAD and canopy reflectance all differentiated sweet corn N response similarly, and they were highly correlated with one another. We concluded that PSNT at V4 to V6 was effective in predicting sweet corn N requirement in this cool and short‐growing region.

Managing Poultry Manure Using the Pre-Sidedress Soil Nitrate Test

Managing Poultry Manure Using the Pre-Sidedress Soil Nitrate TestIntroduction The pre-sidedress nitrate test (PSNT) was originally developed for the humid Eastern U.S. to help producers decide, in season, when it was necessary to apply additional N to obtain optimum corn yields. Once a critical PSNT level for optimum yield has been established for a specific crop, the PSNT allows producers to make a more confident decision on whether or not to sidedress with...Author(s)David QuarlesTroy BauderStefanie Van WychenSourceProceedings of the Water Environment FederationSubjectSession 18: Agricultural Issues IIDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2007ISSN1938-6478SICI1938-6478(20070101)2007:3L.994;1-DOI10.2175/193864707787976137Volume / Issue2007 / 3Content sourceResiduals and Biosolids ConferenceFirst / last page(s)994 - 996Copyright2007Word count105

Nutrient Accumulation and Movement from Poultry Litter

Poultry broiler litter (BL) is widely used as an alternative source of N, P, and K for crops and forages and is often applied at excessive rates of both N and P. Soil samples were periodically collected from experiments with BL at two locations in Alabama, a Coastal Plain site and a Tennessee Valley site, from 1991 though 2000. The objective was to determine the accumulation and movement of plant nutrients and metals in soil profiles when BL is compared with ammonium nitrate (AN) as a source of N for cotton (Gossypium hirsutum L.) and corn (Zea mays L.). The Tennessee Valley site was fertilized and cropped for 3 yr, and the Coastal Plain site was fertilized and cropped for 12 yr. The two N sources were applied at rates from 0 to 269 kg N ha−1 based on total N in the material. Incremental soil samples to a depth of 1 m were taken periodically from 1990 through 2000. Broiler litter maintained surface soil pH on the coarse‐textured soil at the Coastal Plain site whereas AN resulted in a decline in pH. There were no significant differences in surface soil pH due to source on the finer textured Tennessee Valley site. Application of BL resulted in increasing accumulations of total soil organic C, total N, and Mehlich‐1 extractable Ca, Mg, P, K, B, Zn, and Cu as the rates increased from 134 to 269 kg N ha−1 as BL (approximately 4.48–8.96 Mg ha−1 yr−1) over a 10‐yr period. While differences in NH4–N and NO3–N were observed to a 1‐m depth due to treatment, soil concentrations were very low compared with standards used in the presidedress soil nitrate test for corn (PSNT). No significant accumulations of heavy metals were observed during the experiments.

Testes de nitrato no solo como indicadores complementares no manejo da adubação nitrogenada em milho

A recomendação de nitrogênio (N) para a cultura do milho teve um avanço expressivo recentemente na região Sul do Brasil, quando passou a considerar a cultura anterior em adição ao teor de matéria orgânica do solo e a expectativa do rendimento de grãos. A busca de otimização do sistema de recomendação é constante e, nesse sentido, há grande potencial da inclusão de parâmetros de solo e de planta como indicadores complementares da disponibilidade de N no solo, principalmente em sistemas altamente produtivos e com aplicação de altas doses de N. Dentre os parâmetros de solo destacam-se os testes de nitrato, os quais indicam a quantidade de N disponível e são denominados testes de intensidade. Em função da época de realização, os testes de nitrato podem ser divididos basicamente em (i) teste de pré-semeadura - TPS ("preplant soil nitrate test" - PPNT), (ii) teste de pré-aplicação de N em cobertura - TPNC ("pre-sidedress soil nitrate test" - PSNT), e (iii) teste de pós-colheita - TPC ("post-harvest soil nitrate test" - PHNT). Dentre estes testes, destaca-se o TPNC, o qual tem sido mais estudado e difundido, principalmente nos EUA, pois permite avaliar a variação da disponibilidade de N do solo durante o ciclo da cultura, possibilitando o manejo da adubação nitrogenada em situações específicas. Esta revisão visa abordar o potencial dos testes de nitrato na avaliação da disponibilidade de N no decorrer do ciclo do milho e sua utilização na predição da necessidade de N a ser suplementado. A hipótese é de que a utilização dos testes de nitrato resultem em maior flexibilidade no manejo da adubação nitrogenada em milho.

Use of a pre-sidedress soil nitrate test (PSNT) to determine nitrogen fertilizer requirements for irrigated corn

In the present study, a 2-year N rate response experiment was conducted in different fields to monitor NO3-N soil profiles, N accumulation by the crop and final crop performance, in order to assess if soil NO3-N at pre-sidedressing (Pre-Sidedress Soil Nitrate Test, PSNT) is a reliable indicator for soil N availability for corn in the irrigated area served by canal d’Urgell (Lleida, Spain), and if the test can be used to separate responsive fields from non-responsive fields to sidedress N fertilizer applications. Preliminary soil N availability (N sidedress fertilizer rate + PSNT) critical levels to identify fields that need supplementary N fertilizer applications were established at ca. 300 and 210 kg NO3-N·ha–1, for PSNTrooting–zone and PSNT0–30 cm, respectively (for a yield goal of 14 t grain·ha–1).