Pre-sidedress Nitrate Test Research Articles

Effect of soil sample handling and storage on inorganic nitrogen determination: Implications for the presidedress nitrate test

AbstractThe presidedress nitrate test (PSNT) is a nitrogen (N) fertilizer decision support system (DSS) that uses soil test nitrate (NO3−) to provide an N rate recommendation for corn. We studied the effect of soil sample storage and handling on soil test NO3−, ammonium (NH4+), and the N rate recommended by the PSNT. Soils from 35 agricultural fields located in southern Ontario, Canada, were collected in June and July and underwent two soil storage treatments and four soil handling treatments. Soils were either handled immediately or frozen (−15°C) for 3 months before handling. Soil handling included (1) immediate extraction in a moist state or oven‐drying for 24 h at (2) 35°C, (3) 65°C, or (4) 105°C. Samples were extracted with a 2.0 M KCl solution for inorganic N determination and immediate, fresh‐extracted samples served as baseline soil test values. Ammonium‐N was increased by freezing and drying at any temperature, while NO3− test values were significantly affected by freezing only. However, oven‐drying samples changed PSNT DSS N rate recommendations in 34%–43% of location‐years when handled immediately and 51%–68% of samples when initially frozen, depending on drying temperature. Most of these deviations were underapplications and relatively small when handled immediately (20 kg N ha−1) or frozen (37 kg N ha−1). We conclude that PSNT samples should not be frozen and that oven‐drying often alters PSNT‐based N rate recommendations.

Monolith soil core sampling to develop nitrate testing protocol for manure injection

AbstractInjecting manure and commercial fertilizer beneath the soil surface is an important nutrient management practice that conserves ammonia‐nitrogen (N) but creates distinct bands of N below the soil surface. To date, no widely accepted soil nitrate sampling protocol has been developed to account for the extreme heterogeneity created by injection. To develop sampling recommendations for Pre‐Sidedress Nitrate Test (PSNT), we quantified patterns of NO3−‐N concentrations in soil of corn (Zea mays L.) plots injected with liquid dairy cattle (Bos taurus L.) manure at 76 cm spacing over 2 years. Soil monoliths were collected to allow precise sampling of 30 cm deep by 2.5 cm soil cores from which a mid‐season PSNT was determined. Monte Carlo simulation was conducted to simulate the effects of alternative soil sampling protocols on bias and error. Results from the simulation support the following equispaced sampling protocol: five, 30‐cm deep soil cores are spaced 15 cm apart and oriented in a line perpendicular to the injected manure bands, collected at four locations in the field, to produce a single composite of 20 samples for NO3− analysis. It is not necessary to know manure band location. As spatially discrete manure application patterns become more prevalent with the expansion of manure injection, we believe this PSNT sampling protocol balances risk of error with practical concerns needed to promote adoption.

Soil‐nitrogen, potentially mineralizable‐nitrogen, and field condition information marginally improves corn nitrogen management

AbstractAnaerobic potentially mineralizable nitrogen (PMN) combined with preplant nitrate test (PPNT) or pre‐sidedress nitrate test (PSNT) may improve corn (Zea mays L.) N management. Forty‐nine corn N response studies were conducted across the U.S. Midwest to evaluate the capacity of PPNT and PSNT to predict grain yield, N uptake, and economic optimal N rate (EONR) when adjusted by soil sampling depth, soil texture, temperature, PMN, and initial NH4–N from PMN analysis. Pre‐plant soil samples were obtained for PPNT (0‐ to 30‐, 30‐ to 60‐, 60‐ to 90‐cm depths) and PMN (0‐ to 30‐cm depth) before corn planting and N fertilization. In‐season soil samples were obtained at the V5 corn development stage for PSNT (0‐ to 30‐, 30‐ to 60‐cm depths) at 0 kg N ha−1 at‐planting rate and for PMN when 0 and 180 kg N ha−1 was applied at planting. Grain yield, N uptake, and EONR were best predicted when separating soils by texture or sites by annual growing degree‐days and including PMN and initial NH4–N with either NO3–N test. Using PSNT (mean R2 = .30)‐instead of PPNT (mean R2 = .19)‐based models normally increased predictability of corn agronomic variables by a mean of 11%. Including PMN and initial NH4–N with PPNT or PSNT only marginally improved predictability of grain yield, N uptake, and EONR (R2 increase ≤ .33; mean R2 = .35). Therefore, including PMN with PPNT or PSNT is not suggested as a tool to improve N fertilizer management in the U.S. Midwest.

Evaluating effects of dairy manure application method on soil health and nitrate

Liquid manures are typically applied via surface broadcasting; however, subsurface injection is an alternative characterized by greater nutrient retention and a spatially distinct application pattern, altering management strategies and nutrient cycling dynamics. Thus, a field study was conducted from spring of 2016 through fall of 2018 on seven sites to assess pre-sidedress nitrate test (PSNT) methodology, seasonal soil nitrate nitrogen (NO3−-N) trends, corn (Zea mays L.) silage and grain yield, estimated milk production via MILK 2006, and biological soil health among surface broadcast and subsurface injection applications of dairy slurry. A weighted sampling method had a coefficient of variation of 37%, ~8% higher relative to random (28%) and equispaced (30%) sampling methods. Soil NO3−-N was greater in 7 out of 25 measurements under subsurface injection and 30% higher under injection on average during the corn PSNT. There were no significant differences in crop yield or milk production between surface and injected slurry applications, but means were always higher for injection. Biological soil health tests were highly variable, and analyzing carbon mineralization (C-min) took considerably more time than other tests. There were no significant differences in C-min between manure application methods; although, mineralization values increased with soil organic matter. Estimated microbial biomass was on average 46% lower under subsurface injection relative to surface broadcast in 2017, but results were inconsistent in 2016 and 2018. Overall, the biological indicators of soil health were not productive in showing differences between application methods. Nevertheless, it is apparent that injection can decrease chemical sidedress N applications, and either the standard method of PSNT soil sampling or an equispaced method can be used in injected fields.

Using the pre‐sidedress nitrate test to prescribe variable‐rate nitrogen in Minnesota

The availability of new technology for rapidly analyzing soil samples for nitrate in recent years has led to renewed interest in using the pre‐sidedress nitrate test (PSNT) as a method for prescribing variable‐rate nitrogen. This study compared pre‐plant application of nitrogen fertilizer, split application, and a split treatment using a base rate plus a variable rate determined using the PSNT. Earn 0.5 CEUs in Nutrient Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/645.

Assessment of In‐Season Soil Nitrogen Tests for Corn Planted into Winter Annual Cover Crops

Core Ideas The Solvita 1‐d CO2 mineralization test could be a new tool to improve in‐season N rate recommendations for corn. Solvita and soil NO3–N tests may be useful for predicting the level of early‐season N mineralization from winter cover crops (WCCs). Soil NO3–N collected at the V4 growth stage of corn at 0 to 15 cm was positively correlated (R2 = 0.45) with corn check yield. Neither the Solvita nor the presidedress nitrate test detected WCC N mineralization consistently enough to use them in rate recommendations. Environmental and economic goals encourage the use of soil N tests to improve fertilizer N (FN) management in corn (Zea mays L.). Recently, the Solvita 1‐d CO2 burst test, which proposes to estimate soil potentially mineralizable N (PMN), has been promoted as a tool for FN recommendations. We aimed to compare the Solvita test with the established presidedress nitrate test (PSNT) for estimating optimum sidedressed FN rates in a typical corn crop rotation in the Mid‐Atlantic United States that includes winter annual cover crops (WCCs). Research was conducted at eight locations from 2012 to 2014. Three WCC treatments [cereal rye (Secale cereale L.), hairy vetch (Vicia villosa Roth ssp. villosa) or a cereal rye–hairy vetch mix] were the main plots and 10 FN rates were the subplots. The WCCs affected preplanting (PP) Solvita results at one location, V4 NO3–N at 0 to 15 cm (PSNT15) at four locations, and V4 NO3–N at 0 to 30 cm (PSNT30) at two locations. Correlations between soil N test parameters and relative corn yields ranged from 0.31 to 0.13. Values for PSNT15 and PSNT30 correlated positively with corn check yields (r = 0.41 and 0.39 respectively). Solvita did not provide additional information to PSNT for predicting preplanting PMN, V4 PMN, or corn check yields. The advantages of the Solvita test were its simplicity, speed of analysis, and lower coefficient of variation relative to the PSNT. Neither method was consistently effective for predicting WCC effects on soil N or relative corn yield.

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.

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.

Plant‐available nitrogen in the soil: Relationships between pre‐plant and pre‐sidedress nitrate tests for corn production

AbstractCorn (Zea mays L.) producers in the rainfed regions sometimes sidedress fertilizer N according to pre‐plant–nitrate test (PPNT) results based on the assumption that there is a linear relationship between pre‐sidedress nitrate test (PSNT) and the PPNT. There has been no report on such relationship in Ontario (Canada) and elsewhere in the nonirrigated corn‐growing regions. A field study was conducted near Ottawa, Canada for 7 y to (1) determine changes in soil available N from pre‐planting to shortly after the sidedress stage (late June) for corn and (2) establish a quantitative relationship between PPNT and PSNT. In each year, soil samples from fields of three to four plot experiments with different cropping histories, soil textures, and management levels, taken at 7 to 10 d intervals, and from on‐farm trials taken at pre‐planting and pre‐sidedress, were extracted with 2 M KCl. The concentrations of NO$ _3^- $‐N were determined colorimetrically. It was found that soil NO$ _3^- $‐N concentration of PSNT was a linear function of PPNT with an average slope of 1.7. However, the slope of the regression equations differed dramatically among cropping sequences, and to a lesser extent, soil textures. The NO$ _3^- $‐N concentration after planting to pre‐sidedress was influenced by air temperature and precipitation during this period of time. Both PPNT and PSNT positively correlated with corn‐grain yield. Our data suggest that cautions must be taken when deciding the rate of fertilizer N for sidedress application to corn based on PPNT test, especially under more humid northern climate conditions.

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

Soil Tests for Predicting Corn Response to Nitrogen Fertilizer in New York

The presidedress nitrate test (PSNT) is currently the best tool available for Northeastern producers to determine if corn (Zea mays L.) will benefit from sidedress N. The PSNT requires 0‐ to 30‐cm soil samples, which can be difficult to obtain on stony soils, and samples need to be taken in late‐spring, an inopportune time for dairy (Bos taurus) farmers. Additionally, the in‐season nature of the PSNT prevents its use by producers who apply preplant broadcast N. The Illinois soil N test (ISNT) is a simple test that estimates a potentially mineralizable fraction of soil organic N, amino sugar N. The test was able to identify sites that are nonresponsive to sidedress N fertilization in Illinois. From 2002 to 2004, 33 field trials were conducted to assess the effectiveness of the ISNT as compared with the PSNT in New York. Results confirmed the ability of the PSNT to separate responsive from nonresponsive corn sites. The ISNT was not an effective predictor by itself. However, when ISNT results and soil organic matter (OM) were considered, critical values could be developed that separated fields that were responsive to sidedress N from nonresponsive sites for corn silage dry matter yield, N concentration, N uptake, and estimated milk yield (kg of milk per ha predicted based on yield and quality of the silage). Further evaluation of the ISNT with consideration for OM could improve the accessibility of soil N testing to corn producers who apply N as sidedress as well as those who fertilize with preplant broadcast applications in the Northeast.

Optimization of Liquid Swine Manure Sidedress Rate and Method for Grain Corn

Sidedressing may provide a better window of opportunity for land application of liquid swine (Sus scrofa) manure than early spring or fall application. Rates could be fine‐tuned to match crop N demand using the presidedress nitrate test (PSNT) if: (i) the yield response function to sidedress rate is consistent and (ii) yield and PSNT are positively correlated. To optimize application rate and method, we measured corn (Zea mays L.) grain yield response to in‐row injection (INJ) and topdress (TD) of liquid swine manure (LSM) sidedressed at different rates on clay loam (51‐cm rows in 1999) and silt loam (75‐cm rows from 2000–2002). Yields exceeded local long‐term averages with INJ in all but the wettest year, were variable with TD, and were 2 Mg ha−1 greater with INJ than TD at 37.4 m3 LSM ha−1. From the quadratic yield response to sidedress injection rate, optimal rate (to achieve 95% maximum yield) ranged from 38 to 63 m3 ha−1 (plot‐scale data; four 6‐m sections per plot) and 37 to 49 m3 ha−1 (field‐scale data; 0.2‐ha plots). Yields were correlated with the PSNT (r = 0.75 for no LSM sidedress; r = 0.24 for all treatments). Given the consistent yield response to sidedress INJ rate and accurate (correct 88% of the time) PSNT‐based predictions of additional N requirements (from comparisons of N fertilizer recommendation and relative yield), sidedress injection of LSM using the PSNT to fine‐tune rates according to crop N requirements can be considered as a best management practice.

Nitrate leaching as affected by liquid swine manure and cover cropping in sandy soil of southwestern Ontario

To assess the risk that liquid swine manure (LSM) application posed to groundwater quality and determine how to manage excess nitrates, LSM pre-plant injected at 75% (LSMlow) and >100% (LSMhigh) of corn (Zea mays L.) N requirements was compared to inorganic fertilizer (Fert), with (RC) or without (NC) a rye (Secale cereale L.) cover crop in 2 dry years (1999, 2001) and 1 wet year (2000) on sandy soil in Ontario. Corn yields in LSM and Fert treatments were comparable each year. When drainage potential was high, solution nitrates below the root zone in Fert (14 mg L-1) > LSM (7 mg L-1) in 1999, but in LSM (39 mg L-1) > Fert (13 mg L-1) in 2000. Occasionally in 2001, solution nitrates in LSMhigh > LSMlow and/or Fert plots, but drainage potential was low. Earlier N application in LSM (pre-plant) than Fert (77% of N sidedressed) plots in relation to rain events may have increased solution nitrates in LSM plots in 2000. Rye cover reduced solution nitrates from 8.8 mg L-1 (NC) to 4.3 mg L-1 (RC, average of all dates), regardless of nutrient source. In-season risk of NO3 leaching can be reduced by split application of N between pre-plant and sidedress, while overseeding cereal rye into standing corn minimizes leaching post-harvest (fall and spring). Key words: Zea mays, Secale cereale, pre-sidedress nitrate test, swine manure, nitrate leaching

Nitrate Leaching and Nitrogen Budget as Affected by Maize Nitrogen Rate and Soil Type

AbstractLeaching loss as nitrate (NO3) is a growing concern because of its potential effect on water resources. Leaching of NO3 with drainage water from subsurface‐drained field plots seeded to maize (Zea mays L.) in 1992, 1993, and 1994 was measured on two soil types (a clay loam and a loamy sand) and for three N fertilization rates (22, 100, and 134 kg N ha−1). The 100 kg ha−1 rate was based on the results of a presidedress nitrate test (PSNT). Nitrate nitrogen (NO3‐N) leaching was similar between fertilizer N treatments at both sites in 1992, the first year after sod plowdown, but concentrations were greater than 10 mg L−1. For the subsequent two years, losses were similar for the 22 kg N ha−1 and the PSNT‐based treatments, but significantly higher for the 134 kg N ha−1 treatment on the clay loam. On the loamy sand, losses increased from the lowest to the highest N rate. Nitrate leaching losses were consistently higher on the loamy sand than on the clay loam. The N budget results showed that the 134 kg N ha−1 rate had the highest residual soil NO3‐N in the three years at both sites. On the clay loam, significant N losses occurred from denitrification following alfalfa plowdown and the subsequent fall and spring. Results indicate that N use efficiency rapidly decreases with overfertilization, even with N fertilization rates that only slightly exceed (134%) crop requirements. The PSNT‐based rate reduced N leaching losses while maintaining maize yields.

Hybrid and Nitrogen Source Affect Yield and European Corn Borer Damage

ABSTRACT Transgenic corn plants that contain cry proteins (Cry1Ab, Cry1Ac, and Cry9C) of Bacillus thuringiensis (Bt) offer corn (Zea mays L.) growers a more practical and environmentally friendly solution to manage European corn borer (ECB) (Ostrinia nubilalis Hübner) induced loss. Bt corn has demonstrated such promising initial results that it may be susceptible to ECB resistance from overuse. The objective of this study was to investigate nitrogen (N) source effects on ECB damage on continuous corn yield. The effects of N source on soil NO3 −-N, plant height, 2nd generation ECB damage, and grain yield were investigated on a Quakertown silt loam (Fine-loamy, mixed, mesic, Typic Hapludult) from 1995 to 1998. Based on ECB damage observations in 1995 and 1996, plots were split in 1997 and corn isolines were evaluated to study the ECB and yield response to Bt corn. Corn yield did not respond to manure plus sidedress N over the 4-yr period of this study because soil N levels were adequate without sidedress N, as indicated by the pre-sidedress nitrate test (PSNT). Second generation ECB damage was greater in manure plots in all 4-yr. In 1997, an outbreak year, and 1998, an endemic year, Bt corn and manure yielded 19 and 7% greater than non-Bt corn and manure. Our findings suggest that Bt corn is of significant value on land receiving manure in continuous corn production where ECB damage is high.

Spatial variability of early season nitrogen availability indicators in corn

The pre‐sidedress nitrate test (PSNT), a soil test used to refine sidedress fertilizer nitrogen (N) recommendations in corn (Zea mays L.), has shown great potential to reduce the excessive use of N fertilizer in corn production systems in the Northeast. The research reported in this paper evaluated the application of the PSNT to site‐specific management by investigating the spatial variability of several early season soil and plant indicators of N availability in a uniformly managed 16‐ha no‐till corn production field. The spatial variation in PSNT nitrate concentrations, total organic carbon (C) and N in the soil, and corn biomass yield and N content at the fifth leaf development stage were characterized from 189 samples taken during the 1994 growing season on a triangular grid with a 30 m minimum separation distance. There were no significant correlations found between any of the variables studied. All the variables studied were normally distributed with the exception of total organic C and biomass yield, both of which approximated a log‐normal distribution. Geostatistical analysis revealed significant spatial variation and spherical semivariogram models were developed for each variable. Results suggest that the average minimum grid size used in this study (30 m) may not have been adequate for an accurate estimation of nugget semivariance in total soil C and N and corn tissue N concentration. Plant indicators exhibited landscape features influencing biomass production and N uptake that were not revealed by the soil variables studied. These results illustrate the potential utility of integrating soil and plant productivity indicators to identify and address limitations to crop production using site‐specific management.

Overseeding rye into corn reduces NO3 leaching and increases yields

Non-irrigated corn (Zea mays L.) produced on coarse-textured soils during droughty years can result in excess NO3 available for leaching. To evaluate the effect of overseeding cereal rye (Secale cereale L.) into corn on yields, NO3 leaching and a pre-sidedress nitrate test (PSNT), we broadcast rye seed (Aug. 1993, 1994 and 1995) into conventional tillage (CT) and no-tillage (NT) corn receiving six fertilizer N rates. There was no corn yield penalty with the cover crop. Corn grain yields and the extent to which NO3 leaching was reduced by the rye cover depended on rainfall. With the rye (compared with no rye) subsoil solution NO3 concentrations were: unchanged (fall 1994) following above normal rainfall and corn yields; reduced by 8 mg NO3N L−1 (fall 1995) following intermediate rainfall and yields; and reduced by 28 mg NO3-N L−1 (fall 1993) and 11 mg NO3-N L−1 (spring 1994) following the driest growing season (average of CT and NT). Improved N availability with the rye was detected by a PSNT under CT, but not under NT. Therefore sidedress N rates can be adjusted for release of rye residue-N under CT, and potential NO3 contamination of groundwater can be reduced by overseeding winter rye into both CT and NT corn systems. Key words:Zea mays, Secale cereale, pre-sidedress nitrate test, tillage, nitrogen fertilization

Implications of Nitrogen Management Strategies for Nitrate Leaching Potential: Roles of Nitrogen Source and Fertilizer Recommendation System

AbstractUsing the soil‐based pre‐sidedress nitrate test (PSNT) rather than the yield‐goal‐based cropping and manure history (CMH) to recommend N for corn (Zea mays L.) frequently results in less N applied. Our objectives were (i) to determine if this reduction in N application substantially reduces the potential for N leaching and (ii) to compare dairy manure and commercial fertilizer as N sources, both within PSNT‐based systems. The 4‐yr field study included (i) a control (no manure or N fertilizer), and three N fertilizer rates based on (ii) PSNT, no manure added (PSNT−M); (iii) cropping and manure history (CMH), no manure added; and (iv) dairy manure application with additional sidedress N if recommended by the PSNT (PSNT + M). The PSNT − M treatment received 112 kg N ha−1 in 1990 and 123 kg N ha−1 in subsequent years, while the CMH treatment received 168 kg N ha−1 in all 4 yr. Corn yield, N uptake (defined as net aboveground N accumulation), spring and fall soil NO‐3 levels, and overwinter NO3‐N losses were measured. Silage yields of PSNT + M generally were greatest (average of 16.5 Mg ha−1), followed by PSNT−M and CMH treatments, which were similar (14.8 Mg ha−1). The CMH system resulted in the highest soil NO3‐N levels (to 120 cm) at harvest and greatest overwinter net profile NO3‐N loss (average 66 kg ha−1). The results indicate (i) a reduced residual N after harvest and therefore reduced potential for N leaching when using the PSNT for N recommendations and (ii) similar or higher yields using manure compared with commercial fertilizer.

Use of Pre-sidedress Nitrate Test and SPAD Meter to Evaluate Nitrogen Needs of Peppers

Hot cherry peppers were grown after incorporation of the following three winter cover crop regimes in Summer 1994—hairy vetch (Vicia villosa) plus winter rye (Secale cereale), hairy vetch alone, and no cover crop. For each main effect there were three N rates applied to peppers in three applications over the course of the season: 0, 85, and 170 kg·ha–1. The pepper yield was significantly higher with hairy vetch plus rye than rye alone or no cover crop. There was also no significant yield increase with the addition of N fertilizer to the peppers grown with hairy vetch. Soil nitrate–N levels taken just prior to N sidedress were significantly higher in plots that had hairy vetch plus rye compared to other treatments. There was also a significant linear relationship of the soil nitrate–N levels among the three N rates. Based on the results of this study, sidedressing peppers would be recommended when soil nitrate levels are above the 25 ppm that is the current threshold for other crops. SPAD readings were taken several times during the season. There was a high correlation of SPAD readings to pepper yield very early and very late in the season. The correlation of SPAD readings to pepper yield was poorest when taken at the time of N sidedress.

Use of Pre-sidedress Nitrate Test and SPAD Meter to Evaluate Nitrogen Needs of Peppers

Hot cherry peppers were grown after incorporation of the following three winter cover crop regimes in Summer 1994—hairy vetch (Vicia villosa) plus winter rye (Secale cereale), hairy vetch alone, and no cover crop. For each main effect there were three N rates applied to peppers in three applications over the course of the season: 0, 85, and 170 kg·ha–1. The pepper yield was significantly higher with hairy vetch plus rye than rye alone or no cover crop. There was also no significant yield increase with the addition of N fertilizer to the peppers grown with hairy vetch. Soil nitrate–N levels taken just prior to N sidedress were significantly higher in plots that had hairy vetch plus rye compared to other treatments. There was also a significant linear relationship of the soil nitrate–N levels among the three N rates. Based on the results of this study, sidedressing peppers would be recommended when soil nitrate levels are above the 25 ppm that is the current threshold for other crops. SPAD readings were taken several times during the season. There was a high correlation of SPAD readings to pepper yield very early and very late in the season. The correlation of SPAD readings to pepper yield was poorest when taken at the time of N sidedress.