| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a USDA-ARS, P.O. Box E, Fort Collins, CO 80522
b Colorado State Univ., Arkansas Valley Res. Cent., 27901 Road 21, Rocky Ford, CO 81067
* Corresponding author (adhalvor{at}lamar.colostate.edu)
Received for publication July 18, 2001.
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Abbreviations: DM, dry matter • Ndff, nitrogen derived from fertilizer • -NF, no nitrogen fertilizer applied • +NF, nitrogen fertilizer applied • NFUE, nitrogen fertilizer use efficiency • NUE, nitrogen use efficiency
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
The Arkansas River Valley in southeastern Colorado is a major production area for melon (Citrullus lanatus Thunb. and Cucumis melo L.), onion, and other vegetable crops produced in rotation with alfalfa (Medicago sativa L.), corn, sorghum (Sorghum bicolor L.), winter wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.]. A recent water survey of the Arkansas River Valley by the Colorado Department of Public Health and Environment (Austin, 1997) showed that NO3–N levels were high (>10 mg L-1) in 14% of the wells tested in 1994, with most (47%) of the high-testing wells in Otero County, a major vegetable-producing area. Onion is produced in this area with high N fertilizer rates (100–300 kg N ha-1) applied by growers to optimize yields without regard for soil test NO3–N levels (Bartolo et al., 1995, 1997). Ells et al. (1993) reported no response of onion to N fertilization in southeastern Colorado and found that N was lost from the root zone with furrow irrigation.
Soil test results from the lower Arkansas Valley area and Otero County indicate high levels of residual soil NO3–N (L. Sutherland, personal communication, 1998). In addition, salinity of the irrigation water delivered from the Arkansas River is relatively high, thus requiring frequent irrigation to minimize salt damage to emerging onion seedlings (Miyamoto, 1989) and ensure good stand establishment in this low-rainfall, high-evapotranspiration area. The NO3–N content of the irrigation water varies over the season, ranging from 1 to 4 mg L-1 in recent years. Most soils in the area are generally well drained but have shallow water tables (often within 4 m of the soil surface). Because of these factors, there is potential for NO3–N contamination of ground water in this area.
Shock et al. (2000) examined the use of sugarbeet to recover residual fertilizer N remaining in the soil profile following onion. They found that optimum sucrose production was possible without N fertilization following onion when sufficient residual N was present in the soil profile. Sugarbeet recovered a significant portion of the fertilizer N that was not used by the previous onion crop. Hills et al. (1983) also reported that sugarbeet recovered more residual soil profile N than corn. Pelter et al. (1992) recommended growing deep-rooted crops such as wheat (Triticum aestivum L.) or corn following onion to recover residual fertilizer N from the onion crop.
Little information is available on NFUE of onion (Sammis, 1997; Brown et al., 1988b), especially using 15N-labeled fertilizer to determine NFUE. Onion is shallow rooted (generally <50 cm deep); therefore, NFUE is expected to be low in furrow-irrigated fields. The objectives of this study were to determine onion NFUE of N fertilizer applied during onion establishment and vegetative growth stages using 15N-labeled fertilizer and to determine the recovery of residual fertilizer N by corn following onion in rotation.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
A randomized complete block design with four replications was used. Each N plot was four rows wide, with two onion rows (46 cm apart) per bed. The outside rows of each plot were located on half of the adjacent onion bed, with the two center rows of each plot located on the same bed. Furrow to furrow distance was 112 cm. The center two rows of each plot were used for plant sampling.
The 224 kg N ha-1 treatment was applied in split applications of 112 kg N ha-1 on 18 May 1998 and 25 June 1998. For the 15N-labeled plots, the 112 kg N ha-1 KNO3 fertilizer labeled with 15N was applied only once for each application date to the center two onion rows. Unlabeled KNO3 fertilizer was applied at the alternate application date to bring the total split application to 224 kg N ha-1. Unlabeled KNO3 was applied to the two outside rows of the 15N-labeled plots. All of the N fertilizer was band-applied as a liquid solution at a depth of 5 cm on the edge of the raised bed, approximately midway between the bottom of the irrigation furrow and the top of the bed using the "Follett et al. method" (Follett, 2001). Unlabeled N fertilizer was similarly applied to the two outside-border rows of onion in each plot receiving N fertilizer. Plot length for the 15N-labeled plots was 244 cm for the 18 May application date and 183 cm for the 25 June application date. In addition, nonlabeled N fertilizer plots (224 kg N ha-1) with split applications of N were included for biweekly plant sampling and final yield determination. The no fertilizer N (-NF) and nonlabeled fertilizer N (+NF) plots were each 305 cm long. Plot length varied among treatments because of the number of plant sampling times for each treatment.
Onion (variety X202, a sweet Spanish type) was seeded on 25 Mar. 1998 on raised beds with in-row onion spacing of about 7 to 8 cm and a plant population of about 235000 plant ha-1. A uniform stand of onion was established in the plot area. Onion was furrow-irrigated 10 times during the growing season. During the 4, 8, 13, and 24 April irrigations, only enough water was applied to wet the onion row to insure good onion establishment in this low-rainfall, high-evapotranspiration production area. Subsequent irrigations on 19 May, 3 and 25 June, 5 and 14 July, and 20 August 1998 had approximately 5 cm of water applied at each irrigation. Assuming a water application efficiency of 40 to 70% for furrow irrigation with siphon tube (Martin et al., 1991), 2 to 3.5 cm of water was probably retained in the field with each irrigation. Irrigation runs were <120 m. Based on the experiences of the authors, the onion plots were irrigated only when water was needed to avoid stress on the onion plants, and water application was considered conservative compared with local grower practices. The NO3–N concentration in the irrigation water ranged from 1.7 to 2.6 mg L-1. Based on NO3–N analyses of the irrigation water applied, <10 kg N ha-1 was available in the irrigation water during the onion-growing season.
Onion samples (four adjacent plants from each of the two center rows per plot) were collected at 2-wk intervals from the -NF and +NF plots for cumulative growth and N uptake determination from 18 May until harvest (15 Sept. 1998). At harvest, two rows, approximately 1 m long, were harvested from each -NF and +NF plot. In the 18 May 15N-labeled plots, plant samples (four adjacent plants from each of the two center rows per plot) were collected on 24 June, 8 July, and 15 September. In the 25 June 15N-labeled plots, plant samples were similarly collected on 21 July and 15 September. At each sampling, onion was separated into tops and bulbs for dry matter (DM) and N uptake determination. The onion parts were weighed to determine fresh weight and then dried at 60°C to determine DM and water content.
Soil samples from the center of the onion bed of each plot were collected from the 0- to 180-cm profile at planting (23 Mar. 1998) and after onion harvest (17 Sept. 1998) in 30-cm increments for determination of NO3–N content. Soil samples from the bed center of each plot were also collected on 18 May in 30-cm increments to a 60-cm depth for determination of NO3–N content. After onion harvest, soil samples were collected at 15- or 30-cm depth increments from the center of the irrigation furrow, fertilizer band, 15 cm from onion row toward center of bed, and bed center of all plots for 15N analysis.
Soil NO3–N was determined by Cd reduction with an autoanalyzer (Lachat Instruments, 1989) on a 5:1 extract/soil ratio using 1 M KCl extracting solution. Soil test results from the plot area indicated soil pH ranged from 7.6 to 7.8, soil electrical conductivity from 0.1 to 0.2 S m-1, and soil organic matter was 15 g kg-1. Depth to water table at the Arkansas Valley Research Center ranges from 4.5 to 6 m. In November 1997, 49 kg P ha-1 was applied to the plot area as monoammonium phosphate (11–52–0) fertilizer and incorporated by plowing. Before onion in 1998, the plot area was fallowed most of the summer of 1997, Zinnias (Zinnia elegans Jacq.) was produced in 1996, and carrot (Daucus carota L.) was produced in 1995.
The dry plant and soil samples collected for 15N analysis were ground to pass a 150-µm screen and analyzed using a Carlo Erba C/N analyzer (Haake Buchler Instruments, Saddle Brook, NJ)1 for total N concentration. The Carlo Erba was interfaced to a VG micromass 903 isotope-ratio mass spectrometer (VG Isogas, Cheshire, England) for determination of 15N concentration in the soil and plant samples. Samples from the nonlabeled fertilizer plots were also analyzed for 15N to obtain the natural abundance level of 15N in the system. Soil N derived from fertilizer (Ndff) based on 15N analysis is expressed as a percentage of the total soil N at the specified depth.
Nitrogen use efficiency of the onion crop was estimated by dividing the total N uptake of onion by the amount of N available to the crop (soil NO3–N in 0–60 cm depth plus fertilizer N applied). This fraction was multiplied by 100 to obtain percent NUE. The N added through the irrigation water was not included in the calculation because of the small quantity present in the irrigation water and the uncertainty of how much was actually retained in the soil.
Corn (hybrid DK642 IMI) was planted 10 May 1999 on the 1998 onion N plots with a 76-cm row spacing and no additional N fertilizer applied. Seeding rate was 76800 seeds ha-1. The 1998 onion plot area was disked at a shallow depth (<7.5 cm) and harrowed once before reridging and corn planting. Soil samples were collected from each plot within the area occupied by the center two rows of onion in 1998 on 1 April and 9 November 1999 for NO3–N and 15N analysis. The corn plots were irrigated using siphon tubes on 22 June, 9 July, 20 August, and 22 September 1999 with approximately 10 cm of total water application to the plot area with each irrigation. Water was applied to every second irrigation furrow in an attempt to improve NUE of corn (Lehrsch et al., 2001). Assuming a water application efficiency of 40 to 70%, 4 to 7 cm of the applied water was retained in the plot area with each irrigation. The NO3–N concentration of the irrigation water ranged from 1.9 to 2.8 mg L-1. The total amount of NO3–N available in the irrigation water during the corn growing season was <9 kg N ha-1. Corn plant samples were collected from a minimum 1-m2 area of each N treatment on 25 Aug. 1999 for total biomass yield, N uptake determination, and 15N analysis. Corn grain yields were estimated on 5 Oct. 1999 by harvesting the ears from a 2.5-m2 or larger area of each plot. Average yield per N treatment was determined, including grain 15N content.
Precipitation during the 1998 onion-growing period (25 March to 17 September) totaled 221 mm. During the noncrop period from October 1998 through March 1999, an additional 125 mm of precipitation was received. Above-average rainfall (466 mm) fell during the 1999 corn-growing season (April through October). The annual precipitation was 371 mm for 1998 and 507 mm for 1999. The 100-yr average annual precipitation for the site is 301 mm. Both growing seasons had above-average precipitation.
Analysis-of-variance procedures were conducted using SAS statistical procedures (SAS Inst., 1991). All differences discussed are significant at the P 
0.05 probability level unless otherwise stated. An LSD was calculated only when the analysis-of-variance F-test was significant at the P 0.05 probability level.
|
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
|
|
|
|
|
Based on the 15N analysis of onion plants harvested on 24 June (37 d after 18 May 15N application), the Ndff in the tops and bulbs was 30 and 28%, respectively. On 8 July (51 d after 15N application), the Ndff in the tops and bulbs was 17 and 16%, respectively. The decline in Ndff is likely due to the increased availability of residual soil NO3–N as the onion root system expanded. At final harvest on 15 September (120 d after 15N application), the Ndff in the tops and bulbs was 13 and 15%, respectively.
Based on the 15N analysis of onion plants harvested on 21 July (27 d after the 25 June 15N application), the Ndff in the tops and bulbs was 26 and 25%, respectively. At final harvest on 15 September (82 d after 15N application), the Ndff in the tops and bulbs was 25 and 26%, respectively. The final-harvest Ndff data show that the N fertilizer applied on 25 June was more effective in satisfying the onion plant N needs than the 18 May N application.
Based on the total top-plus-bulb N uptake, NFUE was 11% for the 18 May application and 19% for the 25 June application date. The onion NFUE of the 224 kg N ha-1 applied for the season was about 15%. Thus, 85% of the fertilizer N remained in the soil profile or was otherwise unaccounted for after the onion harvest. These NFUE values are slightly lower than those reported by Brown et al. (1988b) in Idaho of 19 to 26% for high N rates, depending on method of N application.
Nitrogen use efficiency of onion, based on soil NO3–N (0–60 cm depth) plus fertilizer N applied (total of 579 kg N ha-1), was very low in this study. Total N uptake in tops plus bulbs, based on DM accumulation and plant N concentration, was only 80 kg N ha-1, with a NUE of 13.8% or 9.2 kg DM ha-1 kg-1 available N for the 224 kg N ha-1 fertilizer treatment. With no N fertilizer applied, NUE was 17% or 12.5 kg DM ha-1 kg-1 available N.
Nitrogen use efficiency based on bulb N removal or harvested portion of the crop was 7.3 kg DM ha-1 kg-1 available N for the 224 kg N ha-1 fertilizer treatment. Total NUE was 11.4% for N removed in bulbs. With no fertilizer N applied, NUE was 12.8% for N removed in bulbs. Nitrogen use efficiency is low in this study because of the high level of available N in the root zone at planting compared with the total amount of N taken up by the onion plants.
Plant samples were collected from inside and outside of the 15N microplot area to detect potential lateral movement of 15N fertilizer and to compute relative fraction of plant 15N inside and outside of the microplots. Results of these measurements (Follett, 2001) show essentially no lateral movement of 15N across the irrigation furrow between onion beds. Average maximum detectable distance that the 15N had moved along the rows, beyond the microplot ends, as a result of cultural practices and irrigation was 0.4 and 0.3 m for the 18 May and 25 June applications of 15N fertilizer, respectively.
Soil samples collected after onion harvest from the 15N-labeled plots show that the N fertilizer applied had moved through the soil profile with irrigation water. The highest concentration of Ndff in the soil was located in the upper 30 cm near the center of the onion bed (Fig. 5 , average of both N application dates). The amount of Ndff was very low in the soil samples collected from the center of the irrigation furrow. The amount of Ndff remaining in the 0- to 60-cm soil profile in the fertilizer band area was slightly higher than in the irrigation furrow but much lower than that found in the onion bed 15 cm in from the onion row (toward bed center) and in the bed center. These data show that the labeled fertilizer had moved from the fertilizer band toward the bed center with the irrigation water, with the highest 15N levels found near the soil surface and levels decreasing with soil profile depth. This is consistent with the soil NO3–N movement toward bed center observed by Brown et al. (1988b) in Idaho. Labeled 15N fertilizer in our study was also found at the 150- to 180-cm soil depth of soil cores taken from the bed center, thus indicating deep leaching of N fertilizer and N loss from the root zone of onion.
|
Residual soil NO3–N levels following onion harvest remained high in the 0- to 60-cm profile and in the 0- to 180-cm profile (Table 1). The -NF plots had soil NO3–N levels that were 300 kg ha-1 NO3–N less in the 0- to 180-cm profile in September 1998 than was present in March 1998. The +NF plots had gained about 100 kg ha-1 NO3–N from March to September 1998. The greater amount of NO3–N in the 120- to 180-cm soil depth in September 1998 after onion harvest compared with March 1998 indicates that NO3–N from the shallower soil depths had moved to the deeper soil depths in the profile during the growing season, which is supported by the soil 15N data in Table 2 and Fig. 5. Sufficient residual soil NO3–N was present after onion harvest to produce a high-yielding corn crop the following year without further N fertilization. The spatial variability of the residual soil NO3–N may be high under the onion bed, as documented by the distribution of fertilizer 15N in the onion bed (Fig. 5).
|
The 1999 corn grain yields on 10 Oct. 1999 following the 1998 onion crop were not significantly different between the -NF and +NF treatments, with yields (155 g kg-1 moisture content) of 15.0 and 14.7 Mg ha-1, respectively. Total grain N uptake was not significantly different between the two N treatments, with N uptake levels of 158.3 and 158.5 kg N ha-1 for the -NF and +NF treatments, respectively. Based on 15N analysis, the amount of N fertilizer recovered in the +NF plots by corn grain in 1999 was 18.8 and 15.0 kg N ha-1 for the 18 May and 25 June 1998 15N applications, respectively, which were significantly different at P = 0.098. Of the 224 kg N ha-1 applied to the onion crop in 1998, about 15% of the N was removed in the corn grain in 1999. With the high levels of available soil NO3–N at planting (Table 1), and addition of a small amount of NO3–N with the irrigation water, the low recovery of the N fertilizer by the onion (15%) and corn (24%) crops was probably to be expected. Approximately 39% of the N fertilizer applied in 1998 was taken up by the two crops in this high residual soil N environment. The 15N analysis on soil samples collected after corn harvest shows that the highest concentration of N fertilizer was still in the 0- to 60-cm depth (Table 2). The average concentration of Ndff in the soil profile (0–180 cm depth) in November 1999 was about 25 to 50% less than that found following onion harvest in September 1998.
Residual soil NO3–N remained high in the 0- to 180-cm profile following corn harvest (Table 1). The soil NO3–N levels were similar between the -NF and +NF treatments after corn harvest in 1999. The reason for the large increase in NO3–N level in the -NF plots and not the +NF plots from April to November 1999 is not understood. Although soil-sampling location was at the center of the onion bed in 1998, land preparations (reridging) for the 1999 corn crop resulted in less exact sampling locations in 1999. This, along with the spatial variability (Fig. 5) that was encountered, may have caused the high and variable soil NO3–N levels observed, especially for the fall 1999 soil sampling. More important is the data in Table 2, which shows that fertilizer N (using 15N tracer) had moved downward in the soil profile to a depth of at least 180 cm by the fall of 1998 and remained at that depth through the fall of 1999. Nitrogen mineralization probably contributed some of the increased soil NO3–N. Irrigation water had <9 kg N ha-1 available during the corn growing season. A rise in the shallow ground-water table during the corn irrigation season could have moved soil NO3–N positioned above the water table upward into the root zone. Martin et al. (1991) point out that NO3–N can move upward into the root zone from shallow water tables. At the November 1999 soil sampling, the soil in the 150- to 180-cm depth was near saturation because free water was visible in the soil sample. Depth to the water table was apparently very shallow. Therefore, upward movement of NO3–N from deeper soil depths may explain some of the high and variable soil NO3–N levels observed after the 1999 corn harvest. Sufficient soil NO3–N remained after corn harvest to produce another high-yielding corn crop with minimal or no N fertilizer needed to optimize grain yields.
|
SUMMARY AND CONCLUSIONS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Recovery by corn in 1999 of fertilizer N applied to onion in 1998 was also low, only 24%. Total recovery of the fertilizer N by the two crops was 39%. Consequently, if an alternative deep-rooted crop that more effectively scavenges residual fertilizer N can be grown following onion in rotation, it needs to be considered in place of corn to reduce the risk of NO3–N contamination of ground water. An estimated 158 kg N ha-1 was removed in the corn grain while 213 kg N ha-1 was removed in the total corn biomass. Therefore, removal of the corn as silage would remove more N from the system than removal as grain.
Fertilizer N applied on the edge of the irrigation furrow near the onion row was moved toward the center of the onion bed with the irrigation water. Planting corn on the onion beds in close proximity to the NO3–N concentration may have improved fertilizer N recovery by the corn crop in this study. This would have required narrow corn row spacing but would have positioned the corn roots near the soil zone with the highest levels of residual fertilizer N. The results from this study indicate that some of the N fertilizer applied to the onion was leached out of both the onion and corn root zones. Onion growers in southeastern Colorado need to delay N fertilizer application until near onion bulbing and base N fertilization rates on available soil NO3–N in the onion root zone to improve NFUE and reduce the potential negative impacts of NO3–N on ground water quality. Soil testing before N fertilizer application to crops in the Arkansas River Valley is recommended to improve NUE and reduce the quantity of NO3–N available for leaching. Slow-release N fertilizers (Brown et al., 1988a, 1988b) and growing cover crops between major crops should be considered to reduce NO3–N leaching potential. Changing to more efficient irrigation methods, such as sprinkler or drip, should improve water management, reduce NO3–N leaching potential, and improve NUE.
|
ACKNOWLEDGMENTS |
|---|
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
1 Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the authors or the USDA-ARS. 
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  A. D. Halvorson, M. E. Bartolo, C. A. Reule, and A. Berrada Nitrogen Effects on Onion Yield Under Drip and Furrow Irrigation Agron. J., June 16, 2008; 100(4): 1062 - 1069. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. D. Halvorson, F. C. Schweissing, M. E. Bartolo, and C. A. Reule Corn Response to Nitrogen Fertilization in a Soil with High Residual Nitrogen Agron. J., July 13, 2005; 97(4): 1222 - 1229. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Crop Science | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
