Agronomy Journal 92:10-15 (2000)
© 2000 American Society of Agronomy
SOIL FERTILITY
Sugarbeet Nitrogen Uptake and Performance Following Heavily Fertilized Onion
Clinton C. Shocka,
Majid Seddigha,
Lamont D. Saundersa,
Timothy D. Stiebera and
John G. Millera
a Malheur Exp. Stn., Oregon State Univ., Ontario, OR 97914 USA
clinton.shock{at}orst.edu
Received for publication October 7, 1998.
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ABSTRACT
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Crop over-fertilization has economic and environmental consequences. Sugarbeet (Beta vulgaris L.) N fertilizer requirements could be lower than expected when planted after shallow rooted onion (Allium cepa L.). Sugarbeet was planted on an Owyhee silt loam (coarse-silty, mixed, mesic Xerollic Durorthid) for 2 yr, where the previous onion crop had received 0, 60, 120, 240, and 480 kg N ha-1. Soil nitrate and ammonium were measured in 0.3-m increments to 1.8 m deep after harvesting onion, and before and after growing sugarbeet. Nitrogen uptake by plant parts, and beet and sucrose yields, were measured. Averaged across years, sugarbeet recovered 336, 316, 338, 400, and 505 kg N ha-1 when N fertilizer of the previous onion crop was 0, 60, 120, 240, and 480 kg ha-1, respectively. The corresponding reduction in available inorganic N from the top 1.8 m of the soil during sugarbeet growth was 27, 82, 62, 120, and 152 kg ha-1. Nitrogen recovered by sugarbeet was largely supplied by sources other than preplant available N. Recovered sucrose yield was near maximum when the N rate on the previous onion crop was 240 kg ha-1, which resulted in preplant NO3–N levels of about 70 kg ha-1 in the top 0.6 m of the soil. Sucrose yield did not improve when petiole NO3–N in late June exceeded 6 g kg-1. In conclusion, sugarbeet may not require fertilizer N when grown after onion fertilized with about 240 kg N ha-1.
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INTRODUCTION
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S UGARBEET contains 4 to 7 kg N per Mg of fresh beet produced (Carter et al., 1974, 1976; Halvorson et al., 1978). Compared with other crops such as corn (Zea mays L.), deep-rooted sugarbeet scavenges the soil profile for residual N and recovers considerably more soil N and relies less on fertilizer N (Hills et al., 1983). Also, because of the negative effects of high soil N level on sucrose concentration and recovery, optimum soil N levels for sucrose production are usually lower than for beet yield (Adams et al., 1983; Anderson and Peterson, 1988).
Optimum N fertilization rates for sugarbeet depend on the region. In a long-term study in Montana, the greatest sucrose yield was obtained with 112 kg fertilizer N ha-1, and NO3–N accumulated in the soil when more than 168 kg N ha-1 was applied (Halvorson and Hartman, 1975). Sucrose yields in Montana were near maximum when spring soil NO3–N plus added N was about 200 to 225 kg ha-1 (Halvorson et al., 1978). In Texas, sucrose yield did not respond to fertilizer N when NO3–N in the top 1.2 m of the soil profile was 180 kg ha-1 at planting (Winter, 1990). In Nebraska, when 35 to 45 kg NO3–N ha-1 was available in the top 1.8 m of the soil at planting, 160 to 220 kg fertilizer N ha-1 was needed to optimize sucrose yield (Anderson and Peterson, 1988). In Wyoming, when soil NO3–N at 0.3 m was about 9 mg kg-1, sucrose yield was maximum with 170 kg fertilizer N ha-1 (Lauer, 1995). Soil N effects on beet and sucrose yield also depend on soil moisture availability. In general, sugar yield increases with higher N rates when soil moisture is not restricting beet growth (Holmes and Devine, 1976; Holmes and Whitear, 1976; Winter, 1990).
Carter et al. (1974) recognized the importance of soil N mineralization for sugarbeet production in southern Idaho and reported that sucrose yield was maximum when NO3–N plus mineralized N at the top 0.4 m of the soil was about 250 to 300 kg ha-1. Optimum N fertilization rates for maximum sucrose yield in southern Idaho could be closely predicted based on measured residual NO3–N and measured or predicted mineralizable N (Carter et al., 1976). According to their study, farmers in that region applied considerably more N fertilizer than required for maximum sucrose production.
In eastern Oregon, sugarbeet is usually grown under furrow irrigation after heavily fertilized onion or potato (Solanum tuberosum L.). Of the 300 kg N ha-1 typically applied to onion under furrow irrigation conditions in southeastern Oregon and southwestern Idaho, only 110 kg is removed with the crop (Shock and Stieber, 1991, p. 182–186), and the residual NO3–N has the potential for contaminating ground water (Brown et al., 1988). Northeastern Malheur County in eastern Oregon was declared a Groundwater Management Area because of the presence of ground water nitrate above the U.S. drinking water standard (Oregon Dep. of Environmental Quality, 1991). The shallow aquifers are susceptible to contamination since their level fluctuates with the onset and end of the irrigation season (Gannett, 1990). Ground water contamination with nitrate can be caused by N fertilizer applications exceeding crop needs and excessive irrigation. Nitrogen fertilizer application for onion production in eastern Oregon was estimated to exceed N removal by 207 kg ha-1 (Shock and Stieber, 1991). With appropriate N fertilization management, the deep-rooted sugarbeet crop has the potential to scavenge soil NO3–N and reduce ground water pollution (Hills et al., 1978).
We measured N uptake and performance of a sugarbeet crop following onion fertilized with different N rates in an attempt to determine if sugarbeet can be grown without additional N fertilizer after a heavily fertilized onion crop. Such information will be useful for developing N fertilizer recommendations for sugarbeet production that are both economically and environmentally sound.
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Materials and methods
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The study was conducted at the Oregon State University Malheur Experiment Station in eastern Oregon on an Owyhee silt loam (coarse-silty, mixed, mesic Xerollic Durorthid) soil. Sugarbeet cv. HM-PM9 was planted in April of 1991 and 1992 in plots where onion N fertility trials were conducted the previous summers. Onion was fertilized with 0, 60, 120, 240, and 480 kg N ha-1, and had been preceded by unfertilized winter wheat (Triticum aestivum L.) to reduce soil fertility differences. The soil was sampled during November of 1990 and 1991 in every plot in 0.3-m increments to 1.8 m deep. Each soil sample for the top 0.3 m of soil consisted of 20 subsamples collected randomly throughout each plot, whereas the samples for the other soil layers consisted of four subsamples. All soil samples were taken with a Giddings hydraulic soil probe (Giddings Machine Company, Ft. Collins, CO) and analyzed for NO3–N and NH4–N. The data were converted to kilograms available N per hectare using soil volume and bulk density. The soil organic matter content was 1.5% in 1991 and 1.6% in 1992.
Sugar beet was furrow-irrigated to meet crop water needs. Weeds, insects, and diseases were controlled using standard commercial procedures. In both years, the beet crop was harvested in late October. Two samples, consisting of seven randomly selected beets from the two central rows of each 8-row plot, were analyzed for sucrose, pulp nitrate, and conductivity. The day before beet harvest, 10 randomly selected plants from the middle two rows of each plot were dug by hand, washed, and separated into leaves, crowns, and beets. The leaves and crowns were weighed fresh, dried, weighed again, ground, and analyzed for Kjeldahl N. The beets were washed, weighed fresh, shredded, subsampled, dried, weighed again, ground, and analyzed for Kjeldahl N. Following the sugarbeet harvest, the soil in the middle of each plot was sampled and analyzed for NO3–N and NH4–N. Nitrate in the samples was determined using the chromotrophic acid method (modified using Sb) and read colorimetrically on a Milton Roy Model 401 spectrophotometer (Milton Roy, Rochester, NY). Ammonium was extracted with KCl and read colorimetrically on the spectrophotometer.
A randomized complete-block design with four replications was used. Individual plots were 15.2 m long and 4.5 m wide, and had 6 m between plots. Sugarbeet plots and row widths coincided exactly with onion rows and plots of the same size. The plot width accommodated eight rows of beets. Only beets in the middle 9.1 m of the center two rows were used to determine beet yield, beet quality, and N recovery. Beet yields were corrected for tare (dirt attached to the beet when harvested).
Regression analysis was performed within each year to test the effects of various N rates applied to the previous onion crop on performance of the following sugarbeet crop. Correlations between different variables of sugarbeet crop, with petiole nitrate N concentration measured on different dates in 1991 and 1992, were also tested. Both linear and quadratic models were used, and the significance of the regression was tested at the 0.01 and 0.001 levels of probability. Coefficients of determination were also calculated.
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Results
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Soil Available Nitrogen
After Onion Harvest
The effects of N rates on soil NH4–N at different depths were consistent between years (Table 1)
. Nitrogen rates applied on onion had relatively little effect on NH4–N at different soil depths. Averaged between years, total NH4–N for the top 1.8 m of the soil was 98 kg ha-1 following unfertilized onion, and ranged between 111 and 154 kg ha-1 for different N rates. Total NO3–N in the top 1.8 m of the soil was also similar between the 2 yr when up to 120 kg N ha-1 was applied. At N rates above 120 kg ha-1, considerably more residual NO3–N in the top 1.8 m of the soil was detected in 1990 than in 1991. Also, there were NO3 increases in the top 0.9 m of the soil when the N rate of the previous crop increased from 120 to 240 kg ha-1 in 1990, and from 240 to 480 kg ha-1 in 1991.
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Table 1 Effects of N rate applied to the previous onion crop on ammonia and nitrate measured at different soil depth before and after sugarbeet in two years
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Before Sugarbeet Planting
Little change in NH4–N levels of the top 1.8 m of the soil was observed after harvesting onion in the fall to spring before planting sugarbeet (Table 1). In contrast, NO3–N decreased considerably from fall to spring, especially at the higher N rates applied to the previous onion crop. For example, at 480 kg fertilizer N ha-1, NO3–N of the top 1.8 m of the soil dropped from 713 to 534 kg ha-1 between fall of 1990 and spring of 1991, and from 447 to 170 kg ha-1 between fall of 1991 and spring of 1992. Before sugarbeet planting, there was only 86 mm of precipitation during the 6 mo from October 1990 through March 1991, and 136 mm of precipitation from October 1991 through March 1992.
After Sugarbeet Harvest
Comparing NH4–N levels at different soil depths before and after the sugarbeet crop indicates that growing sugarbeet had little effect on soil NH4–N (Table 1). Variations for NH4–N among the N rates were also small at all soil depths. Averaged across all N rates, total NH4–N in the top 1.8 m of the soil after sugarbeet harvest was 112 kg ha-1 in 1991 and 126 kg ha-1 in 1992. In contrast, the sugarbeet crop reduced NO3–N levels from all soil depths in both years. For all N rates applied on the previous onion crop, total NO3 in the top 1.8 m of soil decreased more than 60% in 1991 and 40% in 1992 during sugarbeet growth.
In 1991, total NO3–N recovered after beet harvest, at all soil depth increments, increased as the N rate of the previous crop increased (Table 1). The rate of the increase was relatively small, as N rate on the previous crop increased from 60 to 240 kg ha-1, and was noticeably greater as the N rate was further increased to 480 kg ha-1. In 1992, the soil NO3–N concentration after beet harvest was relatively unaffected when the N rate of previous crop was increased from 60 to 240 kg ha-1, but increased as the N rate was further increased to 480 kg ha-1.
Dry Matter Accumulation and Nitrogen Uptake
Increasing N rates on the previous onion crop increased sugarbeet leaf and crown dry weights both years (Table 2)
. Compared with 1991, leaf dry weight was smaller and crown dry weight was greater in 1992. As N rate increased, beet dry weight decreased in 1991, but it increased in 1992. At the greatest N rate, beet dry weight was about 50% higher in 1992 than in 1991. The N rates had little effect on total dry weight in 1991, but total dry weight increased as N rates increased in 1992. Consequently, the proportion of beet dry weight to total dry weight decreased as N rate increased in 1991, but it was not affected in 1992.
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Table 2 Effects of N rate applied to the previous onion crop on dry matter accumulation, N concentration, and N uptake of sugarbeet in 1991 and 1992
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Nitrogen concentration of leaves, crown, and beet increased as N rate increased both years, with the greatest effect being on the crown (Table 2). In general, the N concentration of all plant parts was higher in 1991 than in 1992. Also, N uptake by leaves, beets, and total N uptake were considerably higher in 1991 than in 1992. Averaged across all N rates, total N uptake was 440 kg ha-1 in 1991 and 317 kg ha-1 in 1992.
Nitrogen Budget
Subtracting total available inorganic N (NH4–N + NO3–N) present in the top 1.8 m of soil after sugarbeet harvest from available inorganic N before planting estimates total N lost during sugarbeet cropping (Table 3)
. Total N supplied by sources other than the initial available N, as estimated by the difference between total N recovered by sugarbeet and total N lost from the top 1.8 m of soil during cropping, averaged about 290 kg ha-1 across years and fertilizer N rates (Table 3).
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Table 3 Nitrogen budget for unfertilized sugarbeets grown in 1991 and 1992 on plots where the previous onion crop was fertilized with different N rates
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Crop Performance
In 1991, increasing N rates on onion did not affect beet (fresh beets minus crown and leaves) or sugar yield, but increasing N rate decreased sucrose concentration, increased nitrate concentration in beets, and decreased the percentage of estimated sucrose recovery (Table 4)
. In contrast, increasing N rates on onion increased beet and sucrose yield in 1992, but did not affect sucrose concentration and sucrose recovery.
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Table 4 Effects of nitrogen rate applied to the previous onion crop on fresh beet yield, and sucrose concentration and recovery from fresh beets at harvest in 1991 and 1992
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Petiole Nitrate Concentration
In 1991, leaf and crown dry weights were positively correlated with petiole NO3–N concentration, while beet sucrose concentration was negatively correlated with petiole NO3 concentration (Table 5) . Beet dry weight, total dry weight, beet yield, and recovered sucrose yield were not correlated with petiole NO3–N concentration in that year. In 1992, except for the crown dry weight, all variables were correlated with petiole NO3 concentration.
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Table 5 Coefficients of determination for correlations between different variables of sugarbeet crop with petiole nitrate N concentration on different dates in 1991 and 1992
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Beet yield in 1992 reached a maximum when the petiole NO3–N concentration on the first date approached 6 g kg-1, and was relatively unaffected when the petiole NO3–N concentration further increased (Fig. 1)
. A similar trend was observed in 1991, although the relationship between petiole NO3 concentration and beet yield was not significant (Table 5). In contrast, beet sucrose concentration in both years decreased as petiole NO3–N increased up to 6 g kg-1. However, the rate of increase in beet yield was greater and the rate of decrease in sucrose concentration was smaller in 1992 than in 1991. Consequently, the yield of recovered sucrose was not affected by petiole NO3–N concentration in 1991 (Fig. 1). On the other hand, sucrose yield in 1992 increased as petiole NO3 increased and was maximum at petiole NO3–N concentration of about 6 g kg-1.
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Fig. 1 Relationship between yield performance of sugarbeet and petiole nitrate N concentration measured 30 June 1991 and 18 June 1992
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Nitrogen rate applied on the previous onion crop affected sugarbeet petiole NO3–N concentration measured in June of both years (Fig. 2)
. Petiole NO3 concentration in June of 1991 reached near 6 g kg-1 when the N rate of the previous crop was increased to 120 kg ha-1, and was little affected as N rate was further increased to 240 kg ha-1. In contrast, petiole NO3–N concentration in June of 1992 increased linearly as N rate of the previous crop was increased to 480 kg ha-1.
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Fig. 2 Relationship between fertilizer N rate of the previous onion crop and sugarbeet petiole nitrate N concentration 30 June 1991 and 18 June 1992. Error bars show standard error of the mean
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Discussion and conclusion
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Our results support the findings of Hills et al. (1978)(1983) that sugarbeet is a good scavenger of soil N, and thus can be used to conserve fertilizer N and reduce the potential for nitrate pollution of ground water. Sucrose yield in 1992 was the greatest at the highest N rate of the previous onion crop. However, the curvilinear effect of the N rate of onion crop on sucrose yield indicated that the residual N from an onion crop fertilized with 240 kg N ha-1 was near optimum for sugarbeet production. There were significantly high levels of NO3–N in the soil after harvesting sugarbeet that followed onion fertilized with 480 kg N ha-1. This indicates that the greatest level of N fertilization on onion crop resulted in residual N in excess of the amount recovered by the following sugarbeet.
Fertilizing the onion crop with 240 kg N ha-1 resulted in preplanting soil NO3–N concentration of about 50 kg ha-1 in the top 0.3 m of the soil or 70 kg ha-1 in the top 0.6 m of the soil. The desired soil NO3–N in the top 0.6 mm of the soil before planting sugarbeet is about 100 kg ha-1 in Texas (Winter, 1990) and 130 to 200 kg ha-1 in California (Giles et al., 1975; Hills and Ulrich, 1976). When soil moisture was adequate under nonirrigated conditions in Minnesota, both beet yield and extractable sucrose yield responded positively to fall-applied N to bring soil NO3–N at the 0- to 0.6-m depth to 157 kg ha-1 (Lamb and Moraghan, 1993). Lower requirements of preplanting available N for sugarbeet production in eastern Oregon are attributed to the high capacity of the soils in the area to mineralize N (Carter et al., 1974). Investigating the N budget indicated that close to 300 kg N ha-1 became available from sources other than the residual soil N. Based on measurements on the irrigation water and N content of the onion residue, we calculate that about 50 kg N ha-1 was supplied by the irrigation water and residue breakdown of the previous onion crop, and soil N mineralization could have provided up to 250 kg N ha-1. The importance of soil mineralizable N for sugarbeet uptake was previously reported (Roberts et al., 1972; Carter et al., 1974, 1976; Westermann and Crothers, 1980; Houba et al., 1995). Soils of the region where this experiment was conducted have the capacity to mineralize 200 to 250 kg N ha-1 in the top 0.4 m of their profile alone (Carter et al., 1974). Furthermore, the amount of N supplied through mineralization remains relatively constant when the field is uniformly cropped and fertilized, and thus testing for mineralizable N each year is not necessary (Carter et al., 1974).
Results of the present study also indicate that petiole NO3–N concentration in June could be used to estimate N fertilizer need for maximum sucrose yield with optimum efficiency. However, the efficiency of converting the recovered N to sucrose yield would also depend on the distribution of dry matter within plant parts. In 1992, when plants distributed a higher proportion of their dry matter to beet production than in 1991, sucrose yield was near maximum when petiole NO3 concentration in late June was about 6 g kg-1. Results reported by Winter (1990) also indicated that the yield of recoverable sucrose was little affected by applied N when petiole NO3–N concentration in mid-July exceeded 7 g kg-1. In 1991, while plants recovered more N than in 1992, a relatively higher portion of the N was allocated to leaf and crown production rather than beet production. Consequently, there was not any correlation between petiole NO3–N and sucrose yield in 1991. Crown tissue production in sugarbeet increases linearly as soil available N increases, and N fertilization should be managed to minimize crown production (Halvorson et al., 1978; Halvorson and Hartman, 1980). Anderson and Peterson (1988) reported that the lowest sucrose yields occurred in years with the greatest top yield.
In conclusion, preplant NO3 levels of about 70 kg ha-1 in the top 0.6 m of the soil should be adequate to produce sugarbeet without additional N fertilizer when it follows onion. Sucrose yield did not respond to N fertilization if petiole NO3–N concentration in June was about 6 g kg-1. Near-optimum recoverable sugar yield may be achieved in the area without additional N fertilizer when sugarbeet follows onion fertilized with more than 240 kg N ha-1.
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ACKNOWLEDGMENTS
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We thank the USEPA, Oregon Dep. of Environmental Quality, Oregon Dep. of Agriculture, Nyssa-Nampa Beet Growers Assoc., and Amalgamated Sugar Co. for their support.
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NOTES
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Contribution from Oregon Agric. Exp. Stn., Tech. Paper no. 11254.
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REFERENCES
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TOP
ABSTRACT
INTRODUCTION
