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USDA-ARS, 2150 Centre Ave, Bldg. D, Suite 100, Fort Collins, CO 80526
* Corresponding author (ardell.halvorson{at}ars.usda.gov)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Abbreviations: AN, available N [soil (0–90 cm depth) + fertilizer + irrigation water N] • CT, conventional-till • CT-CC, conventional-till continuous corn • NUE, nitrogen use efficiency • NT, no-till • NT-CB, no-till corn-barley • NT-CC, no-till continuous corn • SOC, soil organic carbon
USDA-ARS, 2150 Centre Ave, Bldg. D, Suite 100, Fort Collins, CO 80526
* Corresponding author (ardell.halvorson{at}ars.usda.gov)
Received for publication December 15, 2006.
Converting irrigated, conventional-till (CT) systems to no-till (NT) production systems can potentially reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions. Nitrogen fertilization effects on irrigated corn (Zea mays L.) and malting barley (Hordeum distichon L.) yields in a corn-barley rotation were evaluated for 6 yr on a clay loam soil to determine the viability of using a NT system and N needs for optimum crop yield. Six N treatments were established with N rates varying from 0 to 224 kg N ha–1 for corn and 0 to 112 kg N ha–1 for barley. Corn and barley grain yields were significantly increased by N fertilization each of 3 yr in the rotation. Three year average corn grain yields were near maximum with an available N (AN) (soil + fertilizer + irrigation water N) level of 274 kg N ha–1. Barley yields increased linearly with increasing N rate with grain protein content near 130 kg protein Mg–1 grain at the highest N rate. Nitrogen use efficiency (NUE) by corn and barley, based on grain N removal, decreased with increasing AN level and ranged from 204 to 39 and 68 to 31 kg grain kg–1 AN for the low and high N treatments for corn and barley, respectively. Total plant N uptake required to produce one Mg grain at near maximum yield in this study averaged 21 kg N for corn and 27 kg N for barley. Corn and barley residue production increased with increasing N rate. Irrigated, NT corn yields obtained in this corn-barley rotation were acceptable (>10 Mg ha–1) for northern Colorado; however, barley yields did not meet our expected yield goal of 5.4 Mg ha–1 with the N rates used in this study, but grain protein was near maximum for malting barley. An irrigated, NT corn-barley production system appears to be feasible in northern Colorado.
Abbreviations: AN, available N [soil (0–90 cm depth) + fertilizer + irrigation water N] • CT, conventional-till • CT-CC, conventional-till continuous corn • NUE, nitrogen use efficiency • NT, no-till • NT-CB, no-till corn-barley • NT-CC, no-till continuous corn • SOC, soil organic carbon
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Information on the effectiveness of irrigated NT systems in the semiarid central Great Plains is limited (Cahoon et al., 1999; Halvorson et al., 2006; Halvorson and Reule, 2006; Sims et al., 1998). Observations from the Western-Corn Belt and eastern Nebraska suggest that NT systems may produce lower continuous corn grain yields than CT systems (Wilhelm and Wortmann, 2004; Vetsch and Randall, 2002, 2004; Sims et al., 1998). Halvorson et al. (2006) reported 16% lower continuous corn yields with NT compared with CT at maximum yield in northern Colorado. Halvorson and Reule (2006) found that NT corn yields in a corn-soybean [Glycine max (L.) Merr.] rotation exceeded those of CT and NT continuous corn in northern Colorado. Cooler soil temperatures at planting time in NT, continuous corn systems can delay early crop development and final yield (Halvorson et al., 2006; Mosier et al., 2006). Including a lower-residue crop like barley in rotation with corn could reduce surface residue levels enough at corn planting to result in higher soil temperatures in early spring than with a NT continuous corn system.
Little if any research has been conducted in the South Platte River Valley in northern Colorado on the effects of a NT production system on irrigated malting barley yields. Dryland NT malting barley production in the U.S. Pacific Northwest is influenced by water stress and N fertilization rate (Clancy et al., 1991) which affected yields, grain protein content, and plump kernel percentage. Higher N rates increased yield and grain protein, but tended to decrease kernel plumpness. Malting barley cultivar grown has been shown to greatly affect malting quality and response to N fertilization (Clancy et al., 1991; Varvel and Severson, 1987; Weston et al., 1993). Lauer and Partridge (1990) reported that delayed planting reduced malting barley yields and kernel plumpness in a multiyear irrigated study in Wyoming. Nitrogen rate did not affect kernel plumpness, but did increase grain protein. Early planting was recommended for best malting barley yield and quality. McKenzie and Jackson (2005) reported a N requirement of 25 kg N Mg–1 grain for malting barley in the northern Great Plains. Stark and Brown (1987) found that malting barley yields were maximized with an AN level (soil plus fertilizer N) of 118 kg N ha–1 under irrigated conditions in Idaho. They also reported a decline in kernel plumpness with increasing AN level.
Farmers in the South Platte River Valley in northern Colorado produce alfalfa (Medicago sativa L.), corn, winter wheat (Triticum aestivum L.), barley, and dry bean (Phaseolus vulgaris L.) using predominantly intensive tillage (including the moldboard plow) to prepare a seedbed. Soil erosion due to wind and water is a common problem in this irrigated area. Converting to an irrigated, NT production system could reduce soil erosion, reduce fossil fuel consumption through less tillage and fewer field operations, and potentially reduce greenhouse gas emissions through increased SOC sequestration (Halvorson et al., 2006; Halvorson and Reule, 2006; Mosier et al., 2006).
Halvorson et al. (2006) reported reduced corn yields with NT compared with CT within a continuous corn production system, due to cooler soil temperatures and slower plant development in the NT system. Halvorson and Reule (2006) found NT corn yields in a corn-bean rotation exceeded CT and NT continuous corn yields in northern Colorado. Our objectives were (i) to determine N fertilizer needs for optimizing corn and barley grain yields and the influence of N fertilization on crop residue production in an irrigated, NT corn-barley production system; and (ii) to compare corn yields from the corn-barley rotation with CT and NT continuous corn yields reported by Halvorson et al. (2006) and NT corn yields in a corn-soybean rotation reported by Halvorson and Reule (2006). We hypothesized that NT corn yields in a corn-barley rotation under irrigation in the central Great Plains would equal or exceed the continuous corn yields under CT and NT production systems reported by Halvorson et al. (2006) due to less residue accumulation on the soil surface with the corn-barley rotation, resulting in warmer spring soil temperatures, and the benefits of crop rotation.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Using a NT system, corn and barley were directly planted into the previous year's crop residue each spring without any other field operations for seedbed preparation, followed by application of herbicides for weed control, and then harvest. Triple super phosphate (0–46–0) was band applied below the soil surface (56 kg P ha–1) to the entire plot area before barley planting in 1999, and 28 kg P ha–1 before corn in 2004, and 28 kg P ha–1 broadcast applied without incorporation before barley in 2005. The soil had an average pH of 7.8 (soil to 0.01 M CaCl2 solution ratio 1:2), organic matter content of 19 g kg–1, electrical conductivity of 0.9 dS m–1 (soil to water ratio 1:1), sodium bicarbonate extractable P content of 16 mg kg–1, and a clay and silt content of 321 and 276 g kg–1, respectively, in the 0- to 15-cm depth.
Six N rates (0, 34, 67, 101, 134, and 202 kg N ha–1 referred to as N1, N2, N3, N4, N5, N6, respectively) were used in 2000 and 2002 for corn production. The 202 kg N ha–1 rate of N application was increased to 224 kg N ha–1 in 2004 to ensure that adequate N was available to maximize grain yields, based on NT corn yields reported by Halvorson et al. (2006). The N rates for barley in 2001, 2003, and 2005 were 0, 22, 45, 67, 90, and 112 kg N ha–1 for the N1, N2, N3, N4, N5, and N6 treatments, respectively. The above rates of N were applied to the same plots (N treatments) each year depending on crop grown. Based on malting barley yield goal and N fertilizer recommendations for this area (Cardon et al., 1997; Mortvedt et al., 1996), a maximum N fertilizer rate of 112 kg N ha–1 was used to limit the protein content of the grain to less than 130 g kg–1 to achieve malting quality barley (American Malting Barley Association, 2005) and prevent lodging. The 112 kg N ha–1 treatment was expected to produce malting barley yields in the range of 5.4 to 6.4 Mg ha–1.
The N source was urea-ammonium nitrate (UAN, 32–0–0) which was applied with a liquid fertilizer applicator which banded the N about 5 cm below the soil surface in bands spaced 33 cm apart (parallel to the corn or barley row, but at varying distance from the row) the day before corn or barley planting. Liquid starter P and K fertilizer was applied directly with the seed at planting, except in 2001 and 2005 when no starter fertilizer was applied. The experimental design was a randomized complete block with three replications. Plot size was 10.7 by 15.2 m.
Corn hybrid Pioneer Brand 38B22 Bt LL was planted with a 76 cm row spacing on 27 April 2000; Pioneer Brand 37H26 LL on 24 April 2002; and Pioneer Brand 38P04 LL on 27 April 2004.1 Corn hybrid varied between years due to availability of seed and the desire to optimize yield potential as new hybrids became available. Planting rates were approximately 84,000 seeds ha–1 in 2000 and 2004 and 96,000 seeds ha–1 in 2002. All corn hybrids had about a 94-d relative maturity. Corn plant populations were estimated each year by counting the number of plants in two rows 7.6 m long that were used for grain harvest. Spring malting barley, cultivar Busch B2601, was planted on 23 Mar. 2001 using a John Deere model 1560 NT-grain drill with 19-cm row spacing, and cultivar Moravian 37 on 11 April 2003, and cultivar Moravian 37 on 29 March 2005. All cultivars used in this study were two-row barley. Barley planting rates were approximately 3.7 million seeds ha–1, but established plant populations were not determined. Herbicides applied for weed control included glufosinate-ammonium, pyridate, and atrazine for corn; 2,4-D amine for barley; and glyphosate during the noncrop periods, all used at the recommended rates. The plots were relatively weed free during the study period.
The corn and barley crops were sprinkler irrigated with a linear move system as needed [determined weekly by the feel method (Klocke and Fischbach, 1998)] during the growing season each year. Irrigation amounts each month are shown in Table 1 . The irrigation water contained an average of 2.8 mg NO3–N L–1 in 2002, 3.6 mg NO3–N L–1 in 2003, 2.1 mg NO3–N L–1 in 2004, and 4.5 mg NO3–N L–1 in 2005. In 2000 and 2001, N level in the water was not monitored, but was assumed to be similar to that in 2002 to 2004. The total N contribution from the irrigation water to the plot area was estimated to be 10 kg N ha–1 in 2000, 5.5 kg N ha–1 in 2001, 14 kg N ha–1 in 2002, 6.1 kg N ha–1 in 2003, 8 kg N ha–1 in 2004, and 6.5 kg N ha–1 in 2005 during irrigation with no observed runoff from the plot area.
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Crop residue cover on the soil surface was measured each spring just before planting using the line-transect method. Soil NO3–N levels in the 0- to 183-cm depth were monitored from 2000 through 2005, and were measured before spring fertilization. One soil core sample was collected from each plot (0- to 183-cm depth) before planting each crop year in increments of 0 to 7.6, 7.6 to 15.2, 15.2 to 30.5 cm, then 30.5 cm increments to a depth of 183 cm for determination of gravimetric soil water and soil NO3–N content. Soil NO3–N was determined by cadmium reduction (Lachat Instruments, 2001) using a continuous flow analyzer (Lachat QuickChem FIA+8000 Series, Lachat Instruments, Loveland, CO) after extraction with 1 M KCl (soil–solution ratio 1:5). Soil bulk density was determined on the soil cores from the 0- to 30.5-cm depths from each plot during the fall sampling. Soil bulk density was determined for the 30.5- to 183-cm soil depths at three locations within each replication and an average value calculated for the study area. Soil bulk density was used to calculate soil NO3–N mass on an area basis.
The grain and crop residue samples collected for N analysis were ground to pass a 150-µ screen and analyzed for N content using a Carlo Erba C/N analyzer (Haake Buchler Instruments, Inc., Saddle Brook, NJ). Because of the long-term nature of this study and declining residual soil N levels with time in the zero fertilizer N plots (N1), an accurate estimation of fertilizer NUE could not be made for any of the N fertilizer treatments. Therefore, NUE was estimated by dividing grain yield by AN [soil N (0–90 cm depth) + fertilizer N + irrigation water N] similar to that reported by Moll et al. (1982) and Sabata and Mason (1992). Nitrogen use efficiency was also estimated by dividing the grain N uptake by AN multiplied by 100 to obtain percentage NUE similar to that reported by Halvorson and Reule (2006).
Grain yields were generally determined in mid-July (barley) and mid-October to early-November (corn) each year by hand harvesting a 2.3-m2 area in 2001 and combine harvesting a 18-m2 area in 2003 and 2005 of each barley plot and the ears from an 11.6-m2 area of each corn plot in 2000, 2002, and 2004. The corn ears were shelled with a corn sheller to determine grain and cob weights. Corn grain yields were measured at physiological maturity at about 170 to 180 g kg–1 moisture content and final grain yield was expressed at 155 g kg–1 moisture content. Above-ground corn biomass was determined in mid-September in 2000 and 2002 and mid-October in 2004 by hand harvesting 15 whole corn plants from a 1.5 m2 or larger area from each plot. Except for 2000, the corn plants were separated into grain, cobs, and stover for total biomass determination. Barley grain yields were expressed at 120 g kg–1 moisture content. Above-ground biomass of barley was determined at physiological maturity from a 2 m2 area of each plot on 7 July 2001, 21 July 2003, and 20 July 2005. The grain was separated from the total biomass before analysis for N content. Grain protein concentration was calculated by multiplying the determined N concentration by 6.25.
Analyses of variance were performed using Analytical Software Statistix8 program (Analytical Software, 2003) to determine treatment effects. A split-plot ANOVA was used with N as main treatment and years treated as a subplot fixed effect. All statistical comparisons were made at 
= 0.05 probability level unless otherwise stated using the least significant difference method for mean separation. If the ANOVA indicated a significant F value for N rate, either a linear or quadratic function was fit to the N response data using regression functions present in the graphics program (SigmaPlot version 10, Systat Software, Inc., Point Richmond, CA).
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Grain Yield
Corn
Corn plant populations did not vary between N treatments but were significantly different in 2000, 2002, and 2004 with respective plant populations of 76,200, 97,500, and 82,000 plants ha–1, which reflects the higher seeding rate in 2002 compared with 2000 and 2004. Corn plant populations among years were significantly different as follows: 2002 > 2004 > 2000. Corn grain yields increased each year with increasing N fertilizer rates with no significant N treatment x year interaction, therefore, only the average grain yield for all three crop years is shown in Fig. 1
. Grain yields varied significantly with year with 2004 (9.32 Mg ha–1) having significantly lower average yield than 2000 (10.16 Mg ha–1) and 2002 (10.71 Mg ha–1). Soil NO3–N levels in the 0- to 91-cm depth (Table 2
) at corn planting were similar for all 3 yr, so differences in soil NO3–N levels probably did not contribute to the lower grain yields in 2004. Nitrogen applied with the irrigation water was lowest in 2004 (8 kg N ha–1) compared with 10 and 14 kg N ha–1 in 2000 and 2002, respectively, which may have impacted yield slightly. Cumulative growing degree day heat units calculated on Celsius basis from planting until close to maturity (30 September) were 1345, 1363, and 1192 for 2000, 2002, and 2004, respectively, which may have contributed to the lower corn yield in 2004 compared with 2000 and 2002.
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Expressing corn grain yield as a function of AN [soil NO3–N (0- to 90-cm depth) + fertilizer N + irrigation water N] for all 3 yr (Fig. 3 ) shows grain yield increasing with increasing N availability. Based on the regression equation for the 3-yr average, the amount of total AN needed to maximize grain yield was 274 kg N ha–1. This range in AN level for maximum corn yield in this corn-barley rotation is similar to that reported by Halvorson et al. (2006) for the NT and CT continuous corn systems, 268 and 276 kg N ha–1, respectively, and Halvorson and Reule (2006) for NT corn (257 kg N ha–1) in a corn-soybean rotation. Halvorson et al. (2005) also reported maximum yields in furrow irrigated continuous corn occurred at 265 kg N ha–1 of AN (soil + fertilizer N) in southeastern Colorado.
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In 2001, the Busch cultivar showed a linear increase (graph not shown) in grain protein (Table 3), approaching the maximum desirable grain protein content of 130 kg protein Mg–1 grain for malting barley (American Malting Barley Association, 2005) at the highest N rate. In 2003 and 2005, the Moravian barley had high protein at the two lowest N rates decreasing to a low with the medium rates then increasing toward 120 to 130 kg protein Mg–1 grain at the highest N rate. This resulted in a significant N rate x year interaction. Therefore, the grain protein for each year was analyzed separately in Table 3. At the lower N rates in 2003 and 2005, a lot of immature green heads caused by late tillering of the Moravian barley were present, creating a harvest situation where > 70% of the grain was fully mature and ready to harvest, but the green, immature heads were weeks from maturity. The high grain protein observed in the Moravian barley at the two lowest N rates was probably due to the low grain yields in 2003 and 2005 (Table 3) which probably resulted in minimal dilution of the N taken up by the grain and a high grain N content and consequently a high protein content. In contrast, the Busch barley in 2001 had more than twice the grain yields of the 2003 and 2005 Moravian barley (Table 3) at the two lowest N rates, which diluted the grain N taken up by the Busch barley compared with the Moravian barley. As N rate increased in 2003 and 2005, there were fewer green barley heads at harvest, with almost no green heads at the two highest N rates. Grain protein was near the maximum protein content of 130 kg protein Mg–1 grain desired by the malting barley industry at the highest N rates in all 3 yr. Thus, higher rates of N fertilization may have resulted in higher barley grain yields, but with unacceptable levels of grain protein. Fertilizer N rates for barley in this study will be increased in the future to increase grain yield potential.
Nitrogen Use Efficiency
Corn
Nitrogen use efficiency by corn decreased each year with increasing AN level with a significant N treatment x year interactions (Table 4
). Therefore, each year was analyzed separately in Table 4. The interaction probably resulted from the very high NUE value for the 0 and 34 kg N ha–1 treatments in 2002 compared with 2000 and 2004. All other N treatments had similar NUE values among years.
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Crop Residue
Corn
Corn residue (leaves, stalks, and cobs) production increased with increasing N rate (Fig. 1) similarly each year. The N rate x year interaction was not significant. Averaged over N rates, corn residue production was 7285, 8543, and 7966 kg ha–1 for 2000, 2002, and 2004, respectively, with significantly more residue in 2002 than in 2000.
The amount of N in the corn residue at harvest increased with increasing N rate (Fig. 5), with no significant N rate x year interaction. Thus the higher N rates had more N cycling back to the soil with the residue than the lower N rates. The greater amount of residue N cycling back to the soil surface with the higher residue amounts should contribute to greater SOC sequestration with time in this corn-barley system (Varvel, 1994). The highest N rate contributed about 1552 kg ha–1 more corn residue than the zero-N rate (Fig. 5) when averaged over 2000, 2002, and 2004. Corn residue production with increasing N rate in this NT corn-barley rotation was similar to those reported for the CT and NT continuous corn production systems by Halvorson et al. (2006).
Barley
Barley residue production increased with increasing N rate, with a significant N rate x year interaction (Table 6
). Therefore, each year was analyzed separately in Table 6. A linear increase in residue production was observed in 2000 and a curvilinear increase in residue in 2003 and 2005 (graphs not shown) reflecting the barley cultivar differences. At the lower N rates, residue production in 2001 was higher than in 2003 and 2005, but at the higher N rate, residue production was higher in 2003 and 2005 than in 2001 reflecting the cultivar differences which probably contributed to the significant N treatment x year interaction.
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Total N Uptake and Total N Requirements
Corn
The total N uptake (grain + residue) for the 2000, 2002, and 2004 corn crops is shown in Table 7
. Total N uptake increased with increasing N rate and biomass production each year with a significant N treatment x year interaction, so each year is shown separately in Table 7. The increases in total N uptake with increasing N rate were curvilinear in 2000 (nonsignificant) and nearly linear in 2002 and 2004 (significant) (graphs not shown). Except for the highest N rate, total N uptake was greater in 2000 than in 2002 and 2004, with 2004 tending to have the lowest level of N uptake at the lower N rates. Averaged over same years and N rates, this NT-CB rotation had a significantly greater total N uptake (162 kg N ha–1) by corn than for the CT (148 kg N ha–1) and NT (133 kg N ha–1) continuous corn systems reported by Halvorson et al. (2006). This may indicate a slight contribution of mineralized soil N from the longer fallow (noncrop) period between barley harvest and corn planting than occurs in the continuous corn system and the benefit of crop rotation, especially at the lower N rates.
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Barley
Total N uptake (grain + residue) by barley (Table 6) increased curvilinearly (graph not shown) each year with 2001 having a greater N uptake than 2003 and 2005 which had similar N uptake levels which resulted in a significant N treatment x year interaction. Therefore, each year was analyzed separately in Table 6. Total N uptake was significantly greater in 2001 than in 2003 or 2005. The higher grain yields at the lower N rates in 2001 compared with 2003 and 2005 contributed to this significant interaction. Total N uptake by barley was less than that of corn, reflecting the lower grain and residue yield with barley. Total N required to produce one Mg of barley grain was 27 kg N at the highest N rate which also had the greatest yield. Nitrogen rates were not high enough to maximize barley grain yields in this study, but were high enough to maximize the protein content of the grain to the desired limit for malting quality.
Soil Nitrate
Soil NO3–N levels just before planting each spring are reported in Table 2 for each year. In 2000 and 2001, soil NO3–N levels were not significantly different between N treatments in the 0- to 91-cm depth. In 2001, soil NO3–N levels had declined in all N treatments. Soil NO3–N levels tended to be lower at corn planting in 2002 than at barley planting in 2001, increasing with increasing N rate. In 2003, 2004, and 2005, residual soil N levels in the 0- to 183-cm depth at the highest N rates were significantly greater than those at the lower N rates. The residual soil NO3–N levels in 2004 appear to be normal for an irrigated cropping system and were similar to the NT continuous corn system reported by Halvorson et al. (2006).
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SUMMARY |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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This work shows that irrigated, NT corn production would benefit from crop rotation, especially at low N fertility levels. An irrigated, NT production system has potential for replacing irrigated, CT production systems in the central Great Plains area when high residue crops like corn are rotated with lower residue crops like barley and with adequate N applied. The study shows that corn in this NT corn-barley system responded similarly to AN supply when compared with the CT continuous corn system reported by Halvorson et al. (2006). Corn yields at low fertilizer N rates benefited most from rotation with barley.
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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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. 
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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