Published February 25, 2015 Crop Economics, Production & Management
Nitrogen Applications for Wheat Production across Tillage Systems in Alabama K. S. Balkcom* and C. H. Burmester ABSTRACT
Alabama wheat (Triticum aestivum L.) farmers are changing management practices, which include using higher N fertilizer rates and planting wheat with no-tillage or other conservation tillage systems to maximize yields. Experiments were conducted to (i) determine the level of tillage necessary to optimize wheat yields across different regions of Alabama and (ii) determine if N requirements change across tillage systems and regions in Alabama at four locations resulting in 9 site-year comparisons. Each experiment consisted of a split-plot design with tillage as the main plot and 12 N fertilizer treatments as subplots, replicated four times to compare Zadoks’ Growth Stage (GS)-30 tiller densities, tiller N concentrations, tiller biomass, GS-31 wheat biomass, biomass N concentration, wheat yields, and grain crude protein. Nitrogen treatments consisted of different rates across fall, GS-30, and GS-31 application times. Tillage systems had no effect on tiller density, tiller N concentration, or tiller biomass, but fall N increased tiller density 15% and tiller biomass 34% across Coastal Plain locations. Non-inversion tillage increased wheat yields 13% on Coastal Plain soils compared to conventional tillage. Fall N increased wheat yields 10%, and N applied at GS-30 improved yields 18% compared to delaying application until GS-31, indicating application of fall N and applying total N by GS-30 was imperative for successful wheat production on Coastal Plain soils. Neither tillage system nor N applications affected wheat production extensively across the Limestone Valley. Non-inversion tillage or no-tillage with current recommended N practices can be successfully used in Alabama wheat production.
Favorable wheat prices received by growers during the
2008/2009 growing season increased global wheat production (Vocke and Ali, 2013) and renewed interest in soft red winter wheat production across the Southeast United States. Growers in Alabama, Florida, Georgia, and South Carolina planted approximately 89,000; 4900; 101,000; and 77,000 hectares of wheat, respectively, during the 2011/2012 growing season (NASS, 2013). The increase in production prompted questions from growers regarding whether higher N fertilizer rates should be used in conjunction with conservation tillage systems that minimize surface soil disturbance. These systems preserve residue on the soil surface and reduce field operations compared to conventional tillage. Advantages of conservation tillage that maintains surface residue are numerous and major benefits include reducing erosion and improving soil water availability (Unger and McCalla, 1980). These and other specific benefits of conservation tillage have been documented for various summer crops grown across
K.S. Balkcom, USDA-ARS, National Soil Dynamics Lab., 411 S. Donahue Dr., Auburn, AL 36832; and C.H. Burmester, Crop, Soil and Environmental Sciences Dep., Auburn Univ., Tennessee Valley Research and Extension Center, P.O. Box 159, Belle Mina, AL 35615. Received 6 Mar. 2014. Accepted 19 Nov. 2014. *Corresponding author (
[email protected]). Published in Agron. J. 107:425–434 (2015) doi:10.2134/agronj14.0132 Copyright © 2015 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
the Southeast United States that include corn (Zea mays L.) (Box and Langdale, 1984; Campbell et al., 1984a), cotton (Gossypium hirsutum, L.) (Brown et al., 1985; Causarano et al., 2006), peanut (Arachis hypogaea L.) (Balkcom et al., 2010; Johnson et al., 2001), and soybean (Glycine max L.) (Campbell et al., 1984b; Edwards et al., 1988). Deep tillage is traditionally performed, before wheat planting, in the fall as many soils in the southeastern United States contain a hardpan that restricts root growth. Deep tillage typically causes significant incorporation of crop residue (Frederick and Bauer, 1996; NeSmith et al., 1987). While incorporation of surface residues increases potential for erosion and thus decreases benefits associated with conservation systems (Balkcom et al., 2007a, 2013), the presence of surface residues increases concerns with delayed wheat emergence and development (Rasmussen et al., 1997; Weisz and Bowmann, 1999; Weisz et al., 2001). Karlen and Gooden (1987) examined tillage effects across three Coastal Plain soil series and concluded that moldboard or chisel plowing was the optimum tillage system, which included comparisons to no-tillage. The scientists also conducted a greenhouse study that showed poor seed-soil contact in notillage was detrimental to wheat stands. Karlen and Gooden (1987) recommended that a different seeding drill compared to the one used in their study would be required to successfully
Abbreviations: EVS, E.V. Smith Research Center; GCS, Gulf Coast Research Extension Center; TVS, Tennessee Valley Research and Extension Center; WGS, Wiregrass Research and Extension Center.
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no-till plant wheat into residue in the future, particularly into heavy residue such as that remaining after corn harvest. Frederick and Bauer (1996) recognized wheat was not grown using conservation tillage practices across the Southeast United States. They attributed insufficient planting equipment and the need for deep tillage due to the dominance of non-shrinking and swelling clays as primary contributing factors preventing conservation tillage adoption for wheat. Partially in response to their study, tillage equipment has been developed that could eliminate potential subsurface hardpans, while maintaining surface residues. Using this type of conservation tillage equipment, wheat production was possible and yields should be similar to conventional tillage. The authors also noted that yield could be enhanced if drought stress occurred early in the wheat growing season. However, the researchers noted in their study that seedling emergence was still reduced in these systems (Frederick and Bauer, 1996). Further advances in tillage equipment and development of modern seeding equipment have enhanced the ability of growers to plant wheat into surface residues and eliminate planting issues associated with poor seed–soil contact. Raper et al. (2000) showed that a rye (Secale cereale L.) cover crop, grown during the winter months on Alabama Limestone Valley soils, could reduce soil penetration resistance (bulk density) for a subsequent cotton crop. This reduction was attributed to increased soil moisture from surface residue. This also demonstrates that a small grain crop, like wheat, may also be able to thrive on similar soils during the winter months without prepatory deep tillage. Precipitation commonly exceeds evapotranspiration during winter months across the Southeast United States (Balkcom et al., 2007b; Frederick and Bauer, 1996) which helps maintain soil moisture closer to field capacity in fine-textured soils. We hypothesized that on these silt loam soils, increasing soil moisture would reduce soil strength, allowing wheat roots to penetrate any hardpan that might be present. The ability to successfully establish wheat in a no-tillage system would help to offset the short time between harvest of a late maturity crop, such as cotton and fall wheat planting (Wiatrak et al., 2006). Tapley et al. (2013) demonstrated the potential adverse effect of delayed seeding dates on wheat yields in Alabama. Nitrogen rate and timing required for wheat production are factors that are constantly being evaluated. The presence of surface residues increases the likelihood that surface applied N fertilizers may be immobilized increasing N fertilizer requirements for conservation tillage systems (Rice and Smith, 1984). Karlen and Gooden (1987) indicated that wheat fertilizer N should be increased 25 to 50% compared to conventional tillage wheat N requirements. Jacobsen and Westermann (1988) used prediction equations to determine that broadcast N application should be increased 28 kg ha–1 for continuous no-tillage wheat compared to conventional tillage wheat. Efforts to overcome delayed wheat growth and tiller development associated with reduced tillage systems have focused on increasing N rates and applying N in early spring at either Zadoks’ GS-25 or GS-30 (Scharf and Alley, 1994; Weisz et al., 2001; Zadoks et al., 1974). Maximum N uptake for soft red winter wheat occurs following GS-30. Applying the majority of N at GS-30 would coincide better with the period of maximum 426
N uptake (Baethgen and Alley, 1989; Scharf and Alley, 1993). This approach also allows growers to eliminate a trip across the field with a single in season application compared to a split application. The potential for increased soil moisture over the winter months could dictate that N applications occur at GS-30 or later because high rainfall during late fall and early winter could promote N denitrification and/or leaching before planting (Scharf and Alley, 1993, 1994). Eliminating potential dentrification losses would be beneficial on silt loam soils in northern Alabama, while reduced leaching would be more beneficial on sandy soils in southern Alabama. Applying some pre-plant N has been part of a wheat N fertilization strategy in other wheat growing regions (Scharf and Alley, 1993). Examining the effect of a pre-plant N application on tiller production across tillage systems has not been previously examined in Alabama. Our objectives were (i) determine the level of tillage necessary to optimize wheat yields across different regions of Alabama and (ii) determine if N requirements differ across tillage systems and regions in Alabama. Materials and Methods Field experiments were conducted across Alabama during the 2007/2008, 2008/2009, 2009/2010 and 2010/2011 growing seasons resulting in 9 site-year comparisons. These locations included the Tennessee Valley Research and Extension Center (TVS) in northern Alabama (34°41.3¢ N, 86°52.9¢ W), the Field Crops Unit of the E.V. Smith Research Center (EVS) in central Alabama (32°25.4¢ N, 85°53.4¢ W), the Wiregrass Research and Extension Center (WGS) in southeastern Alabama (31°21.4¢ N, 85°19.4¢ W), and the Gulf Coast Research and Extension Center (GCS) in southwestern Alabama (30°32.7¢ N, 87°52.8¢ W). The TVS location represented Limestone Valley soils, while the other three locations represented Coastal Plain soils. Limestone Valley soils are typically characterized as red, clayey soils with silt loam textures, while soils in the lower Coastal Plain have loamy subsoils with sandy loam to loamy sand surface layers (Mitchell, 2008). Soil types, wheat cultivars, planting dates, N application dates, and harvest dates are shown in Table 1. Pre-plant applications of P, K, and lime were based on composite soil samples collected to 30 cm in depth from each location to ensure soil test ratings were considered “High” based on Alabama Experiment Station recommendations (Adams et al., 1994). The seed of each cultivar was treated with a fungicide. Seeding was 387.1 to 413.1 seed m–2 on either a 19 or 20 cm row spacing, depending on location. Wheat was planted following cotton at each location. The experimental design was a split-plot with tillage as main plot and N fertilizer treatments as subplots with four replications. Subplot dimensions were 3.0 m (GCS and TVS) or 3.6 m wide (EVS and WGS) by 7.6 m long. At TVS, tillage variables included a conventional tillage operation that consisted of fall chisel plowing following a leveling operation compared to no-tillage. At the Coastal Plain sites, conventional tillage consisted of disking twice (15-cm deep), chisel plowing (25-cm deep), and a field cultivation operation (10-cm deep) compared to a single pass with a KMC Gen II subsoiler-leveler (33-cm deep) (Kelley Manufacturing Com., Tifton, GA) designed to minimize surface soil disturbance and maximize belowground disruption. The subsoiler-leveler operation will be referred to Agronomy Journal • Volume 107, Issue 2 • 2015
Table 1. Planting dates, N application dates, harvest dates, soil types, and cultivars for each of the nine location/year combinations included in this analysis. Year/Location† 2007/2008 TVS§ 2008/2009 EVS TVS WGS 2009/2010 EVS
Soil series‡ Decatur sil
Family fine, kaolinitic, thermic Rhodic Paleudults
Compass ls
coarse-loamy, siliceous, subactive, thermic Plinthic Paleudults Decatur sil fine, kaolinitic, thermic Rhodic Paleudults Orangeburg ls fine-loamy, kaolinitic, thermic Typic Kandiudults
Cultivar
Planting date
Nitrogen application GS-30 GS-31
Harvest date
USG 3209
13 Nov.
11 Feb.
6 Mar.
20 June
USG 3209
7 Nov.
11 Feb.
9 Mar.
2 June
USG 3209 Pioneer 26R31
29 Oct. 19 Nov.
10 Feb. 2 Feb.
6 Mar. 28 Feb.
22 June 3 June
Compass ls
coarse-loamy, siliceous, subactive, thermic Plinthic Paleudults
AGS 2060
19 Nov.
9 Mar.
1 Apr.
3 June
2010/2011 EVS
Compass ls
AGS 2060
19 Nov.
22 Feb.
18 Mar.
1 June
GCS
Malbis fsl
AGS 2060
23 Nov.
16 Feb.
3 Mar.
18 May
TVS WGS
Decatur sil Dothan sl
coarse-loamy, siliceous, subactive, thermic Plinthic Paleudults fine-loamy, siliceous, subactive, thermic Plinthic Paleudults fine, kaolinitic, thermic Rhodic Paleudults fine-loamy, kaolinitic, thermic Plinthic Kandiudults
AGS 2060 AGS 2060
9 Nov. 22 Nov.
23 Feb. 23 Feb.
21 Mar. 16 Mar.
14 July 23 May
† EVS, Field Crops Unit at the E.V. Smith Research Center; GCS, Gulf Coast Research and Extension Center; TVS, Tennessee Research and Extension Center; WGS, Wiregrass Research and Extension Center. ‡ fsl, fine sandy loam; ls, loamy sand; sl, sandy loam; sil, silt loam. § All TVS locations represent the Limestone Valley soil category, while the remaining locations represent the Coastal Plain soil category.
as non-inversion tillage throughout the manuscript, and was performed immediately after planting wheat. This eliminated potential tractor tire ruts in the plots, but did not affect wheat seeding depth because the operation results in minimal surface disturbance. Twelve N fertilizer treatments consisting of fall and spring N applications are described in Table 2. Fall N was applied by hand at planting as granular urea (46–0–0) at TVS and as NH4 NO3 (34–0–0) at the other locations. Streaming fertilizer tips were used to apply 28% urea-ammonium nitrate (UAN) (28–0–0) fertilizer containing 5% sulfur [created by blending UAN with ammonium thiosulfate (12–0–0; 26% S)] to corresponding treatments at approximately Zadoks’ GS-30 and GS-31 using a self-propelled plot sprayer or a spray apparatus mounted on a four-wheeler. These growth stages typically occur around mid-February and mid-March, respectively, and are usually separated by about 1 mo (Table 1). Early to mid-February is normally the earliest timing of the first spring N application in our region due to environmental related constraints (i.e., wet soils), regardless of wheat growth stage. Wheat tiller counts were determined at GS-30 by digging all plants within a 0.09 m2 section in each plot, placing plants in plastic bags for transport to the laboratory, washing all roots to remove soil, and counting all tillers with three or more leaves from the entire sample. Roots were clipped and discarded, while the aboveground tissue was dried in a forced air oven for 72 h at 55°C and weighed to determine aboveground dry matter biomass. All dry tissue was ground to pass through a 2-mm screen with a Wiley mill (Thomas Scientific, Swedesboro, NJ) then ground further to pass through a 1-mm screen with a Cyclone grinder (Thomas Scientific, Swedesboro, NJ). Subsamples were analyzed for total N by dry combustion on a LECO TrueSpec-CN analyzer (Leco Corp., St. Joseph, MI). A second plant sample was collected from a different 0.09 m2 area within each plot at GS-31 to determine dry matter production and N concentration. All aboveground plant material
was clipped at the soil surface, brought back to the laboratory, and subjected to the same drying and analytical procedures described previously at GS-30. Wheat yield was determined by harvesting an area 1.5 by 7.6 m long in the center of each plot using a self-propelled combine designed for small plot research. If equipped, moisture contents were measured with a sensor on the combine or subsamples were collected to measure moisture contents with a moisture machine immediately following grain harvest. All grain weights were adjusted to a moisture content of 135 g kg–1. A subsample of grain was obtained from each plot and analyzed for total N by dry combustion using procedures described previously. Crude protein in the grain was determined by multiplying all N concentration values by the conversion factor of 6.25. Data were analyzed using linear mixed models procedures in SAS PROC GLIMMIX (SAS Institute, 2013). All dependent variables were first analyzed to measure the effect of years and locations as fixed effects that allowed us to measure the magnitude of year and location interactions with treatments. Table 2. Rates and times of N application for each of the 9 site-years examined across Alabama.
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N Treatment 1 2 3 4 5 6 7 8 9 10 11 12
Spring N timing Fall N GS-30 GS-31 ————————— kg N ha–1 ————————— 0 0 67.2 0 0 100.8 0 0 134.4 0 33.6 33.6 0 50.4 50.4 0 67.2 67.2 22.4 44.8 0 22.4 78.4 0 22.4 112 0 22.4 0 44.8 22.4 0 78.4 22.4 0 112
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Fig. 1. Monthly precipitation levels across growing seasons compared to a 60 yr (1951–2011) normal with 95% confidence intervals around the normal mean for the Coastal Plain soil category. These site-years represent the E.V. Smith Research Center (EVS).
Fig. 3. Monthly precipitation levels across growing seasons compared to a 60 yr (1951–2011) normal with 95% confidence intervals around the normal mean for the Coastal Plain soil category. These site-years represent the Wiregrass Research and Extension Center (WGS).
Dependent variables collected early in the growing season had a different treatment structure compared to variables collected at the end of the growing season because various treatments may not have been administered at the time of data collection. For example, tiller counts, tiller N content, and tiller biomass could only be affected by tillage and fall N at the time of data collection compared to yield and crude protein that could be affected by all treatment variables. Preliminary analyses indicated that location exhibited a stronger effect compared to year for all variables. Further analyses indicated that differences among locations could be
explained by soil type category (Coastal Plain vs. Limestone Valley) as evidenced by significant interactions across dependent variables between soil type category and treatments. Therefore, all variables were analyzed by soil type category. A random variable called environment was used to represent all multiple year experiments by combining all site-years of data representing different environmental conditions within each soil type category. Environment was treated as random to average results across the 9 site-years.
Fig. 2. Monthly precipitation levels across the growing season compared to a 60 yr (1951–2011) normal with 95% confidence intervals around the normal mean for the Coastal Plain soil category. These site-years represent the Gulf Coast Research and Extension Center (GCS).
Fig. 4. Monthly precipitation levels across growing seasons compared to a 60 yr (1951–2011) normal with 95% confidence intervals around the normal mean for the Limestone Valley soil category. These site-years represent the Tennessee Valley Research and Extension Center (TVS).
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Table 3. Analysis of variance for tiller density, tiller N concentration, and tiller biomass measured at GS-30 for each soil type category across 9 siteyears in Alabama. Soil type category Coastal Plain
Limestone Valley
Effect Tillage (T) Fall N (N) T×N T N T×N
df 1 1 1 1 1 1
Tiller density F value P value 2.64 0.1650 49.10 F was ≤0.05. Comparisons among two or more treatment means were separated by the least significant difference. Results and Discussion Precipitation The amount of precipitation recorded for each month of specific growing seasons compared to a 60 yr (1951–2011) normal precipitation level across those same months at all corresponding experimental locations are shown in Fig. 1 to 4. Each location highlights the observed variability in recorded rainfall across growing seasons compared to the 60 yr normal. The 95% confidence intervals for the normal mean at each location are also displayed in each figure. At EVS, the first half of the 2008/2009 growing season received below normal precipitation, except for November, but the second half was normal or above normal (Fig. 1). During the 2009/2010 growing season, half of the 8 mo growing season was above normal and the other half was below normal, with the majority of the below normal precipitation recorded during February to April (Fig. 1). The 2010/2011 growing
Tiller N F value 0.29 2.57 1.65 1.17 0.08 0.14
P value 0.5967 0.1356 0.2236 0.4746 0.7811 0.7124
Tiller biomass F value P value 1.14 0.3336 53.35
