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Crop production and soil water storage in long-term winter wheat–fallow tillage experiments
Soil & Tillage Research 49 (1998) 19±27
Crop production and soil water storage in long-term winter wheat±fallow tillage experiments Drew J. Lyona,*, Walter W. Stroupb, Randall E. Brownc b
a Panhandle Research and Extension Center, 4502 Avenue I, Scottsbluff, NE 69361, USA Panhandle Research and Extension Center, 103 Miller Hall, University of Nebraska 103 Miller Hall, Lincoln, NE 68583-0712, USA c Panhandle Research and Extension Center, P.O. Box 786, Colby KS 67701-0786, USA
Received 24 September 1997; accepted 3 April 1998
Abstract Soil water is the major limiting factor in dryland crop production in the Central Great Plains. No-till fallow management increases soil water storage and reduces soil erosion potential. Two experiments were initiated in 1969 and 1970 near Sidney, NE to compare effects of moldboard plow (Plow), sub-tillage (Sub-till) and no-tillage (No-till) fallow systems on winter wheat (Triticum aestivum L.) grain yield, grain protein, residue production, and soil water accumulation during fallow. The ®rst experiment was established in 1969 on an Alliance silt loam that had been previously cultivated prior to study initiation. This experiment contained a nitrogen (N) fertilizer split of 0 and 45 (kg N) haÿ1 within each tillage treatment. The second experiment was established in 1970 on a Duroc loam that was in native mixed prairie sod. No fertilizer was applied at this site. At both sites, soil water storage was greatest with the no-till and least with the plow system. Winter wheat grain yields failed to consistently respond to increased soil water storage in the no-till system during the 24±26 years of the experiments. Grain yields with the plow system were 8% greater than with sub- and no-till systems at the Previously Cultivated site when N was not applied. The addition of N at this site eliminated yield differences due to fallow tillage systems. Grain protein averaged 13.8, 13.3 and 12.8% for all plow, sub- and no-till treatments, respectively. The addition of N at the Previously Cultivated site increased residue dry weights by an average of 5% in all tillage systems. Neither grain protein nor residue dry weights were affected by tillage system at the Native Sod site. Winter wheat±fallow is probably not a sustainable production system for the Central Great Plains, regardless of the fallow management system used. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Triticum aestivum; No-till; Sub-till; Plow; Grain yield; Grain protein; Soil water
1. Introduction Water is the most limiting resource for dryland crop growth in the semi-arid areas of the U.S. Great Plains (Smika, 1970). Summer fallow, the practice of con*Corresponding author. Tel.: +1 308-632-1266; fax: +1 308-6321365; e-mail address: [email protected]
trolling all plant growth during the non-crop season, was quickly adopted to stabilize winter wheat production in this region (Snyder and Burr, 1909). In the Central Great Plains, the 14 months of fallow begin in July after wheat harvest and continue until wheat seeding in September of the following year. In addition to storing soil water for the succeeding crop, fallow also enhances accumulation of nitrate through
0167-1987/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0167-1987(98)00151-2
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D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
mineralization of organic matter, and control of problem weeds, diseases, and insects (Smika, 1983). Winter wheat±fallow has been the predominant crop rotation in the U.S. Central Great Plains for the past 75 years (Hinze and Smika, 1983). During the U.S. Dust Bowl era of the 1930s, when 60±80 million hectares of land were scarred by wind erosion from Texas to the Dakotas (Miller et al., 1985), it became evident that farming practices had to be changed to protect land from erosion. Prior to the Dust Bowl, fallow tillage typically involved use of the moldboard or one-way disk plow, which inverted the soil and buried most crop residues (Johnson et al., 1983). During the 1940s and 1950s, non-inversion sub-till techniques replaced inversion tillage (black fallow) on the more erosive soils (Johnson et al., 1983). Over the past 30 years, herbicides have replaced tillage in many crop production practices (Lyon et al., 1996). The primary method of reducing wind erosion on agricultural lands is to keep the soil protected with surface residues (Fryrear and Skidmore, 1985). In order to produce suf®cient crop residues, soil water must be managed to support ample crop growth. In addition to reducing soil erosion, the amount of precipitation stored as soil water during the fallow period increased as the amount of surface mulch increased (Unger, 1978). Several researchers have reported increased grain yields with the use of herbicides to control weeds during the fallow period in the winter wheat±fallow rotation (Fenster and Wicks, 1982; Peterson et al., 1993). In Wyoming, yield for a notill winter wheat±fallow system was similar to yield for a conventional fallow system (Krall et al., 1990). In 1969 and 1970, research was initiated at two sites near Sidney, NE, to compare the effects of no-till, subtill, and plow systems of fallow on winter wheat grain yield, grain protein, residue retention, soil NO3±N accumulation, and soil water accumulations during fallow (Fenster and Peterson, 1979). Additional studies have also been conducted at these sites to investigate the in¯uence of different tillage practices on various aspects of soil fertility (Lamb et al., 1985; Elliott, 1986; Follett and Peterson, 1988; Tracy et al., 1990; Cambardella and Elliott, 1992, 1994), soil physics (Mielke et al., 1984, 1986), and soil microbiology (Doran, 1980, 1987; Broder et al., 1984; Linn and Doran, 1984; Lamb et al., 1987; Follett and
Schimel, 1989). Our objectives were to update the report made by Fenster and Peterson (1979), and to determine if any of the three fallow tillage systems have provided superior long-term crop production bene®ts. 2. Methods The sites were located near Sidney, NE (41810 N latitude, 1038W longitude). 2.1. Previously Cultivated site The ®rst experiment was established in 1969 on an Alliance silt loam (®ne-silty, mixed, mesic Aridic Argiustoll; FAO ± Luvic Kastanaozem). The slope of the land was 1%. This land had been farmed from 1920 until 1957, and then seeded to crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] for 10 years prior to being broken out of sod with a moldboard plow in 1967. The site was divided into two major sections (Tillage A and B); one section was seeded to winter wheat and the other left fallow each year. The sections were cropped alternately to complete the winter wheat±fallow rotation. Fallow management treatments in each major section were plow, sub-till, and no-till. Each fallow management treatment area was divided into two equal subplots, one receiving no N fertilizer and the other receiving 45 (kg N) haÿ1. Fallow treatment plots were 8.5 m by 72.7 m and arranged in a randomized block design with four replications. The N fertilizer was surface broadcast as ammonium nitrate to growing wheat in April. Phosphate fertilizer was applied at seeding according to University of Nebraska soil test recommendations. 2.2. Native Sod site The second experiment was established in 1970 on a Duroc loam (®ne-silty, mixed, mesic Pachic Haplustoll; FAO ± Haplic Kastanaozem) located 5 km north of the Previously Cultivated site. The slope of the land was 0.1%. The site was located in a natural ¯ood plain and experienced two ¯ooding events (June 1974 and July 1981). The site had remained in native mixed grass sod (predominately buffalograss [BuchloeÈ dactyloides (Nutt.) Engelm.], blue grama [Bouteloua
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
gracilis (Kunth) Lag. ex Steud.], sideoats grama [Bouteloua curtipendula (Michx.) Torr.], western wheatgrass [Pascopyrum smithii (Rydb.) A. LoÈve], and needle and thread (Stipa comata Trin. and Rupr.)) until 1970 when it was broken out of sod with a moldboard plow. This site was also divided into two major sections (Tillage C and D); one section was seeded to winter wheat and the other left fallow each year. Sections were cropped alternately to complete the winter wheat±fallow rotation. Fallow management treatments in each major section were plow, sub-till, and no-till. A sod treatment plot (native mixed prairie species) was maintained in each replicate to serve as a control. The sod treatment plots were not hayed or grazed, but grass was burned in spring 1980 and 1994 to reduce residue accumulation and promote growth of warm-season species. Fallow- and sod-treatment plots were 8.545.5 m2 and arranged in a randomized block design with three replications. No fertilizer was applied. Plots at both sites were tilled with the same equipment (Table 1). For the plow treatment, a moldboard plow was used to a depth of ca. 15 cm in the spring, followed by two or three operations with a ®eld cultivator or tandem disk and then one or two operations with a rotary rod-weeder. On sub-till fallow treatment plots, tillage was performed with 90±150cm sweeps, two-to-four times a year to a maximum depth of ca. 10 cm, followed by one or two operations with a rotary rod-weeder. Initial tillage operations were performed at the deepest depth, with subsequent operations conducted at decreasing depths to provide a ®rm, mellow seedbed. For the no-tillage treatment, herbicides such as glyphosate [N-(phosphonomethyl)glycine], paraquat (1,10 -dimethyl-4,40 -bypyridinium
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ion), 2,4-D [2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-2-methoxybenzoic acid), cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2yl]amino]-2-methylpropanenitrile}, and atrazine [6chloro-N-ethyl-N0 -(1-methylethyl)-1,3,5-triazine-2,4diamine] were applied at labeled rates as needed to control weeds. Seeding was the only crop management operation that caused soil disturbance in no-till plots. Wheat in all non-sod treatment plots was seeded in September with a drill equipped with large coulters, slot openers for the seed, and press wheels spaced 30 cm apart. For the period 1971 to 1983, `Centurk' winter wheat was used. Beginning in 1984, wheat cultivars varied. Winter wheat was harvested in July with a combine. Residue data were collected by clipping standing stubble and gathering all surface residue from three 1-m2 quadrats per plot. Residue was washed, ovendried, and weighed. Grain protein was determined by standard Kjeldahl techniques. From 1970 through 1981, soil water was determined prior to winter wheat seeding by neutron attenuation using two 1.8-m aluminum access tubes (1.2 m tubes used from 1970 through 1971) per plot. Beginning in 1982, soil water was determined gravimetrically from two locations per plot. Depth of sampling varied and was limited by soil dryness. Data for the Previously Cultivated site were analyzed as a split-plot experiment with repeated measures. The whole-plot treatment factor was tillage arranged in randomized complete blocks. Fertilizer level was the split-plot factor. The repeated measurements were observations taken such that each block was measured in alternating years; thus, annual effects
Table 1 Characteristics and timing of tillage operations for the Previously Cultivated and Native Sod plots at Sidney, NE from 1970 to 1995 Field equipment
Moldboard plow Sweep plow Field cultivator a Rotary rodweeder Sprayer Hoe drill a
Depth
Operations ÿ1
Fallow tillage system
(cm)
(No. year )
plow (month)
sub-till (month)
no-till (month)
15 7±10 5±7.5 2±5 4±10
1 2±4 2±3 1±2 As needed 1
Apr±May Ð Apr±Jul Jul±Sep Ð Sep
Ð May±Aug Ð Jul±Sep Ð Sep
Ð Ð Ð Ð Apr±Sep Sep
Tandem disk used since 1990.
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D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
were nested within blocks. Because of the repeated measures split-plot, there are several error terms associated with whole-plot, split-plot, and within-split-plot repeated measurement error. The mixed model procedure of SAS was used in order to compute appropriate statistics for this analysis. See Littel et al. (1996) for a discussion on the statistical issues involved in such models. Data for the Native Sod site were analyzed as a standard repeated measures experiment without the split-plot aspect. 3. Results Average annual precipitation during the 26 years of the experiment (1970 through 1995) was 440 mm, with the majority of the precipitation occurring in May through July. Winter wheat seasonal precipitation (September through June) varied from a low of 180 mm for the 1988±1989 season to a high of 540 mm for the 1994±1995 season. Average annual mean temperature during the experiment was 168C, with average monthly temperatures ranging from a high of 228C in July to a low of ÿ48C in January. 3.1. Previously Cultivated site The effect of fallow tillage system, fertility level and their interactions on winter wheat grain yields varied from year to year (Fig. 1). Due to the long-term nature of the experiment, it was dif®cult to explain the causes for these differences within individual years. However, during the 26 years of the experiment, several treatment effects were discernable. Without the addition of fertilizer, average yields were 190 kg haÿ1 (8%) greater with the plow system than with either the sub- or no-till systems (Table 2). The addition of fertilizer increased yields in the sub- and no-till systems and eliminated yield differences due to fallow tillage treatments. As for grain yield, the effect of fallow tillage system, fertilizer level and their interaction on grain protein varied from year to year (data not shown). However, the long-term average protein levels were affected by tillage and fertilizer treatments. Averaged over all tillage systems, protein increased from 12.4% with no fertilizer to 14% with the addition of fertilizer (Table 2). Grain protein was greatest for the plow treatments and least for the no-till treatments. Effects
Fig. 1. Mean annual winter wheat grain yields (0.125 kg kgÿ1 moisture basis) from the Previously Cultivated long-term tillage research site at Sidney, NE.
of fallow tillage and fertilizer application did not interact. In non-fertilized treatment plots, the 26-year average harvest index was less in no-till (0.61) than in plow and sub-till (0.71) (Table 2). However, in fertilized treatment plots, no differences in this ratio were observed due to tillage treatments. Addition of fertilizer consistently increased residue production in all fallow tillage systems. Over the course of study, residue dry weights averaged 200 kg haÿ1 (5%) greater with fertilized treatments than with non-fertilized treatments (Table 3). However, the effect of fallow tillage treatment on residue production varied from year to year (data not shown). The long-term average residue dry weight was nearly 400 kg haÿ1 (10%) greater with no-till than with subtill (Table 3). After 14 months of fallow, and just prior to wheat seeding, residue dry weights on the soil surface had declined to an average level of 170, 1020, and 2610 kg haÿ1 in the plow, sub-till and no-till system plots, respectively. Soil water data were not consistently collected from fertilized treatment plots, so the effect of fertility level on soil water content was not analyzed. The effect of fallow tillage treatment on soil water content in the top 1.2 m of soil prior to wheat seeding varied from year to year (data not shown). This was probably the result of annual changes in rainfall pattern in relation to tillage events. Despite this annual variability, the 26-year average soil water content in the top 1.2 m of soil
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
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Table 2 Mean annual winter wheat grain yields (0.125 kg kgÿ1 moisture basis), grain protein (0.125 kg kgÿ1 moisture basis), and harvest index from two long-term tillage studies conducted near Sidney, NE from 1970 through 1995 Fallow system
Site Previously Cultivated
No fertilizer plow sub-till no-till sd Fertilizer plow sub-till no-till sd Plow vs. sub- and no-till (PvSN) Sub-till vs. no-till (SvN) No fertilizer vs. fertilizer PvSN by fertilizer SvN by fertilizer
Native Sod
grain yield (kg haÿ1)
grain protein (%)
harvest index
grain yield (kg haÿ1)
grain protein (%)
harvest index
2620 2430 2430 54
12.9 12.2 12.0 0.14
0.71 0.71 0.61 0.03
2440 2570 2490 73
13.9 13.4 13.0 0.18
0.64 0.71 0.70 0.03
0.68 0.67 0.65 0.03
Ð Ð Ð Ð
Ð Ð Ð Ð
Ð Ð Ð Ð
0.002 0.045 Ð Ð Ð
0.116 0.806 Ð Ð Ð
2620 14.5 2580 14.2 2630 13.5 54 0.14 Significance of contrast 0.011 0.001 0.510 0.021 0.001 0.001 0.018 0.479 0.498 0.152
0.207 0.054 0.605 0.383 0.067
Ð Ð Ð
0.556 0.653
Table 3 Mean annual winter wheat residue dry weights from two long-term tillage studies conducted near Sidney, NE from 1970 through 1995 Site Fallow system
No fertilizer plow sub-till no-till sd Fertilizer plow sub-till no-till sd Plow vs. sub- and no-till (PvSN) Sub-till vs. no-till (SvN) No fertilizer vs. fertilizer PvSN by fertilizer SvN by fertilizer
Previously Cultivated (kg haÿ1)
Native Sod (kg haÿ1)
4050 3700 4090 174
3990 3880 3790 180
4060 Ð 3990 Ð 4390 Ð 174 Ð Significance of contrast 0.963 0.346 0.038 0.609 0.030 Ð 0.110 Ð 0.933 Ð
prior to wheat seeding was greater in no-till (0.187 kg kgÿ1) than in plow and sub-till (0.181 kg kgÿ1) plots (Table 4).
Fig. 2. Mean annual winter wheat grain yields (0.125 kg kgÿ1 moisture basis) from the Native Sod long-term tillage research site at Sidney, NE.
3.2. Native Sod site The effect of tillage system on grain yield varied from year to year (Fig. 2). As in the Previously Cultivated site, reasons for the yearly variation are dif®cult to discern. Despite the variation, the 24-year average grain yields for the experiment did not differ
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D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
Table 4 Mean water content in the surface 1.2 m of soil prior to winter wheat seeding at two long-term tillage studies conducted near Sidney, NE from 1970 through 1995 Fallow system
Site Previously cultivated (kg kgÿ1)
No fertilizer plow sub-till no-till sd Plow vs. sub- and no-till Sub-till vs. no-till
Native Sod (kg kgÿ1)
0.181 0.153 0.180 0.161 0.187 0.168 0.003 0.003 Significance of contrast 0.095 0.014 0.052 0.161
due to tillage systems (Table 2), indicating different tillage systems were superior in different years. The response of grain protein to tillage treatments was consistent from year to year (data not shown). As in the Previously Cultivated site, protein was greatest with the plow treatment and least with the no-till treatment (Table 2). No differences in harvest index were observed due to tillage systems (Table 2). The effect of tillage treatment on residue dry weight was consistent from year to year (data not shown). No differences were observed in dry weight due to tillage systems (Table 3). After 14 months of fallow, and just prior to wheat seeding, residue dry weights had declined to an average level of 200, 1260, and 2710 kg haÿ1 in the plow, sub-till and no-till system plots, respectively. The effect of tillage system on soil water storage in the top 1.2 m of soil prior to wheat seeding varied from year to year (data not shown), with the 24-year average being greater in sub- and no-till (0.161 and 0.168 kg ÿ1, respectively) than in plow (0.155 kgÿ1) treatment plots (Table 4). 4. Discussion Grain yields in a winter wheat±fallow rotation did not appear to bene®t from the increased soil water storage in no-till plots (Tables 2 and 4). This has been observed by other researchers in the Great Plains
(Peterson et al., 1996). Greater N immobilization with no-till has been suggested as a possible explanation for the lack of yield response to increased soil water storage with no-till (Doran et al., 1998; Power and Peterson, 1998). However, in a prior 3-year experiment conducted at the Previously Cultivated site, Varvel et al. (1989) concluded that N immobilization was not a factor in explaining why wheat growth fails to respond to the extra soil water conserved in no-till fallow. An apparent decrease in root function resulted in reduced pro®le water extraction and N uptake in minimum- and no-till systems in northern Idaho (Hammel, 1995). Increased root impedance, or possibly, greater root disease pressure were cited as possible explanations for decreased root function and subsequent grain yield reductions. Wilhelm et al. (1989) found that winter wheat developed more slowly during the vegetative stage with no-till, due to cooler soil temperatures, than with tilled treatments. It is dif®cult to determine why grain yield failed to consistently respond to increased soil water with no-till in this experiment. Despite the assertion that water is the most limiting resource for dryland crop production in the semi-arid Great Plains (Smika, 1970), other environmental or cultural factors must be more limiting to no-till winter wheat grain yield than available soil water. These long-term tillage studies were consistently managed through 1982 (Fenster and Peterson, 1979), but from 1983 through 1989, the management was less consistent. During this latter period, downy brome (Bromus tectorum L.) infested the sub- and no-till treatments at both sites. Winter wheat yields in Nebraska have been reduced 30% by downy brome populations of 11 to 22 plants mÿ2 (Wicks, 1984). Downy brome densities >50 plants mÿ2 have been observed in the no-till plots at the Previously Cultivated site. Selective chemical control of downy brome in winter wheat is dif®cult because of biological similarities between the two species. Tillage has long been the standard means of downy brome control in a winter wheat-fallow system and moldboard plowing has been more effective than conservation tillage (Wicks, 1984). The mid-1980s infestation of downy brome probably had a negative in¯uence on no-till winter wheat grain yields during the second half of the experiment as indicated by data in Fig. 3. The inability to control winter annual grass weeds in no-till winter
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
Fig. 3. The effect of fallow tillage systems on winter wheat grain yields during the first and second 13-year periods at the Previously Cultivated site near Sidney, NE. Downy brome (Bromus tectorum L.) infested sub- and no-till systems during the second half of the experiment.
wheat±fallow systems has been a major reason for the lack of adoption of this system in the Central Great Plains. At the Previously Cultivated site, grain yields in the plow±fallow system were not affected by fertilizer treatment (Table 2), but grain yields were less in the sub- and no-till systems when N fertilizer was not applied. Whether this was due to greater N immobilization or reduced root function in sub- and no-till is unclear. However, Wilhelm (1998) found less root dry matter with the sub-till treatment than with the plow or no-till treatments. Fallow tillage system had no effect on grain yield at the Native Sod site. Perhaps N mineralization rates are still adequate, even in no-till, to meet plant needs at this site. Organic C and total N contents of the top 20 cm of soil at the start of the two studies were about twice as great at the Native Sod site as at the Previously Cultivated site (Fenster and Peterson, 1979). Consequently, grain yields at the Native Sod site responded to the tillage treatments similarly to grain yields with fertilized treatments of the Previously Cultivated site (Table 2). With continued cropping and a subsequent decline in native fertility, differences in grain yield due to tillage systems may be expected at the Native Sod site. However, as of 1995, no such trend was evident (Fig. 2). Grain protein levels were always greatest in plow, intermediate in sub-till and least in the no-till system plots regardless of fertilizer treatment or site. However, grain yields were not affected by tillage system at
25
the Native Sod site or at the Previously Cultivated site when N fertilizer was applied. In an experiment conducted in eastern Colorado, winter wheat grain yield response to N fertilizer was dependant on precipitation and residual soil NO3, while grain protein responded to N fertilizer regardless of precipitation and residual NO3 levels (Vaughan et al., 1990). This suggests that plant uptake of N increases as tillage intensity increases, and that while N uptake may be limiting yields with sub- and no-till systems, some factor other than N, e.g. soil water, is limiting grain yield potential with plow±fallow systems. 5. Conclusions Despite all the bene®ts of no-till fallow, including improved soil water storage ef®ciency (Unger, 1978), reduced organic C losses (Lyon et al., 1997), and reduced soil erosion potential (Fryrear and Skidmore, 1985), the long-term yield potential of continuous notill fallow is no better than plow fallow. In fact, the dif®culty of controlling winter annual grass weeds such as downy brome, jointed goatgrass (Aegilops cylindrica Host), and volunteer cereal rye (Secale cereale L.) without tillage has limited the adoption of no-till winter wheat±fallow in the Central Great Plains. Winter wheat±fallow systems, with or without tillage, probably are not sustainable in the Central Great Plains. Plowing, and to a lesser extent sub-tillage, resulted in unacceptable levels of soil erosion and depletion of soil organic matter. Even though no-till fallow reduces the rate of soil erosion and organicmatter loss, organic-matter losses continue due to the low amounts of residues returned to the system from only one crop every other year (Doran et al., 1998). This conclusion is similar to that made by Boehm and Anderson (1997) from their work in the Canadian prairie. Thus, none of the tillage systems studied resulted in sustainable agriculture. The use of no-till systems in combination with more frequent cropping intensity, e.g. winter wheat±corn (Zea mays L.)±fallow or winter wheat±corn±proso millet (Panicum miliaceum L.)±fallow, may increase net returns and reduce ®nancial risk (Dhuyvetter et al., 1996), increase water use ef®ciency (Peterson et al., 1996), and effectively control winter annual grass
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D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
weeds in the winter wheat crop (Lyon and Baltensperger, 1995). Producers in the semi-arid Central Great Plains may need to adopt these systems in order to remain competitive in the future. Acknowledgements The authors acknowledge the hard work and dedication of the numerous scientists, graduate students and research technicians who contributed to the long-term management of these experiments. Special recognition is made to Mr. Charles Fenster, Professor Emeritus, University of Nebraska for his vision and hard work in establishing these experiments. References Boehm, M.M., Anderson, D.W., 1997. A landscape-scale study of soil quality in three prairie farming systems. Soil Sci. Soc. Am. J. 61, 1147±1159. Broder, M.W., Doran, J.W., Peterson, G.A., Fenster, C.R., 1984. Fallow tillage influence on spring populations of soil nitrifiers, denitrifiers, and available nitrogen. Soil Sci. Soc. Am. J. 48, 1060±1067. Cambardella, C.A., Elliott, E.T., 1992. Particulate soil organicmatter changes across a grassland cultivation sequence. Soil Soc. Sci. Am. J. 56, 777±783. Cambardella, C.A., Elliott, E.T., 1994. Carbon and nitrogen dynamics of soil organic matter fractions from cultivated grassland soils. Soil Sci. Soc. Am. J. 58, 123±130. Dhuyvetter, K.C., Thompson, C.R., Norwood, C.A., Halvorson, A.D., 1996. Economics of dryland cropping systems in the Great Plains: A review. J. Prod. Agric. 9, 216±222. Doran, J.W., 1980. Soil microbial and biochemical changes associated with reduced tillage. Soil Sci. Soc. Am. J. 44, 765±771. Doran, J.W., 1987. Microbial biomass and mineralizable nitrogen distributions in no-tillage and plowed soils. Biol. Fertil. Soils 5, 68±75. Doran, J.W., Elliott, E.T., Paustian, K., 1998. Soil microbial activity, nitrogen cycling, and long-term changes in organic carbon pools as related to fallow tillage management. Soil Tillage Res., in review. Elliott, E.T., 1986. Aggregate structure and C, N, and P in native and cultivated soils. Soil Sci. Soc. Am. J. 50, 627±633. Fenster, C.R., Peterson, G.A., 1979. Effects of no-tillage fallow as compared to conventional tillage in a wheat±fallow system. Nebraska Exp. Stn. RB 289. Fenster, C.R., Wicks, G.A., 1982. Fallow systems for winter wheat in western Nebraska. Agron. J. 74, 9±13.
Follett, R.F., Peterson, G.A., 1988. Surface soil nutrient distribution as affected by wheat±fallow tillage systems. Soil Sci. Soc. Am. J. 52, 141±147. Follett, R.F., Schimel, D.S., 1989. Effect of tillage practices on microbial biomass dynamics. Soil Sci. Soc. Am. J. 53, 1091± 1096. Fryrear, D.W., Skidmore, E.L., 1985. Methods of controlling wind erosion. In: Follett, R.F., Stewart, B.A. (Eds.), Soil Erosion and Crop Productivity, ASA, CSSA, and SSSA, Madison, WI, pp. 443±457. Hammel, J.E., 1995. Long-term tillage and crop rotation effects on winter wheat production in northern Idaho. Agron. J. 87, 16±22. Hinze, G.O., Smika, D.E., 1983. Cropping practices: Central Great Plains. In: Dregne, H.E., Willis, W.O. (Eds.), Dryland Agriculture, ASA, CSSA, and SSSA, Madison, WI, pp. 293± 295. Johnson, W.C., Skidmore, E.L., Tucker, B.B., Unger, P.W., 1983. Soil conservation: Central Great Plains winter wheat and range region. In: Dregne, H.E., Willis, W.O. (Eds.), Dryland Agriculture, ASA, CSSA, and SSSA, Madison, WI, pp. 197± 217. Krall, J.M., Dalrymple, A.W., Miller, S.D., 1990. Fertilizer responses and soil moisture conditions in dryland winter wheat conservation tillage systems. In: Proceedings Great Plains Conservation Tillage Symposium. Great Plains Agricultural Council, Ft. Collins, CO, pp. 125±131. Lamb, J.A., Peterson, G.A., Fenster, C.R., 1985. Fallow nitrate accumulation in a wheat±fallow rotation as affected by tillage system. Soil Sci. Soc. Am. J. 49, 1441±1446. Lamb, J.A., Doran, J.W., Peterson, G.A., 1987. Nonsymbiotic dinitrogen fixation in no-till and conventional wheat±fallow systems. Soil Sci. Soc. Am. J. 51, 356±361. Linn, D.M., Doran, J.W., 1984. Aerobic and anaerobic microbial populations in no-till and plowed soils. Soil Sci. Soc. Am. J. 48, 794±799. Littel, R.C., Milliken, G.A., Stroup, W.W., Wolfinger, R.D. 1996. SAS System for Mixed Models. SAS Institute, Inc., Cary, NC. Lyon, D.J., Baltensperger, D.D., 1995. Cropping systems control winter annual grass weeds in winter wheat. J. Prod. Agric. 8, 535±539. Lyon, D.J., Miller, S.D., Wicks, G.A., 1996. The future of herbicides in weed control systems of the Great Plains. J. Prod. Agric. 9, 209±215. Lyon, D.J., Monz, C.A., Brown, R.E., Metherell, A.K., 1997. Soil organic matter changes over two decades of winter wheat± fallow cropping in western Nebraska. In: Paul, E.A., Paustian, K., Elliott, E.T., Cole, C.V. (Eds.), Soil Organic Matter in Temperate Agroecosystems: Long-term Experiments in North America, CRC Press, Inc., Boca Raton, FL, pp. 343±351. Mielke, L.N., Wilhelm, W.W., Richards, K.A., Fenster, C.R., 1984. Soil physical characteristics of reduced tillage in a wheat± fallow system. Trans. Am. Soc. Agric. Eng. 27, 1724±1728. Mielke, L.N., Doran, J.W., Richards, K.A., 1986. Physical environment near the surface of plowed and no-tilled soils. Soil Tillage Res. 7, 355±366. Miller, F.P., Rasmussen, W.D., Meyer, L.D., 1985. Historical perspective of soil erosion in the United States. In: Follett, R.F.,
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27 Stewart, B.A. (Eds.), Soil Erosion and Crop Productivity, ASA, CSSA, and SSSA, Madison, WI, pp. 23±48. Peterson, G.A., Westfall, D.G., Cole, C.V., 1993. Agroecosystem approach to soil and crop management research. Soil Sci. Soc. Am. J. 57, 1354±1360. Peterson, G.A., Schlegel, A.J., Tanaka, D.L., Jones, O.R., 1996. Precipitation use efficiency as affected by cropping and tillage systems. J. Prod. Agric. 9, 180±186. Power, J.F., Peterson, G.A., 1998. Nitrogen transformations, utilization, and conservation as affected by fallow. Soil Tillage Res. 49, 37±47. Smika, D.E., 1970. Summer fallow for dryland winter wheat in the semiarid Great Plains. Agron. J. 62, 15±17. Smika, D.E., 1983. Cropping practices: Introduction. In: Dregne, H.E., Willis, W.O. (Eds.), Dryland Agriculture, ASA, CSSA, and SSSA, Madison, WI, pp. 293±295. Snyder, W.P., Burr, W.W., 1909. Crop production in western Nebraska. Nebraska Exp. Stn. RB 109. Tracy, P.W., Westfall, D.G., Elliott, E.T., Peterson, G.A., 1990.
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Tillage influence on soil sulfur characteristics in winter wheat± summer fallow systems. Soil Sci. Soc. Am. J. 54, 1630±1634. Unger, P.W., 1978. Straw-mulch rate effect on soil water storage and sorghum yield. Soil Sci Soc. Am. J. 42, 480±491. Varvel, G.E., Havlin, J.L., Peterson, T.A., 1989. Nitrogen placement evaluation for winter wheat in three fallow tillage systems. Soil Sci. Soc. Am. J. 53, 288±292. Vaughan, B., Westfall, D.G., Barbarick, K.A., 1990. Nitrogen rate and timing effects on winter wheat grain yield, grain protein, and economics. J. Prod. Agric. 3, 324±328. Wicks, G.A., Integrated systems for control and management of downy brome (Bromus tectorum) in cropland. Weed Sci. 32, Suppl. 1 (1984) 26±31. Wilhelm, W.W., 1998. Dry matter partitioning and leaf area of winter wheat grown in long-term fallow tillage comparisons in the US Central Great Plains. Soil Tillage Res. 49, 49±56. Wilhelm, W.W., Bouzerzour, H., Power, J.F., 1989. Soil disturbance-residue management effect on winter wheat growth and development. Agron. J. 81, 581±588.
Crop production and soil water storage in long-term winter wheat±fallow tillage experiments Drew J. Lyona,*, Walter W. Stroupb, Randall E. Brownc b
a Panhandle Research and Extension Center, 4502 Avenue I, Scottsbluff, NE 69361, USA Panhandle Research and Extension Center, 103 Miller Hall, University of Nebraska 103 Miller Hall, Lincoln, NE 68583-0712, USA c Panhandle Research and Extension Center, P.O. Box 786, Colby KS 67701-0786, USA
Received 24 September 1997; accepted 3 April 1998
Abstract Soil water is the major limiting factor in dryland crop production in the Central Great Plains. No-till fallow management increases soil water storage and reduces soil erosion potential. Two experiments were initiated in 1969 and 1970 near Sidney, NE to compare effects of moldboard plow (Plow), sub-tillage (Sub-till) and no-tillage (No-till) fallow systems on winter wheat (Triticum aestivum L.) grain yield, grain protein, residue production, and soil water accumulation during fallow. The ®rst experiment was established in 1969 on an Alliance silt loam that had been previously cultivated prior to study initiation. This experiment contained a nitrogen (N) fertilizer split of 0 and 45 (kg N) haÿ1 within each tillage treatment. The second experiment was established in 1970 on a Duroc loam that was in native mixed prairie sod. No fertilizer was applied at this site. At both sites, soil water storage was greatest with the no-till and least with the plow system. Winter wheat grain yields failed to consistently respond to increased soil water storage in the no-till system during the 24±26 years of the experiments. Grain yields with the plow system were 8% greater than with sub- and no-till systems at the Previously Cultivated site when N was not applied. The addition of N at this site eliminated yield differences due to fallow tillage systems. Grain protein averaged 13.8, 13.3 and 12.8% for all plow, sub- and no-till treatments, respectively. The addition of N at the Previously Cultivated site increased residue dry weights by an average of 5% in all tillage systems. Neither grain protein nor residue dry weights were affected by tillage system at the Native Sod site. Winter wheat±fallow is probably not a sustainable production system for the Central Great Plains, regardless of the fallow management system used. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Triticum aestivum; No-till; Sub-till; Plow; Grain yield; Grain protein; Soil water
1. Introduction Water is the most limiting resource for dryland crop growth in the semi-arid areas of the U.S. Great Plains (Smika, 1970). Summer fallow, the practice of con*Corresponding author. Tel.: +1 308-632-1266; fax: +1 308-6321365; e-mail address: [email protected]
trolling all plant growth during the non-crop season, was quickly adopted to stabilize winter wheat production in this region (Snyder and Burr, 1909). In the Central Great Plains, the 14 months of fallow begin in July after wheat harvest and continue until wheat seeding in September of the following year. In addition to storing soil water for the succeeding crop, fallow also enhances accumulation of nitrate through
0167-1987/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0167-1987(98)00151-2
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mineralization of organic matter, and control of problem weeds, diseases, and insects (Smika, 1983). Winter wheat±fallow has been the predominant crop rotation in the U.S. Central Great Plains for the past 75 years (Hinze and Smika, 1983). During the U.S. Dust Bowl era of the 1930s, when 60±80 million hectares of land were scarred by wind erosion from Texas to the Dakotas (Miller et al., 1985), it became evident that farming practices had to be changed to protect land from erosion. Prior to the Dust Bowl, fallow tillage typically involved use of the moldboard or one-way disk plow, which inverted the soil and buried most crop residues (Johnson et al., 1983). During the 1940s and 1950s, non-inversion sub-till techniques replaced inversion tillage (black fallow) on the more erosive soils (Johnson et al., 1983). Over the past 30 years, herbicides have replaced tillage in many crop production practices (Lyon et al., 1996). The primary method of reducing wind erosion on agricultural lands is to keep the soil protected with surface residues (Fryrear and Skidmore, 1985). In order to produce suf®cient crop residues, soil water must be managed to support ample crop growth. In addition to reducing soil erosion, the amount of precipitation stored as soil water during the fallow period increased as the amount of surface mulch increased (Unger, 1978). Several researchers have reported increased grain yields with the use of herbicides to control weeds during the fallow period in the winter wheat±fallow rotation (Fenster and Wicks, 1982; Peterson et al., 1993). In Wyoming, yield for a notill winter wheat±fallow system was similar to yield for a conventional fallow system (Krall et al., 1990). In 1969 and 1970, research was initiated at two sites near Sidney, NE, to compare the effects of no-till, subtill, and plow systems of fallow on winter wheat grain yield, grain protein, residue retention, soil NO3±N accumulation, and soil water accumulations during fallow (Fenster and Peterson, 1979). Additional studies have also been conducted at these sites to investigate the in¯uence of different tillage practices on various aspects of soil fertility (Lamb et al., 1985; Elliott, 1986; Follett and Peterson, 1988; Tracy et al., 1990; Cambardella and Elliott, 1992, 1994), soil physics (Mielke et al., 1984, 1986), and soil microbiology (Doran, 1980, 1987; Broder et al., 1984; Linn and Doran, 1984; Lamb et al., 1987; Follett and
Schimel, 1989). Our objectives were to update the report made by Fenster and Peterson (1979), and to determine if any of the three fallow tillage systems have provided superior long-term crop production bene®ts. 2. Methods The sites were located near Sidney, NE (41810 N latitude, 1038W longitude). 2.1. Previously Cultivated site The ®rst experiment was established in 1969 on an Alliance silt loam (®ne-silty, mixed, mesic Aridic Argiustoll; FAO ± Luvic Kastanaozem). The slope of the land was 1%. This land had been farmed from 1920 until 1957, and then seeded to crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] for 10 years prior to being broken out of sod with a moldboard plow in 1967. The site was divided into two major sections (Tillage A and B); one section was seeded to winter wheat and the other left fallow each year. The sections were cropped alternately to complete the winter wheat±fallow rotation. Fallow management treatments in each major section were plow, sub-till, and no-till. Each fallow management treatment area was divided into two equal subplots, one receiving no N fertilizer and the other receiving 45 (kg N) haÿ1. Fallow treatment plots were 8.5 m by 72.7 m and arranged in a randomized block design with four replications. The N fertilizer was surface broadcast as ammonium nitrate to growing wheat in April. Phosphate fertilizer was applied at seeding according to University of Nebraska soil test recommendations. 2.2. Native Sod site The second experiment was established in 1970 on a Duroc loam (®ne-silty, mixed, mesic Pachic Haplustoll; FAO ± Haplic Kastanaozem) located 5 km north of the Previously Cultivated site. The slope of the land was 0.1%. The site was located in a natural ¯ood plain and experienced two ¯ooding events (June 1974 and July 1981). The site had remained in native mixed grass sod (predominately buffalograss [BuchloeÈ dactyloides (Nutt.) Engelm.], blue grama [Bouteloua
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
gracilis (Kunth) Lag. ex Steud.], sideoats grama [Bouteloua curtipendula (Michx.) Torr.], western wheatgrass [Pascopyrum smithii (Rydb.) A. LoÈve], and needle and thread (Stipa comata Trin. and Rupr.)) until 1970 when it was broken out of sod with a moldboard plow. This site was also divided into two major sections (Tillage C and D); one section was seeded to winter wheat and the other left fallow each year. Sections were cropped alternately to complete the winter wheat±fallow rotation. Fallow management treatments in each major section were plow, sub-till, and no-till. A sod treatment plot (native mixed prairie species) was maintained in each replicate to serve as a control. The sod treatment plots were not hayed or grazed, but grass was burned in spring 1980 and 1994 to reduce residue accumulation and promote growth of warm-season species. Fallow- and sod-treatment plots were 8.545.5 m2 and arranged in a randomized block design with three replications. No fertilizer was applied. Plots at both sites were tilled with the same equipment (Table 1). For the plow treatment, a moldboard plow was used to a depth of ca. 15 cm in the spring, followed by two or three operations with a ®eld cultivator or tandem disk and then one or two operations with a rotary rod-weeder. On sub-till fallow treatment plots, tillage was performed with 90±150cm sweeps, two-to-four times a year to a maximum depth of ca. 10 cm, followed by one or two operations with a rotary rod-weeder. Initial tillage operations were performed at the deepest depth, with subsequent operations conducted at decreasing depths to provide a ®rm, mellow seedbed. For the no-tillage treatment, herbicides such as glyphosate [N-(phosphonomethyl)glycine], paraquat (1,10 -dimethyl-4,40 -bypyridinium
21
ion), 2,4-D [2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-2-methoxybenzoic acid), cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2yl]amino]-2-methylpropanenitrile}, and atrazine [6chloro-N-ethyl-N0 -(1-methylethyl)-1,3,5-triazine-2,4diamine] were applied at labeled rates as needed to control weeds. Seeding was the only crop management operation that caused soil disturbance in no-till plots. Wheat in all non-sod treatment plots was seeded in September with a drill equipped with large coulters, slot openers for the seed, and press wheels spaced 30 cm apart. For the period 1971 to 1983, `Centurk' winter wheat was used. Beginning in 1984, wheat cultivars varied. Winter wheat was harvested in July with a combine. Residue data were collected by clipping standing stubble and gathering all surface residue from three 1-m2 quadrats per plot. Residue was washed, ovendried, and weighed. Grain protein was determined by standard Kjeldahl techniques. From 1970 through 1981, soil water was determined prior to winter wheat seeding by neutron attenuation using two 1.8-m aluminum access tubes (1.2 m tubes used from 1970 through 1971) per plot. Beginning in 1982, soil water was determined gravimetrically from two locations per plot. Depth of sampling varied and was limited by soil dryness. Data for the Previously Cultivated site were analyzed as a split-plot experiment with repeated measures. The whole-plot treatment factor was tillage arranged in randomized complete blocks. Fertilizer level was the split-plot factor. The repeated measurements were observations taken such that each block was measured in alternating years; thus, annual effects
Table 1 Characteristics and timing of tillage operations for the Previously Cultivated and Native Sod plots at Sidney, NE from 1970 to 1995 Field equipment
Moldboard plow Sweep plow Field cultivator a Rotary rodweeder Sprayer Hoe drill a
Depth
Operations ÿ1
Fallow tillage system
(cm)
(No. year )
plow (month)
sub-till (month)
no-till (month)
15 7±10 5±7.5 2±5 4±10
1 2±4 2±3 1±2 As needed 1
Apr±May Ð Apr±Jul Jul±Sep Ð Sep
Ð May±Aug Ð Jul±Sep Ð Sep
Ð Ð Ð Ð Apr±Sep Sep
Tandem disk used since 1990.
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D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
were nested within blocks. Because of the repeated measures split-plot, there are several error terms associated with whole-plot, split-plot, and within-split-plot repeated measurement error. The mixed model procedure of SAS was used in order to compute appropriate statistics for this analysis. See Littel et al. (1996) for a discussion on the statistical issues involved in such models. Data for the Native Sod site were analyzed as a standard repeated measures experiment without the split-plot aspect. 3. Results Average annual precipitation during the 26 years of the experiment (1970 through 1995) was 440 mm, with the majority of the precipitation occurring in May through July. Winter wheat seasonal precipitation (September through June) varied from a low of 180 mm for the 1988±1989 season to a high of 540 mm for the 1994±1995 season. Average annual mean temperature during the experiment was 168C, with average monthly temperatures ranging from a high of 228C in July to a low of ÿ48C in January. 3.1. Previously Cultivated site The effect of fallow tillage system, fertility level and their interactions on winter wheat grain yields varied from year to year (Fig. 1). Due to the long-term nature of the experiment, it was dif®cult to explain the causes for these differences within individual years. However, during the 26 years of the experiment, several treatment effects were discernable. Without the addition of fertilizer, average yields were 190 kg haÿ1 (8%) greater with the plow system than with either the sub- or no-till systems (Table 2). The addition of fertilizer increased yields in the sub- and no-till systems and eliminated yield differences due to fallow tillage treatments. As for grain yield, the effect of fallow tillage system, fertilizer level and their interaction on grain protein varied from year to year (data not shown). However, the long-term average protein levels were affected by tillage and fertilizer treatments. Averaged over all tillage systems, protein increased from 12.4% with no fertilizer to 14% with the addition of fertilizer (Table 2). Grain protein was greatest for the plow treatments and least for the no-till treatments. Effects
Fig. 1. Mean annual winter wheat grain yields (0.125 kg kgÿ1 moisture basis) from the Previously Cultivated long-term tillage research site at Sidney, NE.
of fallow tillage and fertilizer application did not interact. In non-fertilized treatment plots, the 26-year average harvest index was less in no-till (0.61) than in plow and sub-till (0.71) (Table 2). However, in fertilized treatment plots, no differences in this ratio were observed due to tillage treatments. Addition of fertilizer consistently increased residue production in all fallow tillage systems. Over the course of study, residue dry weights averaged 200 kg haÿ1 (5%) greater with fertilized treatments than with non-fertilized treatments (Table 3). However, the effect of fallow tillage treatment on residue production varied from year to year (data not shown). The long-term average residue dry weight was nearly 400 kg haÿ1 (10%) greater with no-till than with subtill (Table 3). After 14 months of fallow, and just prior to wheat seeding, residue dry weights on the soil surface had declined to an average level of 170, 1020, and 2610 kg haÿ1 in the plow, sub-till and no-till system plots, respectively. Soil water data were not consistently collected from fertilized treatment plots, so the effect of fertility level on soil water content was not analyzed. The effect of fallow tillage treatment on soil water content in the top 1.2 m of soil prior to wheat seeding varied from year to year (data not shown). This was probably the result of annual changes in rainfall pattern in relation to tillage events. Despite this annual variability, the 26-year average soil water content in the top 1.2 m of soil
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
23
Table 2 Mean annual winter wheat grain yields (0.125 kg kgÿ1 moisture basis), grain protein (0.125 kg kgÿ1 moisture basis), and harvest index from two long-term tillage studies conducted near Sidney, NE from 1970 through 1995 Fallow system
Site Previously Cultivated
No fertilizer plow sub-till no-till sd Fertilizer plow sub-till no-till sd Plow vs. sub- and no-till (PvSN) Sub-till vs. no-till (SvN) No fertilizer vs. fertilizer PvSN by fertilizer SvN by fertilizer
Native Sod
grain yield (kg haÿ1)
grain protein (%)
harvest index
grain yield (kg haÿ1)
grain protein (%)
harvest index
2620 2430 2430 54
12.9 12.2 12.0 0.14
0.71 0.71 0.61 0.03
2440 2570 2490 73
13.9 13.4 13.0 0.18
0.64 0.71 0.70 0.03
0.68 0.67 0.65 0.03
Ð Ð Ð Ð
Ð Ð Ð Ð
Ð Ð Ð Ð
0.002 0.045 Ð Ð Ð
0.116 0.806 Ð Ð Ð
2620 14.5 2580 14.2 2630 13.5 54 0.14 Significance of contrast 0.011 0.001 0.510 0.021 0.001 0.001 0.018 0.479 0.498 0.152
0.207 0.054 0.605 0.383 0.067
Ð Ð Ð
0.556 0.653
Table 3 Mean annual winter wheat residue dry weights from two long-term tillage studies conducted near Sidney, NE from 1970 through 1995 Site Fallow system
No fertilizer plow sub-till no-till sd Fertilizer plow sub-till no-till sd Plow vs. sub- and no-till (PvSN) Sub-till vs. no-till (SvN) No fertilizer vs. fertilizer PvSN by fertilizer SvN by fertilizer
Previously Cultivated (kg haÿ1)
Native Sod (kg haÿ1)
4050 3700 4090 174
3990 3880 3790 180
4060 Ð 3990 Ð 4390 Ð 174 Ð Significance of contrast 0.963 0.346 0.038 0.609 0.030 Ð 0.110 Ð 0.933 Ð
prior to wheat seeding was greater in no-till (0.187 kg kgÿ1) than in plow and sub-till (0.181 kg kgÿ1) plots (Table 4).
Fig. 2. Mean annual winter wheat grain yields (0.125 kg kgÿ1 moisture basis) from the Native Sod long-term tillage research site at Sidney, NE.
3.2. Native Sod site The effect of tillage system on grain yield varied from year to year (Fig. 2). As in the Previously Cultivated site, reasons for the yearly variation are dif®cult to discern. Despite the variation, the 24-year average grain yields for the experiment did not differ
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D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
Table 4 Mean water content in the surface 1.2 m of soil prior to winter wheat seeding at two long-term tillage studies conducted near Sidney, NE from 1970 through 1995 Fallow system
Site Previously cultivated (kg kgÿ1)
No fertilizer plow sub-till no-till sd Plow vs. sub- and no-till Sub-till vs. no-till
Native Sod (kg kgÿ1)
0.181 0.153 0.180 0.161 0.187 0.168 0.003 0.003 Significance of contrast 0.095 0.014 0.052 0.161
due to tillage systems (Table 2), indicating different tillage systems were superior in different years. The response of grain protein to tillage treatments was consistent from year to year (data not shown). As in the Previously Cultivated site, protein was greatest with the plow treatment and least with the no-till treatment (Table 2). No differences in harvest index were observed due to tillage systems (Table 2). The effect of tillage treatment on residue dry weight was consistent from year to year (data not shown). No differences were observed in dry weight due to tillage systems (Table 3). After 14 months of fallow, and just prior to wheat seeding, residue dry weights had declined to an average level of 200, 1260, and 2710 kg haÿ1 in the plow, sub-till and no-till system plots, respectively. The effect of tillage system on soil water storage in the top 1.2 m of soil prior to wheat seeding varied from year to year (data not shown), with the 24-year average being greater in sub- and no-till (0.161 and 0.168 kg ÿ1, respectively) than in plow (0.155 kgÿ1) treatment plots (Table 4). 4. Discussion Grain yields in a winter wheat±fallow rotation did not appear to bene®t from the increased soil water storage in no-till plots (Tables 2 and 4). This has been observed by other researchers in the Great Plains
(Peterson et al., 1996). Greater N immobilization with no-till has been suggested as a possible explanation for the lack of yield response to increased soil water storage with no-till (Doran et al., 1998; Power and Peterson, 1998). However, in a prior 3-year experiment conducted at the Previously Cultivated site, Varvel et al. (1989) concluded that N immobilization was not a factor in explaining why wheat growth fails to respond to the extra soil water conserved in no-till fallow. An apparent decrease in root function resulted in reduced pro®le water extraction and N uptake in minimum- and no-till systems in northern Idaho (Hammel, 1995). Increased root impedance, or possibly, greater root disease pressure were cited as possible explanations for decreased root function and subsequent grain yield reductions. Wilhelm et al. (1989) found that winter wheat developed more slowly during the vegetative stage with no-till, due to cooler soil temperatures, than with tilled treatments. It is dif®cult to determine why grain yield failed to consistently respond to increased soil water with no-till in this experiment. Despite the assertion that water is the most limiting resource for dryland crop production in the semi-arid Great Plains (Smika, 1970), other environmental or cultural factors must be more limiting to no-till winter wheat grain yield than available soil water. These long-term tillage studies were consistently managed through 1982 (Fenster and Peterson, 1979), but from 1983 through 1989, the management was less consistent. During this latter period, downy brome (Bromus tectorum L.) infested the sub- and no-till treatments at both sites. Winter wheat yields in Nebraska have been reduced 30% by downy brome populations of 11 to 22 plants mÿ2 (Wicks, 1984). Downy brome densities >50 plants mÿ2 have been observed in the no-till plots at the Previously Cultivated site. Selective chemical control of downy brome in winter wheat is dif®cult because of biological similarities between the two species. Tillage has long been the standard means of downy brome control in a winter wheat-fallow system and moldboard plowing has been more effective than conservation tillage (Wicks, 1984). The mid-1980s infestation of downy brome probably had a negative in¯uence on no-till winter wheat grain yields during the second half of the experiment as indicated by data in Fig. 3. The inability to control winter annual grass weeds in no-till winter
D.J. Lyon et al. / Soil & Tillage Research 49 (1998) 19±27
Fig. 3. The effect of fallow tillage systems on winter wheat grain yields during the first and second 13-year periods at the Previously Cultivated site near Sidney, NE. Downy brome (Bromus tectorum L.) infested sub- and no-till systems during the second half of the experiment.
wheat±fallow systems has been a major reason for the lack of adoption of this system in the Central Great Plains. At the Previously Cultivated site, grain yields in the plow±fallow system were not affected by fertilizer treatment (Table 2), but grain yields were less in the sub- and no-till systems when N fertilizer was not applied. Whether this was due to greater N immobilization or reduced root function in sub- and no-till is unclear. However, Wilhelm (1998) found less root dry matter with the sub-till treatment than with the plow or no-till treatments. Fallow tillage system had no effect on grain yield at the Native Sod site. Perhaps N mineralization rates are still adequate, even in no-till, to meet plant needs at this site. Organic C and total N contents of the top 20 cm of soil at the start of the two studies were about twice as great at the Native Sod site as at the Previously Cultivated site (Fenster and Peterson, 1979). Consequently, grain yields at the Native Sod site responded to the tillage treatments similarly to grain yields with fertilized treatments of the Previously Cultivated site (Table 2). With continued cropping and a subsequent decline in native fertility, differences in grain yield due to tillage systems may be expected at the Native Sod site. However, as of 1995, no such trend was evident (Fig. 2). Grain protein levels were always greatest in plow, intermediate in sub-till and least in the no-till system plots regardless of fertilizer treatment or site. However, grain yields were not affected by tillage system at
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the Native Sod site or at the Previously Cultivated site when N fertilizer was applied. In an experiment conducted in eastern Colorado, winter wheat grain yield response to N fertilizer was dependant on precipitation and residual soil NO3, while grain protein responded to N fertilizer regardless of precipitation and residual NO3 levels (Vaughan et al., 1990). This suggests that plant uptake of N increases as tillage intensity increases, and that while N uptake may be limiting yields with sub- and no-till systems, some factor other than N, e.g. soil water, is limiting grain yield potential with plow±fallow systems. 5. Conclusions Despite all the bene®ts of no-till fallow, including improved soil water storage ef®ciency (Unger, 1978), reduced organic C losses (Lyon et al., 1997), and reduced soil erosion potential (Fryrear and Skidmore, 1985), the long-term yield potential of continuous notill fallow is no better than plow fallow. In fact, the dif®culty of controlling winter annual grass weeds such as downy brome, jointed goatgrass (Aegilops cylindrica Host), and volunteer cereal rye (Secale cereale L.) without tillage has limited the adoption of no-till winter wheat±fallow in the Central Great Plains. Winter wheat±fallow systems, with or without tillage, probably are not sustainable in the Central Great Plains. Plowing, and to a lesser extent sub-tillage, resulted in unacceptable levels of soil erosion and depletion of soil organic matter. Even though no-till fallow reduces the rate of soil erosion and organicmatter loss, organic-matter losses continue due to the low amounts of residues returned to the system from only one crop every other year (Doran et al., 1998). This conclusion is similar to that made by Boehm and Anderson (1997) from their work in the Canadian prairie. Thus, none of the tillage systems studied resulted in sustainable agriculture. The use of no-till systems in combination with more frequent cropping intensity, e.g. winter wheat±corn (Zea mays L.)±fallow or winter wheat±corn±proso millet (Panicum miliaceum L.)±fallow, may increase net returns and reduce ®nancial risk (Dhuyvetter et al., 1996), increase water use ef®ciency (Peterson et al., 1996), and effectively control winter annual grass
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weeds in the winter wheat crop (Lyon and Baltensperger, 1995). Producers in the semi-arid Central Great Plains may need to adopt these systems in order to remain competitive in the future. Acknowledgements The authors acknowledge the hard work and dedication of the numerous scientists, graduate students and research technicians who contributed to the long-term management of these experiments. Special recognition is made to Mr. Charles Fenster, Professor Emeritus, University of Nebraska for his vision and hard work in establishing these experiments. References Boehm, M.M., Anderson, D.W., 1997. A landscape-scale study of soil quality in three prairie farming systems. Soil Sci. Soc. Am. J. 61, 1147±1159. Broder, M.W., Doran, J.W., Peterson, G.A., Fenster, C.R., 1984. Fallow tillage influence on spring populations of soil nitrifiers, denitrifiers, and available nitrogen. Soil Sci. Soc. Am. J. 48, 1060±1067. Cambardella, C.A., Elliott, E.T., 1992. Particulate soil organicmatter changes across a grassland cultivation sequence. Soil Soc. Sci. Am. J. 56, 777±783. Cambardella, C.A., Elliott, E.T., 1994. Carbon and nitrogen dynamics of soil organic matter fractions from cultivated grassland soils. Soil Sci. Soc. Am. J. 58, 123±130. Dhuyvetter, K.C., Thompson, C.R., Norwood, C.A., Halvorson, A.D., 1996. Economics of dryland cropping systems in the Great Plains: A review. J. Prod. Agric. 9, 216±222. Doran, J.W., 1980. Soil microbial and biochemical changes associated with reduced tillage. Soil Sci. Soc. Am. J. 44, 765±771. Doran, J.W., 1987. Microbial biomass and mineralizable nitrogen distributions in no-tillage and plowed soils. Biol. Fertil. Soils 5, 68±75. Doran, J.W., Elliott, E.T., Paustian, K., 1998. Soil microbial activity, nitrogen cycling, and long-term changes in organic carbon pools as related to fallow tillage management. Soil Tillage Res., in review. Elliott, E.T., 1986. Aggregate structure and C, N, and P in native and cultivated soils. Soil Sci. Soc. Am. J. 50, 627±633. Fenster, C.R., Peterson, G.A., 1979. Effects of no-tillage fallow as compared to conventional tillage in a wheat±fallow system. Nebraska Exp. Stn. RB 289. Fenster, C.R., Wicks, G.A., 1982. Fallow systems for winter wheat in western Nebraska. Agron. J. 74, 9±13.
Follett, R.F., Peterson, G.A., 1988. Surface soil nutrient distribution as affected by wheat±fallow tillage systems. Soil Sci. Soc. Am. J. 52, 141±147. Follett, R.F., Schimel, D.S., 1989. Effect of tillage practices on microbial biomass dynamics. Soil Sci. Soc. Am. J. 53, 1091± 1096. Fryrear, D.W., Skidmore, E.L., 1985. Methods of controlling wind erosion. In: Follett, R.F., Stewart, B.A. (Eds.), Soil Erosion and Crop Productivity, ASA, CSSA, and SSSA, Madison, WI, pp. 443±457. Hammel, J.E., 1995. Long-term tillage and crop rotation effects on winter wheat production in northern Idaho. Agron. J. 87, 16±22. Hinze, G.O., Smika, D.E., 1983. Cropping practices: Central Great Plains. In: Dregne, H.E., Willis, W.O. (Eds.), Dryland Agriculture, ASA, CSSA, and SSSA, Madison, WI, pp. 293± 295. Johnson, W.C., Skidmore, E.L., Tucker, B.B., Unger, P.W., 1983. Soil conservation: Central Great Plains winter wheat and range region. In: Dregne, H.E., Willis, W.O. (Eds.), Dryland Agriculture, ASA, CSSA, and SSSA, Madison, WI, pp. 197± 217. Krall, J.M., Dalrymple, A.W., Miller, S.D., 1990. Fertilizer responses and soil moisture conditions in dryland winter wheat conservation tillage systems. In: Proceedings Great Plains Conservation Tillage Symposium. Great Plains Agricultural Council, Ft. Collins, CO, pp. 125±131. Lamb, J.A., Peterson, G.A., Fenster, C.R., 1985. Fallow nitrate accumulation in a wheat±fallow rotation as affected by tillage system. Soil Sci. Soc. Am. J. 49, 1441±1446. Lamb, J.A., Doran, J.W., Peterson, G.A., 1987. Nonsymbiotic dinitrogen fixation in no-till and conventional wheat±fallow systems. Soil Sci. Soc. Am. J. 51, 356±361. Linn, D.M., Doran, J.W., 1984. Aerobic and anaerobic microbial populations in no-till and plowed soils. Soil Sci. Soc. Am. J. 48, 794±799. Littel, R.C., Milliken, G.A., Stroup, W.W., Wolfinger, R.D. 1996. SAS System for Mixed Models. SAS Institute, Inc., Cary, NC. Lyon, D.J., Baltensperger, D.D., 1995. Cropping systems control winter annual grass weeds in winter wheat. J. Prod. Agric. 8, 535±539. Lyon, D.J., Miller, S.D., Wicks, G.A., 1996. The future of herbicides in weed control systems of the Great Plains. J. Prod. Agric. 9, 209±215. Lyon, D.J., Monz, C.A., Brown, R.E., Metherell, A.K., 1997. Soil organic matter changes over two decades of winter wheat± fallow cropping in western Nebraska. In: Paul, E.A., Paustian, K., Elliott, E.T., Cole, C.V. (Eds.), Soil Organic Matter in Temperate Agroecosystems: Long-term Experiments in North America, CRC Press, Inc., Boca Raton, FL, pp. 343±351. Mielke, L.N., Wilhelm, W.W., Richards, K.A., Fenster, C.R., 1984. Soil physical characteristics of reduced tillage in a wheat± fallow system. Trans. Am. Soc. Agric. Eng. 27, 1724±1728. Mielke, L.N., Doran, J.W., Richards, K.A., 1986. Physical environment near the surface of plowed and no-tilled soils. Soil Tillage Res. 7, 355±366. Miller, F.P., Rasmussen, W.D., Meyer, L.D., 1985. Historical perspective of soil erosion in the United States. In: Follett, R.F.,
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Tillage influence on soil sulfur characteristics in winter wheat± summer fallow systems. Soil Sci. Soc. Am. J. 54, 1630±1634. Unger, P.W., 1978. Straw-mulch rate effect on soil water storage and sorghum yield. Soil Sci Soc. Am. J. 42, 480±491. Varvel, G.E., Havlin, J.L., Peterson, T.A., 1989. Nitrogen placement evaluation for winter wheat in three fallow tillage systems. Soil Sci. Soc. Am. J. 53, 288±292. Vaughan, B., Westfall, D.G., Barbarick, K.A., 1990. Nitrogen rate and timing effects on winter wheat grain yield, grain protein, and economics. J. Prod. Agric. 3, 324±328. Wicks, G.A., Integrated systems for control and management of downy brome (Bromus tectorum) in cropland. Weed Sci. 32, Suppl. 1 (1984) 26±31. Wilhelm, W.W., 1998. Dry matter partitioning and leaf area of winter wheat grown in long-term fallow tillage comparisons in the US Central Great Plains. Soil Tillage Res. 49, 49±56. Wilhelm, W.W., Bouzerzour, H., Power, J.F., 1989. Soil disturbance-residue management effect on winter wheat growth and development. Agron. J. 81, 581±588.