Published July, 1997
CROPS Response of Spring Barley to Crop Rotation, Conservation Tillage, and Weed ManagementIntensity Anne L6g6re,* Nathalie Samson, Romain Rioux, Denis A. Angers, and R6gis R. Simard ABSTRACT Constraints to the adoption of conservation tillage in central and eastern Quebecpotentially include cool wet springs, short growing seasons, and variable precipitation patterns. This study was conducted to determinethe suitability of conservation tillage practices to cereal cropping systems in this area of Quebec.The effects of crop rotation [spring barley (Hordeumvulgare L.) monoculture; spring barley-red clover (Trifollum pratense L.) rotationl, tillage [fall moldboardplow (MP); fall chisel plow (CP), and direct-seeded no-till (NT)], and managementintensity (intensive, moderate, minimum)on populations and dry weights of crop and weeds at midseason, and on wain yields and yield components were examined on a Kamouraskaclay and a Saint-Andr6 gravelly-sandy loam. On the clay site, moderate weed managementin NT treatments resulted in crop establishment, growth, and yields comparableto those in MPtreatments. Over five years, wain yields in NTtreatments averaged 2877 kg ha 1, compared with 2870 and 2260 kg ha-1 in MPand CP, respectively. Grain yields were also consistently but not statistically higher in the rotation (3014 kg ha 1) than in the monoculture(2322 kg ha-l). On the loam site, crop establishment, growth, and yields respondednegatively to reductions in tillage andweedmanagement intensity. Barley stand establishment and weed control in CP and NT treatments on the loam site were less successful in the monoculturethan in the rotation. No-till grain yields (1494 kg ha-t) were on average 7%lower than CP yields (1608 kg ha-l), and 29%lower than MPyields (2076 kg ha-l). Rotation had no effect on wain yields on the loam site. Findings confirm the potential of conservation tillage to generate sustained yield returns in spring barley cropping systems, provided that proper attention is given to critical aspects of the cropping system, including crop establishment and weed management.
C
ONSTRAINTS to the adoption of conservation tillage appear to be site-specific, according to either region, soil, or crop (Karlen, 1990). For example, some of the major limitations associated with direct drilling of corn (Zea mays L.), such as delayed emergence and reduced plant populations (Haynoe et al., 1993), may not apply to spring cereals, partly because of differences in physiology, growth patterns, and cropping requirements. In terms of climatic constraints, limitations to conservation tillage in central and eastern Quebec are comparable to those described by Carter and Kunelius (1990) for cool humid regions. The cool wet springs, A. LEg6re, Sainte-Foy and Saskatoon Research Centres, AAFC,107 Science Dr., Saskatoon SK, Canada, S7N 0K2; N. Samson, 226 Chemin des Granites, Lac Beauport QC, Canada, G0A2C0; R. Riou×, Ferme ¯ de recherches sur le mouton, AAAC,1642, 2e Rang ouest, C.P. 400, La Pocati~re QC, Canada, G0R 1Z0; D.A. Angers and R.R. Simard, Centre de recherche et de d6veloppement sur les sols et les grandes cultures, AAAC,2560, boul. Hochelaga, Sainte-Foy QC, Canada, G1V2J3. Contribution No. 528 of the Sainte-Foy Res. Ctr. Received 1 July 1996. *Corresponding author (
[email protected]).
short growing seasons, and variable precipitation patterns typical of eastern Quebec could possibly impede adoption of conservation tillage. However,as was shown by the work of Carter’s group in Atlantic Canada and of Cox’s group in the northeastern USA, conservation tillage practices do offer a feasible alternative, despite climatic limitations (Carter et al., 1988; Carter, 1991; Coxet al., 1992). Approximately 65% of agricultural land in eastern Quebec is under cereal and forage production (Quebec Agric. Stat. Serv., 1995). Mostof this land is still being cropped with conventional methods, including primary tillage in the fall and secondary tillage in the spring, just prior to seeding. Although some progress has been achieved, particularly in the southwestern part of the province, adoption of conservation tillage practices in Quebec is still lagging compared with other areas of North America. Until the late 1980s, conservation tillage studies in eastern Quebec focused largely on the use of direct drilling of forage crops (Rioux, 1979, 1984; Belzile, 1988). Very little consideration was given to the potential of using this technique for cereal production. Barnett and coworkers (1984) examined the effect of various tillage practices, herbicides, and seeding dates on spring barley (Hordeumvulgare L.) for two contrasting soil types. The NT treatment was unfortunately abandoned after the first year of experiment, because yields in this treatment were lower and weed abflndance greater than in the more intensive tillage treatments. Hence, it was concluded that tillage was more important to yield than herbicides. Weed management has often been considered a determining factor in the successful implementation of conservation tillage practices, with the corollary that reduced tillage often results in increased herbicide use (Froud-Williams et al., 1981). Nonetheless, in their recent review, Moyeret al. (1994) indicate that successful conservation tillage systems in wheat (Triticum aestivum L.) do not necessarily increase herbicide use and costs compared with conventional tillage systems. This positive response of cereals to conservation tillage may be related to the competitiveness of these crops (Lutmanet al., 1994), as well as to their relative tolerance of cooler temperatures (Anonymous, 1988). Despite the one previous study reporting unsuccessful Abbreviations: ANOVA, analysis of variance; Clay site, Kamouraska clay at La Pocatibre, Quebec; CP, chisel plowtillage; Loamsite, SaintAndr6 gravelly-sandy loam at La Pocati6re, Quebec; MANCOVA, analysis of covariance; MANOVA, multivariate analysis of variance; MP, moldboard plow tillage; NT, no-till.
Published in Agron. J. 89:628-638 (1997).
628
629
LI~GI~RE ET AL.: ROTATION,TILLAGE, ANDWEEDMANAGEMENT EFFECTS IN SPRING BARLEY
experimentwas conductedfrom1988to 1993on the Claysite, and from 1988 to 1992 on the Loamsite. Quantitative data were collected from 1989 onwardsand are presented in this paper. The experiment was conducted according to a split-split plot design withcrop rotation as the mainplot factor, tillage intensity as the subplot factor, and weedmanagement level as the sub-subplot factor. Treatmentswere replicated four times. The sub-subplotsize was5 by 9 mon the Claysite, and 7 by 7 mon the Loamsite. The crop rotation factor included a spring barley monocultureand a spring barley-red clover rotation. Eachphase of the crop rotation (Phase I: spring barley underseededwith red clover; PhaseII: red clover forage production) was present every year. Tillage treatments were: MP,moldboardplowin the fall (15-18 cm), followedby spring secondarytillage; CP,chisel plowin the fall (12-15 cm), followedby spring secondarytillage; and NT,direct-seeded notill. Weedmanagement levels (minimum,moderate, and intensive) weredeterminedby varying herbicides and their timing, and application rates (Table 1). Plots were plowedwhereappropriate at the end of October of each year in the monocultureand every other year in the rotation. Spring secondarytillage consisted of two passes of a rigid-tooth finishing harrow. Barley cv. L6ger was seeded in tilled areas with a conventionaldrill (International 6200) in 15-cmrows at a rate of 160 kg ha-1 in the monocultureand at a lowerrate of 110 kg ha-1 in the rotation, as recommended whenbarley is underseededwith forage species. No-till seeding was usually done a few days to a weekahead of conventional planting (late April-early May),but at the sameseeding rates. No-till barley wasseededin 20-cmrows,using a no-till drill (Tye). In the rotation treatments, red clover cv. Florex was seededat a rate of 10 kg ha-~ with a Brillion seeder. In spring 1988, lime was applied to the Loamsite at a rate of 2 Mgha 1, whichraised the pHto 5.8. Cropswere fertilized as recommended,according to soil analysis (AFEQ,1987). Nitrogen was applied in the form of NHnNO3at a rate of 70 kg ha-1 in the barley monoculture,and 40 kg ha-1 in the barley phase of the rotation, whichaccountedfor a contribution of 30 kg ha 1 of Nby red clover in the rotation. In the barley monoculture,P and K were applied at 50 kg ha-~ in 1988, and at 20 kg ha-1 in all subsequentyears. In the barley phaseof the rotation, P rates wereas in the monoculture,but K rates ranged between 20 and 56 kg ha -1. In the red clover phase -~, of the rotation, P rates varied between35 and 70 kg ha and K rates ranged from 40 to 113 kg ha-1. Fertilizers were broadcast at or shortly after crop emergence.
use of NTpractices in eastern Quebec, we believed that cereals have inherent characteristics that would make them suitable for conservation tillage in this region, provided that an adequate weed management strategy is included in the system. To our knowledge, no study had yet considered the interactive effects of rotation, tillage, and weed managementintensity simultaneously in a cereal cropping system in eastern Canada. The objective of our study was thus to determine the effects of conservation tillage practices and weed management intensity on populations and dry weights of crop and weeds at midseason, and on grain yields and yield components in a spring barley monoculture and a spring barley-red clover rotation, on two soils of contrasting texture. MATERIALS AND METHODS General Field Procedures The experimentwas conductedat the Agriculture and AgriFood CanadaExperimental Farmin La Pocati6re in Quebec ’ N, 70o02 ’ W).La Pocati~reis located at the northeast(47021 ern edge of the St-Laurent lowlands ecoregion, whichis one of the four divisions of the MixedWoodPlain ecozone of Canada(Ecological Stratification WorkingGroup,1994). The climate of this region is describedas variable, and characterized by temperature extremes and prolonged periods of wet or dry weather (Gullett and Skinner, 1992). Oneof the two experimentalsites was located on a Kamouraska clay (hereafter referred to as the Claysite), a fine, mixed,frigid Typic Humaqueptwith 10%sand, 30%silt, and 60%clay in the surface horizon (pH = 5.9; organic matter = 4.5 g kg-1; P 94 kg ha-1, Mehlich 3 extractable; K = 305 kg ha-a). The other site was located on a Saint-Andr6gravelly-sandy loam (hereafter referred to as the Loamsite), a coarse-loamy, mixed, frigid SombricFragiorthod with 58%sand, 27%silt, and 15%clay in the surface horizon (pH = 5.3; organic matter = 6.1 g kg-1; P = 150kg ha-a, Mehlich3 extractable; K= 130 kg ha-l). Physical and mineralogical characteristics of each soil are described in Simardet al. (1990). The Clay site had beencroppedwith rye (Secale cereale L.) in the five years prior to the beginningof the experiment.TheLoamsite was under forage production, with timothy (Phleum pratense L.), smoothbromegrass(Bromusinermis Leyss.), and alfalfa (Medicagosativa L.) as the mainspecies. The present
Table1. Summary of weedcontroloperationsat LaPocati~re,Quebec,accordingto rotation, tillage, andweedmanagement intensity. Herbicide and rate, by weed management intensity
Tillage’~
Timing of application
Intensive Years
Herbicide
Moderate Rate
Herbicide
Rate -1 kg ha
Herbicide
Rate -~ kg ha
Cyanazine-MCPA
--
--
--
--
--~: Glyphosate
-1.4
----$ Glyphosate
---1.4
kg ha i Barley monoculture MP Spring Fall CP Spring Fall NT Spring Fall Barley-redclover rotation MP Spring CP Spring NT Spring Fall
Minimum
1988-1993 1988-1992 1988-1993 1988-1992 1988-1993 1988-1992
Cyanazine-MCPA Glyphosate Cyanazine-MCPA Glyphosate Cyanazine-MCPA~ Glyphosate
0.28-0.56 1.4 0.28-0.56 1.4 0.28-0.56 2.5
Cyanazine-MCPA:~ Glyphosate
0.28-0.56 .... 0.28-0.56 .... 0.28-0.56 1.4
1988-1993 1988-1993 1988-1993 1988-J992
MCPB-MCPA MCPB-MCPA MCPB-MCPA~: Glyphosate
1.60-0.11 1.60-0.11 1.60-0.11 2.5
MCPB-MCPA MCPB-MCPA MCPB-MCPA~ Glyphosate
1.00-0.07 1.00-0.07 1.00-0.07 1.4
Cyanazine-MCPA
"~ MP, moldboard plow;CP, chisel plow; NT,no-till. :~ Glyphosate wasappliedto all no-till plots at a rate of 2.5 kg ha-1 in the springof 1988.
630
AGRONOMY JOURNAL,VOL. 89, JULY-AUGUST 1997
Herbicide treatments (Table 1) were applied with a Vicon -~. sprayer pressurized at 245 kPa, and delivering 330 L ha Glyphosate [N-(phosphonomethyl)glycine] treatments were applied at the end of September or early October. CyanazineMCPA {2-[[4-chloro-6-(ethylamino)-l,3,5-triazin-2-yl]amino]2-methylpropanenitrile and [(4-chloro-o-tolyl)oxy]acetic acid} was applied at the 2- to 5-leaf stage of barley in the monoculture. MCPB([(4-chloro-o-tolyl)oxy]butyric acid)-MCPA applied to barley underseeded with red clover at the threetrifoliate-leaf stage of red clover. No herbicides were applied during the forage production phase of the rotation. Barley was harvested at grain maturity using a commercial combine (International Axial 1420) with a 4.35-m cutting bar. Grain fresh weight was measured. Grain yields were adjusted to correct for moisture content. One-thousand-grain weights were measured in all years but 1989. The number of barley heads per meter of row was estimated just prior to harvest, by counting barley heads on one meter of row, from four rows in 1992 and two rows in all other years. These data were converted to an area basis (heads m-2), given the different row-widths in tilled and NTplots. Barley and weeds were sampled on both sites at 2 to 3 wk after postemergence herbicide application: 16-23 June 1989, 13-28 June 1990, 2-11 July 1991, 17-25 June 1992, and (Clay site only) 16-30 June 1993. Twoquadrats, 33 by 75 cm, were positioned according to a grid of random coordinates chosen to exclude those from previous years such that an area was sampled only once during the course of the experiment. Weed and barley plants within the quadrats were counted, oven dried at 65°C for 48 h, and weighed. Given shortage of labor and the uncertainty of weather conditions during the midseason sampling period, monoculture treatments were sampled before rotation treatments to ensure that at least a complete set of data covering all years would be available for the monoculture on both sites. The 1990 rotation on the Loamsite was not sampled for the above reasons. Statistical
analysis
Analysis of repeated measures was conducted on multiyear data sets for barley population and biomass, using multivariate analysis of variance (MANOVA) to evaluate tillage and weed managementeffects and interactions for each rotation separately (SAS Inst., 1985). Since a number of year × factor interactions were significant, analysis of variance (ANOVA) was also performed for single-year data sets. Weeddensity and crop yield data :from all years were analyzed using the polynomial regression method (Allen et al., 1983; L6gbre and Schreiber, 1989). This methodconsists in first fitting a polynomial to each profile of measurement (for example, weed density over years for each cell of the experimental design; i.e., each replicate of a given treatment) and then, performing
multivariate analysis on the regression coefficients. The degree of polynomial is chosen such that all treatment profiles are adequately described. The polynomial regression method is advantageous, in that it reduces the number of parameters to be comparedfor within subject effects and offers the possibility of handling missing data for subjects (von Ende, 1993). third-degree polynomial was fitted to either weed density or grain yield data from each cell of the experimental design. A MANOVA analysis was performed on the regression coefficients thus obtained in order to test the effect of rotation, tillage, weed managementlevel, and their interactions on the variable of interest. The polynomials were of the form y = bo + b~x + b2x2 + bax3, where y is the weed density or grain yield and x is time in years after the start of the experiment. Multivariate analysis of covariance (MANCOVA) was performed to determine the contribution of yield components in explaining the response of grain yield to the factors investigated (Tabachnick and Fidell, 1996, p. 375-440). A seconddegree polynomial was fitted to either barley head density or 1000-grain weight data from each cell of the experimental design. The polynomials were of the form y = bo + b~x + b2x2, where y is barley head density or 1000-grain weight and x is time in years after the start of the experiment. Parameters from each yield component regression curve were used as covariates in MANCOVA; parameters from yield regression curves (used in the MANOVA) were used as dependent variables. It was assumed that yield components explained the response of grain yields to a given factor when the effect considered significant according to MANOVA became nonsignificant in the MANCOVA. Alternatively, yield components were considered to only partially explain yield response when the effect, significant according to MANOVA, remained significant in MANCOVA.Significance levels in MANOVA and MANCOVA were determined according to Wilks’ criterion. Orthogonal contrasts were used to test the significance of a priori hypotheses in MANOVA, MANCOVA, and ANOVAanalyses. RESULTS Synopsis
AND DISCUSSION of Weather Patterns
Weather patterns in La Pocati~re varied considerably over the years of the study, especially precipitation (Table 2). Precipitation was below the long-term average in five out of six years. Precipitation was 30% below the long-term average in 1991, and nearly 30% above average in 1992. Monthly patterns of precipitation distribution also varied greatly within a growing season, except in 1993, when rainfall was fairly uniformly distributed.
Table 2. Summary of seasonal weatherdata from La Pocati~re, Quebec,for 1988 to 1993. Precipitation Year
May
June
July
Aug.
mm 1988 102 (37)¶ 43 (15) 79(29) 49 (17) 1989 142 (48) 87 (29) 37(12) 34 (11) 1990 71 (23) 81 (26) 42(13) 119 (38) 1991 61 (25) 32 (13) 35(14) 117 (48) 1992 40(9) 126(28) 167(37) 119(26) 1993 77 (27) 84 (29) 60 (21) 67(23)
Thermaltime~ Total, %of longMay-Aug. termavg.’~ 273 300 313 245 452 288
% 78 86 91 71 128 81
May
June
205 (15)¶ 189(14) 134(10) 186(13) 226 (18) 174(13)
309 (23) 309(23) 329(25) 357(26) 305(24) 321(24)
July
Total, Aug. May-Aug.
degreedays 446 (33) 400 437 (32) 424 (31) 434 (32) 445 (33) 437 (32) 403 (29) 339 (27) 377 (30) 400 (30) 422 (32)
Long-term precipitationaveragesare basedon 77 yr priorto 1988. Degreedayswitha baseof 5°C. Long-term precipitationaverageis basedon 12 yr priorto 1988. Valuesin parentheses are the relative proportion of total seasonalprecipitationor degree-days recordedin eachmonth.
1360 1359 1342 1384 1247 1318
%of longtermavg.§ % 106 107 104 107 96 101
631
LI~GI~RE ET AL.: ROTATION, TILLAGE, AND WEEDMANAGEMENT EFFECTS IN SPRING BARLEY
Heat unit accumulation did not vary as muchas precipitation. Heat unit accumulation was roughly 5% above the long-term average for all years but 1992 (for which total seasonal degree days recorded were 4% below the long-term average) (Table 2). Seasonal patterns of heat unit accumulation were similar over years. Extremes in precipitation were correlated with extremes in heat unit accumulation. Based on long-term averages, 1991 had the lowest precipitation (71% of long-term average) and the highest degree-day accumulation (107% of long-term average). Inversely, 1992 had the highest precipitation (128%of long-term average) and the lowest degree-day accumulation (96% of longterm average).
tions in NT treatments were generally comparable to that in tilled (MP, CP) treatments in all years (MP&CP vs. NTcontrast: nonsignificant in 9 out of 10 instances). Over five years, barley populations in the monoculture averaged 339 plants m-2 in NT, compared with 328 plants m-2 in tilled treatments (MPand CP). In the rotation, average barley density was 228 plants m-2 in NT, compared with 217 plants m-2 in tilled treatments. Arshad and coworkers (1995), working in the northern prairies, also found no-till barley populations to be comparable to that in conventional treatments on a clay soil. Hence, clay soils and cool humid early-spring conditions, generally considered as limitations to conservation tillage, wouldnot necessarily impede the establishment of barley populations under no-till conditions. Conservation tillage was less favorable to barley establishment on the Loamthan on the Clay Site (Table. 3). Although the significance of this effect varied ac-
Barley Populations Establishment of barley was quite successful in the NTtreatment on the Clay site (Table 3). Barley popula-
Table 3. Effects of tillage and weed managementintensity on barley population density in monoculture and in rotation with red clover, grown on two soils at La Pocati~re, Quebec. Barley population Claysite Treatment
1989
1990
1991
Loamsite 1992
1993 plants
1989
1990
1991
1992
323 338 344
353 322 204
452 442 346
367 321 374
323 338 345 68
308 276 296 84
475 390 374 166
371 319 372 67
-2 m
Monoculture Tillage (T) Moldboard (MP) Chisel (CP) No-till (NT) Weed management (W) Intensive(lnt) Moderate (Mod) Minimum(Min) SD Sourceof variation T W T × W Contrasts MP & CP vs. NT(T) MPvs. CP(T) lnt & Modvs. Min(W) Int vs. Mod(W) CV, % Tillage Moldboard Chisel No-till Weed management Intensive Moderate Minimum SD Sourceof variation T W T × W Contrasts MP & CP vs. NT(T) MPvs. CP(T) Int & Modvs. Min(W) Int vs. Mod(W) CV, %
353 375 351
387 358 326
367 254 365
335 260 345
367 346 365 73
365 333 373 75
366 317 304 69
348 293 299 63
334 286 279 60 ANOVA
298 288 313
NS NS NS
NS NS ***
* ** NS
NS ** *
NS ** NS
NS NS NS
** NS NS
* NS NS
NS * **
NS NS NS NS 20.2
NS NS NS NS 21.1
NS * * * 20.9
NS NS NS *** 20.1
NS NS * ** 19.9 Rotation
NS NS NS NS 22.2
*** NS NS NS 28.6
** NS NS NS ~10.3
NS NS NS ** 18.9
212 201 219
223 185 228
252 193 250
290 198 256
207 222 203 51
213 202 221 74
255 226 214 130
272 247 224 75
204 204 192 64 ANOVA
NS NS NS
NS NS NS
NS * *
* * NS
NS NS NS NS 20.5
NS NS NS NS 33.2
NS * * NS 22.1
NS * * NS 27.1
*,**,***Significantat the 0.05, 0.01, and0.001probabilitylevels, respectively. Data not available.
196 216 188
188 212 178
--~" ---
280 261 169
229 190 220
186 194 196 51
-----
230 252 229 41
241 202 196 46
* NS NS
NS NS NS
----
*** INS NS
NS ** NS
* * NS NS 19.1
NS NS NS NS 26.7
------
*** NS NS NS 17.0
NS NS * ** 22.0
632
AGRONOMY JOURNAL, VOL. 89, JULY-AUGUST1997
cording to year, populations were generally lower in the NTthan in the tilled treatments. No-till barley populations averaged 317 and 189 plants m-2 in the monoculture and rotation respectively, compared with 365 and 227 plants m-z in the tilled plots. Adequateseed placement at planting was difficult to achieve on this soil. The gravelly texture of the Saint-Andr6 loam made direct seeding a difficult operation, often leaving the seed on the soil surface. Rioux et al. (1986) identified seed placement as a determining factor for barley yields on the Saint-Andr6 loam. Inadequate seed placement and the consequent moisture deficit in the germination zone could thus explain our poor results compared with other studies indicating a lack of overall tillage effect on cereal populations grown on light soils under conservation tillage (Carter, 1991; Lafond et al., 1994). The fall glyphosate treatment included in the intenTable 4. Effects of tillage and weed managementintensity two soils at La Pocati~re, Quebec.
sive weed managementlevel was beneficial to the establishment of barley populations from 1991 onwards on the Clay site, and in 1992 on the Loamsite. Adequate crop establishment in tilled plots required intensive weed management, particularly in the CP treatment (Table 3, significant tillage x weedmanagementeffect), confirming the need for efficient perennial weed control in barley, in all tillage systems (Rioux, 1984; L6g6re et al., 1993; Samsonet al., 1996). Midseason Barley Biomass On the Clay site, tillage affected barley biomass in most years in the monoculture, but only once in the rotation (Table 4). In the monoculture, barley produced 118 g m-2 in the CP treatments, compared with 148 and 162 g m-2 in the MPand NT treatments, respectively.
on barley biomass in monocuiture and in rotation with red clover,
grownon
Barley biomass Claysite Treatment
1989
1990
Loamsite
1991
1992
1993
1989
1990
1991
1992
-2 g m
Monoculture Tillage (T) Moldboard (MP) Chisel (CP) No-till (NT) Weed management (W) Intensive (Int) Moderate (Mod) Minimum(Min) SD
161 158 162
85 77 43
273 150 267
109 74 196
111 129 144
198 201 120
249 233 77
396 274 202
210 167 172
172 150 159 38
78 58 68 21
292 206 192 71
166 118 94 61
198 105 80 46
166 167 185 56
189 188 172 57
336 278 259 96
195 155 199 46
ANOVA Sourceof variation T W T × W Contrasts MP & CP vs. NT(T) MP vs. CP(T) lnt & Modvs. Min(W) Int vs. Mod(W) CV, %
NS NS NS
* ** *
* *** **
* *** ***
NS *** ***
** NS NS
** NS **
NS NS NS
NS * NS
NS NS NS * 23.5
* NS NS *** 30.8
NS ** ** *** 30.8
* NS ** ** 48.0
NS NS *** *** 35.9
** NS NS NS 32.6
*** NS NS NS 31.0
NS NS NS NS 33.1
NS NS NS * 25.0
Rotation Tillage Moldboard Chisel No-till Weed management Intensive Moderate Minimum SD Source of variation T W T × W Contrasts MP & CP vs. NT(T) MPvs. CP(T) lnt & Modvs. Min(W) Int vs. Mod(W) CV, %
191 252 246
289 158 251
464 379 475
197 100 206
145 205 193
251 241 135
--~ ---
471 479 204
202 125 210
241 242 207 50
259 227 211 73
502 441 374 129
202 160 142 74
211 177 156 64 ANOVA
209 207 211 81
-----
401 425 328 131
224 152 161 61
NS * **
NS NS NS
NS ** NS
* * NS
NS * NS
** NS NS
----
NS NS NS
NS * NS
NS NS ** NS 21.9
NS * NS NS 31.4
NS NS ** NS 29.5
NS * * NS 48.0
NS NS * NS 35.2
** NS NS NS 38.7
* NS NS NS 34.2
NS NS NS * 34.4
*,**,***Significantat the 0.05, 0.01, and0.001 probabilitylevels, respectively. Datanot available.
----* --
LI~GI~RE
ET AL.:
ROTATION, TILLAGE,
633
AND WEED MANAGEMENTEFFECTS iN SPRING BARLEY
In both the monoculture and rotation, barley biomass generally decreased as weed managementintensity was reduced. Weedmanagementeffects in the monoculture varied with tillage in four out of five years. Increasing weed managementintensity had a more positive effect on barley biomass in tilled than in NTtreatments, and more so in the CP than in the MP treatments (data not shown). On the Loamsite, barley biomass was greatly reduced in the NT compared with tilled treatments in 1989 and 1990 in the monoculture, and in 1989 and 1991 in the rotation (P < 0.01) (Table 4). In 1992, barley biomass was lower under moderate weed management in the monoculture (P < 0.05), and under moderate and minimumweed management in the rotation (P < 0.05). Overall, growing conditions on the Clay site were adequate for barley, given that an appropriate level of weed managementwas applied to the tilled treatments. On the Loamsite, poor barley biomass production in NTtreatments could at times be related to inadequate crop establishment. Nonetheless, a relatively low barley biomass was obtained in NT treatments in 1989 on the Loamsite, despite successful crop establishment. Reduced barley yields on the Saint-Andr6 loam has previously been attributed to the poor water-holding capacity of these soils, triggering precocious maturity particularly during seasons with below average precipitation (Rioux et al., 1986). Barley can tolerate drought during early growth stages but will eventually suffer from prolonged dry conditions, mainly because of limited root development (Anonymous, 1988). Weed Stands According to the polynomial regression analysis performed on data from all years, the rotation factor had no overall effect on total weed density on either site (Clay: P = 0.170; Loam:P = 0.199). On the Clay site, tilled treatments resulted in fewer weeds than NTtreatments (P = 0.013). Weed density increased over the years, even in MPtreatments, where total density in 1993 had reached four times that of 1989 (157 vs. 679 plants m-z) (Fig. 1). Weeddensities in the NTtreatment were relatively high in 1989, but consistently lower than in the CP treatment (P = 0.003). On the Loamsite, weeddensity increased as tillage intensity was reduced (P = 0.005) (Fig. 1). However, the magnitude of increase varied with year. Very dense weed stands were recorded in NTtreatments as early as 1990. On both sites, weed density increased as weed managementintensity was reduced (P < 0.001) (Fig. 2). effect was more pronounced in MP and CP than in NT treatments on the Clay site (P = 0.005) (data shown). On the Loamsite, increasing the weed management level from moderate to intensive consistently provided some additional level of weed suppression, even though this effect was not statistically significant (P 0.202). The weeddensity data suggest a directional trend of increasing densities over time, the trend being more pronounced as weed managementintensity was reduced (Fig. 2). However,this trend and that described above
Moldboard
plow ~ Chisel
plow 1 No-till
1400
Kamouraska Clay
1200 1000
800 600 400 200
0 8990 91 92 93
89 90 91 92 93
89 90 91 92 93
1400
_
Saint-Andr~Loam
1200
]-
~ 1000 800 600 400
~
200 0 89 90 91 92 89 90 91 92 89 90 91 92 Fig. L Effects of tillage on weed density in sp~ng barley grown on Kamouraska clay (1989-1993) and Saint-Andr~ loam (1989-1992) at La Pocati~re, Quebec.
concerning tillage effects on weed population over time should be interpreted with caution, given the short time span of this experiment. Examination of data sets covering longer-term experiments has shown that environmental variability has a strong influence in determining fluctuations in weedpopulations (L6g6re et al., 1996). Analysis of total weed density data is indicative of overall treatment effects on weed stands, but provides no information on the dynamicsof species shifts or the relative abundanceof species, especially with regard to Intensive 1200
Weed management ~ Moderate ~ Minimum
Kamouraska Clay
~ lOOO ~ 800 ~- 600 ~
400
-o
200
~
0 89 90 91 92 93
89 90 91 92 93
89 90 91 92 93
1200 000
Saint-Andr~
Loam~
~
800 600 400
200
o
89 90 91 92 89 90 91 92 89 90 91 92 Fig. 2. Effects of weed management intensity on weed density in spring barley grown on Kamouraska clay (1989-1993) and SaintAndr~ loam (1989-1992) at La Pocati~re, Quebec.
634
AGRONOMYJOURNAL, VOL. 89,
Table 5. Summary of polynomial regression analysis of barley (COV1) or 1000-grain weights (COV2) used as covariables.
yields,
JULY-AUGUST 1997
conducted
without
covariables
(MAN) and with either
heads
Significance level, according to Wilks’ criterion Clay site
Loam site
Factors
MAN
COV1
MAN
COV1
COV2
Crop rotation (R) Tillage (T) Weed management R × T R × W T × W R × T x W
0.290
