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Soil water availability for spring growth of winter wheat (Triticum aestivum L.) as influenced by early growth and tillage
Soil & Tillage Research, 14 (1989) 185-196
185
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Soil Water Availability for Spring Growth of Winter Wheat (Triticum aestivum L.) as Influenced by Early Growth and Tillage* WILLIAM F. HEER' and EUGENE G. KRENZER, JR. e
1Agronomy Department, Kansas State University, Manhattan, KS 66506 (U.S.A.) eAgronomy Department, Oklahoma State University, Stillwater, OK 74078-0507 (U.S.A.) (Accepted for publication 25 October 1988)
ABSTRACT Heer, W.F. and Krenzer, Jr., E.G., 1989. Soil water availability for spring growth of winter wheat (Triticum aestivum L.) as influenced by early growth and tillage. Soil Tillage Res., 14: 185-196. This study was designed to determine to what extent tillage and fall growth as affected by planting date influence profile soil water for spring growth and yield of monoculture winter wheat (Triticum aestivum L.). The study was conducted for 3 crop years ( 1982-1985) at Stillwater and Lahoma, OK. A randomized-block design with a split-plot arrangement was used where main units were tillage and subunits were 4 plantings spaced 1 month apart. Soil water was measured using the neutron-scattering method. The effects of tillage and amount of fall growth on profile soil water (PSW), total soil water in the 1.2-m soil profile, differed between the two locations. At Stillwater, neither tillage nor differences in fall growth affected soil water. During the third year at Lahoma, where precipitation was more limiting, a significant tillage effect on PSW developed at jointing. No-till (NT) was significantly greater than that of the conventional tillage (CT). This effect was observed consistently through the 1.2-m profile. The effect of fall growth on spring PSW was not consistent. The fall growth effect on grain yield was significant at both locations in all 3 years except for Stillwater in 1982-1983. However, there was no tillage by planting date interaction. The mid-September and October planting dates consistently had higher yields than the mid-August and November planting dates. The use of NT has a potential to increase spring profile soil water for the production of monoculture winter wheat in the South Central Great Plains. However, the potential to deplete this increase through increased fall growth by planting early exists and there is further need to evaluate the benefits of additional forage obtained with earlier planting vs. the depletion of stored soil water and the potential effect upon grain yields.
INTRODUCTION N o - t i l l p r o d u c t i o n ( N T ) p r a c t i c e s f o r w i n t e r w h e a t ( T r i t i c u m aestivum L. ) are gaining acceptance in Oklahoma and other Great Plains states (CTIC, *Contribution of the Department of Agronomy, Oklahoma State University. Published as Journal Article No. 5055 Oklahoma Agriculture Experiment Station.
0167-1987/89/$03.50
© 1989 Elsevier Science Publishers B.V.
186 1988). As these N T methods gain acceptance, they must be considered in the evaluation of monoculture wheat production. Of particular concern is how profile soil water and grain yield are affected under different tillage systems at different levels of fall growth. Several researchers have addressed the effect of tillage methods on soil water content (SWC) and wheat grain yields under wheat-fallow and wheat sorghum-fallow practices (Wicks and Smika, 1973; Fenster and Peterson, 1979; Johnson and Davis, 1980). In all the above research, the wheat was planted at typical planting times for the particular location after an extended fallow period (11-18 months). Soil water content (SWC) is the amount of water present in a particular segment of a soil profile, determined on a gravimetric or volumetric basis, and presented as percent water or m 3 of water per m 3 of soil. Profile soil water (PSW) determined gravimetrically or volumetrically is a measure of the total water present in that portion of the soil profile referred to. Previous work at Oklahoma State University with monoculture wheat {Davidson and Santelmann, 1973) reported SWC was greater for NT than conventional tillage (CT). With the reported increase in SWC and lower soil temperatures under NT wheat-fallow conditions as compared with CT wheat-fallow (Blevins et al., 1971; Smika and Ellis, 1971; Unger, 1978; Fenster and Peterson, 1979; Russelle and Bolton, 1980; Fenster and Wicks, 1982; Smika, 1983; Tanaka, 1985), it would be expected that SWC for spring growth and grain yield in annually cropped monoculture winter wheat planted N T would be equal to or greater than that in CT planted wheat. Lower soil temperature can reduce the impact of post-harvest dormancy as well as reduce high-temperature stress which causes a reduction in tillering. Therefore, potentially earlier germination and increased fall growth (increased tillering) owing to this reported lower soil temperature and increased soil moisture could result in grain yield of monoculture N T wheat planted before the usual planting time for a given location being higher than that of monoculture CT wheat planted at the same time. Russelle and Bolton (1980) showed that earlier planted cereals often utilize excessive amounts of soil water in the fall, are more susceptible to winter killing, and are frequently subject to disease. Darwinkel et al. (1977) showed that delaying the planting of CT wheat caused a distinct reduction in yield, but planting earlier (prior to the usual planting time) increased yields only slightly. Fenster et al. (1972) showed an increase in grain yield as planting date was delayed from mid-August to late September and a decrease in yield as planting was delayed from late September to early October. Their study also showed that CT yielded more than N T in the early plantings, but in the later plantings the N T yielded more than the CT. The optimum time for seeding winter wheat in Oklahoma is generally considered the last week of September through the first week of October. But, it is unknown how earlier planting of winter wheat affects the soil water, diseases and grain yield under both CT and NT. The objectives of this study were to determine to what extent spring profile
187
soil water and grain yield for monoculture winter wheat produced in the South Central Great Plains are i n f u e n c e d by tillage and amount of fall growth as influenced by planting date. MATERIALS AND METHODS
The study was conducted on a Pulaski fine sandy loam (coarse-loamy, mixed, thermic Typic Ustifluvent) with 0-2 % slope at the Oklahoma State University North Agronomy Research farm, Stillwater, OK, and on a Grant silt loam (fine, mixed, thermic Argiustoll) with 3-5% slope at the Oklahoma State University North Central Research Station, Lahoma, OK. Data were collected over 3 growing seasons, 1982-1984, at both locations. Both sites were planted in wheat the year prior to the beginning of the study. Precipitation was measured at nearby research station headquarters at both locations. The experimental design was a randomized complete block with a split-plot arrangement of treatments and 4 replications. Main plot treatments were 30 m by 23 m and consisted of two tillage systems, CT and NT. At Stillwater, the CT consisted of moldboard plowing to a depth of 0.2 m as soon after wheat harvest as soil conditions allowed. These plots were then disked, as needed, for weed control and seedbed preparation. Final seedbed preparation consisted of running a mulch treader over the plots just prior to planting. At Lahoma, the CT plots were disked with an offset disk immediately after wheat harvest. These plots were then disked or swept with 0.2-m sweeps spaced 0.2-m apart as needed for weed control and residue incorporation. At both locations, the NT consisted of planting directly into the residue of the previous year's crop. Weed control in the N T plots during the period from harvest to seeding was achieved through the use of herbicides. Subplot treatments consisted of different amounts of biomass in the fall established through 4 planting dates; mid-August, mid-September, mid-October and mid-November. Therefore, planting date will be used throughout the discussion to denote different levels of fall growth. Subplots were 7.6 m by 23 m. The same tillage planting date treatment was repeated on a given plot all 3 years of the study. TAM W-101 hard red winter wheat was used throughout the study. Planting was performed with a Crustbuster double disk opener notill drill. A row spacing of 0.25 m and a seeding rate of 67 kg ha -1 was used in all 3 years of the study at both locations and all dates. Soil fertility was maintained by using the Oklahoma State University Soil Testing Lab indexes to determine the total amount of nitrogen, phosphorus and potassium needed. These needs were met through broadcast application of nitrogen as ammonium nitrate (34-0-0) and potassium as muriate of potash (0-0-60) prior to planting. Phosphorus was applied in the rows at planting as diammonium phosphate (18-46-0). Annual applications were 100, 20 and 60 kg h a - 1 of N, P and K, respectively.
188 Soil water content for each t r e a t m e n t was monitored with a neutron probe depth moisture gauge with 2 access tubes per subplot. Readings were taken at 0.15-m intervals from 0.15 to 1.8 m below the surface at Stillwater and from 0.15 to 1.2 m below the surface at Lahoma. Moisture readings were taken at each planting date for those plots which were planted and several times through the growing season. The last reading each crop year at each location was taken on the day of harvest. Heads m - 1 of row data were collected using two 1-m of row subsamples per plot, collected just prior to harvest. Kernels per head were determined using 10 subsamples from the above samples. Grain yield and kernel weight data were based on combine-harvested weights. Grain yields were adjusted to a moisture content of 135 g kg -1 and a test weight of 772 kg m -3 each year. For each time that water measurements were obtained, split-plot analyses of variance were performed for SWC at each depth increment and for PSW. The split-plot analysis of variance procedure was also used for heads m -1, kernels head -1, kernel weight and grain yield data. The F Test (Steel and Torrie, 1960) was used to determine significant tillage and planting date differences and the Duncan Multiple Range Test was used to separate planting date means. Least-squares means were calculated using SAS; G L M procedure was used when a t r e a t m e n t was missing resulting in an unbalanced design. RESULTS AND DISCUSSION Several treatments did not germinate and were replanted at a later date (Table 1). These treatments were eliminated from the statistical analyses. Also eliminated were the 1983-1984 October CT and N T treatments at Lahoma and the August and September CT treatments at Stillwater for 19841985. The two treatments at L a h o m a were planted late owing to wet conditions, and the two at Stillwater germinated and became established after sufficient precipitation occurred around mid-October. The precipitation at L a h o m a was somewhat evenly distributed except for TABLE 1 Subplot planting dates for Stillwater and Lahoma 1982-1984 crop years Location
August
September
October
November
1982 1983 1984 1982 1983 1984 1982 1983 1984 1982 1983 1984 Stillwater 1 Lahoma 24
2 16
15 16
13 14
24 23
19 18
15 19
14 3
15 15
17 16
16 15
14 15
IPlanted 27 August but did not germinate. Was replanted 24 September 1982. 2Planted 17 August but the C T did not germinate. Replanted the C T plots on 14 October 1983. 3Wet conditionsforced the delay of planting from 15 October to 2 November.
189
the unusually large amounts of precipitation received in May and October 1983, March 1984 and February and April 1985 (Table 2). Even though planting dates were 30 days apart, forage yields, 2.5 mg ha -1 in 1984 and 1.5 mg ha -1 in 1985, prior to early jointing were not significantly different. August plantings had more forage in the fall and less in the early spring than October plantings (data not presented). Forage production is environmentally dependent and is very inconsistent from year to year in Oklahoma (Hubbard and Harper, 1949). Statistically significant differences in PSW between CT and NT plots on the respective planting dates in 1982-1983 at Lahoma (Fig. 1A and B) were probably the result of a lack of sufficient weed control in the NT plots during the fallow period just prior to the establishment of the study. This lack of weed control resulted in the CT treatments having more PSW until sufficient precipitation was received to recharge the NT plots. The PSW curves for 19831984 (Fig. 1C and D) show the beginning of a trend toward higher soil water in the NT treatments when compared with the CT treatments. This trend becomes statistically significant in the 1984-1985 data with NT having significantly more water in the profile than CT (Fig. 1E and F). The PSW data from Lahoma (Table 3) also showed that a statistically significant planting date effect existed from jointing through maturity in all years of the study; however, TABLE 2 Monthly precipitation (mm) distribution for Stillwater and Lahoma for individual crop years compared with the long-term average Month
Long-term average 1
1982-1983
1983-1984
1984-1985
Stillwater Lahoma Stillwater Lahoma Stillwater Lahoma Stillwater Lahoma July August September October November December January February March April May June
90 82 86 71 47 34 30 34 47 73 117 108
67 74 87 78 50 24 29 17 71 69 84 61
50 35 58 25 70 59 8 76 78 41 189 93
82 2 18 4 39 38 21 41 87 85 109 145
0 22 52 193 55 10 5 18 130 73 68 135
0 36 95 121 42 5 0 47 145 84 30 43
16 26 30 123 56 101 77 116 127 136 43 162
2 21 12 33 33 78 20 140 60 132 36 114
Total
818
711
782
711
761
648
1013
681
iStillwater 91-year average, Lahoma 30-year average.
190
0
35 70 105 140 175 210 245 280 315 0 ,
r
,
.
.
.
A
330
~
3101
EE
35 70 105 140 175 210 245 280 315
.
B
330
987.83
310
290
290
270
270
250 !
250
230
230
3so1988 CI
L
I
I
~
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q
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I 350 330 310 290 270
,=.330
~=~ 310 290
--
270 ~'=~ 250 2302
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CT NT August O • September ~ •
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250 230 210 190
October
O nE
3so 330
1 F ~///~.~
1984-85
310 290
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190
- 330 310 ~ 290 270 250 230 210 190
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35 70 105 140 1'~5 2~0 2,~5 280 315
0
315 7~) 1135 110 175 2~0 2145 21°0 3~5
TIME (DAYS AFTER AUGUST 1) Fig. 1. Tillage and planting date effects upon profile soil water content in the top 1.2 m of soil at selected dates of observation at Lahoma. A, C and E are August and September planting dates while B, D and F are October and November planting dates.
no one planting date consistently had the lowest PSW values although the trend was toward the earliest date. There was not a statistically significant planting date by tillage interaction for PSW during the dates shown in Table 3. Differences in SWC by depth for planting dates at Lahoma first appeared in the fall of 1983, when the August planted treatments had a lower SWC than
191 TABLE 3 Planting date effect upon 1.2-m PSW from jointing stage of wheat until harvest at Lahoma Planting date 1982-1983 Day ~ August September October November 1983-1984 Day August September October November 1984-1985 Day August September October November
215
257
271
276
299
311
324
334
320 b 335 ~ 341 ~ 343 ~
312 c 326 b 341" 345 ~
275 b 285 b 31C 312 ~
269 b 281 b 306 ~ 307 ~
243 b 252 ~b 266 ~ 263"
223 b 227 b 24C 242 ~
253 ~ 265 ~ 265 ~ 263 ~
272 ~ 288 ~ 282 a 278 ~
214
261
275
283
290
297
304
312
332
302 ¢ 326 b 341 a 346 ~
320 b 328 b 346 a 349 ~
299 b 308 b 330 a 33C
280 b 286 b 317 ~ 319 ~
252 b 253 b 291 a 296 ~
241 b 243 b 282" 288 ~
225 b 222 b 258 ~ 271 ~
213 b 213 b 237 a 251 ~
222 b 229 b 236" 260 a
238
251
258
267
274
281
289
296
300
331 ¢ 344 a 333 bc 342 ab
302 b 320 a 302 b 322 a
296 b 316 a 295 b 32C
283 b 308 a 283 b 302 a
300 bc 32C 296 c 319 ab
292 b 31C 285 b 300 ~b
258 bc 286 a 248 c 265 b
232 b 258 a 222 b 236 b
283 ~b 294 a 268 bc 265 ~
1Days after 1 August. Means within a day followed by the same superscripts are not significantly different at the 5% level according to DMR. Means of 4 blocks and two tillage systems. any other treatment
(Fig. 2A) (Data for November planting date, not shown
for clarity of the graph, was similar to September and October data). The lower W C i n A u g u s t p l a n t i n g s is c a u s e d b y g r e a t e r w a t e r u s e i n p l o t s h a v i n g p l a n t s transpiring over the longest period. This difference continued through Februa r y 1984. H o w e v e r , a s a r e s u l t o f t h e u n u s u a l l y h i g h p r e c i p i t a t i o n i n M a r c h 1984, t h e A u g u s t N T S W C w a s r e p l e n i s h e d t o e q u a l t h e o t h e r t r e a t m e n t s ( F i g s . 1C a n d 2 B ) . N o t e t h a t e v e n w i t h t h e h e a v y p r e c i p i t a t i o n t h e A u g u s t C T s t i l l r e m a i n e d d r i e r t h a n t h e o t h e r t r e a t m e n t s ( F i g . 2 B ). T h i s d i f f e r e n t i a l r e s p o n s e i n S W C b e t w e e n t h e e a r l y p l a n t e d N T a n d C T is c o n s i s t e n t w i t h t h o s e r eported by Zingg and Whitfield (1957) and Russelle and Bolton (1980). This is o n e o f t h e f e w t i m e s t h r o u g h o u t t h e 3 y e a r s o f t h i s s t u d y w h e r e p l a n t i n g d a t e by tillage interaction was statistically significant. Statistical analysis of the Lahoma 1984-1985 SWC and PSW data showed N T t o b e s i g n i f i c a n t l y (P= 0 . 0 5 ) w e t t e r a t al l r e a d i n g d a t e s . E v e n w h e n t h e P S W r e a c h e d i t s m a x i m u m o n 9 M a r c h 1985, t h e C T p r o f i l e s d o e s n o t a p p e a r
192 0.00 I
I
I
I
I
I
B
I
|
I
I
I
I
0.00 0.15 0.30 0.45
0.60~
°9°11.05 l 1.20
..j
0.60
!
0.75 I-
0.75 0.90 1.05 1.20
C
Mar.9, 1985
~B
oo°'rlooto.,. °°:°t
-
_
0.15
°
0.30
,.,
0.45 0.60
0.75 I"
0.75
0.90 l 1.05 I"
0.90 (
1.05 1.20
1.20 F
I
I
I
0.08 0.12 0.16 0.20
I
I
I
0.24 0.28 0.32
I 0.12 0.16 0.20
I
0.24 0.28 0.32
0.36
SOIL WATER CONTENT (m31m3) Fig. 2. Soil water content by depth at differenttimes throughoutthe tillage and planting date study at Lahoma. to have completely recharged (Fig. 2C). However, there were changes in the SWC throughout the 1.2-m profile, which is inconsistent with the findings of Blevins et al. (1971) who reported only minimal changes in the SWC below the 0.45-m depth. By the end of the 1984-1985 crop year, the SWC in the NT treatments had never decreased to the levels of the SWC in the CT treatments (Fig. 2D). Precipitation at the Stillwater location was 5% below the long term average in 1982-1983, 7% below in 1983-1984, and 23% above in 1984-1985 (Table 2). No consistent planting date or tillage effect on SWC or PSW could be recognized at this location. Therefore, the responses observed at Lahoma are site specific. Even though the Lahoma NT plots generally had higher SWC and PSW than CT plots, the presence of a definite pattern where one tillage treatment had consistently higher grain yields than the other did not develop. The CT yields were significantly larger than the NT in 1983-1984 at Lahoma and in 1984-1985 at Stillwater. The NT yield was significantly larger than the CT in
193
1982-1983 at Stillwater (Tables 4 and 5). It can be seen from Table 5 that the trend for equal or higher yields in N T compared with CT also exist in 19821983 and 1984-1985 at Lahoma. From the literature one would have expected the N T to have a yield advantage over the CT. Some likely reasons why the early planted N T treatments did not have higher yields may be disease a n d / o r insect related. It may also be true that, even though as reported, the N T systems have lower soil temperatures and increased soil water in the seed zone compared with CT systems; these differences are not sufficient to give the early planted NT winter wheat the yield advantage one would expect. It is also possible that water was not the yield limiting factor. The planting date effect on grain yield was significant at both locations in TABLE 4
Yield and yield component data for Stillwater location containing two tillagesystems and four planting dates. Planting date
Heads m-lofrows
CT
NT
118 159 142 140
117 153 132 134
-195 194 136
210 250 219 116
--
169 130 113 56 84
1982-1983 23 Aug. 13 Sept. 15 Oct. 17Nov. Average 1983-1984 15 Aug. 24 Sept. 24 Oct. 16Nov. Average 1984-1985 15 Aug. 19 Sept. 15 Oct. 14Nov. Average
K e r n e l s h e a d -1
Average C T
NT
Average C T
Average C T
22 22 20 21
22 20 20 21
22 ~ 21 ~ 20 ~ --
-26 28 26
22 22 21 30
-
24 24 22 31 27
150 108 1292
NT
Average
24.7 32.4 29.3 29.6
25.5 31.4 31.8 28.8
25.1 b 31.9 ~ 30.6 a --
2.58 3.50 3.10 3.05*
3.11 3.47 3.14 3.24
2.85 ~ 3.48 a 3.11 ~ --
1
-32.9 30.8 31.1 31.62
28.1 29.0 29.2 31.4 29.9
-31.0 a 30.0 ~ 31.2 a --
-4.42 3.96 2.79 3.72
3.37 4.29 3.68 2.42 3.46
-4.36 a 3.82 a 2.61 b --
--23 b 34 a --
--29.3 27.1 28.2
27.0 28.3 28.1 25.8 27.0
--28.7 a 26.4 a --
--2.70 2.14 2.42*
2.29 2.44 2.40 0.89 1.65
--2.55 a 1.52 b --
B
118 c 156 a 137 b --
1
--131 a 82 b --
--24 36 30*
Yield ( M g h a - 1 )
NT
m
-
K e r n e l w e i g h t (g 1000 -1 )
_
_
1Significant tillage by p l a n t i n g date i n t e r a c t i o n exists. L S D for tillage m e a n s w i t h i n dates a n d date m e a n s w i t h i n tillage for h e a d s m - 1 of r o w 1983-1984 = 34.00. L S D for tillage m e a n s w i t h i n dates a n d date m e a n s w i t h i n tillage for kernels h e a d - 1 1983-1984 = 5.38. 2Tillage m e a n s are a c r o s s p l a n t i n g d a t e s h a v i n g d a t a for b o t h tillage s y s t e m s only. D a t e m e a n s followed b y different s u p e r s c r i p t s are significantly different at t h e P = 0 . 0 5 level as d e t e r m i n e d b y t h e D u n c a n Multiple R a n g e Test. *Significant at t h e 0.05 p r o b a b i l i t y level.
194 TABLE 5 Yield and yield component data for Lahoma location containing two tillage systems and four planting dates. Planting date
Heads m - ~of row
Kernels head- ~
Kernel weight (g 1000 - 1)
CT
NT
Average CT
NT
Average CT
88 113 96 91
168 152 117 121
~
26 26 26 24 25
23 22 21 20 22
24~ 24~ 24~ 22~ --
30.7 32.7 30.9 29.6 31.0
1983-1984 16 Aug. 134 23 Sept. 177 02 Oct. -15 Nov. 140 Average 150
154 168 -101 141
144 173~ -121 b --
22 19
21 18
22~ 18~
22 21
21 20
21 ~ --
1984-1985 16 Aug. 18 Sept. 15 Oct. 15 Nov. Average
128 112 144 118 125
126~b 110b 138~ 104b --
25 22 22 30
22 24 22 24
1982-1983 23 Aug. 14 Sept. 19 Oct. 16 Nov. Average
124 108 133 90 114
Yield (mg h a - ~)
NT
Average CT
NT
Average
30.1 31.5 32.2 30.2 31.0
30.4 be 33.1a 31.5 ab 29.9 ¢ --
3.15 3.28 2.64 2.42 2.87
3.02 3.36 2.84 2.84 3.02
3.10 a 3.32 a 2.74 b 2.63 b --
17.0 14.0 15.5b 21.8 16.5 19.F
3.02 3.64
2.95 2.98 b 2.79 3.21~
16.2 15.1 15.6~ 18.3 1 5 . 6 -
2.23 2.16 2.20 b 2.96* 2.63 - -
30.1 30.2 30.3 20.6
2.47 2.34 3.10 1.69 2.40
30.6 1 32.0 30.1 25.0
2.50 2.55 2.84 1.77 2.41
2.48 b 2.44 b 2.96 ~b 1.73c --
1Significant interaction exist. LSD for tillage means within dates and date means within tillages for heads m - 1of row 1982-1983 = 24.8. LSD for date means within tillage for kernels head- 119841985=4.1. LSD for tillage means within dates for kernels head -1 1984-1985= 19.7. LSD for date means within tillage for kernel weight 1984-1985 = 7.3. LSD for tillage means within dates for kernel weight 1984-1985 = 26.3. Date means followed by different superscripts are significantly different at the P = 0.05 level as determined by the Duncan Multiple Range Test. *Tillage means significant at the P = 0.05 level.
all y e a r s o f t h e s t u d y e x c e p t for t h o s e at S t i l l w a t e r for t h e 1982-1983 crop y e a r ( T a b l e s 4 a n d 5 ). T h e g r a i n y i e l d s a t b o t h l o c a t i o n s i n c r e a s e d as t h e p l a n t i n g date was delayed from mid-August to mid-September and October. As the p l a n t i n g date was d e l a y e d f r o m m i d - O c t o b e r to m i d - N o v e m b e r , a yield dec r e a s e w a s o b s e r v e d . T h i s p a t t e r n w a s a l s o o b s e r v e d b y F e n s t e r e t al. ( 1 9 7 2 ) only with decreases beginning in mid-September owing to the more northerly location. The yields from the mid-September and October planting dates were the highest with neither of the two planting dates having a consistent yield advantage. In that no significant planting date by tillage interaction existed the ideal planting date for both tillage systems appears to be the same.
195
The yield components, heads m - i of row, kernels head-1 and weight per 1000 kernels, were analyzed to try to determine if any particular component had a significant effect on the yields observed. At Stillwater a significant tillage by date interaction (P=0.05) existed for heads m -1 and kernels head -1 in 1983-1984. At Lahoma a significant tillage by date interaction existed for heads m - 1 in 1982-1983 and for kernels head- 1 and weight per 1000 kernels in 19841985. When significant interactions did not exist, the NT treatments had a significantly greater number of heads m - 1 in only one instance - that being at Lahoma in 1982-1983 (Table 5). As with grain yield, the mid-September and October planting dates usually had the highest number of heads m - 1. The CT treatments always had a greater number of kernels head- 1 than the NT treatments (Tables 4 and 5 ). This is also true of the weight per 1000 kernels except for Lahoma in 1984-1985. In the treatment where NT had more heads m -1, there seems to have been an adjustment in the kernels head-1 and weight per 1000 kernel values such that no significant increase in yield was realized. The values for the above yield components within a tillage treatment followed the same trend as grain yield, with September and October having the highest values. Therefore, it appears that the planting date yield differences were caused by the net effect of all yield components and not predominantly any single yield component. CONCLUSIONS
Potential yield increase for NT compared with CT monoculture winter wheat did not occur. The early seeded NT treatments had comparable yields to those of the early seeded CT treatments. But, they did not have yields that were significantly higher than the mid-September or mid-October NT or CT planted treatments. The trend for earlier emergence and establishment in the early seeded NT winter wheat compared with CT was followed by a trend for a greater number of heads area- 1. Treatments having greater numbers of heads frequently had fewer kernels head -1 and/or lower kernel weight, resulting in yields which were not significantly different. When yields were different, a combination of yield components contributed to the increase rather than one component being dominant. For the locations and rainfall conditions experienced, the potential for the growth from the early plantings to reduce severely the PSW to a deficit level appears to be relatively low. Once the tillage differences in SWC and/or PSW at Lahoma were established, the NT continued to have the highest values. Therefore, it is unlikely that soil water was the limiting factor causing the lower yields in the NT treatments when compared with the CT treatments. It appears, however, that as precipitation becomes more limiting the SWC and the PSW for monoculture NT winter wheat production will be greater than
196 t h o s e of m o n o c u l t u r e C T w i n t e r w h e a t . T h u s , if w a t e r is a y i e l d - l i m i t i n g factor, i n c r e a s e d soil w a t e r u n d e r m o n o c u l t u r e N T w i n t e r w h e a t p r o d u c t i o n s h o u l d allow for yield increases in d r y e r y e a r s or a r e a s of lower a n n u a l p r e c i p i t a t i o n w h e n c o m p a r e d w i t h C T w i n t e r w h e a t o n a n y o f t h e four p l a n t i n g dates.
REFERENCES Blevins, R.L., Cook, D., Phillips, S.H. and Phillips, R.E., 1971. Influence of no-tillage on soil moisture. Agron. J., 63: 593-596. CTIC (Conservation Tillage Information Center), 1988. 1987 National survey conservation tillage practices. Conservation Tillage Information Center, West Lafayette, IN, 142 pp. Darwinkel, A., Ten Hag, B.A. and Knizenga, J., 1977. Effect of sowing date and seeding rate on crop development and grain production of winter wheat. Neth. J. Agric. Sci., 25: 83-94. Davidson, J.M. and Santelmann, P.W., 1973. An evaluation of various tillage systems for wheat. Agric. Exp. Stn. Bull., B-711 Oklahoma State Univ, 17 pp. Fenster, C.R. and Peterson, G.A., 1979. Effects of no-tillage fallow as compared to conventional tillage in a wheat-fallow system. Agric. Exp. Stn. Bull., 289, Univ. Nebraska, Lincoln. Fenster, C.R. and Wicks, G.A., 1982. Fallow systems for winter wheat in western Nebraska. Agron. J., 74: 9-13. Fenster, C.R., Boosalis, M.G. and Wirhing, J.L., 1972. Date of planting studies of winter wheat and winter barley in relation to root and crown rot grain yields and quality. Agric. Exp. Stn. Bull., 250. Univ. Nebraska, Lincoln, 31 pp. Hubbard, V.C. and Harper, H.T., 1949. Effect of clipping small grains on composition and yield of forage and grain. Agron. J., 41: 85-92. Johnson, W.C. and Davis, R.G., 1980. Yield-water relationships of summer-fallowed winter wheat a precision study in the Texas panhandle. USDA-ARR-S-5/July, 43 pp. Russelle, M.P. and Bolton, F.E., 1980. Soil temperature effects on winter wheat and winter barley emergence in the field. Agron. J., 72: 823-827. Smika, D.E., 1983. Soil water changes as related to position of wheat straw mulch on the soil surface. Soil Sci. Soc. Am. J., 47: 988-991. Smika, D.E. and Ellis Jr., R., 1971. Soil temperature and wheat straw mulch effects on wheat plant development and nutrient concentration. Agron. J., 63: 388-391. Steel, R.G.D. and Torrie, J.H., 1980. Principles and procedures of statistics. McGraw-Hill, New York, NY. Tanaka, D.L., 1985. Chemical and stubble-mulch fallow influences on seasonal soil water contents. Soil Sci. Soc. Am. J., 49: 728-733. Unger, P.W., 1978. Straw-mulch rate effects on soil water storage and sorghum yield. Soil Sci. Soc. Am. J., 42: 486-491. Wicks, G.A. and Smika, D.E., 1973. Chemical fallow in a winter wheat-fallow rotation. J. Weed Sci. Soc. Am., 21: 97-102. Zingg, A.W. and Whitfield, C.J., 1957. A summary of research experience with stubble-mulch farming in the western states. Tech. Bull. No. 1166, USDA, 55 pp.
185
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Soil Water Availability for Spring Growth of Winter Wheat (Triticum aestivum L.) as Influenced by Early Growth and Tillage* WILLIAM F. HEER' and EUGENE G. KRENZER, JR. e
1Agronomy Department, Kansas State University, Manhattan, KS 66506 (U.S.A.) eAgronomy Department, Oklahoma State University, Stillwater, OK 74078-0507 (U.S.A.) (Accepted for publication 25 October 1988)
ABSTRACT Heer, W.F. and Krenzer, Jr., E.G., 1989. Soil water availability for spring growth of winter wheat (Triticum aestivum L.) as influenced by early growth and tillage. Soil Tillage Res., 14: 185-196. This study was designed to determine to what extent tillage and fall growth as affected by planting date influence profile soil water for spring growth and yield of monoculture winter wheat (Triticum aestivum L.). The study was conducted for 3 crop years ( 1982-1985) at Stillwater and Lahoma, OK. A randomized-block design with a split-plot arrangement was used where main units were tillage and subunits were 4 plantings spaced 1 month apart. Soil water was measured using the neutron-scattering method. The effects of tillage and amount of fall growth on profile soil water (PSW), total soil water in the 1.2-m soil profile, differed between the two locations. At Stillwater, neither tillage nor differences in fall growth affected soil water. During the third year at Lahoma, where precipitation was more limiting, a significant tillage effect on PSW developed at jointing. No-till (NT) was significantly greater than that of the conventional tillage (CT). This effect was observed consistently through the 1.2-m profile. The effect of fall growth on spring PSW was not consistent. The fall growth effect on grain yield was significant at both locations in all 3 years except for Stillwater in 1982-1983. However, there was no tillage by planting date interaction. The mid-September and October planting dates consistently had higher yields than the mid-August and November planting dates. The use of NT has a potential to increase spring profile soil water for the production of monoculture winter wheat in the South Central Great Plains. However, the potential to deplete this increase through increased fall growth by planting early exists and there is further need to evaluate the benefits of additional forage obtained with earlier planting vs. the depletion of stored soil water and the potential effect upon grain yields.
INTRODUCTION N o - t i l l p r o d u c t i o n ( N T ) p r a c t i c e s f o r w i n t e r w h e a t ( T r i t i c u m aestivum L. ) are gaining acceptance in Oklahoma and other Great Plains states (CTIC, *Contribution of the Department of Agronomy, Oklahoma State University. Published as Journal Article No. 5055 Oklahoma Agriculture Experiment Station.
0167-1987/89/$03.50
© 1989 Elsevier Science Publishers B.V.
186 1988). As these N T methods gain acceptance, they must be considered in the evaluation of monoculture wheat production. Of particular concern is how profile soil water and grain yield are affected under different tillage systems at different levels of fall growth. Several researchers have addressed the effect of tillage methods on soil water content (SWC) and wheat grain yields under wheat-fallow and wheat sorghum-fallow practices (Wicks and Smika, 1973; Fenster and Peterson, 1979; Johnson and Davis, 1980). In all the above research, the wheat was planted at typical planting times for the particular location after an extended fallow period (11-18 months). Soil water content (SWC) is the amount of water present in a particular segment of a soil profile, determined on a gravimetric or volumetric basis, and presented as percent water or m 3 of water per m 3 of soil. Profile soil water (PSW) determined gravimetrically or volumetrically is a measure of the total water present in that portion of the soil profile referred to. Previous work at Oklahoma State University with monoculture wheat {Davidson and Santelmann, 1973) reported SWC was greater for NT than conventional tillage (CT). With the reported increase in SWC and lower soil temperatures under NT wheat-fallow conditions as compared with CT wheat-fallow (Blevins et al., 1971; Smika and Ellis, 1971; Unger, 1978; Fenster and Peterson, 1979; Russelle and Bolton, 1980; Fenster and Wicks, 1982; Smika, 1983; Tanaka, 1985), it would be expected that SWC for spring growth and grain yield in annually cropped monoculture winter wheat planted N T would be equal to or greater than that in CT planted wheat. Lower soil temperature can reduce the impact of post-harvest dormancy as well as reduce high-temperature stress which causes a reduction in tillering. Therefore, potentially earlier germination and increased fall growth (increased tillering) owing to this reported lower soil temperature and increased soil moisture could result in grain yield of monoculture N T wheat planted before the usual planting time for a given location being higher than that of monoculture CT wheat planted at the same time. Russelle and Bolton (1980) showed that earlier planted cereals often utilize excessive amounts of soil water in the fall, are more susceptible to winter killing, and are frequently subject to disease. Darwinkel et al. (1977) showed that delaying the planting of CT wheat caused a distinct reduction in yield, but planting earlier (prior to the usual planting time) increased yields only slightly. Fenster et al. (1972) showed an increase in grain yield as planting date was delayed from mid-August to late September and a decrease in yield as planting was delayed from late September to early October. Their study also showed that CT yielded more than N T in the early plantings, but in the later plantings the N T yielded more than the CT. The optimum time for seeding winter wheat in Oklahoma is generally considered the last week of September through the first week of October. But, it is unknown how earlier planting of winter wheat affects the soil water, diseases and grain yield under both CT and NT. The objectives of this study were to determine to what extent spring profile
187
soil water and grain yield for monoculture winter wheat produced in the South Central Great Plains are i n f u e n c e d by tillage and amount of fall growth as influenced by planting date. MATERIALS AND METHODS
The study was conducted on a Pulaski fine sandy loam (coarse-loamy, mixed, thermic Typic Ustifluvent) with 0-2 % slope at the Oklahoma State University North Agronomy Research farm, Stillwater, OK, and on a Grant silt loam (fine, mixed, thermic Argiustoll) with 3-5% slope at the Oklahoma State University North Central Research Station, Lahoma, OK. Data were collected over 3 growing seasons, 1982-1984, at both locations. Both sites were planted in wheat the year prior to the beginning of the study. Precipitation was measured at nearby research station headquarters at both locations. The experimental design was a randomized complete block with a split-plot arrangement of treatments and 4 replications. Main plot treatments were 30 m by 23 m and consisted of two tillage systems, CT and NT. At Stillwater, the CT consisted of moldboard plowing to a depth of 0.2 m as soon after wheat harvest as soil conditions allowed. These plots were then disked, as needed, for weed control and seedbed preparation. Final seedbed preparation consisted of running a mulch treader over the plots just prior to planting. At Lahoma, the CT plots were disked with an offset disk immediately after wheat harvest. These plots were then disked or swept with 0.2-m sweeps spaced 0.2-m apart as needed for weed control and residue incorporation. At both locations, the NT consisted of planting directly into the residue of the previous year's crop. Weed control in the N T plots during the period from harvest to seeding was achieved through the use of herbicides. Subplot treatments consisted of different amounts of biomass in the fall established through 4 planting dates; mid-August, mid-September, mid-October and mid-November. Therefore, planting date will be used throughout the discussion to denote different levels of fall growth. Subplots were 7.6 m by 23 m. The same tillage planting date treatment was repeated on a given plot all 3 years of the study. TAM W-101 hard red winter wheat was used throughout the study. Planting was performed with a Crustbuster double disk opener notill drill. A row spacing of 0.25 m and a seeding rate of 67 kg ha -1 was used in all 3 years of the study at both locations and all dates. Soil fertility was maintained by using the Oklahoma State University Soil Testing Lab indexes to determine the total amount of nitrogen, phosphorus and potassium needed. These needs were met through broadcast application of nitrogen as ammonium nitrate (34-0-0) and potassium as muriate of potash (0-0-60) prior to planting. Phosphorus was applied in the rows at planting as diammonium phosphate (18-46-0). Annual applications were 100, 20 and 60 kg h a - 1 of N, P and K, respectively.
188 Soil water content for each t r e a t m e n t was monitored with a neutron probe depth moisture gauge with 2 access tubes per subplot. Readings were taken at 0.15-m intervals from 0.15 to 1.8 m below the surface at Stillwater and from 0.15 to 1.2 m below the surface at Lahoma. Moisture readings were taken at each planting date for those plots which were planted and several times through the growing season. The last reading each crop year at each location was taken on the day of harvest. Heads m - 1 of row data were collected using two 1-m of row subsamples per plot, collected just prior to harvest. Kernels per head were determined using 10 subsamples from the above samples. Grain yield and kernel weight data were based on combine-harvested weights. Grain yields were adjusted to a moisture content of 135 g kg -1 and a test weight of 772 kg m -3 each year. For each time that water measurements were obtained, split-plot analyses of variance were performed for SWC at each depth increment and for PSW. The split-plot analysis of variance procedure was also used for heads m -1, kernels head -1, kernel weight and grain yield data. The F Test (Steel and Torrie, 1960) was used to determine significant tillage and planting date differences and the Duncan Multiple Range Test was used to separate planting date means. Least-squares means were calculated using SAS; G L M procedure was used when a t r e a t m e n t was missing resulting in an unbalanced design. RESULTS AND DISCUSSION Several treatments did not germinate and were replanted at a later date (Table 1). These treatments were eliminated from the statistical analyses. Also eliminated were the 1983-1984 October CT and N T treatments at Lahoma and the August and September CT treatments at Stillwater for 19841985. The two treatments at L a h o m a were planted late owing to wet conditions, and the two at Stillwater germinated and became established after sufficient precipitation occurred around mid-October. The precipitation at L a h o m a was somewhat evenly distributed except for TABLE 1 Subplot planting dates for Stillwater and Lahoma 1982-1984 crop years Location
August
September
October
November
1982 1983 1984 1982 1983 1984 1982 1983 1984 1982 1983 1984 Stillwater 1 Lahoma 24
2 16
15 16
13 14
24 23
19 18
15 19
14 3
15 15
17 16
16 15
14 15
IPlanted 27 August but did not germinate. Was replanted 24 September 1982. 2Planted 17 August but the C T did not germinate. Replanted the C T plots on 14 October 1983. 3Wet conditionsforced the delay of planting from 15 October to 2 November.
189
the unusually large amounts of precipitation received in May and October 1983, March 1984 and February and April 1985 (Table 2). Even though planting dates were 30 days apart, forage yields, 2.5 mg ha -1 in 1984 and 1.5 mg ha -1 in 1985, prior to early jointing were not significantly different. August plantings had more forage in the fall and less in the early spring than October plantings (data not presented). Forage production is environmentally dependent and is very inconsistent from year to year in Oklahoma (Hubbard and Harper, 1949). Statistically significant differences in PSW between CT and NT plots on the respective planting dates in 1982-1983 at Lahoma (Fig. 1A and B) were probably the result of a lack of sufficient weed control in the NT plots during the fallow period just prior to the establishment of the study. This lack of weed control resulted in the CT treatments having more PSW until sufficient precipitation was received to recharge the NT plots. The PSW curves for 19831984 (Fig. 1C and D) show the beginning of a trend toward higher soil water in the NT treatments when compared with the CT treatments. This trend becomes statistically significant in the 1984-1985 data with NT having significantly more water in the profile than CT (Fig. 1E and F). The PSW data from Lahoma (Table 3) also showed that a statistically significant planting date effect existed from jointing through maturity in all years of the study; however, TABLE 2 Monthly precipitation (mm) distribution for Stillwater and Lahoma for individual crop years compared with the long-term average Month
Long-term average 1
1982-1983
1983-1984
1984-1985
Stillwater Lahoma Stillwater Lahoma Stillwater Lahoma Stillwater Lahoma July August September October November December January February March April May June
90 82 86 71 47 34 30 34 47 73 117 108
67 74 87 78 50 24 29 17 71 69 84 61
50 35 58 25 70 59 8 76 78 41 189 93
82 2 18 4 39 38 21 41 87 85 109 145
0 22 52 193 55 10 5 18 130 73 68 135
0 36 95 121 42 5 0 47 145 84 30 43
16 26 30 123 56 101 77 116 127 136 43 162
2 21 12 33 33 78 20 140 60 132 36 114
Total
818
711
782
711
761
648
1013
681
iStillwater 91-year average, Lahoma 30-year average.
190
0
35 70 105 140 175 210 245 280 315 0 ,
r
,
.
.
.
A
330
~
3101
EE
35 70 105 140 175 210 245 280 315
.
B
330
987.83
310
290
290
270
270
250 !
250
230
230
3so1988 CI
L
I
I
~
I
I
I
t
I
I
I
q
I
(
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J
I 350 330 310 290 270
,=.330
~=~ 310 290
--
270 ~'=~ 250 2302
~
--
CT NT August O • September ~ •
!-
[] •BB November ~(~
~_ (
250 230 210 190
October
O nE
3so 330
1 F ~///~.~
1984-85
310 290
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190
- 330 310 ~ 290 270 250 230 210 190
I
0
35 70 105 140 1'~5 2~0 2,~5 280 315
0
315 7~) 1135 110 175 2~0 2145 21°0 3~5
TIME (DAYS AFTER AUGUST 1) Fig. 1. Tillage and planting date effects upon profile soil water content in the top 1.2 m of soil at selected dates of observation at Lahoma. A, C and E are August and September planting dates while B, D and F are October and November planting dates.
no one planting date consistently had the lowest PSW values although the trend was toward the earliest date. There was not a statistically significant planting date by tillage interaction for PSW during the dates shown in Table 3. Differences in SWC by depth for planting dates at Lahoma first appeared in the fall of 1983, when the August planted treatments had a lower SWC than
191 TABLE 3 Planting date effect upon 1.2-m PSW from jointing stage of wheat until harvest at Lahoma Planting date 1982-1983 Day ~ August September October November 1983-1984 Day August September October November 1984-1985 Day August September October November
215
257
271
276
299
311
324
334
320 b 335 ~ 341 ~ 343 ~
312 c 326 b 341" 345 ~
275 b 285 b 31C 312 ~
269 b 281 b 306 ~ 307 ~
243 b 252 ~b 266 ~ 263"
223 b 227 b 24C 242 ~
253 ~ 265 ~ 265 ~ 263 ~
272 ~ 288 ~ 282 a 278 ~
214
261
275
283
290
297
304
312
332
302 ¢ 326 b 341 a 346 ~
320 b 328 b 346 a 349 ~
299 b 308 b 330 a 33C
280 b 286 b 317 ~ 319 ~
252 b 253 b 291 a 296 ~
241 b 243 b 282" 288 ~
225 b 222 b 258 ~ 271 ~
213 b 213 b 237 a 251 ~
222 b 229 b 236" 260 a
238
251
258
267
274
281
289
296
300
331 ¢ 344 a 333 bc 342 ab
302 b 320 a 302 b 322 a
296 b 316 a 295 b 32C
283 b 308 a 283 b 302 a
300 bc 32C 296 c 319 ab
292 b 31C 285 b 300 ~b
258 bc 286 a 248 c 265 b
232 b 258 a 222 b 236 b
283 ~b 294 a 268 bc 265 ~
1Days after 1 August. Means within a day followed by the same superscripts are not significantly different at the 5% level according to DMR. Means of 4 blocks and two tillage systems. any other treatment
(Fig. 2A) (Data for November planting date, not shown
for clarity of the graph, was similar to September and October data). The lower W C i n A u g u s t p l a n t i n g s is c a u s e d b y g r e a t e r w a t e r u s e i n p l o t s h a v i n g p l a n t s transpiring over the longest period. This difference continued through Februa r y 1984. H o w e v e r , a s a r e s u l t o f t h e u n u s u a l l y h i g h p r e c i p i t a t i o n i n M a r c h 1984, t h e A u g u s t N T S W C w a s r e p l e n i s h e d t o e q u a l t h e o t h e r t r e a t m e n t s ( F i g s . 1C a n d 2 B ) . N o t e t h a t e v e n w i t h t h e h e a v y p r e c i p i t a t i o n t h e A u g u s t C T s t i l l r e m a i n e d d r i e r t h a n t h e o t h e r t r e a t m e n t s ( F i g . 2 B ). T h i s d i f f e r e n t i a l r e s p o n s e i n S W C b e t w e e n t h e e a r l y p l a n t e d N T a n d C T is c o n s i s t e n t w i t h t h o s e r eported by Zingg and Whitfield (1957) and Russelle and Bolton (1980). This is o n e o f t h e f e w t i m e s t h r o u g h o u t t h e 3 y e a r s o f t h i s s t u d y w h e r e p l a n t i n g d a t e by tillage interaction was statistically significant. Statistical analysis of the Lahoma 1984-1985 SWC and PSW data showed N T t o b e s i g n i f i c a n t l y (P= 0 . 0 5 ) w e t t e r a t al l r e a d i n g d a t e s . E v e n w h e n t h e P S W r e a c h e d i t s m a x i m u m o n 9 M a r c h 1985, t h e C T p r o f i l e s d o e s n o t a p p e a r
192 0.00 I
I
I
I
I
I
B
I
|
I
I
I
I
0.00 0.15 0.30 0.45
0.60~
°9°11.05 l 1.20
..j
0.60
!
0.75 I-
0.75 0.90 1.05 1.20
C
Mar.9, 1985
~B
oo°'rlooto.,. °°:°t
-
_
0.15
°
0.30
,.,
0.45 0.60
0.75 I"
0.75
0.90 l 1.05 I"
0.90 (
1.05 1.20
1.20 F
I
I
I
0.08 0.12 0.16 0.20
I
I
I
0.24 0.28 0.32
I 0.12 0.16 0.20
I
0.24 0.28 0.32
0.36
SOIL WATER CONTENT (m31m3) Fig. 2. Soil water content by depth at differenttimes throughoutthe tillage and planting date study at Lahoma. to have completely recharged (Fig. 2C). However, there were changes in the SWC throughout the 1.2-m profile, which is inconsistent with the findings of Blevins et al. (1971) who reported only minimal changes in the SWC below the 0.45-m depth. By the end of the 1984-1985 crop year, the SWC in the NT treatments had never decreased to the levels of the SWC in the CT treatments (Fig. 2D). Precipitation at the Stillwater location was 5% below the long term average in 1982-1983, 7% below in 1983-1984, and 23% above in 1984-1985 (Table 2). No consistent planting date or tillage effect on SWC or PSW could be recognized at this location. Therefore, the responses observed at Lahoma are site specific. Even though the Lahoma NT plots generally had higher SWC and PSW than CT plots, the presence of a definite pattern where one tillage treatment had consistently higher grain yields than the other did not develop. The CT yields were significantly larger than the NT in 1983-1984 at Lahoma and in 1984-1985 at Stillwater. The NT yield was significantly larger than the CT in
193
1982-1983 at Stillwater (Tables 4 and 5). It can be seen from Table 5 that the trend for equal or higher yields in N T compared with CT also exist in 19821983 and 1984-1985 at Lahoma. From the literature one would have expected the N T to have a yield advantage over the CT. Some likely reasons why the early planted N T treatments did not have higher yields may be disease a n d / o r insect related. It may also be true that, even though as reported, the N T systems have lower soil temperatures and increased soil water in the seed zone compared with CT systems; these differences are not sufficient to give the early planted NT winter wheat the yield advantage one would expect. It is also possible that water was not the yield limiting factor. The planting date effect on grain yield was significant at both locations in TABLE 4
Yield and yield component data for Stillwater location containing two tillagesystems and four planting dates. Planting date
Heads m-lofrows
CT
NT
118 159 142 140
117 153 132 134
-195 194 136
210 250 219 116
--
169 130 113 56 84
1982-1983 23 Aug. 13 Sept. 15 Oct. 17Nov. Average 1983-1984 15 Aug. 24 Sept. 24 Oct. 16Nov. Average 1984-1985 15 Aug. 19 Sept. 15 Oct. 14Nov. Average
K e r n e l s h e a d -1
Average C T
NT
Average C T
Average C T
22 22 20 21
22 20 20 21
22 ~ 21 ~ 20 ~ --
-26 28 26
22 22 21 30
-
24 24 22 31 27
150 108 1292
NT
Average
24.7 32.4 29.3 29.6
25.5 31.4 31.8 28.8
25.1 b 31.9 ~ 30.6 a --
2.58 3.50 3.10 3.05*
3.11 3.47 3.14 3.24
2.85 ~ 3.48 a 3.11 ~ --
1
-32.9 30.8 31.1 31.62
28.1 29.0 29.2 31.4 29.9
-31.0 a 30.0 ~ 31.2 a --
-4.42 3.96 2.79 3.72
3.37 4.29 3.68 2.42 3.46
-4.36 a 3.82 a 2.61 b --
--23 b 34 a --
--29.3 27.1 28.2
27.0 28.3 28.1 25.8 27.0
--28.7 a 26.4 a --
--2.70 2.14 2.42*
2.29 2.44 2.40 0.89 1.65
--2.55 a 1.52 b --
B
118 c 156 a 137 b --
1
--131 a 82 b --
--24 36 30*
Yield ( M g h a - 1 )
NT
m
-
K e r n e l w e i g h t (g 1000 -1 )
_
_
1Significant tillage by p l a n t i n g date i n t e r a c t i o n exists. L S D for tillage m e a n s w i t h i n dates a n d date m e a n s w i t h i n tillage for h e a d s m - 1 of r o w 1983-1984 = 34.00. L S D for tillage m e a n s w i t h i n dates a n d date m e a n s w i t h i n tillage for kernels h e a d - 1 1983-1984 = 5.38. 2Tillage m e a n s are a c r o s s p l a n t i n g d a t e s h a v i n g d a t a for b o t h tillage s y s t e m s only. D a t e m e a n s followed b y different s u p e r s c r i p t s are significantly different at t h e P = 0 . 0 5 level as d e t e r m i n e d b y t h e D u n c a n Multiple R a n g e Test. *Significant at t h e 0.05 p r o b a b i l i t y level.
194 TABLE 5 Yield and yield component data for Lahoma location containing two tillage systems and four planting dates. Planting date
Heads m - ~of row
Kernels head- ~
Kernel weight (g 1000 - 1)
CT
NT
Average CT
NT
Average CT
88 113 96 91
168 152 117 121
~
26 26 26 24 25
23 22 21 20 22
24~ 24~ 24~ 22~ --
30.7 32.7 30.9 29.6 31.0
1983-1984 16 Aug. 134 23 Sept. 177 02 Oct. -15 Nov. 140 Average 150
154 168 -101 141
144 173~ -121 b --
22 19
21 18
22~ 18~
22 21
21 20
21 ~ --
1984-1985 16 Aug. 18 Sept. 15 Oct. 15 Nov. Average
128 112 144 118 125
126~b 110b 138~ 104b --
25 22 22 30
22 24 22 24
1982-1983 23 Aug. 14 Sept. 19 Oct. 16 Nov. Average
124 108 133 90 114
Yield (mg h a - ~)
NT
Average CT
NT
Average
30.1 31.5 32.2 30.2 31.0
30.4 be 33.1a 31.5 ab 29.9 ¢ --
3.15 3.28 2.64 2.42 2.87
3.02 3.36 2.84 2.84 3.02
3.10 a 3.32 a 2.74 b 2.63 b --
17.0 14.0 15.5b 21.8 16.5 19.F
3.02 3.64
2.95 2.98 b 2.79 3.21~
16.2 15.1 15.6~ 18.3 1 5 . 6 -
2.23 2.16 2.20 b 2.96* 2.63 - -
30.1 30.2 30.3 20.6
2.47 2.34 3.10 1.69 2.40
30.6 1 32.0 30.1 25.0
2.50 2.55 2.84 1.77 2.41
2.48 b 2.44 b 2.96 ~b 1.73c --
1Significant interaction exist. LSD for tillage means within dates and date means within tillages for heads m - 1of row 1982-1983 = 24.8. LSD for date means within tillage for kernels head- 119841985=4.1. LSD for tillage means within dates for kernels head -1 1984-1985= 19.7. LSD for date means within tillage for kernel weight 1984-1985 = 7.3. LSD for tillage means within dates for kernel weight 1984-1985 = 26.3. Date means followed by different superscripts are significantly different at the P = 0.05 level as determined by the Duncan Multiple Range Test. *Tillage means significant at the P = 0.05 level.
all y e a r s o f t h e s t u d y e x c e p t for t h o s e at S t i l l w a t e r for t h e 1982-1983 crop y e a r ( T a b l e s 4 a n d 5 ). T h e g r a i n y i e l d s a t b o t h l o c a t i o n s i n c r e a s e d as t h e p l a n t i n g date was delayed from mid-August to mid-September and October. As the p l a n t i n g date was d e l a y e d f r o m m i d - O c t o b e r to m i d - N o v e m b e r , a yield dec r e a s e w a s o b s e r v e d . T h i s p a t t e r n w a s a l s o o b s e r v e d b y F e n s t e r e t al. ( 1 9 7 2 ) only with decreases beginning in mid-September owing to the more northerly location. The yields from the mid-September and October planting dates were the highest with neither of the two planting dates having a consistent yield advantage. In that no significant planting date by tillage interaction existed the ideal planting date for both tillage systems appears to be the same.
195
The yield components, heads m - i of row, kernels head-1 and weight per 1000 kernels, were analyzed to try to determine if any particular component had a significant effect on the yields observed. At Stillwater a significant tillage by date interaction (P=0.05) existed for heads m -1 and kernels head -1 in 1983-1984. At Lahoma a significant tillage by date interaction existed for heads m - 1 in 1982-1983 and for kernels head- 1 and weight per 1000 kernels in 19841985. When significant interactions did not exist, the NT treatments had a significantly greater number of heads m - 1 in only one instance - that being at Lahoma in 1982-1983 (Table 5). As with grain yield, the mid-September and October planting dates usually had the highest number of heads m - 1. The CT treatments always had a greater number of kernels head- 1 than the NT treatments (Tables 4 and 5 ). This is also true of the weight per 1000 kernels except for Lahoma in 1984-1985. In the treatment where NT had more heads m -1, there seems to have been an adjustment in the kernels head-1 and weight per 1000 kernel values such that no significant increase in yield was realized. The values for the above yield components within a tillage treatment followed the same trend as grain yield, with September and October having the highest values. Therefore, it appears that the planting date yield differences were caused by the net effect of all yield components and not predominantly any single yield component. CONCLUSIONS
Potential yield increase for NT compared with CT monoculture winter wheat did not occur. The early seeded NT treatments had comparable yields to those of the early seeded CT treatments. But, they did not have yields that were significantly higher than the mid-September or mid-October NT or CT planted treatments. The trend for earlier emergence and establishment in the early seeded NT winter wheat compared with CT was followed by a trend for a greater number of heads area- 1. Treatments having greater numbers of heads frequently had fewer kernels head -1 and/or lower kernel weight, resulting in yields which were not significantly different. When yields were different, a combination of yield components contributed to the increase rather than one component being dominant. For the locations and rainfall conditions experienced, the potential for the growth from the early plantings to reduce severely the PSW to a deficit level appears to be relatively low. Once the tillage differences in SWC and/or PSW at Lahoma were established, the NT continued to have the highest values. Therefore, it is unlikely that soil water was the limiting factor causing the lower yields in the NT treatments when compared with the CT treatments. It appears, however, that as precipitation becomes more limiting the SWC and the PSW for monoculture NT winter wheat production will be greater than
196 t h o s e of m o n o c u l t u r e C T w i n t e r w h e a t . T h u s , if w a t e r is a y i e l d - l i m i t i n g factor, i n c r e a s e d soil w a t e r u n d e r m o n o c u l t u r e N T w i n t e r w h e a t p r o d u c t i o n s h o u l d allow for yield increases in d r y e r y e a r s or a r e a s of lower a n n u a l p r e c i p i t a t i o n w h e n c o m p a r e d w i t h C T w i n t e r w h e a t o n a n y o f t h e four p l a n t i n g dates.
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