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Progress Report-2002 |
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TITLE: Influence of Fallow Tillage on Jointed Goatgrass Emergence and Competition in Winter Wheat. PRINCIPAL INVESTIGATORS:
Gail A. Wicks,
University of Nebraska TIME LINE: July 1, 1998 to June 30, 2003.
ORIGINAL HYPOTHESIS:
Tillage immediately after winter wheat harvest will aid in
germination of jointed goatgrass (JGG) during the fallow period more
than delaying tillage until the following spring.
SUMMARY OF PROGRESS: Two cycles of the winter wheat-fallow rotation have been completed at three diverse precipitation and geographic locations. From these results it appears that post-harvest tillage has a minimal effect on JGG germination after wheat harvest. Sufficient precipitation is needed for timely germination of JGG seeds. Rain after harvest improved JGG germination with tillage at North Platte, NE and Blue Creek Utah, but low rainfall amounts in Moro, Oregon prevented JGG germination. Rain too late allows the low JGG seeding density to increase in density so differences between low and high seeding rates are similar in the succeeding wheat crop. When low amounts of precipitation occur there is an advantage for tillage during the fallow season with low JGG densities. Under high JGG densities the advantage of tillage timing is not sufficient to prevent competition with the winter wheat. More drastic tillage such as moldboard plowing or burning in the spring + moldboard plowing once is needed to reduce initial JGG infestations to a manageable level in the two-year rotation.
NEBRASKA: Tillage timing initiated during the 2000-2001 fallow period did not improve JGG emergence during the fallow season nor affect JGG density in the wheat crop. The 2002 wheat yields were not affected by when tillage timing began or from JGG competition differences among treatments. However during the 2001-2002 fallow period, less JGG emerged in the no-till treatment, but emergence was greater after the wheat emerged.
OREGON: Early April jointed goatgrass plant counts in wheat stubble during the 2000-2001 fallow period showed more JGG emergence in the May and No-till treatments than the other times of tillage initiation. However, no difference in JGG density was observed in the 2002 wheat crop. In the 2001-2002 fallow period, counts taken March 27, 2002 showed the same results.
UTAH: Current research reveals that post harvest tillage, initiated either in fall or spring fallow, had negligible effects on jointed goatgrass infestations in a subsequent winter wheat crop. A three-year drought interrupted by an unexpectedly heavy rainfall at planting in 2000 and 2001 (4 plus inches) confounded experimental results because treatments with no jointed goatgrass throughout the fallow period had hundreds of reproductive tillers when the ensuing wheat crop was harvested.
OBJECTIVES: To determine the correct timing of shallow tillage to hasten JGG germination of the soil seedbank in a winter wheat-fallow rotation and if winter wheat yields are affected by JGG competition.
EXPERIMENTAL DESIGN: Adjacent field studies were established in cereal stubble fields September 1998 and 1999 at Blue Creek, Utah; Moro, Oregon; and North Platte, Nebraska. All sites had no previous history of JGG infestation. The studies were arranged as RCB designs with 5 replications. Main plots were 30 ft. by 50 ft. in size. At North Platte and Moro, JGG was seeded into plots of standing cereal stubble before the first tillage treatment in 1998 and in 1999 at adjacent site. At Blue Creek, JGG was seeded at both sites in 1998. Treatments consisted of six post-harvest stubble tillage timings: A.) Early post-harvest tillage, B.) tilled in late fall, C.) tilled in early spring, D.) tilled in late spring, E.) tilled at all tillage timings, and F.) No tillage. Glyphosate was applied as needed to control weeds during the fallow period. A mulch treader was used once at North Platte and at Moro and Blue Creek a tandem disk with 20-inch discs was used twice to incorporate the JGG seeds into the surface soil for each treatment.
PROGRESS/CONCLUSIONS:
NEBRASKA. During Sept. and October following wheat harvest, the most JGG seedlings emerged in the multiple-tillage plots, but early tillage did not necessarily reduce the amount of JGG that emerged in the winter wheat The results from the second crop cycle will be different than the first because of the drought in 2000 allowing for germination of the JGG after wheat sowing in Block 2 . 2000-2002 Block 1. Differences in the initial seeding rate of 5 and 75 spikelets/m2 still exists with 3 times more seedlings emerged in the 75 spikelets seeding rate initiated in 1998. Ground cover taken in 2001 after wheat seeding was considerably below the other two years because drought and hail affected wheat growth and stubble retention. During the 2000-2001 fallow period, tillage improved germination of JGG as indicated by counts taken Sept. 25, 2001, but total JGG emergence during the fallow period was not different (Table 1).
No JGG emerged following wheat seeding or in the fall of 2002 because of no precipitation to germinate the seeds. Winter wheat stubble ground cover taken in the growing wheat ranged from 5% on multiple tillage treatments to 31% on the treatment that was not tilled. 2001-2003 Block 2. This W-F sequence had extremely high JGG emergence in the fall of 2001, little during the spring, and a large amount in the fall of 2002. Rain following wheat seeding in 2002 caused the highest JGG emergence since the block of the experiment was initiated in 1999. The no-till plots had greater JGG emergence. The only difference between the 5 and 75 JGG seeding rate occurred May21, Sept. 20 and Nov. 5 when the higher seeding rate had greater densities. Ground cover taken in the newly seeded winter wheat showed that three levels of wheat residues were present (Table 2). No-till had 47%, June plots tilled once had 24%, and those tilled four times had 9%.
Table 1.Effect of tillage timing (2nd crop cycle) on jointed goatgrass densities during the 2000-2001 fallow period and in the 2002 winter wheat crop following initial seeding at 5 and 75 spikelets/m2 in 1998. Counts were taken in five permanent 1-m2 area/plot.a Block 1 plots 1-60. North Platte, NE.
a Glyphosate at 0.7 lb ae/A was applied after each count during the fallow period. b Counts taken after wheat emergence. Winter wheat was planted September 28, 2001. c Counts were taken following winter wheat harvest.
Table 2. Effect of tillage-timing treatments on jointed goatgrass densities during the 2001-2002 fallow period and in the 2003 winter wheat crop following initial seeding at 5 and 75 spikelets/m2 in 1999. Counts were taken in five permanent 1-m2 areas/plot.a Block 2 plots 61-120. Data from the 5 and 75 spikelets seeding rate are combined. North Platte, NE.
a Glyphosate at 0.75 lb ae/A was applied after each count during the fallow period. b Counts taken after wheat emergence. Winter wheat was planted September 27, 2002. c Counts will be taken following winter wheat harvest. d Counts will be taken after jointed goatgrass emerged after wheat is harvested in 2003.
OREGON: No glyphosate was applied to wheat stubble in the fall on any treatments due to dry autumn conditions. Glyphosate was applied to fallow ground in spring immediately prior to primary tillage to establish summer fallow. After the disking treatments, fallow operations consisted of chisel plowing, cultivating, and rodweeding. Percent residue cover on the first study was estimated December 9, 1999. Jointed goatgrass plant counts were estimated in wheat stubble each spring before final fallow tillage operations were performed (Table 3). Wheat and JGG plant counts, spike counts and biomass estimates were obtained each year that plots were planted to winter wheat (Tables 4, 5, and 6). Wheat yield and jointed goatgrass dockage were estimated each crop year (Table 7). Table 3. Jointed goatgrass plant density in wheat stubble initiated in 1998 and 1999. Moro, OR.
a Time when tillage occurred after wheat harvest. Table 4. Jointed goatgrass plant density in wheat crop initiated in 1998 and 1999. Moro, OR.
a Time when tillage occurred after wheat harvest.
Table 5. Late-season wheat and jointed goatgrass spike counts initiated in 1998 and 1999. Moro, OR.
a Time when tillage occurred after wheat harvest.
Table 6. Wheat and jointed goatgrass plant biomass initiated in 1998 and 1999. Moro, OR.
a Time when tillage occurred after wheat harvest. Results from the completed study indicate that post-harvest tillage (disking) had a relatively minor effect on percent crop residue cover (data not shown). The high JGG density sub-treatments had greater JGG densities, spike counts, and biomass each year than did the low JGG density sub-treatments (Tables 3-6). Further, the high JGG density sub-treatment reduced wheat yield and increased dockage in both years (Table 7). Early March tillage eliminated JGG plants when counted in late March, and fall tillages (2-5 day post-harvest or October) resulted in reduced JGG plant densities (in the high JGG density plots) when estimated in late March when compared with the no tillage or spring tillage treatments (Table 3). However, this did not translate to differences in JGG density (Table 4) or wheat yield (Table 7) in the subsequent wheat crop. Jointed goatgrass plant counts (Table 4), spike counts (Table 5), and biomass (Table 6) in crop generally reflected an increasing JGG population from 2000 to 2002. Although wheat yield dropped from 2000 to 2002, not all the wheat yield decrease can be attributed to JGG competition because the 2001-02 crop year was dry (8.43 in per crop year vs. 20 yr average of 11.2 in). No tillage effects on JGG population were notable from either study at this time. Table 7. Wheat yield and dockage initiated in 1998 and 1999. Moro, OR.
a Time when tillage occurred after wheat harvest.
UTAH: The wheat production seasons of 2000 and 2001 in northern Utah were extremely dry periods and winter wheat yields were measurably lower than normal. However, this same region experienced an unusually high amount of precipitation in October 2000 immediately after planting the 2001 winter wheat crop on site 2 (Table 8). Although jointed goatgrass seedlings only appeared in two of the six tillage treatments throughout the fallow season of 1999-2000, the immense rainstorms after planting apparently triggered great numbers of jointed goatgrass spikelets in the soil to germinate concomitantly with the fall crop and resulted in greatly exaggerated numbers of weeds recorded in the crop at harvest in July 2001.
The two tillage treatments having measurably higher jointed goatgrass seedling emergence during the 1999-2000 fallow period than all other tillage treatments, were early spring tillage and tillage repeated at four intervals (multiple tillage). Reproductive jointed goatgrass tillers numbering in the hundreds per square meter had not previously been observed in this or adjacent fields. Perhaps the May thru August period of almost no rainfall prevented normal winter wheat competition with jointed goatgrass and crop yields were predictably low. No measurable differences existed among the tillage treatments regarding numbers of jointed goatgrass reproductive tillers in the crop nor in winter wheat yield. The wheat dockage was an order of magnitude greater than previously observed in other years.
Table 8. Jointed goatgrass populations in fallow and at harvest, crop yield and dockage in site 2 with six fallow tillage intervals and 75/m2 jointed goatgrass spikelets seeded in 1998. Wheat planted in 2000 at Blue Creek, UT.
The 2002 results suggest that numbers of jointed goatgrass plants appearing in the fallow season or subsequently in an ensuing winter wheat crop is not strongly correlated with tillage timing after crop harvest. On the other hand, precipitation patterns appear to have greater impacts on jointed goatgrass numbers in either the fallow season or in winter wheat than does tillage timing. Our fallow tillage investigation has completed four years of an anticipated five-year project and three of the four have been drought years ranging from 61 to 66 percent of the 38-year average annual precipitation, with the most recent two years experiencing rainfall quantities at or near planting of about half that received during the entire year (Table 9).
Table 9. Precipitation Summary Data (inches). Blue Creek, UT
The results of this unusual rainfall led to sudden jointed goatgrass infestations of several hundred plants per square meter in wheat following a fallow season where only a few grassy weeds were observed. It also obliterated the differences among tillage timings that appeared evident during the first two years of study. The experiment was designed with two identical fields (sites 1 and 2) in order to have harvestable wheat crops each season of the five-year period. Presently there appears to be a high probability that drought will again occur in 2003 and wheat yields from site 2 may be as drastically low as those recorded at site 1 in 2002 (Table 10). Table 10. Jointed goatgrass populations in fallow and in wheat, crop yield and dockage in site 1 with six fallow tillage intervals and 75/m2 jointed goatgrass spikelets seeded in 1998. Wheat seeded in 2001 at Blue Creek, UT.
Since 1999, Utah and surrounding areas have experienced precipitation patterns and moisture quantities inadequate for profitable winter wheat production. Fall rainfall has occurred as one or two major precipitation events followed by insufficient snowfall and moisture accumulation to satisfactorily sustain the emerged crop. For example, the 2002 yields of winter wheat on producer farms in northern Utah averaged less than 15 bushels per acre, about half of the 20-year average for the corresponding region. These conditions, on the other hand, have proven ideal for jointed goatgrass germination, establishment, and competitive advantage. Wheat stands and vigor at site 1 in 2002 were too meager to harvest (less than 5 bu/A) while jointed goatgrass populations were excessively high (Table 10). Over 250 jointed goatgrass tillers/m2 were counted in the wheat in plots not tilled compared to 56 tillers/m2 when the field was cultivated at least four times during the fallow. A single cultivation performed immediately after harvest of the prior wheat crop or during the ensuing fall or early spring of the fallow period failed to reduce jointed goatgrass populations in wheat when compared with multiple cultivations, but the extremely dry circumstances caused crop failures in all of the treatments.
PUBLICATIONS: Evans, J. O., D. A. Ball, and G. A. Wicks. 2001. “Contrasting jointed goatgrass emergence patterns under uniform fallow-tillage across the western United States”. WSWS 54: Abstract 35.
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