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1999 STEEP III Final ReportRESEARCH TITLE: Modified Wheat-Potato Rotations to Reduce Wind Erosion INVESTIGATORS: Charlotte Eberlein, UI; Edward Souza, UI; Larry Robertson, UI; Paul Patterson, UI INTERIM REPORT: Interim report OBJECTIVES:
KEY WORDS: wheat-potato rotations, weeds, wind erosion STATEMENT OF PROBLEM: In southern Idaho, producers generally rotate from potatoes to spring wheat or barley, which leaves fields bare over the winter and subject to wind and water erosion. Other options for wheat production following potatoes need to be evaluated, including late-seeded winter wheat and dormant-seeded spring wheat. These seeding practices should be compared with standard spring wheat seeding practices for winter and spring soil cover, stand, weed suppression, and yield. ZONE OF INTEREST: Irrigated potato growing areas of southern Idaho; grain-potato, grain-grain-potato rotations. ABSTRACT OF RESEARCH FINDINGS: Alternatives to conventional spring wheat seeding practices in a potato-grain rotation were evaluated in on-station trials at the Aberdeen Research and Extension Center and in on-farm trials in growers' fields. 'Malcolm' winter wheat seeded after potato harvest was compared with 'Treasure' dormant-seeded spring wheat for ground cover, yield, and weed suppression. In 1996-97 trials, unusually wet winter weather followed by freezing temperatures resulted in severe winter injury to dormant-seeded Treasure in on-station trials and in serious winter injury to both late-seeded Malcolm and dormant-seeded Treasure in on-farm trials. In on-station trials, Malcolm winter wheat outyielded dormant-seeded spring wheat by 29 bu/A in herbicide-treated subplots in 1997, and was more competitive with weeds than dormant-seeded Treasure. However, dormant-seeded Treasure outyielded winter wheat by an average of 26 bu/A in on-farm trials. Little winter injury was observed in most 1997-98 trials, but yields in general were reduced by above average temperatures in July, which caused significant embryo abortion. In on-station studies, late-seeded Malcolm and dormant-seeded Treasure had similar yield and test weight in 1998. In contrast, average yields were 11 bu/A higher and test weights averaged 5 lb/bu more for dormant-seeded Treasure than for late-seeded Malcolm in on-farm trials. Thus, dormant-seeded Treasure spring wheat out performed late-seeded Malcolm winter wheat in on-farm trials both years. There was little effect of wheat seeding practice on weed management in the 1997-98 trials. RESULTS AND INTERPRETATION: Soil erosion is a significant problem following potato harvest. In southern Idaho, producers generally rotate from potatoes to spring wheat or barley, which leaves fields bare over the winter. One option for reducing wind erosion is to plant winter wheat after potato harvest. However, several factors limit winter wheat planting. The optimum time for seeding winter wheat is Sept. 15 to Oct. 1. Potato harvest typically begins about Sept. 20 and lasts until about Oct. 10, so waiting until potato harvest is complete puts wheat planting outside the optimum window for stand establishment. During potato harvest, producers face a shortage of equipment and labor for seeding winter wheat. Dormant-seeded spring wheat may give growers an option beyond the optimum planting time for winter wheat. Dormant-seeded spring wheat is planted in late October or early November, after it is too cool for wheat emergence, but before the ground freezes. The seed lies dormant in the soil until it germinates and begins to grow in late winter/early spring, generally before producers could begin working fields for a spring planting. Moreover, dormant seeding eliminates the need for soil disturbance in early spring when wind storms are frequent. To evaluate alternatives to conventional spring wheat seeding practices, late-seeded winter wheat and dormant-seeded spring wheat were compared with conventional spring wheat in field trials at the Aberdeen Research and Extension Center (AREC) near Aberdeen, ID. Five on-farm comparisons of late-seeded winter wheat vs. dormant-seeded spring wheat also were conducted with cooperators at Krown Farms and R&J Farms near Aberdeen, ID. Aberdeen Research and Extension Center (AREC) Trials. Wheat was seeded at 100 lb/A with a commercial grain drill with a 7-inch row spacing. 'Malcolm' winter wheat (WW) was seeded on Oct. 8, 1996 and Oct. 10, 1997; 'Treasure' spring wheat was dormant-seeded (DSS) on Oct. 23, 1996 and Oct. 22, 1997; and 'Penewawa' spring wheat (SW) was seeded on March 28, 1997 and March 31, 1998. The experimental area was naturally infested with common lambsquarters and kochia in the 1996-97 studies and with common lambsquarters, redroot pigweed, and kochia in the 1997-98 studies. Bromoxynil + MCPA (Bronate) was applied at 1.5 pt/A to herbicide-treated subplots on May 7, 1997 (winter wheat and dormant-seeded spring wheat), May 19, 1997 (spring wheat), and May 5, 1998. Untreated subplots were used to measure effects of wheat seeding practices on weeds. Results varied with year. In the 1996-97 trial, mild November temperatures led to emergence of the dormant-seeded spring wheat. Precipitation was higher than normal in December and January, with 4.44 inches of precipitation during this period compared to the long term average of 1.43 inches. Snow melted, then froze in an ice sheet over the experimental area. In early spring, the ice sheet repeatedly thawed and froze, resulting in major stand reductions in the dormant-seeded spring wheat plots. Visual estimates of percent stand in herbicide-treated subplots on April 18, 1997 were: winter wheat, 97% and dormant-seeded spring wheat, 34%; conventional spring wheat was just emerging (59%). Surviving dormant-seeded spring wheat was injured, which delayed development in May (Figure 1). Preharvest stand densities were 12, 8, and 17 plants/ft2, for winter wheat, dormant-seeded spring wheat, and conventional spring wheat, respectively. Dormant-seeded spring wheat compensated for reduced stand densities by increasing tiller densities; tiller densities on July 24 in herbicide-treated subplots were 45, 48, and 56 tillers/ft2 for winter wheat, dormant-seeded spring wheat, and conventional spring wheat, respectively. Wheat yields in herbicide-treated subplots were 132, 103, and 124 bu/A for winter wheat, dormant-seeded spring wheat, and conventional spring wheat, respectively (Table 1). Table 1. Stand, tillers,
yield, and test weight of wheat in herbicide-treated subplots, AREC, ID,
1997.
In the 1997-98 growing season, stand establishment and winter survival of fall-planted winter wheat and dormant-seeded spring wheat were excellent. Wheat densities in Malcolm WW and Treasure DSS plots on April 13 were 23 and 22 plants per square foot, respectively. On May 12, Penewawa plant density was 25 plants per square foot. Wheat development as measured by Feeke's stage is shown in Figure 1. Malcolm WW developed slightly ahead of Treasure DSS until the May 12 evaluation, from which point the two cultivars were similar. Both Malcolm WW and Treasure DSS developed ahead of Penewawa SW. April, May, and June were unusually cool (Figure 2), which provided a long period of vegetative growth and extensive tillering. Malcolm, Treasure, and Penewawa had 77, 68, and 59 tillers per square foot, respectively, on July 20 (Table 2). However, unusually warm weather in July (Figure 2) caused significant embryo abortion and a reduction in test weight. Grain yields for Malcolm, Treasure, and Penewawa were 99, 96, and 86 bu/A, respectively, and test weights were 58, 58 and 57 lb/bu, respectively (Table 2). Figure 1. Wheat development
in AREC trials in 1997 and 1998.
Figure 2. Mean daily air temperatures at Aberdeen in 1998 compared to the 7-year average.
Table 2. Stand, tillers, yield, and test weight of wheat, AREC, ID, 1998.
The major weed species infesting the plots in 1997 were common lambsquarters and kochia. Weed density was monitored regularly from April 15 to May 29; weed density and biomass also were sampled on July 24. Peak weed density in mid-May and weed density and biomass in late July in the no-herbicide subplots are shown in Table 3. Densities were lower in all three wheat seeding treatments in July than in May, illustrating the competitiveness of wheat with weeds. Overall, winter wheat was more competitive than either dormant-seeded or conventional spring wheat; weed biomass was about 80% less in the winter wheat treatment than in either spring wheat treatment. Better competitiveness was reflected in yield; winter wheat yields in the no-herbicide subplots were 128 bu/A (97% of the herbicide-treated yield), while yields in the dormant-seeded and conventional spring wheat plots were 90 bu/A (87% of the herbicide-treated yield) and 108 bu/A (87% of herbicide treated yield), respectively. In 1998, the major weed species infesting the no herbicide subplots were common lambsquarters, redroot pigweed, and kochia. Weed density was monitored regularly from Apr. 20 to May 26, and weed density and biomass also were sampled on July 20. Peak weed density in mid-May and weed density and biomass in late July are shown in Table 3. Wheat in all treatments grew well during the long vegetative period in June and was highly competitive with weeds. Both weed density and weed biomass on July 20 were very low. Weed biomass was less in Malcolm WW and Treasure DSS plots than in Penewawa SW plots (Table 3), but weed growth did not affect grain yield; yields were similar in herbicide-treated and untreated subplots. Table 3. Peak weed
density in May and weed density and biomass in July in no-herbicide subplots
in AREC trials, 1997 and 1998.
On-farm trials. A total of six on-farm trials were conducted, two in cooperation with Krown Farms in 1996-97, two in cooperation with Krown Farms in 1997-98, and two in cooperation with R&J Farms in 1997-98. In each trial, late-seeded winter wheat was compared with dormant-seeded spring wheat. At Krown Farms in 1996-97, wheat was seeded into a rough, reduced tillage seed-bed with a forced air planter equipped with a shank planting shoe. Malcolm winter wheat was seeded at 95 lb/A on Oct. 15, 1996, and Treasure spring wheat was dormant-seeded at the same rate on Nov. 1, 1996. The planting depth generally was shallow (1 inch) with deeper seed placement in the rills created by the stubble disks used for preplant cultivation. Grain emergence generally was poor, although we observed better emergence and establishment in rills where the seed was planted deeper. Shallow-seeded winter wheat that germinated shortly after planting was subjected to a fall period of desiccation. High moisture and standing water over winter cause crusting problems in the spring, and harrowing to break the crust damaged some seedlings. In 1997-98, Treasure spring wheat and Malcolm winter wheat were seeded into a well-prepared seed-bed at Krown Farms on Oct. 16, using a forced-air planter equipped with a shank planting shoe. Emergence of both Treasure and Malcolm was excellent. At R&J Farms, wheat was seeded into a well-prepared seed-bed with a conventional drill on Nov. 2. Emergence of both Treasure and Malcolm at R&J Farms was fair. Weed populations were counted two to three times before fields were sprayed with the grower's broadleaf herbicide treatment. Weed populations usually were similar in the winter wheat and dormant-seeded spring wheat treatments at all locations. The broadleaf herbicides applied provided fair to good control of the major weeds present at each location. In the 1996-97 trials, both winter wheat and dormant-seeded spring wheat yields were relatively low due to poor stand establishment and winter injury (Table 4). However, average yields in the dormant-seeded spring wheat treatment were 26 bu/A higher than yields in the winter wheat plots. Test weights also were higher in the dormant-seeded spring wheat treatment than in the winter wheat treatment. Winter injury was minimal in most of the 1997-98 trials, and Malcolm and Treasure developed similarly through the vegetative growth phase (Figure 3). Unfortunately, yields in the 1997-98 trials at both Krown Farms and R& J Farms were reduced by unusually warm weather in July (Figure 2), which caused significant embryo abortion. At harvest, heads of both Malcolm and Treasure generally lacked tertiary kernels, and often lacked secondary kernels. Analysis of variance indicated that the two cultivars performed similarly at all four on-farm test sites, therefore, locations were combined for analysis. In the combined analysis, there were significant differences in both yield and test weight, with Treasure yielding 11 bu/A more than Malcolm and having a 5 lb/bu higher test weight than Malcolm (Table 4). Thus, dormant-seeded
Treasure spring wheat outperformed late-seeded Malcolm winter wheat both
years in on-farms trials, despite winter injury in 1996-97 and high July
temperatures in 1997-98. INTERACTION (COOPERATION) WITH OTHER SCIENTISTS CONDUCTING RELATED ACTIVITY: None. PUBLICATIONS AND PRESENTATIONS: No publications to date. Two seminars on research results were presented by Dennis Tonks, Postdoctoral Research Fellow; one seminar was in Moscow, ID and one in Prosser, WA. Figure 3. Feeke's stages of wheat development for Malcolm winter wheat and Treasure dormant-seeded spring wheat at Krown Farms from March 16 to May 27, 1998. Wheat development at R&J Farms closely followed the pattern observed at Krown Farms.
Table 4. Wheat yield and test weight in on-farm trials near Grandview and Aberdeen, ID in 1997 and 1998, respectively. Data were averaged over locations each year.
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