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Developing Brassica Crops and Management Strategies For Direct-Seeding SystemsJack
Brown1, Don Wysocki2, and Jim B. Davis1 ABSTRACT Seed yield of spring and winter Brassica crops under direct-seed and conventional seed conditions were examined. Seed yield under direct seeding was significantly reduced compared to conventionally seeded trials. The reduction in winter canola yield was a result of poorer crop establishment in the fall, with smaller seedlings going into winter. Direct-seed winter canola yield can be significantly influenced by tillage management. Burning or flailing straw stubble prior to planting produced significantly higher yields compared to direct seeding into standing straw. Starter fertilizer in direct seed winter canola is essential. Yield of spring Brassica crops in direct seed trials was reduced as a result slower crop establishment, likely due to cooler soil, compared to conventional tillage. Genotype x tillage systems interactions were highly significant in winter canola and yellow mustard. The highest yielding winter canola of yellow mustard cultivars under conventional tillage, were rarely the higher yielding lines when conventionally seeded. Oriental mustard showed a lesser degree of interaction, albeit also significant. Spring canola cultivars had little interaction and the 'best' cultivars under direct seed was also the 'best' under conventional tillage. Overall, it is essential to evaluate breeding lines of winter canola, yellow mustard and oriental mustard for yielding potential under direct seeding conditions if the most adapted cultivars are to be available for direct seed farming situations. INTRODUCTION Concerns over soil
erosion, soil physical properties, and sustainability of farming have
interested a growing number of farmers in direct-seeding practices. In
addition, greater interest in reducing input costs has accelerated growers'
interest in these one-pass planting systems. Direct seeding systems have
the potential to: reduce soil erosion; increase water-use efficiency;
reduce weed problems, and increase profitability. However, few experiments
in the Pacific Northwest have compared yield and quality of Brassica crops
in no tillage situations compared to conventional tillage systems. For example, 60-70%
of Pacific Northwest moisture comes between November and March. Avoiding
fall or spring tillage may allow surface residue to trap more fall moisture,
enhance water infiltration into the soil, and reduce moisture loss due
to evaporation or run off. Therefore direct seeding may result in higher
seed yield and/or expand regions where later maturing Brassica types (i.e.
B. napus) can be grown. Conversely, standing straw stubble can insulate
soil, resulting in colder soil temperatures in spring-time, this could
delay spring crop planting, and slow the rate of crop establishment and
hence reduce seed yield potential. For expansion and
increased adoption of conservation farming technologies, growers need
non-cereal rotation crops. Brassica crops are the most reasonable candidates
to fill this niche. These crops (i.e. canola and mustards) are one of
the few crops that is well adapted to the region and has significant market.
For example, more than 1 million acres of canola could be grown in the
region and still not affect the market. Rainfall in the Pacific
Northwest can vary from high (> 20 inches annually) to low (<8 inches
annually), and the traditional cropping systems have been winter wheat/summer
fallow and wheat/barley/legume rotations. Predominance of monoculture
cereal production in these regions over the past 100 years has resulted
in a buildup of soil-borne diseases. In addition, these cropping systems
are susceptible to severe wind and rain erosion. As a result, farmers
have shown increased interest in annual cropping systems and advantages
of Brassica crops have induced growers to include their in their crop
rotation. At present, growers
in the Pacific Northwest region have the option of planting four different
spring-planted Brassica species. Canola (or rapeseed) can be produced
from either Argentine-types (Brassica napus) or Polish-types (B. rapa).
In addition, growers can grow either yellow mustard (Sinapis alba) or
oriental mustard (B. juncea). More information has become available (i.e.
from the Pacific Northwest Canola Variety Trial and the Pacific Northwest
Yellow Mustard Trial) about which species are most suited for different
climatic regions. From the four species available, B. napus is least heat
and drought tolerant, followed by B. rapa, and B. juncea, with S. alba
showing greatest adaptability to driest regions. It is therefore necessary to examine whether genotype x tillage system interactions exist in winter canola and spring Brassica crops. If such interactions exist then it will be necessary to identify the most appropriate spring Brassica species from different regions throughout the PNW, and to select the most productive cultivars from within each species for direct seeding. Similarly, there will be a need to identify winter canola cultivars that have greatest adaptability to direct seed situations. MATERIAL AND METHODS Winter canola Agronomic trials Straw management was examined in two studies. The first study was planted at Moscow, Idaho, on October 2. Two winter canola cultivars ('Ericka' and 'Selkirk') were planted using a Haybuster® direct seed drill with two seeding rates (8 and 12 lb/acre). The previous crop was spring barley. Five tillage systems were examined: full tillage; minimum tillage; and direct seeding where barley straw was raked from the area, where the straw was burned prior to planting, and with straw remaining. The complete trial was a strip-split-plot design, where strip plots were assigned to tillage treatments, and cultivars and seeding rates assigned to sub-plots within strips. Plots were 7 x 10 m and each treatment combination replicated three times. A second study was carried out at Pendleton, Oregon, using three drills, each with and without starter fertilizer and with and without straw flailing (a total of 12 treatments). The cultivar Ericka was sown at the Columbia Basin Agricultural Research Center, Pendleton, Oregon in a randomized complete block experiment, with 4 replicates. The experiment included three seed drill treatments (Great Plains disk drill, Conserva-Pak shank drill and Conserva-Pack shank drill with residue management wheels, which are rubber-fingered wheels that runs beside the shank), two fertilizer treatments (no starter and 100 lb/acre 16-20-0-14 placed with the seed), two stubble treatments (flail mow and standing). Drills were operated at 4-5 mph at planting. Target seeding depth was 0.75-1.0 inch. Assure II was applied at a 10-oz/acre rate in late February 2000 and 80-lb N/acre where spike wheel injected on 20 March 2000. In both studies a
wide range of characters were recorded and assessed throughout the growing
season and post harvest. Results presented here will concentrate on stand
establishment, seed yield. Two sets of winter canola cultivars were evaluated in 2000 and 2001. These were: (1) entries in the Pacific Northwest Winter Canola Variety Trial (PNWWVT); and (2) advanced breeding lines from the University of Idaho breeding program. The PNWWVT included 12 entries in 2000 and 21 entries in 2001. Fifty advanced winter canola breeding lines were examined in 2000 and 60 genotypes were tested in 2001. Small plot breeder's trials were carried out at Moscow, Genesee and Lewiston, in Idaho, and at Pendleton, Oregon. At each location, entries were planted after traditional tillage on ground previously summer fallowed, and direct seeded into standing straw stubble. Plots were 5' x 20' and planted using a small-plot single cone planer designed and built at the University of Idaho. This planter has five Flexi-coil® stealth openers within five foot wheel centers and each stealth opener two seed row 4 inches apart. Fertilizer is applied at seeding between the 4 inch rows and 1 inch below the seed. Seed depth in summer fallow was to moisture and in direct seeding seed depth was 0.5-1.0 inches. Spring Brassica species Four species experiment Four cultivars from each of four different Brassica species (B. napus, B. rapa, B. juncea, and S. alba) were grown in an split-plot design at 3 locations in 2000 (Genesee and Nez Perce, Idaho, and Davenport, Washington) and 4 locations in 2001 (Moscow, Genesee, Nez Perce, in Idaho, and Davenport, Washington). Seeding treatment (direct seed v conventional seeding) were arranged as main-plots, and species, and cultivars within species were sub-plots and sub-sub-plots respectively. At each location, entries were planted after traditional tillage, and direct seeded into standing straw stubble. Plots were 5' x 20' and planted using a small-plot single cone planter with five Flexi-coil®, Stealth openers (see above). Seed planting depth was 0.1-1.0 inches. Regional cultivar testing In 2000, 38 spring canola cultivars (B. napus), sixteen oriental mustard genotypes (B. juncea) and 10 yellow mustard cultivars (S. alba) were grown at 5 locations (Moscow, Genesee and Nez Perce, Idaho, Pendleton, Oregon, and Davenport, Washington) under direct seed and conventional seed conditions. The canola cultivars included advanced breeding lines from the University of Idaho breeding program along with cultivars developed by commercial breeding groups in the US and Canada. The mustard trials included advanced breeding lines along with named control cultivars. Randomized complete block designs with four replicates were used at each location and treatment. Plot size was 5' x 20' and planted using the small plot planted with Flexi-coil® shank openers (see above). In 2001, 23 spring canola, 9 oriental mustard, and 9 yellow mustard lines were evaluated at 4 locations (Moscow, Genesee and Nez Perce, Idaho, Pendleton, Oregon, and Davenport, Washington) in the same manner as in 2000. RESULTS AND CONCLUSIONS Winter canola Agronomic trials At the Moscow straw management trial, seedling emergence was good in all treatments due to good fall moisture. As expected higher seeding rates resulted in higher plant stands in the fall. Spring stand counts were reduced from 50 to 90%. Highest spring stand counts were from minimum tillage and direct seeding after burn (Table 1). Lowest plant counts were in direct seeding with straw and full tillage. Stand counts in the latter could be attributed to fall seeding depth, while rodent damage was a major contributor in direct seeded with straw. Table 1. Spring plant stand counts when planted after five different seed-bed treatments.
Primary weeds in the trial were wild oat and volunteer barley that had survived the mild winter. Good weed control was achieved without herbicide in burned plots and minimum tillage plots, but weed control was a major problem in all other treatments. Ericka produced better fall and spring stand counts, was more competitive with weeds, and produced higher seed yield (3940 lb/acre) compared to Selkirk (3310 lb/acre). Large differences were found between seed yield of the different treatments (Table 2). Significantly higher seed yield was obtained by direct seeding into burned straw stubble, followed by minimum tillage. Direct seeding after straw raking and full tillage produced similar yields and lowest seed yield was obtained in direct seeded plots without residue management. In conclusion, good straw management is essential when direct-seeding winter canola. Even minimum incorporation of straw can result in significantly getter seedling emergence, establishment and eventual increases in seed yield. Table 2. Seed yield, averaged cultivars, when planted after five different seed-bed treatments.
From the Pendleton seeder/starter fertilizer study, stand establishment was best using the Conserva-pac drill with residue management wheels attached. Speed of operation probably affected the operation of the disk drill more than the shank drill. The Great Plains disk drill was equipped with Turbo opening coulters. Given the plot dimensions (40-ft length) drills could not be operated at more that 4-5 mph. Turbo coulters operate better in the range of 6-8 mph. Addition of 100lb/N starter fertilizer resulted in significant yield increases compared to plots planted without starter fertilizer (Table 3). Significantly higher yield was obtained after planting with the Conserva-pac drill compared to the Great Plains seeder. Adding residue management wheels to the Conserva-pac drill significantly increased seed yield. Table 3. Seed yield of Ericka winter canola planted with three seeder treatments and with and without starter fertilizer.
Comparing straw flailing and non-flailing produced similar results to those for starter fertilizer, above. Flailing straw prior to planting significantly increased seed yield over all planter treatments (Table 4). In summary, drill
operation and seed placement are important when direct drilling winter
canola into wheat stubble. Uniformity of seed placement and seed to soil
contact are critical factors for adequate establishment. Placement of
starter fertilizer diminished stand establishment (data not show) but
crop yield was better in spite of low plant stands. Table 4. Seed yield of Ericka winter canola planted with three seeder treatments and two straw management treatments.
Cultivar evaluation trials Yield of all entries tested were significantly reduced when direct seeded compared to conventionally managed systems. In 2000, under conventional management average seed yield in the PNWWCT was 992 lb/acre less than from conventional tillage summer fallow. Similarly, the following year, average seed yield from conventional tillage was 2505 lb/acre, while under direct seeding the average was only 1867, which was a 25% reduction in yield. There was a poor relationship between cultivars yield potential under the different tillage systems (Figure 1). The relationship was however, positive and significant (r=0.43) in 2000, but there was a slight negative relationship (r=-0.19) in the 2001 trials. Results from the advanced canola lines in the regional trial were similar to the PNWWVT. In 2001, the average yield of the breeding lines under conventional tillage was significantly higher at 4141 lb/acre while the average yield under direct seeding was less than half this (1932 lb/acre). The previous year difference was slightly less than this, but the direct seeded trials yielded almost half the yield of the conventional seeded plots. The relationship in 2001, between performance in tilled and no tilled advanced breeding lines trials was positive (r = 0.25) but relatively small, accounting for slightly more than 6% of the total variation in yield between the tillage treatments. This correlation was almost the same as that found in the previous year study (r = 0.26). Despite the positive correlation for yield, from a practical breeding prospective the relationship was poor (Figure 2). For example, in 2001 the highest yielding line in the conventional seeding trial (5934 lb/acre) was ranked as 13th when direct seeded. Similarly, if the top 10 yielding cultivars was selected based only on their performance under conventional management, then only 2 of these would have been amongst the top 10 yielding lines under direct seeding. Similarly, the highest yielding line when direct seeded (2864 lb/acre) ranked as only 39th when conventionally seeded. Highest yield from conventional tillage was from 'Olsen' (3612 lb/acre), but this cultivar ranked lowest yield under direct seeding. The second highest yielding cultivar when conventionally tilled was 'Athena', which also did comparatively well when direct seeded (2564 lb/acre). The highest yielding entry in the PNWWCT under direct seeding was the advanced University of Idaho breeding line '92.WC.3.134212' (3020 lb/acre). It is perhaps interesting to note that this line was the result of conscious selection in Idaho and Oregon for late-planting potential. Indeed this was one of the few PNWWCT entries with higher yield under direct seeding. Overall, it is obvious that breeding lines must be evaluated under conventional and direct seeding management practices to ensure that cultivars can be released that have greatest yield potential under the different systems. Spring Brassica species Four species experiment Seed yield was reduced in all of the species when direct seeded compared to conventional seeding. Averaged over both years, B. napus and B. rapa (canola) yields were reduced by 356 lb/acre and 284 lb/acre, respectively, when direct seeded compared to conventional seeding. Similarly, B. juncea (oriental mustard) and S. alba (yellow mustard) yields were reduced by 549 lb/acre and 320 lb/acre, respectively, when direct seeded (Table 5). Table 5. Average seed yield of four Brassica species grown under direct-seed and conventional seed situations.
Arguably the most significant and important relationship in plant breeding is the response to selection, which indicates the degree of crop improvement over existing cultivars and is calculated as: R = isph2 where i is the degree of selection pressure, sp is the phenotypic variation, and h2 is the heritability, or proportion of variation which is genetic in nature. Obviously there will be little response to selection if the breeder does not select the better lines and discard inferior types (i.e. i). Similarly, if there is no observable variation (i.e. sp) there would be no way to identify the better lines from those inferior types. The selection intensity (i) and the phenotypic variation (sp) can be controlled, in part, by the breeder. Therefore it is usual that the most important factor that affects response to selection is the heritability. Heritabilities between conventionally tilled and direct seeded trials for canola lines was generally high and ranged between 20.5% to 54.6% (Table 6). On average, heritabilities between tillage systems for oriental mustard were lower (22%), but heritabilities were almost zero for yellow mustard. Indeed examination of the scatter diagrams for yield in the two tillage systems for canola (Figure 3), oriental mustard (Figure 4), and yellow mustard (Figure 5), it is obvious that the higher yielding canola lines do very well irrespective of the tillage system. However, many oriental mustard lines produced high yield under one management system and relatively lower yield on the other. In yellow mustard there is no relationship to yield under one or other system and evaluation of yellow mustard under conventional tillage offered no indication as to performance under direct seeding. Table 6. Average coefficient of heritability for seed yield between direct seeded and conventional seeding.
Perhaps it is significant that the direct seed sites were often planted later as the soil at these sites did not dry as quickly as the black soil areas. Even in instances where planting the direct seed and conventional seed took place on the same day, there were observational differences in the rate of seedling growth and crop establishment, whereby the conventionally seeded planter grow quicker, establisher and flowered earlier Canola is particularly sensitive to high temperatures at flowering and one of the key criteria's of high yielding cultivars is the need to flower early and avoid late season heat. This being the case, it is not surprising that under later planting it is these early lines which again show best yield potential. Oriental mustard and particularly yellow mustard are not as sensitive to high temperatures at flowering and other factors are responsible for adaptability. Some of these factors may be associated with the tillage methods examined in this study. Irrespective of
the cause of the interactions examined in mustards and winter canola it
is obviously essential that the early and intermediate generations of
breeding programs consider selection for adaptation to direct seeding,
else farmers who want to adopt one-pass seeding techniques will not have
the most adapted cultivars that could be available for such systems. LITERATURE CITED Comstock, R.E. and
R.H. Moll, 1963. Genotype-environment interactions. In: Hanson W.D. and
Robinson H.H. (Eds) Statistical genetics and plant breeding. Nat. Acad
Sci. Natl. Res. Publ. 982:164-196. Wysocki, D.J., S.
Ott, M. Stoltz, and T.C. Chastain. 1991. Variety and planting date effects
on dryland canola. Oregon Agricultural Experiment Station Special Report
894, p. 32-37. Figure 1. Seed yield of entries in the PNWWVT, grown under direct seed and conventional seed situation.
Figure 4. Seed yield (lb/acre) of oriental mustard lines (B. juncea), grown under direct seed and conventional seed conditions.
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