Shallots may be grown as an overwinter or spring-planted crop in the Willamette Valley. Major cultural problems in this crop include weed and disease control, effect of planting dates on yield, maturity, and degree of bolting, and the effects of size of, planting stock and planting density on yield and bulb size at harvest. This study was designed to investigate the effects of three planting densities and two bulb sizes on the total yield and mean bulb weight at harvest and on the number of bulbs produced per bulb planted.
Methods
Bulbs of two sizes (small, mean weight of 12.2g; large, mean weight of 27.7g) were planted at three densities (low, 15 cm x 61 cm; medium, 15 cm x 30 cm; high, 15 cm x 15 cm) on September 16, 1981 in a factorial experiment with six treatment combinations. Plots were arranged in randomized complete block design with three replications. Individual plots consisted of four 3-meter rows. Records were taken from the two middle rows of each plot.
The fertilizer program included 1,120 kg/ha of 10-20-10 broadcast and incorporated before planting, and 56 kg/ha of N as ammonium nitrate applied on January 20, March 11, and April 14, 1982, for a total N application of 280 kg/ha. DCPA herbicide at 10 kg/ha was applied immediately after planting. Propachlor at 4.5 kg/ha was applied on January 20 and March 19, 1982, following cultivation. Plots were harvested on July 29, 1982.
Results
Total yield on an area basis was significantly affected by both bulb size at planting (P<0.05) and by spacing or density (P<0.01). Planting larger bulbs produced about a 12% yield increase when compared with smaller planting stock (Table 1). A fourfold increase in planting density produced a doubling of yield. Yield per unit area did not increase proportionally to the increase in planting density since both bulb weight and the number of bulbs produced/bulb planted decreased at higher densities.
Planting large bulbs increased the number of bulbs produced per unit area since the number of bulbs produced/bulb planted was greater with the larger planting stock. However, mean bulb weight tended to decrease slightly (difference not significant at 5% level) with the larger planting stock.
For production of planting stock, high planting densities would be preferable to achieve maximum yields. For markets that require large bulb size, low planting density and small planting stock size should favor production of large bulbs, but with greatly reduced total yield.
Table 1. Yield of Overwintered Shallots in Response to Bulb Size and Planting Density Treatment Total bulb Mean bulb # bulbs produced # bulbs produced yield (kg/m2) wt. (g) per square meter per bulb planter low density, small bulbs 3.33 18.5 199 16.6 low density, large bulbs 3.82 17.3 222 20.6 medium density small bulbs 4.21 14.2 295 13.7 medium density, large bulbs 5.44 13.2 407 18.9 high density, small bulbs 6.91 13.5 510 11.9 high density, large bulbs 7.25 11.4 636 14.8 LSD (0.05) 1.17 2.9 82 3.5 Mean, small bulbs 4.80 15.4 328 14.1 Mean, large bulbs 5.49 14.0 422 18.1 LSD (0.05) 0.67 NSZ 47 2.0 Mean, low density 3.58 17.9 200 18.6 Mean, medium density 4.85 13.8 351 16.3 Mean, high density 7.11 12.5 574 13.3 LSD(0.05) 0.82 2.1 58 2.5 ZNS: no significant difference at 5% level. Difference significant at 10% level.