ONION VARIETY RESPONSE TO PLANT POPULATION AND IRRIGATION SYSTEM

Transcription

1 ONION VARIETY RESPONSE TO PLANT POPULATION AND IRRIGATION SYSTEM Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders, Malheur Experiment Station, Oregon State University, Ontario, OR, 2012 Introduction Changing market opportunities for smaller size onion bulbs and the availability of new onion varieties necessitate evaluations of yield and bulb size response to plant population. These evaluations can aid growers in making planting rate decisions. The objective of this trial was to evaluate the response of four onion varieties to five plant populations under conventional drip irrigation, intense bed drip irrigation, and furrow irrigation. Materials and Methods Onions were grown in 2012 on an Owyhee silt loam with a ph of 7.7 and 1.7 percent organic matter, previously planted to wheat. In the fall of 2011, the wheat stubble was shredded and the field was irrigated. The field was then disked, moldboard plowed, and groundhogged. Based on a soil analysis, 100 lb of phosphorus/acre, 200 lbs of sulfur/acre, 1,000 lbs of gypsum/acre, and 1 lb of boron/acre were broadcast before plowing. On September 25, the field was fumigated with Vapam at 15 gal/acre and bedded at 22 inches. In the spring, the field was divided into irrigation main plots that were 88 inches wide by 136 ft long. The experimental design was a randomized complete block with split-split plots and six replicates. There were three irrigation treatments: conventional drip irrigation, intense bed drip irrigation, and furrow irrigation. Intense bed drip irrigation is a local name used for beds with three drip tapes and six double rows of onions, while conventional drip irrigation is a local name used for beds with two drip tapes and four double rows of onions. Each irrigation main plot was divided into 4 split plots that were 30 ft long. Each split plot in each irrigation main plot was planted to one of four onion varieties ( Vaquero, Nunhems, Parma, ID; Barbaro, Seminis, Payette, ID; Sedona, Bejo, Oceano, CA; Esteem, Crookham, Caldwell, ID) on April 7, 2011 and on March 12, The seed was planted in double-rows at 18 seeds/ft of single row. The single rows were spaced 3 inches apart. In the conventional drip and furrow-irrigation plots, the double rows were spaced 22 inches apart (4 double rows on an 88-inch tractor pass). In the intense bed drip plots, the double rows were spaced 12 inches apart (6 double rows on an 88-inch tractor pass). Planting was done with customized John Deere Flexi Planter units equipped with disc openers. Immediately after planting, the double rows of onion seed received a narrow band of Lorsban 15G at 3.7 oz/1,000 ft of row (0.82 lb ai/acre) and the soil surface was rolled. Onion Variety Response to Plant Population and Irrigation System 35

2 In the conventional drip and furrow-irrigation plots, tape (Toro Aqua-Traxx, Toro Co., El Cajon, CA) with emitters spaced 12 inches apart and an emitter flow rate of 0.15 gal/hour was laid at 4- inch depth between 2 double rows at the same time as planting (2 tapes on an 88-inch pass, 44 inches between tapes, 11 inches between the center of double row and drip tape). In the intense bed drip plots, tape (Toro Aqua-Traxx) with emitters spaced 8 inches apart and flow rate of 0.07 gal/hour was laid at 4-inch depth before planting (3 tapes on an 88-inch tractor pass, 22 inches between tapes, 6 inches between center of double row and drip tape). Onion emergence started on April 2. On May 14, alleys 3 ft wide were cut between the variety split plots, leaving plots 30 ft long. Each variety split plot was then divided into 5 population split-split plots 6 ft long. On May 15, the seedlings in each split-split plot of each variety split plot were hand thinned to one of five plant populations (Table 1). After thinning, the drip tape in the furrow irrigation plots was removed and the furrows between onion rows were cultivated to allow for furrow irrigation. Table 1. Target spacing between onion seedlings after thinning and plant density. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant Spacing in single row Plant density population Conventional bed Intense bed Conventional bed Intense bed plants/acre inches plants/ft , , , , , The onions were managed to minimize yield reductions from weeds, pests, diseases, water stress, and nutrient deficiencies. On April 16, Prowl H 2 O at 0.95 lb ai/acre was applied for weed control. On May 8, Goal at 0.16 lb ai/acre, Buctril at 0.19 lb ai/acre, and Poast at 0.25 lb ai/acre were applied for weed control. The trial was sprayed weekly for thrips control starting on May 30 for a total of 7 applications. The insecticide application sequence included 2 applications of Movento at 5 oz/acre, followed by 2 applications of Radiant at 8 oz/acre, followed by 3 applications of Lannate at 3 pt/acre. Root tissue samples were taken on June 18, July 2, and July 18. Based on the tissue analysis, a total of 150 lb nitrogen/acre, 5 lb magnesium/acre, 5 lb Calcium/acre, and 0.4 lb boron/acre were applied during the season. The nutrients were injected through the drip tape or water-run during irrigations in the furrowirrigated plots. Onions in each conventional and intense bed drip main plot were irrigated automatically and independently to maintain the soil water tension (SWT) in the onion root zone below 20 cb. Soil water tension was measured in each main plot with four granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 200SS, Irrometer Co., Riverside, CA) installed at 8- inch depth in the center of the double row. Sensors had been calibrated to SWT (Shock et al. 1998). The GMS were connected to the datalogger via multiplexers (AM 410 multiplexer, Campbell Scientific, Logan, UT). The datalogger read the sensors and recorded the SWT every hour. The datalogger made irrigation decisions for each drip-irrigated main plot every 12 hours. Onion Variety Response to Plant Population and Irrigation System 36

3 The individual irrigation decisions for each plot were based on the average SWT. The irrigation durations were 7 hours, 10 min for the conventional drip system and 8 hours, 19 min for the intense bed drip system to supply 0.48 inches of water per irrigation. The irrigations were controlled by the datalogger using a controller (SDM CD16AC controller, Campbell Scientific, Logan, UT) connected to solenoid valves in each plot. The water for the drip and sprinkler plots was supplied by a well that maintained a continuous and constant water pressure of 35 psi. The pressure in the drip lines was maintained at 10 psi by pressure regulators in each plot. The amount of water applied to each plot was recorded daily at 8:00 a.m. from a water meter installed between the solenoid valve and the drip tape. The automated irrigation system was started on June 16 and ended on September 5. Onion evapotranspiration (ET c ) was calculated with a modified Penman equation (Wright 1982) using data collected at the Malheur Experiment Station by an AgriMet weather station. Onion ET c was estimated and recorded from crop emergence until the onions were lifted. The furrow-irrigated onions were irrigated manually when the SWT at 8-inch depth reached 25 cb. The field in which this trial was conducted had 1-3 percent slope. To reduce erosion and improve the lateral movement of water during furrow irrigations, straw at 900 lb/acre was applied to the furrow bottoms on May 17. The last furrow irrigation was on August 31. Onions in each split-split plot were evaluated subjectively for the percentage of tops down and leaf dryness on August 17. The number of bolted onions in each split-split plot was determined on August 17. Onions in each split-split plot were evaluated subjectively for severity of symptoms of iris yellow spot virus (IYSV) on September 12. Each plot was given a rating on a scale of 0 to 5 of increasing severity of symptoms. The rating was 0 if there were no symptoms, 1 if 1-25 percent of foliage was diseased, 2 if percent of foliage was diseased, 3 if percent of foliage was diseased, 4 if percent of foliage was diseased, and 5 if 100 percent of foliage was diseased. The onions were lifted on September 13 to field cure. Onions from 5 ft of the middle 2 rows in each conventional drip and furrow-irrigation split-split plot and from 5 ft of the middle 4 rows in the intense bed drip split-split plots were topped by hand and bagged on September 24. Onions were graded on October 4 and 5. During grading all bulbs from each split-split plot were counted. After counting, the bulbs were separated according to quality: bulbs without blemishes (No. 1s), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis allii in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergillus niger). The No. 1 bulbs were graded mechanically (Kerian Speed Sizer, Kerian Machines, Inc., Grafton, ND) according to diameter: small (<2¼ inches), medium (2¼-3 inches), jumbo (3-4 inches), colossal (4-4¼ inches), and supercolossal (>4¼ inches). Bulb counts per 50 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading. Marketable yield consists of No.1 bulbs larger than 2¼ inches. After grading, 25 bulbs from each plot were separated and individually weighed and measured for diameter to understand the ratio of weight to diameter. The bulb diameter was used to calculate the proportion of size categories by diameter and weight for each plot. The yield of bulbs in onion ring processing size (3¼-4½ inch diameter) was calculated using the bulb proportions by diameter and the plot total yield measured at grading. Onion Variety Response to Plant Population and Irrigation System 37

4 Treatment differences were compared using analysis of variance. Means separation was determined using a protected Fisher s least significant difference test at the 5 percent probability level, LSD (0.05). The least significant difference LSD (0.05) values in each table should be considered when comparisons are made between treatments for significant differences in performance characteristics. Differences between treatments equal to or greater than the LSD value for a characteristic should exist before any treatment is considered different from any other treatment in that characteristic. For the regression analyses, the actual plant population in each split-split plot was calculated from the bulb counts during grading. Regression equations were developed by regression of the yield components against the actual plant population. Results and Discussion Intense bed drip and conventional drip irrigation resulted in more uniform soil moisture over time than furrow irrigation (Fig. 1). From onion emergence to the last irrigation, a total of 36.0 inches of water were applied to the conventional drip irrigation plots and a total of 33.1 inches of water were applied to the intense bed drip irrigation plots. Onion ET c, measured from emergence to the last irrigation, totaled 37.1 inches. For varieties and irrigation systems, the actual plant population achieved was different than the target population (Tables 2-5). Analysis of Variance Irrigation system was not a statistically significant factor in the response of onion bulb size to plant population (Tables 2-5). Averaged over irrigation systems and varieties, marketable yield increased with increasing plant population up to 148,000 plants per acre (Table 5). Yield of medium bulbs increased with increasing plant population up to the highest tested of 190,000 plants per acre. Averaged over irrigation systems and varieties, yield of jumbo bulbs was highest with a plant population of 148,000 plants per acre. Averaged over irrigation systems and varieties, yield of colossal plus supercolossal bulbs decreased with increasing plant population. Averaged over irrigation systems, for all four varieties, yield of colossal plus supercolossal bulbs decreased with increasing plant population (Table 6). Averaged over irrigation systems, for all four varieties, yield of small bulbs increased with increasing plant population. The bulb size percentages and bulb yields for the different size categories for typical onion ring processing can be found in Tables 8 and 9. Irrigation system was not a statistically significant factor in the response of onion yield to plant population. Averaged over irrigation systems and varieties, the percentage and yield of bulbs larger than 4 inches in diameter decreased with increasing plant population up to the highest tested of 189,791 plants per acre. Averaged over irrigation systems and varieties, the percentage and yield of bulbs 3-3¼ inches and less than 3 inches in diameter increased with increasing plant population up to the highest tested of 189,791 plants per acre. Averaged over irrigation systems and varieties, the percentage and yield of bulbs 3¼-4½ inches in diameter decreased with increasing plant population (Tables 8 and 9). Onion Variety Response to Plant Population and Irrigation System 38

5 Regression Analysis The response of marketable yields and jumbo yields to plant population varied by variety, population, and irrigation system (Table 7, Figs. 2-11). Yield responses to plant population were similar for conventional bed drip and furrow irrigation systems and different from intense bed drip irrigation. Despite being thinned to the same plant population on a per acre basis as the conventional beds, onions in the intense beds had a higher plant density than the conventional beds (Table 1). The marketable and jumbo yield responses to plant population ranged from none, to linear (yields increased with population), to quadratic (yields increased up to a certain population). For all varieties and irrigation systems, except Vaquero and Esteem under intense bed drip irrigation, marketable yield increased with increasing plant population. For Vaquero and Esteem under intense bed drip irrigation, marketable yield increased up to plant populations of 200,500 and 180,600 plants per acre, respectively. Averaged over varieties and conventional bed irrigation systems, marketable yields increased with increasing plant population (Fig. 10). For the intense bed drip irrigation system, averaged over varieties, marketable yields increased up to a plant population of 210,400 plants per acre (Fig. 11). As the marketable yields increased, average bulb diameter decreased (Fig. 12) with the decrease in colossal bulbs and increase in medium bulbs. Jumbo yield showed a linear increase in response to plant population for all varieties under conventional bed irrigation systems, except Esteem (Figs. 2-9). For Esteem under conventional bed irrigation and all varieties under intense bed drip irrigation, jumbo yield showed a quadratic response to plant population. Under intense bed drip irrigation, jumbo yields increased up to plant populations of 262,900, 223,600, 171,900, and 181,300 plants per acre for Vaquero, Barbaro, Sedona, and Esteem, respectively. For Esteem under conventional drip irrigation, jumbo yields increased up to a plant population of 193,100 plants per acre. For all varieties and irrigation systems, yield of colossal plus supercolossal bulbs decreased and yield of medium and small bulbs increased with increasing plant population (Figs. 2-11). The general responses of bulb market sizes of the varieties to plant populations were similar to the responses found in 2011 (Shock et al. 2012). In 2012, irrigation systems were also not much of a factor in onion response to plant population. For Vaquero, the yield of bulbs 3¼-4½ inches in diameter showed a quadratic response to plant population, with the highest yield at 134,828 plants per acre (Fig. 13). For Barbaro, the yield of bulbs 3¼-4½ inches in diameter was not responsive to plant population (Fig. 14), but the average size of bulbs in the 3¼- to 4½-inch category would decrease with increasing population. The percentage of bulbs larger than 3 inches in diameter had a weak linear decrease with increasing plant population, but remained higher than 80 percent up to the highest population tested (Figs ). Irrigation system was not a statistically significant factor in the response of bolting and percentage of tops down to plant population (Tables 2-5). For all varieties except Barbaro, bolting increased with increasing plant population (Figs ). For Barbaro, bolting was not affected by plant population. For all varieties, the percentage of tops down on August 17 increased with increasing plant population (Figs ). Onion Variety Response to Plant Population and Irrigation System 39

6 Limitations If the length of the irrigation furrows had been of normal field size, 600 to 1,200 ft, we would anticipate greater possibility of uneven water delivery under furrow irrigation and poorer onion performance than what was observed in this trial. The silt loam soil used in this trial has excellent lateral water movement. If the soil had not transmitted moisture well, the intense bed drip irrigation systems should have shown an advantage over conventional drip irrigation, because the bulbs grew closer to the drip tapes. References Shock, C.C., J.M. Barnum, and M. Seddigh Calibration of Watermark Soil Moisture Sensors for irrigation management. Pages in Proceedings of the International Irrigation Show, Irrigation Association, San Diego, CA. Shock, C.C., E. Feibert, and L.D. Saunders Response of four onion varieties to plant population and irrigation system. Oregon State University Agricultural Experiment Station Annual Report 2011, Ext/Crs 141, pages Wright, J.L New evapotranspiration crop coefficients. Journal of Irrigation and Drainage Division, American Society of Civil Engineers 108: Onion Variety Response to Plant Population and Irrigation System 40

7 Figure 1. Soil water tension over time for three irrigation systems in onions. Malheur Experiment Station, Oregon State University, Ontario, OR. Onion Variety Response to Plant Population and Irrigation System 41

8 Table 2. Onion yield and grade in response to plant population for four varieties grown with conventional drip irrigation. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant population Marketable yield by grade Unmarketable Tops Variety Target Actual Total yield Total >4 in >4¼ in 4-4¼ in 3-4 in 2¼-3 in <2¼ in Doubles Rot Bolting down IYSV --- plants/acre cwt/acre % Vaquero 90,000 90, , , , , , , , , average 138, Barbaro 90,000 88, , , , , , , , , average 136, Sedona 90,000 88, , , , , , , , , average 137, Esteem 90,000 90, LSD (0.05) 120, , , , , , , , average 143, Irrigation X Variety NS NS NS NS 26.3 NS 57.5 NS NS NS NS NS NS NS Irr. X Var. X Population NS NS NS NS 65.6 NS NS NS NS NS NS NS NS NS

9 Table 3. Onion yield and grade in response to plant population for four varieties grown with intense bed drip irrigation. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant population Marketable yield by grade Unmarketable Tops Variety Target Actual Total yield Total >4 in >4¼ in 4-4¼ in 3-4 in 2¼-3 in <2¼ in Doubles Rot Bolting down IYSV --- plants/acre cwt/acre % Vaquero 90,000 89, , , , , , , , , average 154, Barbaro 90,000 98, , , , , , , , , average 157, Sedona 90,000 93, , , , , , , , , average 152, Esteem 90,000 91, LSD (0.05) 120, , , , , , , , average 162, Irrigation X Variety NS NS NS NS 26.3 NS 57.5 NS NS NS NS NS NS NS Irr. X Var. X Population NS NS NS NS 65.6 NS NS NS NS NS NS NS NS NS

10 Table 4. Onion yield and grade in response to plant population for four varieties grown with furrow irrigation and for the overall average. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant population Marketable yield by grade Unmarketable Tops Variety Target Actual Total yield Total >4 in >4¼ in 4-4¼ in 3-4 in 2¼-3 in <2¼ in Doubles Rot Bolting down IYSV --- plants/acre cwt/acre % Vaquero 90,000 97, , , , , , , , , average 136, Barbaro 90,000 91, , , , , , , , , average 129, Sedona 90,000 93, , , , , , , , , average 135, Esteem 90,000 94, LSD (0.05) 120, , , , , , , , average 135, Irrigation X Variety NS NS NS NS 26.3 NS 57.5 NS NS NS NS NS NS NS Irr. X Var. X Population NS NS NS NS 65.6 NS NS NS NS NS NS NS NS NS

11 Table 5. Onion yield and grade in response to plant population for three irrigation systems averaged over four varieties and for the overall average. Malheur Experiment Station, Oregon State University, Ontario, OR, Irrigation system Conventional drip Plant population Marketable yield by grade Unmarketable Tops Target Actual Total yield Total >4 in >4¼ in 4-4¼ in 3-4 in 2¼-3 in <2¼ in Doubles Rot Bolting down IYSV --- plants/acre cwt/acre % ,000 89, , , , , , , , , average 138, Intense bed 90,000 93, , , , , , , , , average 157, Furrow 90,000 94, , , , , , , , , average 134, Average 90,000 92, LSD (0.05) 120, , , , , , , , Irrigation 9322 NS NS NS NS NS NS 8.5 NS NS NS NS NS NS Population NS NS NS Irrigation X Population 6126 NS NS NS NS NS NS NS 0.7 NS 6.9 NS

12 Table 6. Onion yield and grade in response to plant population for four varieties averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant population Marketable yield by grade Unmarketable Variety Target Actual Total yield Total >4 in >4¼ in 4-4¼ in 3-4 in 2¼-3 in <2¼ in Doubles Rot --- plants/acre cwt/acre % Vaquero 90,000 92, , , , , , , , , average 143, Barbaro 90,000 92, , , , , , , , , average 141, Sedona 90,000 91, , , , , , , , , average 141, Esteem 90,000 92, , , , , , , , , average 147, LSD (0.05) Variety NS NS NS 40.6 NS 35.7 NS NS NS Variety X Population NS NS NS NS 73.5 NS NS NS NS

13 Table 7. Regression equation parameters for regressions of plant population and onion yield categories for four varieties and three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Irrigation system Variety Total marketable Colossal plus supercolossal, >4 in Jumbo, 3-4 in intercept linear quadratic R 2 P intercept linear quadratic R 2 P intercept linear quadratic R 2 P Conv. Drip Vaquero Barbaro Sedona Esteem X Intense bed Vaquero X X Barbaro X Sedona NS NS X Esteem X X Furrow Vaquero NS X Barbaro NS Sedona Esteem Medium, 2¼-3 in Small, <2¼ in Conv. Drip Vaquero Barbaro Sedona Esteem Intense bed Vaquero X X Barbaro Sedona X Esteem X Furrow Vaquero X Barbaro X X Sedona Esteem

14 Table 8. Response of proportions of bulb size categories to plant population for four onion varieties averaged over three irrigation systems; data were calculated from bulb diameter measurements. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant population Proportion by bulb diameter Variety Target Actual >4½ in 4-4½ in 3¼-4 in 3-3¼ in 3¼-4½ in <3 in >3 in --- plants/acre % Vaquero 90,000 92, , , , , , , , , average 143, Barbaro 90,000 92, , , , , , , , , average 140, Sedona 90,000 91, , , , , , , , , average 141, Esteem 90,000 92, , , , , , , , , average 146, Average 90,000 92, LSD (0.05) 120, , , , , , , , Population NS Variety X Population NS NS NS NS Onion Variety Response to Plant Population and Irrigation System 48

15 Table 9. Response of yield bulb size categories to plant population for four onion varieties averaged over three irrigation systems; data were calculated from bulb diameter and bulb weight measurements. Malheur Experiment Station, Oregon State University, Ontario, OR, Plant population Yield by bulb diameter Variety Target Actual >4½ in 4-4½ in 3¼-4 in 3-3¼ in 3¼-4½ in <3 in >3 in --- plants/acre cwt/acre Vaquero 90,000 92, , , , , , , , , average 143, Barbaro 90,000 92, , , , , , , , , average 140, Sedona 90,000 91, , , , , , , , , average 141, Esteem 90,000 92, , , , , , , , , average 146, Average 90,000 92, , , , , , , , , LSD (0.05) Population 3, Variety X Population NS NS NS NS NS NS Onion Variety Response to Plant Population and Irrigation System 49

16 Figure 2. Yield response of onion bulb size categories to plant population for Vaquero averaged over conventional bed drip and furrow irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 3. Yield response of onion bulb size categories to plant population for Vaquero under intense bed drip irrigation. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 50

17 Figure 4. Yield response of onion bulb size categories to plant population for Barbaro averaged over conventional bed drip and furrow irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 5. Yield response of onion bulb size categories to plant population for Barbaro under intense bed drip irrigation. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 51

18 Figure 6. Yield response of onion bulb size categories to plant population for Sedona averaged over conventional bed drip and furrow irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 7. Yield response of onion bulb size categories to plant population for Sedona under intense bed drip irrigation. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 52

19 Figure 8. Yield response of onion bulb size categories to plant population for Esteem averaged over conventional bed drip and furrow irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 9. Yield response of onion bulb size categories to plant population for Esteem under intense bed drip irrigation. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 53

20 Figure 10. Yield response of onion bulb size categories to plant population averaged over three varieties and over conventional bed drip and furrow irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 11. Yield response of onion bulb size categories to plant population under intense bed drip irrigation and averaged over three varieties. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 54

21 Figure 12. Onion bulb diameter in response to plant population averaged over three varieties and over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 13. Yield of bulbs in onion ring processing size (3¼-4½ inch diameter) in response to plant population for Vaquero averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 55

22 Figure 14. Yield of bulbs in onion ring processing size (3¼-4½ inch diameter) in response to plant population for Barbaro averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 15. Percentage of bulbs larger than 3 inch diameter in response to plant population for Vaquero averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 56

23 Figure 16. Percentage of bulbs larger than 3 inch diameter in response to plant population for Barbaro averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 17. Percentage of bulbs larger than 3 inch diameter in response to plant population for Sedona averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 57

24 Figure 18. Percentage of bulbs larger than 3 inch diameter in response to plant population for Esteem averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 19. Bolting response to plant population for Vaquero averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 58

25 Figure 20. Bolting response to plant population for Barbaro averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 21. Bolting response to plant population for Sedona averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 59

26 Figure 22. Bolting response to plant population for Esteem averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Figure 23. Response of percentage of tops down on August 17 to plant population for Vaquero averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 60

27 Figure 24. Response of percentage of tops down on August 17 to plant population for Barbaro averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, 2012 Figure 25. Response of percentage of tops down on August 17 to plant population for Sedona averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 61

28 Figure 26. Response of percentage of tops down on August 17 to plant population for Esteem averaged over three irrigation systems. Malheur Experiment Station, Oregon State University, Ontario, OR, Onion Variety Response to Plant Population and Irrigation System 62