Introduction
Black plastic ground mulch and row covers have enhanced the growth and yield of many crops. Lily bulb production in the Pacific Northwest takes place on bare ground. The objective of this research was to study the effects of a ground mulch and a hoop-supported row cover (tunnel), as well as flower bud removal and cut flower harvest, on bulb growth and bulblet production of Asiatic lily.
Methods
In 1987, 20-inch-wide raised beds of Willamette silt loam, pH 5.5, were formed on 6-foot centers after broadcast and incorporation of 800 pounds/acre of ION-8.7P-8.3K fertilizer. Lily bulbs were planted 6 inches deep with two rows per bed and 8 inches between bulbs. Main plots consisted of a factorial combination of three mulch treatments (bare ground, mulch, mulch plus row cover) and two disbudding treatments (flower buds removed or left intact) in randomized block design with four replications. These main plots were split by five subplots consisting of the cultivars 'Campfire,' 'Debutante,' 'Impact,' 'Moonfire,' and 'Snowcap.' Including border areas, subplots were 10 feet in length and were planted with 11 bulbs. The 1.5 mil, 4-foot-wide, black polyethylene mulch was installed before bulbs were set. Bulbs were planted on 16 March, 1987, and covers were applied to the appropriate plots on 1 April. The initial covers were 6-foot-wide polypropylene-polyamide (Agronet M) and were supported loosely by 5-foot hoops. Bare ground areas were treated with chloro-IPC at 5.0 pounds active/acre.
Covers were removed on 13 May, the appropriate plots were disbudded, and 10-foot-wide Agronet covers were installed. Alleyways were mechanically cultivated and bare-ground treatment beds were hand-weeded twice during the growing season. Bulbs were dug on 17 September. Bulblets were removed from the stems and counted and weighed separately.
The following changes were made in 1988. The main plots were a factorial combination of two mulch treatments (bare soil or block mulch), two cover treatments (no cover on 10-foot Agronet) and three disbudding treatments (check, disbudded at first bloom, or stem-cut at bloom to 4 inches above ground). Twelve-bulb subplots consisted on 'Connecticut King' or 'Enchantment' cultivars. Bulbs were planted on 22 April and the appropriate plots were immediately covered. The disbudding was on 14 July, cut flower harvest on 22 July. Bulbs were harvested on 22 September.
Results and Discussion
1987
An original objective of this research had been to investigate the use of the row covers to prevent insect-vectored virus transmission in the lilies. The planting stock was found to be virus-infected, however, and this aspect of the project was not pursued. Nevertheless, the row covers remained in place for the entire growing season except during disbudding.
In 1987, black plastic mulch increased the percentage of bulbs producing shoots before 29 April, 1987, by 15 percent (Table 1). Row covers provided no additional benefit.
At harvest in 1987, the number of bulbs recovered was greatest with mulch, least on bare ground. Mean bulb weight was also greatest with mulch and least on bare ground. The number of bulblets produced on each stem tended to be increased by mulch or mulch plus cover. Mean bulblet weight was also increased by the mulch treatments. The mulch plus cover treatment did not increase bulb weight or bulblet production beyond that obtained with mulch alone.
Disbudding the shoots to remove flower buds increased bulblet production but not mean bulblet weight. The number of bulbs recovered also increased with disbudding, as did the mean bulb weight.
The cultivars 'Moonfire' and 'Snowcap' produced fewer bulblets than did the other three cultivars. Bulblets of 'Debutante' and 'Impact' were largest when averaged over main plot treatments. 'Campfire' produced the largest bulbs, 'Snowcap' the smallest.
There was a significant interaction of disbudding and cultivar affecting the number and weight of bulblets produced (Table 2). Disbudding increased bulblet formation for three cultivars but did not affect bulblet formation for 'Campfire' and 'Snowcap.'
There was also a significant interaction of mulch-cover treatment and disbudding affecting mean bulblet weight (Table 3). Neither mulch nor mulch plus cover treatments affected mean bulblet weight for disbudded plants. Mulch and mulch plus cover increased bulblet size for plants which were not disbudded.
The combination of mulch and disbudding produced the largest weight and number of bulblets and the greatest mean bulb weight. Mean bulblet weight was greatest with mulch but no disbudding.
1988
In contrast to 1987, mulch decreased the number of emerged shoots (Table 4) of the cultivar 'Connecticut King' in 1988. However, the number of bulbs recovered at harvest was not affected by mulching (Table 4). The planting date was more than a month later than in 1987. Cooler soils may have been a limiting factor in shoot emergence in 1987 and mulch is known to increase soil temperature. Tunnels had no effect on shoot emergence in 1988 (data not shown).
Just prior to disbudding, all plots were rated for flower bud development (Table 5). Mulch had no consistent effect on the number of flower buds present, but the tunnels reduced the number of buds significantly, perhaps through abrasion of the growing point. Nevertheless, tunnels also advanced the date of first bloom for 'Enchantment' (Tables 5 and 6).
In 1988, there was a trend toward higher bulb weight with mulch, but the effect was not significant (Table 7). As in 1987, the tunnel tended to reduce bulb weight, and disbudding, but leaving the stem intact, tended to increase bulb weight. However, these effects were not statistically significant in 1988. As expected, cut flower harvest, where most of the stem is removed at bloom, reduced bulb size. There were no significant 2-, 3-, or 4-way interactions of mulch, tunnel, disbudding treatment, or cultivar affecting bulb size at harvest, hence only main effects are shown in Table 7.
In 1988, mulch again increased the number of bulblets per stem (Table 7). Tunnels and cut flower harvest tended to reduce bulblet production and disbudding to increase bulblet production, but these effects were not significant. 'Enchantment' produced 3.4 bulblets per stem versus only 1.9 for 'Connecticut King' when averaged over all treatments.
Mulch markedly increased mean bulblet weight. Disbudding had no effect and tunnels tended to decrease bulblet mean weight. Cut flower harvest, not surprisingly, also decreased mean bulblet weight. There were no significant 2-, 3-, or 4-way interactions affecting number of bulbets per stem or mean bulblet weight. 'Connecticut King' produced slightly larger (1.4 g vs. 1.0 g) bulblets than did 'Enchantment.'
The greatest increase in bulb weight occurred with the combination of mulch and disbudding, but no tunnel (+24 g). The greatest number of bulblets per stem also occurred with this combination, but greatest mean bulblet weight was favored by the combination of mulch, no tunnel, and no disbudding. Treatments favoring large bulbs also generally produced more and larger bulblets as bulblet formation increases with maturity. The correlation coefficient for number of bulblets produced versus mean bulb weight was 0.59 (p?0.001); the correlation coefficient for mean bulblet weight versus mean bulb weight was 0.61 (p?0.001).
The practices of using a ground mulch and disbudding clearly favor production of larger lily bulbs and increased bulblet production. In addition, mulch provides soil moisture control and weed control. It may, however, be difficult to plant at the high densities normal in the lily industry when using a plastic mulch.
Table 1. Main effects of mulch and row cover, disbudding, and cultivar on bulb size and bulblet formation in lily, 1987 No. plants No. bulbs Mean bulb No. bulblets Mean bulblet Treatment emerged/plot recovered wt. (g) per stem wt. (g) Bare ground 9.2 9.0 68.7 5.7 1.9 Black mulch 10.6 10.2 88.1 6.4 2.3 Mulch + cover 10.5 9.8 75.9 6.6 2.2 LSD (0.05) 0.9 0.8 6.8 NSZ 0.3 Disbudded 9.9 10.0 80.2 6.8 2.2 Allowed to bloom 10.2 9.3 74.9 5.6 2.1 NS * NS ** NS Cultivar Campfire 10.8 9.7 109.5 9.8 2.0 Debutante 10.2 9.6 77.9 8.5 2.5 Impact 10.5 9.7 86.6 10.2 2.4 Moonfire 9.8 10.3 69.5 1.2 2.2 Snowcap 10.0 9.0 44.2 1.6 1.7 LSD (0.05) NS NS 8.7 1.6 0.3 ZNS, *, **: no significant differences; differences significant at 5% and 1% levels, respectively. Table 2. Interaction of disbudding and cultivar on the number and weight of lily bulblets produced, 1987 No. of Weight of Treatment Cultivar bulblets/stem bulblets (g/plot) Allowed to bloom Campire 9.8 202 Debutante 7.1 173 Impact 8.1 182 Moonfire 0.9 18 Snowcap 1.6 20 Disbudded Campfire 9.7 188 Debutante 9.9 243 Impact 12.1 304 Moonfire 1.4 38 Snowcap 1.6 27 LSD (0.05) 2.2 65 Table 3. Interaction of mulch or cover and disbudding on average bulblet weight of lily, 1987 Mean bulblet wt.(g)Z Treatment Allowed to bloom Disbudded Bare ground 1.7 2.2 Mulch 2.4 2.2 Mulch+Cover 2.2 2.2 ZLSD (0.05) = 0.4 Table 4. Interaction of mulch and cultivar on lily shoot emergence and bulb recovery at harvest, 1988 Treatment No. shoots/plot No. bulbs harvested/plot Conn. King, bare soil 11.8 11.7 Enchantment, bare soil 11.9 11.5 Conn. King, mulched 10.9 11.5 Enchantment, mulched 11.8 11.5 Table 5. Interaction of mulch and tunnel on flower development, 1988 Treatment No. flower buds/shoot Days to first bloom (anthesis) Bare soil 2.8 90.4 Mulch 2.9 89.5 Tunnel 2.4 87.7 Both 1.6 85.4 LSD (0.05) 0.6 4.5 Table 6. Interaction of mulch, tunnel, and cultivar on days to anthesis Treatment Cultivar 'Connecticut King' 'Enchantment' Bare soil 93.3 87.5 Mulch 94.0 85.0 Tunnel 93.5 81.8 Both 91.3 79.5 LSD (0.05) NS 4.1 Table 7. Main effects of mulch, tunnel, disbudding, and cut flower harvest on bulb size and bulblet production, 1988 Treatment Mean bulb No. bulblets Mean bulblet weight (g) per stem weight (g) Bare soil 24.3 1.9 1.0 Mulch 27.9 3.4 1.5 NS ** ** No cover 28.9 2.8 1.3 Tunnel 23.4 2.4 1.2 NS NS NS Check 28.7 aZ 2.7 1.3 a Disbudded 29.8 a 2.9 1.4 a Cut flower 19.9 b 2.2 0.9 b * NS * ZMean separation with columns by Duncan's MRT, 5% level.