Effects of Planting Date and Density on Tuber Production in Sandersonia aurantiaca

Transcription

1 Effects of Planting Date and Density on Tuber Production in Sandersonia aurantiaca Glenn E. Clark Garry K. Burge New Zealand Institute for Crop & Food New Zealand Institute for Crop & Food Research Ltd Research Ltd Pukekohe Research Centre Food Industry Science Centre Cronin Road, RD1 Private Bag 1 Pukekohe Palmerston North New Zealand New Zealand Tel: Fax: clarkg@crop.cri.nz Keywords: Sandersonia aurantiaca, tuber, density, secondary tubers Abstract The effects of three tuber planting dates (1 September, 1 November and 1 January) and three planting densities (192, 256 and 3 tubers/m²) on tuber production in Sandersonia aurantiaca were assessed. Tubers were grown in a commercial peat:pumice media in polystyrene trays located in an unheated glasshouse and using standard growing methods. Tuber numbers, weights (by grade size - 1-3, 3-5, 5-7, 7- and + g) and numbers with secondary tubers were measured. Tuber numbers, weights and the number of secondary tubers decreased with planting date and with increasing planting density. Tubers were mainly in the + g weight grade in the first planting, but were more evenly distributed across all grade sizes in the two later plantings. These results show that planting density can be manipulated along with planting time to maximize tuber numbers in the larger grade sizes and reduce secondary tuber numbers. INTRODUCTION Sandersonia is one of New Zealand s major export tuber and flower crops. Although it can be grown for up to 12 months of the year, most production occurs from August to May. However, tuber yield, weight and quality vary with the time of the year. This has been demonstrated but there are no quantitative data available on tuber production. Brundell & Reyngoud (1986) and Clark & Reyngoud (1997) both showed the influence of planted tuber weight on the resultant daughter tuber. Clark & Burge (1997a) showed that growing environment and planting date affected mean tuber weights, with the heaviest tubers produced indoors over the summer months. However, these conditions increased secondary tuber production. In two studies (Clark & Burge 1997b; Clark & Burge 1999) the effects of planting densities of tubers/m² and production methods on the incidence of secondary tuber formation were examined. These studies showed that density and production methods could be manipulated to reduce the incidence of secondary tuber formation but gave only average tuber weights. The objective of this study was to examine the effects of a commercial range of tuber planting densities grown over the normal tuber production period on lifted tuber weights and quality and provide for the growers the production data necessary to improve tuber production management. MATERIALS AND METHODS A line of small tubers (mean weight 1.3 g) that had been stored at 4 C for 3-4 months following lifting were placed into three polystyrene boxes (/box) between layers of newspaper. The boxes were randomly assigned to one of the three planting Proc. 8th Int. Symp. on Flowerbulbs Eds. G. Littlejohn et al. Acta Hort. 5, ISHS 2 7

2 dates. The two boxes for the second and third planting dates were placed back into storage at 4 C. At each planting date (1 September, 1 November and 1 January 1996) a box of tubers was sprouted at 23 C (Clark 1994) for 7 days. Tubers were then dipped in a protective fungicide mix of.5 g/litre benomyl plus 2. g/litre thiram for min before planting into polystyrene trays (595 x 4 x 1 mm) containing a commercial : peat:pumice mix with incorporated fertilisers. The initial ph and available nutrient content of the potting mix was measured after extraction with water (1:1.5 media : water, v:v) using colorimetry and atomic absorption methods (ph 5.2, Ca 42 mg/litre, K 84 mg/litre, P 34 mg/litre, Mg mg/litre and N 195 mg/litre). Tubers were planted at three densities: 48, 64, and tubers per tray (equivalent to 192, 256 and 3 tubers/m 2 ). Trays were mulched with mm of untreated sawdust and plants grown in an unheated glasshouse with forced air circulation ventilated at o C. The crop was supported with netting. It was sprinkler-irrigated until emergence and then dripirrigated twice daily at 2.5 litres/m². The stems were topped to leave 1-2 flowers remaining 3-4 weeks after % of the stems had two flowers open (7 December, 17 January, 26 March 1995). Six to seven weeks after topping watering ceased and the stems were cut at ground level. Tubers were lifted three weeks later and tuber weights by grade (1-3, 3-5, 5-7, 7- and + g) and the number of tubers with secondary tubers (irrespective of whether they had one or two secondary tubers) were recorded. Greenhouse temperatures at crop level were recorded at 1 min intervals during plant growth. Daily solar radiation data were obtained from an adjacent meteorological site operated by the New Zealand Institute of Water and Atmospheric Research. The trial was a randomised block design with four replicates, and data were analysed by analysis of variance (Genstat 19). Data were transformed where required, but these showed the same pattern of significance as untransformed data. Untransformed means are presented. RESULTS AND DISCUSSION The mean tuber weight of the lifted tubers declined significantly (P<.1) with increasing planting density and was significantly less for the January planting date (Table 1). Similar results were found by Clark & Burge (1997a, b). The lower tuber weight with the January planting is attributed to the lower temperatures and solar radiation during the later stages of tuber growth (April-May) (Table 2). There was little difference in mean lifted tuber weight between the first two planting dates, but when these weights are divided into weight grades it is evident that at all planting densities tubers planted at the first planting date were in the + g weight grade and there was a large number of 1-3 g tubers, but the weights of tubers planted at the second planting were more evenly distributed across all grades (Figure 1). The greater number of 1-3 g tubers with the first planting is due to more of the planted tubers developing both of their two growing points, with the second growing point producing a smaller tuber (Table 1). With the later two plantings, the lowest planting density had greater numbers of tubers in the + g grade size, tubers planted at the middle density were more evenly distributed across all grades but still had the greatest numbers in the + g grade size, and at the highest density tubers were evenly distributed across the lower grade sizes but had the fewest tubers in the + g weight grade. In this study with September, November and January planting times, the greatest incidence of secondary tuber formation occurred with the November planting time and was least with the January planting time (Table 1). In a controlled environment study the incidence of secondary tubers increased with temperature, and at higher temperatures (21-27 C) the incidence increased with increasing irradiance (Brooking et al. 1997). Secondary tubers were observed 28 days after flowering with warm growing conditions of 24 and 27 C, but later for cooler growing conditions (Brooking et al. 1997). Therefore, in the current study this would be during December, February and April-May for the three planting times. Air and soil temperatures were greatest during February (Table 2) but solar radiation was slightly less during February than December. The greater incidence of 8

3 secondary tubers with the November planting time is probably due to the higher temperatures during tuber development. Temperature and solar radiation were markedly lower during tuber development with the January planting, and the incidence of secondary tubers was also less (Table 1 and 2). These findings are similar to a previous study in which secondary tuber formation was markedly lower with a February planting time compared to October or December planting times (Clark & Burge, 1997a). A large proportion of secondary tubers with the November and January plantings were on the small tubers (1-3 g) (Figure1). The reason for this is not known. However, as many of the smaller tubers are believed to be formed at the base of the second shoot that develops on some tubers, a study on the timing of the growth of the second shoot may reveal reasons for this. This study has shown that planting density can be manipulated along with planting time to maximize tuber numbers in the larger grade sizes and reduce secondary tuber numbers. ACKNOWLEDGEMENTS We wish to thank Ray Littler for the statistical analysis. This work was funded by the Foundation for Research, Science and Technology. Literature Cited Brooking, I.R., Davies, L.J., Catley, J.L. and Halligan, E.A. 1997: Temperature and irradiance effects on tuber growth of Sandersonia aurantiaca. Acta Hort. 4: Brundell, D.J. and Reyngoud, J.L. 1986: Observations on the development and culture of Sandersonia. Acta Hort. 177: Clark, G.E. 1994: Assessment of tuber storage and sprouting treatments for Sandersonia aurantiaca. New Zealand journal of crop and horticultural science 22: Clark, G.E. and Burge, G.K. 1997a: Effects of growing environment, planting date and stem treatments on sandersonia tuber weight and secondary tuber development. New Zealand journal of crop and horticultural science 25: Clark, G.E. and Burge, G.K. 1997b: Effects of planting density, stem pruning treatments, and shade on Sandersonia aurantiaca tuber weight and secondary tuber development. New Zealand journal of crop and horticultural science 25: Clark, G.E. and Burge, G.K. 1999: Effects of nutrition, planting density, and stem pruning treatments on tuber weight and secondary tuber development. New Zealand journal of crop and horticultural science 27: Clark, G.E. and Reyngoud, J.L. 1997: Effects of production methods on Sandersonia cut stem quality and daughter tuber size. Acta Hort. 4: Genstat 19. Release 2.2. Lawes Agricultural Trust. Rothamsted Experimental Station, England. 9

4 Tables Table 1. Effects of planting date and tuber density on tuber production in Sandersonia aurantiaca. Treatment Mean tuber weight (g) Tuber number lifted (/m²) Tuber number lifted (/planted tuber) Secondary tubers (%) Planting date 1 September November January LSD (.5) P- value <.1 <.1 <.1.16 Planting density 192/m² /m² /m LSD (.5) P- value <.1 <.1 <.2 <.1 Table 2. Mean monthly glasshouse air and soil temperatures, and outdoor solar radiation the 1995/96 season. Mean monthly glasshouse temperatures ( C) Mean daily solar Air Soil radiation (MJ/m²) September October November December January February March April May

5 Figurese Tuber number- September 1 Planting of secondary tubers - September 1 Planting Tuber number - November 1 Planting of secondary tubers - November 1 Planting Tuber number - January 1 Planting of secondary tubers - January 1 Planting Fig 1. The effect of planting time and density on total tuber numbers lifted and tubers with secondary tubers by weight grade. s lifted are per tubers planted. (Black bar = 192 tubers/m², light grey bar = 256 tubers/m² and medium grey bar = 3 tubers/m²) 311