Effects of Pot Size on Growth of Maize and Sorghum Plants Zongjian Yang13, Graeme Hammer1, Erik van Oosterom1, Delphine Rochais2 and Kurt Deifel1 1
School of Land, Crop and Food Sciences, The University of Queensland, St Lucia, Qld 4072, Australia; 2 Ecole Nationale Agronomique de Rennes, 35042 Rennes, France 3 Corresponding author:
[email protected]
ABSTRACT
Restricted soil volume in small pots can have limiting effects on overall plant growth and influence plant responses to experimental treatments. This study was conducted to assess the effect of pot size on growth and partitioning of maize and sorghum plants. A better understanding of the pot size effect can improve future experimental design to balance the management cost and experimental requirement. Seeds of the commercial sorghum hybrid Buster and maize hybrid Pioneer 34N43 were germinated and grown in PVC pots with diameters and depths of 1540, 1580, 3040, and 3080 cm. The size of pots significantly affected plant growth. Less total shoot mass was produced in plants of either species grown in small pots. However, this was mostly associated with reduced mass of tillers. Proportionally more growth was allocated to roots in small pots, so root/shoot ratio was significantly increased in both species. Plants grown in small pots produced more fibrous roots, and the root system was densely matted. As root density increased in the limited soil volume, competition and barriers to diffusion could affect nutrient acquisition and cause nutrient deficiency. Visible signs of nitrogen deficiency were observed in leaves of plants growing in smaller pots. Reduction in nitrogen uptake and assimilation might have contributed to the reduced shoot growth in the smaller pots.
INTRODUCTION
Studies on plants are often conducted in controlled environments where the plants are grown in pots of different sizes. Small pots with limited space for root growth can strongly affect overall plant growth and influence plant responses to various experimental treatments (Carmi 1995; Ray and Sinclair 1998; Hess and De Kroon 2007). Previous studies on different plant species have shown that physically restricting the space for root growth affects carbohydrate metabolism (Robbins and Pharr 1988; Ronchi, DaMatta et al. 2006), nutrient acquisition (Whitfield, Davison et al. 1996; Zhu, Wang et al. 2006; Yang, Zhu, Wang et al. 2007), transpiration (Ray and Sinclair 1998), hormone production (Carmi 1995; Liu and Latimer 1995), and whole-plant growth. The aim of this study was to assess the effect of pot size on growth and partitioning of maize and sorghum plants when adequate water and nutrients were supplied. A better understanding of the st
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pot size effect can improve future experiment design to balance the management cost and experimental requirement.
MATERIALS AND METHODS
The experiment was conducted in a solarweave enclosure at Gatton, Queensland, Australia (Figure 1). Pots of different sizes were made from PVC pipe with diameters and depths of 1540, 1580, 3040, 3080 cm, which correspond to volumes of approximately 7, 14, 28 and 56 litres, respectively (Figure 1). In addition, plastic ANOVApots® with a volume of approximately 18 litres were also used in the experiment. The ANOVApot® has been developed to save water and prevent root escape. The design incorporates a water storage area at the base of the pot, which serves as a water table allowing continuous wetting of the potting mix by capillary flow.
Figure 1 Pots of different sizes made from PVC pipes.
Pots were filled with a soil mixture consisting of 50% lantana soil (black clay) and 50% decomposed cotton compost. Approximately 6 g Osmocote® slow release fertilizer was applied to each pot during pot filling. Pots were arranged in a randomised block design with four replications per pot size per genotype. Short pots were raised to the same height as taller pots using bricks (Figure 1). Seeds of the commercial sorghum hybrid Buster and maize Pioneer 34N43 were sown on 28 November 2008. Pots were over-sown and thinned to one plant per pot 7 days after emergence.
Pots were irrigated twice daily by hand initially, and when the plants started to grow fast, an automatic dripper system (one for maize and one for sorghum) was set up to irrigate the pots twice daily. The amount of water applied was adjusted at different stages so that no visible sign of water
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stress occurred for plants grown in the different pots and drainage was not excessive. All pots for each species were irrigated using the same amount of water each time. Foliar applications of Ca(NO3)2 were made daily from 4 visible leaves onwards at the rate of 3 g/litre. Sorghum and maize plants were harvested shortly after flowering. Plants were cut at ground level and transported to the laboratory where they were separated into green leaf, dead leaf, panicle (or ear), and stem components for both main shoot and tillers. Dry weight of biomass was determined after drying to constant weight in an oven at 65oC. Analysis of variance was performed using GenStat Release 9.1. Main effects of pot size were tested using Fisher’s LSD method.
RESULTS Small pots (less than 28 litters in volume) significantly inhibited shoot growth; fewer and smaller tillers were produced for both sorghum and maize plants grown in small pots (Table 1 & 2). The reduction in total shoot biomass of sorghum and maize plants in small pots was mainly caused by a decrease in tiller size and number (Table 1 & 2). For maize, there was no significant difference in main shoot biomass among pot-size treatments. For sorghum, main shoots of plants in small pots had slightly greater mass, which likely reflected reduced competition from fewer and smaller tillers.
Table 1 Effect of pot size on growth and partitioning of sorghum plants Main Shoot Dry Weight (g)
Tiller Number
Tiller Leaf Area 2 (cm )
Tiller Dry Weight (g)
Total Shoot Dry Weight (g)
Root Dry Weight (g)
Shoot/Root Ratio
30x80 (cm) 2447 a*
63.76 a
3.75 b
8070 b
143.29 c
207.04 b
45.29 a
4.59 b
30x40 (cm) 2856 ab
62.83 a
3.25 ab
8360 b
134.72 bc
197.55 b
46.42 a
4.40 b
ANOVA
70.37 b
3.75 b
9205 b
126.05 bc
196.42 b
46.25 a
4.36 b
15x80 (cm) 2656 ab
67.60 ab
3.00 a
6743 a
116.03 b
183.63 ab
52.50 a
3.50 a
15x40 (cm) 3061 bc
78.48 c
2.75 a
5399 a
79.72 a
158.19 a
51.67 a
3.09 a
LSD
495.9
6.062
0.674
1303.5
25.71
27.91
12.15
0.752
P
0.009
