Sugarcane: Research Towards Efficient and Sustainable Production. Wilson JR, Hogarth D M , Campbell JA and G a r s i d e AL (Eds).
C S I R O Division of Tropical Crops and Pastures, Brisbane. 1996. p p . 7 3 - 7 4 73
AEROPONIC CULTURE AS A TECHNIQUE TO STUDY SUGARCANE ROOT GROWTH AND ACTIVITY REGHENZANI JR and G R A C E DJ
BSES, PO Box 566, Tully Q 4854, Australia
A B S T R A C T
There currently is a lack of information on the important relationship between root function and tops growth for sugarcane. To rectify this a simple aeroponic facility was constructed and tested using three sugarcane cultivars known to have different shoot:root ratios. Significant cultivar effects on plant shoot and root parameters in aeroponic culture were similar to those observed for field- grown plants. Advantages of aeroponic culture include an ability to observe and control root size and activity and to directly determine root effects on above ground productivity.
I N T R O D U C T I O N
Few detailed studies have been conducted into sugarcane root growth and activity, or into the relationship between roots and above ground productivity. Some reasons for the lack of research on sugarcane root systems include difficulties in observing or sampling root systems over time, and inability in determining the activity of the observed roots.
Due to root system variability, large numbers of samples are required to describe full profile root distribution for crops (Upchurch 1987).
For a fourth ratoon Q122 sugarcane crop, sample numbers for root description were found to exceed practical limits (Reghenzani 1993b), and a sub-sampling strategy was suggested. While both approaches above provide an estimate of root system distribution or relative size, neither was entirely satisfactory. Cost was high, no data were provided on root system activity and limited information was provided on the relationship between roots and above ground productivity.
An effective root system is required for the absorption of water and nutrients. Particularly for sugarcane, due to large crop mass and associated leverage, an extensive root system is required for the anchorage of plants in the soil. Sugarcane has a much greater above ground biomass than wheat, but its root length of almost 34000 km/ha is much less than the 60000 - 100000 km/ha commonly found for wheat (Reghenzani 1993). It has been suggested that large areas of sugarcane are suffering loss of productivity directly attributed to debilitated root systems (Egan et al 1984). While soil factors influencing root growth and health such as microbiology (Magarey 1996), nutrition (Reghenzani 1993a) and compaction (Braunack et al 1993) are being investigated, there is a need to establish the relationship of root systems with above ground growth. An aeroponic technique for growing, manipulating and non-destructively observing sugarcane root systems described in this paper is suggested as a means of establishing the above relationship.
Data on growth of three cultivars with different shoot:root ratios are presented.
MATERIALS A N D M E T H O D S
Aeroponics is defined as the culture of whole plants whose roots are suspended in and fed by nutrient solution spray. Weathers & Zobel (1992) have suggested aeroponics as the optimum soil-less culture system, because root temperature, nutrition, moisture and gaseous phase can be controlled.
Previous aeroponic systems (Smucker & Erickson 1976; Zobel et al 1976) were more complicated than the design reported in this paper.
The initial aeroponic facility reported here consisted of ten circular 55 L black, food grade polyethylene vats, 555 mm in height and 490 mm in diameter. Lids were painted white to reduce heat load and were modified by the addition of a second lip to eliminate light and prevent nutrient solution leakage. Three, evenly spaced 67 mm diameter holes were drilled in each lid for plant access. Nutrient solution was sprayed onto roots through twin foggers each rated at 28 L/h (at 405 kPa), situated at the base of each vat. Nutrient solution drained from the base of vats to a common graduated reservoir holding 40 L. A timer set to 15 min on, 15 min off, operated a 0.6 kW pump which supplied nutrient solution under pressure to the foggers. The system including pump, reservoir tank and vats were enclosed in an air-conditioned bench, similar to that used for glasshouse pot trials (Reghenzani 1984).
Three sugarcane cultivars with a wide range of shoot:root ratios were chosen for a preliminary evaluation trial. T h e cultivars w e r e Q 7 8 (small ratio), Q138 (mid ratio) and Q162 (large ratio). Single-eye setts were germinated in 76 mm planter pots filled with black, high density polyethylene beads, under 200 mM C a ( N 03)2. 4 H20 mist.
T h e mist was applied for 15 min periods on a 3 3 % duty cycle during the day and on a 1 1 % duty cycle during the night. T h e germination solution was replaced at t w o to three day intervals. Plants at the 2-3 leaf stage and approximately 50 mm in height were graded on size and transferred to the glasshouse aeroponic system two weeks after planting. As far as possible, plants of similar size were placed within each of the ten replicate groups.
Observations were made at two week intervals until the twelfth week, when the trial was harvested. An additional observation was made on the eleventh week due to rapid plant growth. The aeroponic nutrient solution was changed every week until the final week, when it was necessary to change mid-week due to high plant usage. Commercial hydroponic twin pack p o w d e r (HydroLogic) supplied by Growth Technology, South Fremantle, was used to make the nutrient solution.
Elements and their nominal concentration (mg/L), when made up according to directions were: N(220), P(31), K(280), Ca(160), Mg(50).
S(66), Fe(3), M n ( l ) . B(0.35), Zn(0.20), Cu(0.15) and Mo(0.05). When made up, the solution contained 2.5 g/L total dissolved solids, with an electrical conductivity of 2.25 mS/cm. Solution pH was adjusted to 6.0 using 1M KOH.
RESULTS A N D DISCUSSION
This initial experiment was conducted to identify and solve problems with the technique, to determine if cultivars reacted as they did in the field with respect to shoot:root ratio, and to observe plant growth and if restricted, correct factors which may have caused the problem. Within the first week of transfer to the aeroponic system Q78, which is known to be susceptible to iron deficiency, showed severe iron chlorosis. A single foliar spray with 1% iron sulfate solution overcame the problem.
There was difficulty in differentiating between sett and shoot roots for the cultivar Q 7 8 . otherwise ease of observation of developing root systems was excellent (Fig. 1).
Shoot: root ratio
At the conclusion of the experiment the three cultivars ranked according to shoot:root ratio in the same order as for previous pot and field trials i.e. Q162, Q 1 3 8 > Q 7 8 (P<0.05): ratios w e r e 3.39, 3.24 and 2.59 respectively. The above finding shows that in aeroponic culture, sugarcane cultivars reacted as expected, and this fact encouraged confidence in results from future trials in the facility.
Water use
Progressive water usage was monitored during the trial. There was no appreciable usage until week seven (Fig. 2). Use over weeks 9 - 1 1 was depressed due to overcast conditions, while the increase in week 12 was consistent with fine, hot conditions, rapid growth and tillering of plants. Although not reported here, rate of nutrient uptake was determined by analysis of the reservoir solution. Both water and nutrient uptake can be used as progressive, non-destructive indicators of root system activity.
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 W e e k
Fig. 3 Total primary root length for three sugarcane cultivars grown in aeroponic culture.
CONCLUSIONS Fig. 1 Top removed from aeroponic vat, exposing root systems of 12
week old Q162 (left), Ql38(centre) and Q78(right).
Fig. 2 Primary shoot height and water use for three sugarcane cultivars grown in aeroponic culture.
Primary shoot height
There was a near linear increase in primary shoot height with time for all three cultivars (Fig. 2), indicating no restriction to growth, except from slight slowing on transfer from the germinating facility and during the period of overcast conditions. Analysis of shoot height data indicated highly significant (P<0.001) effects due to cultivar (Q 162>Q 138>Q78) and time (week 12>11>10>8>6>4>2>0). Observed primary shoot growth compared well with plants in the field and differences between cultivars were consistent with known genetic characteristics.
Total primary root length
Only sett roots were apparent until week four (Fig. 3). By week six, shoot roots emerged and their length then increased at an exponential rate. Analysis of progressive weekly data showed a very significant (P<0.01) root length difference due to cultivar, (Q138>Q 162=Q78) and a h i g h l y significant ( P < 0 . 0 0 1 ) effect due to time ( w e e k 12>11>10>8>6=4=2=0). As for shoot growth, root length appeared to be increasing at a satisfactory rate, with significant cultivar differences probably due to differences in genetic potential.
The initial trial has shown that the early growth of sugarcane shoots and roots, in the absence of imposed constraints, was satisfactory using the aeroponic t e c h n i q u e . As highly significant cultivar differences in shoot and root growth reported in this paper were similar to expected field responses, it is suggested that the facility is suitable for the study of the relationship between root growth and activity, and above ground productivity. Future trials will investigate the effect of imposed root constraints on early shoot growth. There is a need for additional study of root growth and activity conducted on larger and more mature plants.
ACKNOWLEDGMENTS
The work reported in this paper was funded by SRDC and BSES as project CSS2S, and was conducted as part of the yield decline joint venture between BSES, CSIRO and DPI.
REFERENCES
Braunack MV, Wood AW, Dick RG, Gilmour JM (1993) The extent of soil compaction in sugarcane soils and a technique to minimise it. Sugar Cane 5. 12-18.
Egan BT, Hurney AP, Ryan CC, Matthews AA (1984) A review of the northern poor root syndrome of sugarcane in north Queensland. Proceedings of the Australian Society of Sugar Cane Technologists 6, 1-9.
Magarey RC (1996) Microbiological aspects of sugarcane yield decline.
Australian Journal of Agricultural Research 47, 307-322.
Reghenzani JR (1984) Northern poor root syndrome - its profile distribution and the effects of temperature and fallowing. Proceedings of the Australian Society of Sugar Cane Technologists 6, 79-86.
Reghenzani JR (1993a) A survey of the nutritional status of north Queensland sugarcane soils with particular reference to zinc. Proceedings of the Australian Society of Sugar Cane Technologists 15, 298-304.
Reghenzani JR (1993b) Development of techniques to study root systems of sugarcane. Final Report SD93003, SRDC Project BS56S. BSES, Brisbane.
Smucker AIM, Erickson AE (1976) An aseptic mist chamber system: A method for measuring root processes of peas. Agronomy Journal 68, 59-62.
Unchurch DR (1987) Conversion of Minirhizotron root intersections to root length density in Minirhizotron observation tubes. In: Taylor HM (ed) Methods and Applications for Measuring Rhizosphere Dynamics, ASA Special Publication No. 50, Madison, Wisconsin,
Weathers PJ, Zobel RW (1992) Aeroponics for the culture of organisms, tissues and cells. Biotechnology Advances 10, 93-115.
Zobel RW, Del Tredici P, Torrey JG (1976) Method for growing plants aeroponically. Plant Physiology 57, 344-346.
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Sugarcane: Research Towards Efficient and Sustainable Production. Wilson JR, Hogarth D M , C a m p b e l l JA and Garside AL (Eds).
C S I R O Division of Tropical Crops and Pastures, Brisbane. 1996. pp. 7 5 - 7 6 75 SUGARCANE GROWTH IN A CONTROLLED ENVIRONMENT I: TECHNICAL SPECIFICATIONS AND
CULTURAL REQUIREMENTS CAMPBELL JA, K E R S L A K E RG and T U C K E T T PG
CSIRO Division of Tropical Crops and Pastures, 306 Carmody Road, St Lucia, Q 4067 Australia
A B S T R A C T
This paper describes the specifications of the CSIRO Division of Tropical Crops and Pastures' controlled environment facility (CEF) at St. Lucia. Particular mention is made of the need to regulate light quality in controlled environments, and the means by which this is achieved in the CEF is described. Cultural practices (including irrigation, fertiliser application and plant support ) for sugarcane developed over two years are also described. Representative data for growth of sugarcane variety Ql 17 in the CEF are presented which show that it is only in 'tall' rooms that studies of stalk development and hence sucrose accumulation can be achieved under controlled conditions.
I N T R O D U C T I O N
Controlled environment facilities (phytotrons) are useful tools in the study of p l a n t p h y s i o l o g y and b i o c h e m i s t r y . T h e y e n a b l e t h e identification of factors, often discrete environmental parameters, which limit plant growth, development or productivity. Such limits, once defined, can potentially be resolved by altering management practices, by specific breeding or by molecular manipulation. Modern controlled e n v i r o n m e n t facilities a l l o w t i g h t r e g u l a t i o n o f e n v i r o n m e n t a l parameters such as temperature, light, daylength, humidity and C Or
Sugarcane is a vigorous C4 grass which grows 3-7 m tall, has a high nutrient requirement, and has a life cycle of 8-12 months to maturity.
These characteristics make it an especially difficult plant to grow in controlled environment facilities. The CSIRO Division of Tropical Crops and Pastures at St. Lucia has designed and built a controlled environment facility (CEF) specifically to study tropical crop and pasture species. Special (tall) rooms which could accomodate sugarcane and horticultural species were included in the design of the facility.
Sensitive to the high light conditions in which many tropical plants grow, special attention was paid to control of light levels, uniformity and quality. This paper presents detailed technical information about the new facility.
T E C H N I C A L SPECIFICATIONS O F T H E CEF Physical Specifications
There are 14 growth rooms, six 'standard' rooms 3 x 2.7 x 3m high, four 'tall rooms' 3 x 2.7 x 8m high with hydraulic moveable floors, and four 'small' rooms 3 x 1.5 x 3m high. Each growth room has a plant ( a i r c o n d i t i o n i n g ) r o o m a t t h e s i d e a n d a l a m p loft a b o v e . Photosynthetically active radiation (PAR) is supplied by six, 1 kW high pressure metal halide lamps (Sylvania) and six, 1 kW tungsten halogen lamps (Phillips). Photoperiod lighting is provided by six, 150 W tungsten lamps (Phillips) in each room. T h e r e is a 40 mm deep temperature-controlled water bath and 6 mm of toughened plate glass to reduce the heat load from the lights on the plants and equipment. All rooms have full microprocessor control, programming and recording capabilities and operate to the precise specifications given below.
Radiation Specifications
Photon irradiance can be controlled in the range of 300 to 700 umol/
m2/s at the standard plant height of 1200 mm from the floor by the use of a PAR light sensor coupled to a computer-controlled dimming system.
T h i s range of PAR levels is c o n s i s t e n t w i t h r e c e n t l y p u b l i s h e d recommendations for lighting in controlled environments (Dietzer et al 1994).
Cook & Russell (1983) reported that the yearly mean of short wave solar radiation intensity at Townsville (dry tropics) was 19.7 MJ/m2/ day. In the wet tropics, the yearly mean is even lower 17.2 MJ/m2/day (Wilson & Ludlow 1991). Szeicz (1974) determined that PAR is - 5 0 % of short wave solar radiation. As 1 m o l e of natural daylight is
approximately 0.23 MJ of PAR (Charles-Edwards 1982), this means that yearly average PAR values for dry and wet tropics are 996 and 865 pmol/m2/s. Given these data and the observation that plants in controlled environments receive much more indirect (reflected) radiation than plants in the field (Bugbee 1994), we believe the range of PARs in the C E F to be appropriate for plant growth. Figure 1 shows a representative plot of light distribution at 1200 mm from the floor for a 'small' room set to deliver 500 umol/m2/s PAR at that height. Similar trends have been observed for the 'tall' r o o m s used for sugarcane growth. In sugarcane trials plant rows are never closer than 4 5 0 mm to the side walls, where radiation flux is lowest.
Fig. 1 Light distribution at 1200 mm in a CEF 'small' room set to deliver 500 umol/m2/s PAR at that height.
It has been reported that the quality of light in controlled environments can significantly alter plant growth and development in some species (Bugbee 1994). Warrington & Mitchell (1976) reported that blue- or red-biased lighting in controlled environments effected significant changes to the protein (blue-biased) and carbohydrate (red-biased) content of Sorghum bicolor. The spectral composition achieved in the C E F minimises such a potential problem, as the blue (400-500 nm) light to red (600-700 nm) light ratio of the rooms (0.502) is very similar to that of sunlight (0.564) at 0920 h. Figure 2 shows the spectral distribution comparison of C E F irradiance against solar irradiance at 0920 h.
A n o t h e r p a r a m e t e r identified a s a l t e r i n g t h e p h e n o l o g i c a l a n d physiological development of plants in controlled environments is the ratio of red to far red radiation (R:FR). The R:FR ratio has been linked, through phytochrome activity, to variations in the rate of growth and
76
the pattern of development of plants growing in controlled environments (Smith 1994). The R:FR ratio (660 nm/ 730 nm) in the CEF is 1.13, which is within 10% of the observed daylight range R:FR (1.05-1.25).
The CEF has the facility of being able to control photoperiod from 1 to 24 hours, and can provide daylength extension using low wattage tungsten lamps.
Wavelength (nm)
Fig. 2 Spectral distribution comparison of irradiance (uynol/m2/s) in a CEF room (no dimming) (-) and solar radiation at 0920 h in Brisbane (—). Photosynthetically active radiation is 400-700 nm.
Non-radiation Specifications
To investigate the discrete effects of temperature on sugarcane physiology, the CEF rooms can maintain day or night temperatures from 10 to 50°C (± 0.2°C). A special 'frost room' can operate down to -10°C.
In the CEF. dew points in the range of 10°C to 48°C are achieved using steam injection and coil dehumidification. Dew points down to 0°C can be achieved in the 'small' rooms using chemical dehumidifiers.
Control of night time humidity to above 85% has been found to be critically important for normal leaf development in a number of tropical grasses (JR Wilson personal communication). At night time humidities below this threshold, a 'leaf-tip withering' symptom has been observed.
The concentration of C O: is monitored in each room with a capability to enrich to 1000 ppm. Air flow through each room in the CEF is from top to bottom with wind speed of either 0.5 or 1.0 m/s. Fresh air is added at the rate of 35 L/min to help maintain ambient CO, levels.
SUGARCANE CULTURE CONDITIONS
Plants are germinated from setts in seedling trays (300 x 300 x 40 mm), and are transplanted to plastic pots (200 mm internal diameter, 300 mm high) when plant height is approximately 200 mm. The potting mixture for both germination and mature plant growth is the same; 33% coarse sand, 33% vermiculite (Grade 1) and 33% coir fibre peat. Per 6 m3 of this mix. 5 kg each of hydrated lime, dolomite and superphosphate are also added. The potting mixture recipe was originally provided by Dr.
Nils Berding of BSES. The potting mixture is pasteurised at 80°C for 20 min prior to use.
Potted plants are irrigated by individual trickle irrigation 'drippers'.
Pots receive three waterings of 500 mL of tap water each day. Saucers beneath the pots hold a reservoir of water which is used by the plant.
Under this irrigation regime visual signs of water stress such as leaf tip drying or leaf wilting have not been observed.
Fertiliser (Wuxal™ liquid foliar nutrient) is applied fortnightly to all pots. Wuxal™ contains 9.9 % w/v N (as urea), 4.3% w/v P (as P,05), 6.2 % w/v K (as K , 0 ) , 0.15% w/v Mg (as MgS04) and the trace nutrients;
B, Co, Cu, Fe, Mn, Mo and Zn. Wuxal™ is diluted 15 mL in 1 L, and 150 mL is applied directly to each pot. Slow release fertiliser (Osmocote™, 14 % N, 6.1% P, 11.6% K) is applied every 2 months at the rate of 50 g per pot. Librel™ Fe-lo chelated iron is applied every 2 months at the rate of 5 g per pot.
Plants are grown as two, two-pot rows, within C E F rooms. This arrangement allows a maximum of 40 plants per room. Plants are supported by an extendable trellis, which varies from 2 to 3.5 m in height. Individual stalks are attached to the trellis by loose-fitting wire nooses. Earlier trials allowed experimental randomisation by growing plants on movable trolleys, however it was difficult to support tall stalks with this system and sampling caused considerable canopy damage.
Growing plants supported by a fixed trellis limits experimental randomisation. To minimise the variation of plants within a row, twice the number of plants needed for a trial are grown to the small plant (<
200 mm) stage. The heights of the plants are then measured, and the most uniform plants are selected for the trials. This procedure yields data with low levels of variation, essential given the limitations to replication and randomisation within the rooms (Campbell & Bonnett 1996).
Experiments with sugarcane variety Q117 growing under 14 hour days, (PAR of 500 umol/m2/s, 30°C, 65% humidity) and 10 hour nights (20°C, 9 5 % humidity) yielded plants of 2.7 m (base to apex) at 80 days after planting (DAP) and 5.8 m at 160 DAP. Growth rates under such conditions evidently limit the duration of experiments, as plants become too tall for the rooms after approximately 200 days. The meristem to apex length remained constant after 60 DAP at 1.8 m. Given the meristem to apex length, it is clear that only a facility with tall rooms such as the CEF can maintain controlled conditions during the cane- producing phase of sugarcane growdi. A detailed study of sugarcane growth in the CEF compared to field growth is presented in the second paper of this series (Campbell & Bonnett 1996).
ACKNOWLEDGMENTS
The authors acknowledge Dr Merv Ludlow for his contributions to the planning and development of the CSIRO Division of Tropical Crops and Pastures' CEF. We also thank Dr John Wilson and Dr Graham Bonnett for helpful advice and critical review of the manuscript and Roger Davis for collection of light quality and distribution data. This work was partially funded by the Sugar Research and Development
REFERENCES
Bugbee B (1994) Effects of radiation quality, intensity, and duration on photosynthesis and growth. In: Tibbitts TW (ed) 'Proceedings of the International Lighting in Controlled Environments Workshop' pp. 39-50. NASA, Florida.
Campbell JA, Bonnett GD (1996) Sugarcane growth in a controlled environment II: Comparison with growth in field environments.
In: Wilson JR, Hogarth DM, Campbell JA, Garside AL (eds) Sugarcane: Research Towards Efficient and Sustainable Production.
pp. 77-79. CSIRO Division of Tropical Crops and Pastures, Brisbane.
Charles-Edwards DA (1982) Physiological Determinants of Plant Growth Academic Press, Sydney.
Cook SJ. Russell JS (1983) The climate of seven CSIRO field stations in northern Australia. Division of Tropical Crops and Pastures Technical Paper No. 25 CSIRO Division of Tropical Crops and Pastures, Brisbane.
Dietzer G, Langhans R, Sager J, Spomer LA, Tibbitts TW (1994) Guidelines for lighting of plants in controlled environments. In:
Tibbitts TW (ed) 'Proceedings of the International Lighting in Controlled Environments Workshop' pp. 391-393. NASA, Florida.
Smith H (1994) Phytochrome-mediated responses: Implications for controlled environment research facilities. In: Tibbitts TW (ed)
•Proceedings of the International Lighting in Controlled Environments Workshop'pp. 57-67. NASA, Florida.
Szeicz G (1974) Solar radiation for plant growth. Journal of Applied Ecology 11,617-636.
Warrington IJ, Mitchell KJ (1976) The influence of blue- and red-biased light spectra on the growth and development of plants. Agricultural Meteorology. 16, 247-262.
Wilson JR, Ludlow MM (1991) The environment and potential growth of herbage under plantations. In: Shelton HM, Stur WW (eds) 'Forages for Plantation Crops' pp. 10-24. ACIAR, Canberra.