4. Opportunities for improved crop management
4.1 Crop agronomy and yield improvement
Sugarcane: Research Towards Efficient and Sustainable Production. Wilson JR, Hogarth D M , Campbell JA and Garside AL (Eds).
CSIRO Division of Tropical Crops and Pastures, Brisbane. 1996. pp. 157-159 157 YIELD MAPPING FOR THE CANE INDUSTRY
COX G\ HARRIS H D \ PAX R A ' a n d DICK RG2
'Faculty of Engineering and Surveying, University of Southern Queensland, Toowoomba, Q 4350 Australia
2Australian Agricultural Engineering Services, 37 Wilson Street, Bundaberg, Q 4670 Australia
A B S T R A C T
Yield mapping has a range of potential applications in the cane industry, but there are as yet no convenient means for measuring yield as a function of distance along the row. A spatial resolution of 5-10m can be achieved with the simple weigh truck, but it is time consuming and inconvenient to weigh short sections of the cane row. The issues involved in yield mapping are discussed, and preliminary experiments to establish the basic technology required are reported.
A simple calibration has been established, which defines average hydraulic motor power as a function of overall yield as measured by a weigh truck. This calibration has been used to create a yield map for a limited area of a field, which revealed a substantial degree of yield variation both along and between rows. It appears to be possible to develop this approach further, and in conjunction with GPS (Global Positioning System) and GIS (Geographic Information System) inputs, to derive a yield mapping system.
INTRODUCTION
Currently most growers apply chemicals to their crops at a uniform rate calculated from historical field data. An average yield is predicted for individual fields and application rates of fertilisers and chemicals are tailored to the assumed field output (Massey Ferguson Group Ltd 1993). In practice, crop yields vary not only from year to year, between farms and between fields, but significant yield variations also appear within individual fields (Vansichen & de Baerdemaeker 1993; Kirchner
& Lee-Lovick 1991). Variable soil fertility, varieties used, management practices, use of fertilisers, irrigation, control of weeds, pests and diseases, and many other factors explain the spatial variation in sugarcane yields (Humbert 1968, p.4). These variations in field characteristics suggest that the proper placement of the inputs such as fertilisers and chemicals according to spatial location would help reduce production costs. This type of 'site specific' crop management involves the application of crop management practices which are tailored to a specific area in a field (Clark et al 1987).
McBratney & Whelan (1995) proposed that site-specific farming should be investigated for use in the Australian cotton industry. They discussed the use of spatially measured soil attributes as inputs to managerial intervention such as soil tillage, fertiliser application, nitrification inhibitor application, gypsum application, seeding rates, crop variety, pesticide application and the application of irrigation. Measurement of soil attributes involves the development of suitable sensors for nitrogen, organic matter, soil salinity, soil moisture content and soil compaction.
The crop itself shows the overall effect of the management regime and the soil status, and so the measurement of yield over small areas within the crop will provide information on the effects of these variables.
Yield maps provide essential information on crop performance within and between fields, for spatial analysis and evaluation of crop management. This information can be an input to decision making for field o p e r a t i o n s d u r i n g the next growing season (Vansichen &
Baerdemaeker 1993). Detailed measurement of crop yield, which integrates the influence of many variables, is considered to be the most practical method of assessing management techniques for site specific farming practices.
Yield maps can also greatly improve information available for making longer term strategic management decisions and will also highlight problems with drainage, disease or weed infestation (Clark et al 1987). Accurate yield maps give a clear indication of good and poor areas of the field, and a farm manager can then investigate the many possible reasons for these yield variations. Some reasons for yield variations are relatively easy to rectify, for example, by subsoiling compacted areas. Other reasons can be established by soil analysis, where the yield map allows this task to be performed more selectively than traditional 'random sample' methods (Massey Ferguson Group Ltd 1993).
'The sugarcane plant, Saccharum officinarum L., has been described as the most efficient of all storers of the suns energy' (Humbert 1968, p. 16). If its maximum yield potential is to be approached, the soil- plant relationship must be at an optimum. The many factors controlling growth must be integrated into an optimum environment. The fact that sugar production in Australia ranges from 160 to 60 tonnes per hectare highlights the range in productivity that can occur due to different soils, climatic conditions and crop management. Even within ten adjacent rows of a crop we have measured a yield variation of this order, which illustrates the potential for maximising yield by improving crop management. Kingston & Hyde (1995) have also reported high intra- field variation of commercial cane sugar content (CCS), which has consequences for both the growing and milling sectors of the industry, and will compound the task of maximising overall return.
These considerations justify support for the application of yield mapping technology to sugarcane agriculture. It will allow the fine tuning of resource inputs and management, and improve the sustainability of sugarcane production.
DEVELOPING YIELD MAPS
There are two major approaches to measuring the spatial variability of yield in cane. The first of these is based on remote sensing technology, and the second is based on measuring mass flow rate through the harvester, with this information being spatially referenced using a Global Positioning System (GPS). For this application, we consider that spatial location with a sub metre accuracy is realistic and achievable.
Remote sensing
Remote sensing is a technique using light reflected from earth. A recording instrument, such as a camera, can record the spectral data from the plant reflected back to the receiver, and this information can be interpreted in many ways. The extension of this method to separately measure and record different sections of the light spectrum is known as multispectral sensing, which can provide additional data on crop condition. Specifically, information about crop biomass can be obtained and from this information yield maps can be devised. However, Colwell (1983) has stated that spectral biomass techniques have been found to be accurate for low to medium biomass quantities, but are of little value at yields over 5t/ha. Lee-Lovick & Kirchner (1991) reported on the assessment of remote sensing technology capable of resolution of an area 30mx30m square. For sugarcane, they found that "crop canopy moisture levels appear(ed) to dominate the spectral signature, masking long term stalk development trends", so that CCS or yield at harvest could not be predicted. They concluded that the technology was inappropriate for the Australian sugar industry.
Global Positioning System
The GPS is a satellite based radio navigation system developed and operated by the U.S. Department of Defence. There are two modes of
158
operation, Differential GPS (DGPS) and Absolute GPS (AGPS). AGPS requires the use of only one receiver and is also known as "stand-alone"
G P S , and delivers an accuracy varying from t w o meters to over 100 metres (Harrison 1992), DGPS is designed to improve the accuracy of GPS-derived positioning information. A stationary receiver at a known location (the "base station") receives signals from the satellites, and calculates its own position. Since the actual position of the base station is known, the errors in the satellite signals can be accurately calculated.
This error information can be recorded in a computer data file for later use (post processing) and/or transmitted to a mobile receiver (the
"rover") over a radio link in real time (Shropshire 1993). For yield mapping, post processing would be acceptable because the real time location of the harvester is not required. Position accuracy for a simple system is presently at the sub-metre level.
GPS location hardware could easily be incorporated into yield mapping.
Installation would be a matter of mounting an antenna on the cabin of the harvester and securing the receiver in the cabin. Location data would be interfaced with the necessary data logging equipment, which would simultaneously log yield measurements. Post processing of the location data would simply involve software application on a personal computer.
Measuring cane m a s s flow rate
Because GPS and data acquisition technology are available in a variety of forms, we have focussed our attention on the development of a cane m a s s flow rate sensor. In defining its functional and performance requirements, we have assessed recommendations made in the literature for grain mass flow sensors, and adapted them to the needs of the cane industry.
A measurement technique for yield mapping of corn silage by measuring chopper power was devised by Vansichen & de Baerdemaeker (1993).
Although the harvesting of silage is notably different from that of sugarcane, the similarity lies in the fact that both methods involve the removal and billeting of a whole crop. T h e rotary drum chop system (chopper system) of a sugarcane harvester uses seven cuts per second to billet sugarcane at a rate of up to 50 kg/s. Measuring chopper power should therefore provide an approach to measuring mass flow rate.
Another component of a sugarcane harvester, whose power consumption may be related to the material flow rates, is the elevator. This system is driven by two hydraulic motors, coupled at the top of the elevator.
Billeted cane is lifted some 2 to 3 vertical metres over the length of the elevator, and obviously energy is required to overcome gravity and the effect of friction on the elevator floor as the sugarcane is dragged up t h e elevator. T h e p o w e r r e q u i r e d t o e l e v a t e t h e c a n e s h o u l d b e proportional to the mass flow rate.
F I E L D T R I A L S
Field trials were set up to assess the potential for measuring chopper and elevator power as indicators of cane mass flow rate.
Instrumentation
Power for an hydraulic motor can be calculated as the product of pressure drop and flow through the motor. For these preliminary experiments we measured supply pressure only, and not the pressure drop, and inferred the oil flow rate by measuring the speed of the motor, knowing the displacement per revolution of the motor.
Pressure transmitters were installed in the chopper and elevator supply lines. T h e chopper hydraulic system also supplies the feed train rollers, but it was not convenient to separate these systems. Only one of the t w o elevator motors w a s instrumented.
C h o p p e r speed w a s measure directly with a speed sensor, and the elevator motor speed w a s inferred from the speed of an idler sprocket at the base of the elevator. We also measured engine speed and ground speed of the harvester using similar sensors.
Data from the pressure transmitters and speed sensors were recorded on a seven track analogue tape recorder ( A M P E X FR 1300) mounted in t h e c a b and powered by a generator tied to the p u m p box. Each reel of tape had a capacity for fifteen minutes of recording.
Measurements
T h e Bureau of Sugar Experiment Station (BSES) Bundaberg provided all personnel and harvesting equipment, which included an A U S T O F T 7000 harvester and a weigh truck.
T h e three days of testing included different weather conditions and changes in crop variety and quality. Day one was fine and dry, harvesting a crop of Q146-2R, which yielded heavily at 120 t/ha and was harvested ' g r e e n ' . Day t w o and three of testing were carried out on a different field with variety Q146-3R, which was harvested 'burnt' and also yielded approximately 120 t/ha. Day two was wet and drizzly, and day three
The hypothesis being tested was whether the mass flow rate of sugarcane through the harvester was related to the power required to process it. A range of mass flow rates was achieved by driving the harvester at a different speed for each test run. Assuming that the crop yield was somewhat uniform over the field, each run would produce a mass flow rate roughly proportional to the ground speed of the harvester.
Test runs were over approximately 100 m of row, when the weigh truck would stop to measure and record the mass harvested in that run. This m a s s was expressed as an average mass flow rate over that run, and compared with the average pressures and powers recorded during the run to give a calibration for mass flow rate in terms of chopper and elevator pressures and powers. This calibration process was repeated for a number of runs.
We found a highly significant linear correlation between both average pressures and both average powers, and the average mass flow rates.
T h i s finding s u p p o r t e d the h y p o t h e s i s that p r o c e s s i n g p o w e r i s proportional to mass flow rate.
A typical relationship for chopper power as a function of mass flow rate is that established on the first day of testing,
chopper p o w e r ( W ) = 6239 + 173.5 flowrate(kg/s) This correlation has R2 = 0.96 and an average absolute error of 1.4%
full scale, or MOW. It was used to calculate the variation of mass flow rate during the run, which was then combined with the ground speed data for that run to give the mass of cane per metre and the yield map.
Fig. 1 Yield map produced using the chopper power data.
Figure 1 shows a typical yield map derived from the chopper data. T h e yield depression around 105m is an artefact of the testing technique, where the harvester was stopped and restarted to allow the weigh truck to measure the accumulated cane.
C O N C L U S I O N S
We have discussed an approach to a yield mapping system in cane. Our conclusions are that differential G P S is suitable and sufficiently accurate for spatial location, and that it appears possible to measure cane mass flow rate through the harvester by monitoring pressures and powers.
F r o m a preliminary series of measurements under real conditions, we have derived yield m a p s for a section of a field.
159 These yield maps immediately raise the question of what is causing the
yield variation, but the a n s w e r s to that question await further investigation. The data that we have presented suggest that the technique for measuring mass flow rate shows promise, given that the effects of other variables such as chopper sharpness and the elevator/cane friction interaction have not yet been resolved.
A complete yield map system will involve integration of spatial information, mass flow rate and ground speed data. We suggest that this processing should take place post-harvest on a daily basis, and be combined with GIS software to produce yield maps keyed to the field and the known inputs. These maps would then be the main source of information for crop management.
A C K N O W L E D G M E N T S
The Sugar Research and Development Corporation provided financial support to this project, which was undertaken by G Cox as a final year undergraduate honours project. BSES Bundaberg provided much appreciated support and assistance for the field trials.
REFERENCES
Clark SJ, Schrock M D , Young SC (1987) Agricultural engineering research for Agriculture 2000. ASAE paper 87-2016. American Society of Agricultural Engineers, St Joseph, MI, USA.
Colwell RN, (1983) Manual of Remote Sensing. Vol. 2, 2nd edition, Sheridan Press. USA.
Harrison J D , irrel J, Sudduth KA, Borgelt SC (1992) Global Positioning System applications for site specific farming research.
ASAE paper 92-3615. American Society of Agricultural Engineers, St Joseph, MI, USA.
Humbert R P ( 1968) The Growing of Sugar Cane. Elsevier, Amsterdam.
Kirchner L, Lee-Lovick G (1991) The use of Landsat TM data for the assessment and monitoring of sugarcane. Remote Sensing , 1087- 1095.
Kingston G, Hyde RE (1995) Intra-field variation of commercial cane sugar (ccs) values. Proceedings of Australian Society of Sugar Cane Technologists, Bundaberg Conference, 30-38.
Lee-Lovick G, Kirchner L (1991) Limitations of Landstat TM data in monitoring growth and predicting yields in sugarcane. Proceedings of Australian Society of Sugar Cane Technologists, Bundaberg Conference, 124-130.
McBratney AB, Whelan BM (1995) The potential for site-specific management of cotton farming systems. Discussion Paper No 1.
Cooperative Research Centre for Sustainable Cotton Production, Narrabri, NSW.
Massey Ferguson Group Ltd (1993) Yield Mapping System, MF 30/40 series combines. Product information, Massey Ferguson UK.
Shropshire G, Peterson C, Fisher K (1993) Field experience with differential G P S . ASAE paper 9 3 - 1 0 7 3 . American Society of Agricultural Engineers, St Joseph, MI, USA.
Vansichen R, de Baerdemaker J (1993) A measurement technique for yield mapping of corn silage. Journal of Agricultural Engineering Research, Vol 55, 1-10.
Sugarcane: Research Towards Efficient and Sustainable Production. Wilson J R , H o g a r t h D M , C a m p b e l l JA a n d G a r s i d e AL ( E d s ) . 160 C S I R O Division of Tropical C r o p s and Pastures, Brisbane. 1996. p p . 160-161
PLANTING IN CANE HOLES WITH SINGLE-EYE TRANSPLANTS IN POLYETHYLENE BAGS T I A N C O A P
Central Azucarera Don Pedro, Nasugbu, Batangas 4231, Philippines
A B S T R A C T
A planting system called the hole planting method (HPM) has been developed to resolve the problem of lack of planting material and reduce the cost of seedcane. The technique involves germination of single-bud cuttings in 130 mm x 200 mm polyethylene bags before transplanting 10,000 40-day old seedlings/ha at the onset of the first heavy monsoon rains.
Although there were 8% less millable stalks at harvest 9-10 months after transplanting at 1 m row and hole spacings, individual stalks in HPM were 13% heavier compared with stalks in the conventional method (CM) using 40,000 three-node seedpieces/ha.
Cane and sugar yields with HPM were 5% higher than those of CM using six cultivars for a crop cycle (a plant crop and one ratoon).
In addition to the 85% saving in planting material and excellent establishment, other cultural advantages which derive mostly from the spatial arrangement of the millable stalks are cited. It may be possible to adapt the system to machine operations.
I N T R O D U C T I O N
T h e cost of planting material, which can reach from 2 0 % to 4 0 % of total production cost in the Philippines, is one of the major items of e x p e n s e . F o r e a r l y - p l a n t e d c a n e a t t h e s t a r t o f t h e m i l l i n g season, tops as planting material are readily available. W h e n milling ends before the start of the rainy season, seedpieces b e c o m e scarce and expensive. Maintaining seed farms is one solution but most planters are hesitant to cut back vigorously-growing plant cane.
The quantity of seedcane required for planting is generally dictated by practical considerations and is determined by furrow width and spacing of seedpieces in the row. To a large extent, the amount of planting material used does not appear to greatly affect yield because sugarcane has a big capacity to compensate for differences in the number and weight of millable stalks produced. This capability has been confirmed by local experiments on planting rate and furrow width (Villarico & Panol 1972).
C a n e used to be planted in holes in Barbados, Mauritius, the drier parts of Jamaica, and on sloping land in Antigua (Blackburn 1984). A system was devised to markedly reduce the amount of planting material required by planting or dibbling in holes using a row spacing of 1 m, and spacing holes 1 m apart within rows. T h e requirements of 4-5 t (tonnes) of planting material (assuming 10,000 seedpieces weigh 1.3 t) can be reduced to only 0.5 t/ha with the H P M method. The remaining 3.5-4.5 t of cane can be crushed. The savings in cash flow can be substantial even after considering the materials and labor to produce the bagged seedlings (Tianco & O c a m p o 1992).
A different version of H P M was tried using bare-root seedlings from bud chips weighing 300 kg instead of 8 t used normally (Ramaiah et al 1977). T h e polyethylene bag transplanting technique (similar to HPM) is used in Punjab, India to accelerate the multiplication of promising varieties to eventually reduce the time of release from 10 years to 5 years, and to replant ratoons (Kanwar 1991).
M A T E R I A L S A N D M E T H O D S
T h e study w a s c o n d u c t e d from 16 J u n e 1993 to 15 April 1994 in t h e p l a n t c r o p and to 24 Jan 1995 in the first r a t o o n in N a s u g b u , B a t a n g a s . A split-plot design in four replications w a s u s e d with c o m m e r c i a l varieties Phil 5 6 2 2 6 , Phil 6 6 0 7 , Phil 6 7 2 3 , Phil 7 5 4 4 , Phil 8 0 1 3 , and V M C 7 1 3 9 a s m a i n p l o t s . M e t h o d s o f p l a n t i n g a s subplots w e r e : 1) c o n v e n t i o n a l m e t h o d ( C M ) with 4 0 , 0 0 0 three- b u d d e d s e e d p i e c e s / h a u s i n g a r o w spacing of 1 m ; and 2 ) hole planting ( H P M ) with 10,000 4 0 - d a y old b a g g e d s e e d l i n g s / h a with h o l e s 1 m apart w i t h i n r o w s . Plots w e r e 6 r o w s at 1 m s p a c i n g x 8 m long. Seedlings w e r e grown from o n e - n o d e seedpieces 50 mm long.
A m m o n i u m sulfate as basal fertilizer w a s applied at the base of each hole at 42 g/hill equivalent to 90 kg N/ha during transplanting for H P M , w h i l e t h e s a m e r a t e w a s applied e v e n l y along t h e r o w u n d e r t h e seedpieces in C M . A second dose of fertilizer as urea was applied about 2 months after planting/ratooning at 20 g/hill in H P M or at the s a m e rate spread along the row in C M , making the total fertilizer applied equivalent to 180 kg N/ha in each treatment. Similar rates and forms of fertilizer were used in the ratoon. Usual practices of weeding and cultivation were followed.
Yield components were measured at harvest time on each plot. Millable stalks were counted while cane yield was measured by weighing the cane from the two middle rows for the plant crop, and calculated from 10-stalk sample weight and number of stalks for the first ratoon. The 10 stalks per plot were also crushed for juice analysis.
RESULTS A N D DISCUSSION Number of millable stalks
CM produced more millable stalks/m2 at harvest in plant cane, except for cultivar Phil 8013 (Table 1). This method also produced more millable stalks in the first ratoon, except for cultivar V M C 7139. Although there was some varietal variation, H P M produced 8% fewer millable stalks/m2
Table 1 Effect of hole planting (HPM) and conventional planting (CM) methods with six varieties on stalk population (millable stalks/m2)'
Varieties Phil 56226 Phil 6607 Phil 6723 Phil 7544 Phil 8013 VMC 7139 Mean Average of four replications
HPM 8.83 a 7.97 a 8.17a 7.91 a 7.59 a 7.28 a 7.96
Plant cane CM
9.11 ab 8.82 abc 10.38 a 8.52 bc
7.41 c 7.87 bc
8.68
Difference -0.28ns
-0.85 ns -2.21**
-0.61ns
0 .1 8 n s
-0.59ns
-0.72*
Mean separation in a column by DMRT at 5% level.
HPM 5.97 b 7.13 ab 6.11 b 7.83 a 6.43 ab 7.84 a 6.88
* = significant at 1% level
First ratoon CM 6.75b 7.78 ab 8.29 a 8.08 ab 6.58 b 7.21 ab 7.45
Difference -0.78n s
-0.65n s
-2.18**
-0.25ns
-0.15n s
0.63n s
-0.57*
* = significant at 5% level, ns = not significant