Ultra High Pressure (UHP) waterjets

Transcription

1 seeding without soil engagement Ultra High Pressure (UHP) waterjets are one of the world s fastestgrowing categories of industrial tools and are now used by a vast number of industry sectors to cut everything from pavlova to titanium. In agriculture we are almost constantly cutting something, whether it s slashing weeds, slicing stubbles, opening soils, cutting hay, reaping crops or chopping straw. SANTFA has been investigating the potential for use of UHP tools in sustainable farming systems and there are some very interesting and potentially advantageous applications on the horizon. Most industrial applications of UHP are in fixed locations where quality water is on tap and can be recycled. That is not the case in agriculture. Most agricultural cutting is done by travelling machines in a paddock setting were water isn t readily on hand and probably won t be recovered easily, if at all. SANTFA has therefore focused on applications were a volume of material is being carted across the paddock to achieve farming objectives, such as carrying fertiliser at seeding time or water when spraying weeds. A simple yet potentially groundbreaking application for UHP is a liquid coulter to replace the leading metal coulter on a disc seeding unit and SANTFA has lodged a pending patent for the use of this technology (Figure 1). A liquid coulter, which could be supplied by manufactures as an option on new seeding systems or be retrofitted to existing seeding bars, comprises a UHP water-jet integrated into a seeding system. Multiple cutting head systems are already used for various applications in other industries (Figure 2). This integration can be achieved in a variety of ways but one design option is to position the cutting jet close to the soil surface immediately ahead of the seeding disc or discs and set it on a reverse rake angle to compliment the arc of the seeding disc/s. Greg Butler, SANTFA R&D FIGURE 1: The liquid coulter concept employs UHP water-jets as a means of slicing through stubbles and opening soils. FIGURE 2: The slitter system is a multiple cutting-head application that provides a vision for future in-field agricultural applications. Use of a liquid coulter is expected to improve stubble management and result in less compaction, smearing and hair pinning than a metal coulter used in the same conditions. UHP components are fabricated from 316 stainless steel, and while the technology was developed using water, a variety of liquids, including fertilisers, may be used in a liquid coulter. Products such as anhydrous ammonia are used for UHP applications including the decommissioning of unexploded artillery shells. Other cleaning and caustic substances are used in UHP applications in the surface preparation industry. A range of hostile liquid fertilisers such as phosphoric acid are being tested for precipitation under pressure, service life impacts and performance characteristics to determine whether or not they are suitable for use as cutting agents in a liquid coulter. The effect of a liquid coulter on Seed Bed Utilisation (SBU) when a liquid fertiliser or chemical such as a fungicide is injected into the seedbed as part of the cutting process is yet to be fully tested under field conditions. However, with a fertiliser, the dispersion of the liquid stream as it cuts though the soil seems likely to yield advantages including reduced incidence of fertiliser toxicity and increased the uptake of nutrients through greater root interception. This could be very useful, especially for crops like canola, which can be difficult to seed into thick residues, is quite hungry for nutrition but can be desiccated in marginal moisture conditions. 44

2 FIGURE 3: A definitive cut was achieved through relatively thick layers of stubble on wet clay soils Living biological products such as inoculants will not survive the ultra high pressure in the pump or the g-forces at the nozzle, so won t be recommended for delivery through a liquid coulter. The primary use for a liquid coulter is in front of disc-seeding system but it could be used as a stubble management tool in a tined system. In a tined system, if fertiliser or fungicide application through the cutting jet is one of the objectives it would be important to monitor the point s excavation of the liquid stream from the furrow. In some circumstance this might limit the coulter s usefulness as a delivery agent in tined systems. Where the technology is used for the sole purpose of stubble management, however, water use could be significantly reduced by employing cleaning cycles (similar in concept to the intermittent operation of windscreen wipers), timing strategies (three seconds on, three seconds off, for example), sensed demand regulators that turn the jet on only when the stubble build up justifies it, or manual control by the operator. Testing To determine the feasibility of the liquid coulter a series of bench tests were performed during March 2011 at Flow International s UHP Advanced Testing Facility in Jeffersonville, Indiana. Flow is a global market leader in the development and supply of UHP water-jet technologies with expertise in development of integrated applications as well as outright performance. SANTFA and Flow are working together towards creating a distribution mechanism that would provide access of UHP tools to farmers and seeder manufactures around the world. FIGURE 4: In a tined system, UHP may be used as a stubble management tool. 45 The aim of the testing, which was influenced by the vision for the liquid coulter and the constraints inherent to a

3 FIGURE 5: Flow International s Principal Research Engineer, Robert Niblock, and the inventor of the abrasive water-jet, Dr Mohamed Hashish, are keen to explore the benefits of deploying UHP technologies in Conservation Agriculture with SANTFA s Greg Butler. mobile application, was to get a feel for the viability of UHP as an agricultural tool. Parameters applied and aspects explored in the tests were: The liquid coulter is a device operating at 10 kph to 20 kph. Most of the UHP cutting was performed at 15 kph. This generally represents the faster end of the ground speed for disc seeding, although some operators seed at speeds of 18 to 20 kph. Liquid rates from 80 L to 220 L/ha to match current carting capacity and nutritional requirements for common crops. 46 Changing row spacing is a major variable in the per hectare water rate; the closer the rows, the more water required and conversely, the wider the row spacing the less water is needed per hectare. A row spacing of 330 mm was used as standard for the testing and water rates tested based on this row spacing varied from 35 L/ha [delivered through a.005 inch (.005 ) 20,000 psi] up to 354 L/ha 45,000 psi]. The interaction between nozzle size, water volume and nozzle wear. Nozzles with small orifices use low volumes of water but have higher wear rates than nozzles with large orifices, that use more water but are less prone to wear. The formula for calculating the area of a circle is πr2, so changing the radius (r) of the orifice by a small amount can have a significant effect on the flow rate. To illustrate: doubling the radius of the nozzle quadruples the flow rate and halving nozzle radius will reduce the flow rate to a quarter of the original. The impact of UHP power requirements on operational factors.

4 FIGURE 6: The test bed at FLOW s Advanced Testing Facility at Jeffersonville is capable of accurately applying UHP cutting at a huge range of ground speeds, pump pressures and water volumes. The power needed to operate a liquid coulter is similar to that required for many current seeding technologies but a liquid coulter imposes no draught force on the tractor and opens the way for fewer wheel assemblies and lighter bars because less engineered strength is needed. Direct-drive UHP pumps are quite efficient (92%) in converting energy into water pressure but are limited in outright performance (20,000 psi to 50,000 psi). Hydraulic intensifier UHP pumps are less efficient (70%) in converting energy to water pressure but have much greater capacity (60,000 psi to 100,000 psi). Because of the energy efficiency advantages of the direct drive pump, the testing focused on the upper end of the direct drive s performance (40,000 to 45,000 psi), which appears to be enough to cut through stubbles and penetrate the soil to seeding depths. Method The test bed at Flow s Advanced Testing Facility consists of a UHP intensifier pump capable of producing a large range of ultra high pressures. The pump connects to a cutting head attached to a programmable variable speed track. The cutting head can be fitted with different nozzles and adjusted to test cutting performance at angles from 40 forward through to 40 reverse rake angle. Testing of performance in different soil types was performed in the vertical position and at a reverse rake angle of 30. Nozzles with orifices of.005,.008,.010 and.013 were used in the performance tests, which were carried out in samples representing clays, sands and soils with high levels of organic matter. The simulated soil samples comprised multiple layers of parchment paper separated by 25 mm of soil. Each sample was built up by placing parchment paper in the bottom of a deep tray and covering it with 25 mm of sample soil. Another layer of parchment paper was then laid on top of the soil, another 25 mm of soil added, and so on until the tray was full. The sample was then weighed for the purpose of calculating a bulk density. Because the soil was handled while preparing the samples some structure was lost and the bulk densities recorded for the samples are likely to have been higher than the bulk density of the same soils in the paddock. 47 Once the tray was full the sample was covered with 15 mm of stubble, with the straw laid perpendicular to the direction of travel. This is equivalent to a stubble load of approximately 6 t/ha, and having the straw across the direction of travel represented the worst possible stubble management scenario. The cutting head was positioned 5 mm above the stubble surface and the performance of each nozzle in each soil type was assessed with the soil sample moist, waterlogged or dry following a period of oven baking. Test results were assessed on the condition of the stubble, soil sample and parchment paper to determine effective cutting depth. Video and still photos were taken of every cut and results recorded into a spreadsheet. Results Reasonable stubble cutting was achieved with all the nozzle and pressure configurations tested including the.005 nozzle operated at 25,000 psi. This configuration did not however adequately open the soils and is limited in application as a residue management tool only. At higher pressures with larger nozzles the UHP water-jet delivered a definitive

5 FIGURE 7: No smearing was evident when cutting clays. The grain of the cut can be clearly seen running top to bottom 30 off centre. cut through stubble residues, even if they were wet, ropey and covering sticky soils. Hair-pinning was not an issue on most soils and for most nozzle/pressure configurations. However, the larger orifice sizes coupled with higher pressures 45,000 psi] did induce some hair-pinning-like symptoms on very soft soils because the high water volume drew stubble into the furrow. This was eliminated when a wooden ruler was clipped to either side of the cutting line to provide stability to the stubble; similar in concept to a modern zero-till stubble ski. Satisfactory soil penetration was achieved with several mid-range nozzle/pressure combinations 40,000 psi 45,000 psi] and the results for these tests are summarised in the Graph 1. Larger nozzles and higher pressures improved penetration but the water rates and power requirements for these apertures and pressures were close to the limits of what is achievable on a mobile agricultural platform. Discussion Preliminary assessments of the practical deployment of UHP water-jet technologies for conservation agriculture is promising, with stubble cutting and soil penetration achieved with water rates and power consumption within the target ranges. In terms of agronomic benefits, the liquid coulter may significantly expand the sowing window in dry and wet conditions. In wet conditions, a liquid coulter is likely to remain operational when conventional seeding systems need to stop due to issues with residue management and sticky soils. In dry conditions, the ultra-low disturbance should minimise exposure of moist soil and subsequent lost of moisture to the atmosphere, allowing crops to be established on more marginal moisture than is possible using currently available technologies. In addition, the retained ground cover and intact soil structure may limit further drying as well as preventing erosion when rain eventually falls. It is possible to adjust UHP nozzle/ pressure configurations to optimise performance in a specific situation and adjust penetration depth to meet the needs of specific crop types. A liquid coulter does not increase draught like a tine or to a lesser extent a disc - because it runs above the soil surface. Given this, it is logical to assume that a liquid coulter would be less affected by variable soil strength and less subject to crabbing due to variability in the paddock. Reducing the draught should lessen the tractor power required and may reduce the need for dual and triple wheel assemblies, thus reducing compaction and poor furrow closure and potentially enhancing the soil improvement benefits from controlled traffic farming (CTF). In addition, having less components dragging through the soil may significantly reduce the engineering strength required in the frame of the seeding bar, which could allow for lighter, more cost-effective designs and materials and possibly greater spans. From an operational perspective, a liquid coulter is likely to simply move less soil than a mechanical device. In theory, moving less soil will require less energy, but power is required to generate the high pressures required for this technology. The horsepower (hp) required for UHP pressure pumps is likely to be at the middle to upper end of the power required for current disc-seeder assembles that range from 3.5 hp to as much as 11 hp per module. 1 Disc-seeders often work better in standing stubbles, but increasing herbicide resistance is driving farm operators to consider weed-seed collection at harvest (using a chaff cart or similar) as part of their weed control program. One potential clash between weed seed collection at harvest and disc seeding is that stubbles need to be cut low to 48

6 furrow depository created by the liquid fertiliser jet stream. The furrow is then closed with a seed-firmer or similar device such as a closing wheel. Ideally the penetration of the liquid coulter and depth control for seed placement by the air-gun would be controlled by a mechanical or electromagnetic soil-density sensor that could be configured for soil type and crop requirements. FIGURE 8: Parchment paper was layered through the soil sample at 25mm intervals as a means of estimating the soil penetration of the various UHP configurations. maximise weed seed capture, and cut stubble ends up on the ground, increasing the chance of hair-pinning and blockage when the next crop is sown. Based on current knowledge, the liquid coulter would be of significant benefit to farmers who want to capture weed seed at harvest and use an ultra low-disturbance seeding system. The concept of goes one step further than the liquid coulter by replacing the trailing disc or discs in a zero-till seeder with an air-gun to shoot seed into the furrow created by the UHP water-jet. This has the potential to further reduce draught and soil disturbance. The vision for the seeder is to use a liquid coulter to slice through surface material and cut a narrow furrow into the soil, simultaneously depositing liquid nutrient along the seeding row. The air-gun is positioned immediately behind the liquid coulter to deliver seeds into the The liquid coulter could operate continuously along the row or be pulsed or synchronised with seed delivery from the air-gun. Pulsing or synchronisation to coincide with seed delivery has the potential to reduce water-rates and power requirements and could be a good fit for crops that have traditionally been sown with precision planters. FIGURE 9: A furrow was still evident on a moist gravely sand when most of the stubble was removed following the UHP treatment. GRAPH 1: The soil opening potential of is proportional to the soil bulk density and the configuration of the UHP water-jet. 49

7 There is virtually no draught associated with the concept and reduced weight may also lessen rolling resistance. The non-contact, nil-draught characteristics associated with seeding may make it possible to change row-spacing on-the-fly ; effectively sowing a grid of seed designed to achieve maximum seedbed utilisation and capitalise on all the moisture and nutrient available. This also has the potential to improve crop uniformity and make better use of crop competition as weed control tool in an integrated weed management (IWM) program. The liquid coulter seeding system is ultralow soil-disturbance and should reduce the recruitment of weeds such as rye grass and wild radish that are stimulated by tillage. Reduced tillage also lessens the spread of problematic perennial weeds around paddocks. Ultra-low disturbance is well suited to the new generation of pre-emergent herbicides but is not such a good fit for older-generation pre-emergence herbicides that require incorporation by sowing (IBS). Carbon, erosion and sustainability In broad terms, current knowledge indicates soil carbon is destroyed by cultivation, stabilises in a no-till system and slowly accumulates under zero-till. Whilst the specifics are debated, there is a clear trend that reducing soil disturbance is better for soil carbon accumulation. It is therefore reasonable to expect that an ultra-low-disturbance, high-stubble system, such as the envisaged system using liquid coulters and air-gun seeders, should further improve the prospects for soil carbon accumulation and in so doing, help growers adapt to seasonal variability and help reduce the load of atmospheric CO 2. Reducing disturbance and increasing the retained stubble load will also further protect agricultural soils from wind and water erosion. Future SANTFA is working closely with Flow to set up and field test a small-scale liquid coulter system in SA. It is also likely that UHP equipment could be used for other on-farm applications such as inter-row weed slashing. Acknowledgements SANTFA members; particularly the SANTFA board for backing innovation. Flow International Corporation, for investment of time, materials and expertise. GRDC, which provided part funding for a preliminary desktop study. References 1. Ashworth, Desbiolles & Tola: Disc seeding in zero-till farming systems, 2010, ISBN For more information: Manufacturers of seeding equipment and interested growers are encouraged to contact greg@santfa.com.au 50