Weed Management Using GPS Guidance

Nicholas Meyer BROMET (2006). Weed Management Using GPS Guidance PhD Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

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Author Nicholas Meyer BROMET
Thesis Title Weed Management Using GPS Guidance
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2006-08
Thesis type PhD Thesis
Supervisor Adkins, Stephen W.
George, Douglas
Gupta, Madan L.
Tullberg, Jeffrey N.
Subjects 300000 Agricultural, Veterinary and Environmental Sciences
Formatted abstract Weeds are a serious threat to cropping systems both as agents of direct yield loss and indirectly in terms of control strategy expense and detrimental effects, ranging from the creation of herbicide resistant populations to environmental degradation (erosion, contamination). Current public perceptions of danger in herbicide dominated farming systems has led to Government restrictions on herbicide use (especially in the European Union [EU]) and investigations of alternative management strategies.
This thesis reports an investigation of precision-guided mechanical weed management, as an alternative to herbicide treatment. The mechanical option was selected because it provides rapid control, is well suited for in-crop use, and appears more attractive following the development of "autosteer" precision in-field equipment guidance systems using the Global Positioning System (GPS). The investigation was also timely because GPS guidance systems have become commercially accepted over the past decade as their reliability and accuracy have improved, and price decreased.
The general objective of the work was to evaluate engineering and agronomic factors affecting the weed management effectiveness of a precision (GPS) automatic steering system on a tractor operating planting and mechanical weed control equipment in the production of wide-row and narrow row crops on a black cracking clay soil in South-East Queensland, Australia. Three experiments were designed to:
. • evaluate the in-field steering accuracy of a tractor and implement equipped with an ‘RTK DGPS’ automatic steering system (i.e. ones dependent on Real Time Kinematic Differential corrections to Global Positioning System -based navigation. (Chapter 3);
. • evaluate the effect of mechanical weed control variables (varying speed, tool variables and tool position) on weed control and crop damage (Chapter 5); and
. • compare the energy requirements for weed management by overall herbicide application with those of banded herbicide or banded mechanical weed control (Chapter 6).

An RTK DGPS automatic steering system (Beeline® Technologies B2K®) was used to establish a controlled traffic system on two experimental sites. These sites had string-lines to provide a linear datum for assessment of system steering accuracy using a video camera when measuring deviation of a tractor or implement. A separate video camera was used to collect data on weed density; accuracy was checked by hand counting. Yield and/or biomass of crop and weeds was measured at the completion of each trial.
The automatic steering system steering performed better than an operator guided system, maintaining the tractor within ± 20 mm deviation > 96 % of the time when operating at 6 km h-1. Deviation between runs was smaller if the same runs were performed in the same direction, and implement deviations were smaller with three-point-linkage-mounted than trailed implements.
A video weed density assessment system was developed (Chapter 4) to provide efficient documentation of inter-row weed numbers that was both reliable and unambiguous at lower weed densities. Weed densities exceeding 80 weeds m-2 still required time-consuming manual counting when many small weeds were obscured by other weeds.
Adjustment of cultivator speed, depth, frequency and distance from the crop row demonstrated that mechanical weed management could achieve 100 % weed kill at 4 km h-1 with some (15 %) injury to wheat (Triticum aestivum L.) even at narrow (20 cm) row spacing under ideal conditions of low surface soil moisture. Typically, mean weed kill for all treatment dates was in the range 80 – 84 % for mechanical weed management.
The use of RTK DGPS steering allowed shielded spraying of glyphosate close to the crop row and 92 % weed kill was maintained when inter-row mechanical control was combined with banded herbicide on either side of the row. The work showed this combination banded treatment could be achieved with less herbicide and less energy than broadcast herbicide application.
The use of RTK DGPS steered inter-row mechanical weed management produced weed kills comparable to glyphosate with mechanical weed management requiring 106 MJ ha-1 less energy input at a depth of 2 to 3 cm. Mechanical weed management also appeared to increase crop yield. Future research might combine mechanical weed management with other technology such as banded fertilisers to reduce the number of operations and energy required.
The ability to carry out mechanical weed control treatments close to crop rows using automatic steering may prove particularly beneficial to organic producers, by reducing the labour requirement for hand weeding. The same technology might also be beneficial in conventional production systems, where mechanical weed control used occasionally in place of herbicide control might extend the life of herbicides by slowing the development of resistant weed populations

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