If your notion of what robots are like comes from movies and television, or reports about drone strikes, you might think I'm daft for even suggesting that the application of robotics to agriculture might make it a safer occupation.
Well, granting that some of those fictional portrayals are poignant warnings about particular potential developments in robotics, they aren't representative of the field as a whole. Most robots currently in existence are either the industrial variety, isolated from people because they aren't designed to recognize our presence, or vacuum sweepers – too small and light to do any serious damage to an adult, so, provided you don't allow an infant to crawl on the floor one of them is cleaning, it makes little difference if they can't tell a person from a bookcase.
On the farm, robotic technologies have been finding their way into tractors and other large equipment, but mostly not yet the sorts of technologies that would allow such equipment to identify a human in their path. So, at this stage, to the extent that these machines are left to drive themselves, one might argue that they are actually less safe than equivalent machines under the direct control of human operators. Perhaps, perhaps not. The straight lines, smooth curves, and complete coverage with minimal overlap those automatic guidance systems produce require considerable concentration when performed by a human operator, not leaving much spare attention for the path ahead, and continuous concentration tends to make the mind wander. This is why you'll occasionally see human-operated equipment lose the pattern and go rambling across a field at odd angles, until the driver snaps to and gets it back on track.
A more interesting question than whether robotic technology currently in use results in greater or lesser safety for a bystander is whether there might be a point, in the improvement of such technology, beyond which one is safer standing in the path of a tractor than riding in the cab. Tractors are rather easy to overturn; they sometimes catch fire; they occasionally get hit by lightning; they rock, lurch, buck, vibrate, and produce a mind-numbing noise. Hydraulic fluid spraying out of a crack can cut through flesh. Unguarded PTO shafts can grab loose clothing and pull the wearer to their death. Tractors are built for raw torque and force, and possess a potential for mayhem comparable to a bulldozer, in the event their operators should pass out or otherwise become incapacitated.
Automated guidance systems can sound an audible alert as they are nearing the end of a row, and shut down if the operator doesn't respond, but there's a lot more that can be gained from the utilization of robotic technologies. A whole range of sensors is available, from ordinary digital video to infrared to LIDAR, and a good deal of work has already gone into integrating the information provided by multiple sensors. Even better, these technologies are moving towards being reasonably priced off-the-shelf plug-ins, as with the Kinect. Millimeter radar, when it becomes widely available, will add another, extraordinarily useful option.
Tractors and other such large equipment present a special challenge in that, in operation, they are nearly always surrounded by a cloud of dust. Moreover, the nature of that dust varies depending on the type of rock form which the mineral portion of the soil weathered, or whether the source of the dust is soil disturbance (tillage) or rough handling of dry plant material (harvesting). A technology that effectively penetrates one sort of dust may not work well when confronted with another. Stereo sensors and processing which extracts useful information from noisy data will undoubtedly be important components of any thoroughly adequate solution.
So much for adapting robotic technologies to conventional equipment. In my opinion the greatest gains in safety are to be had from reducing the size and power of the equipment in use, refocusing on detailed operations like planting single seeds, pruning single twigs and leaves, picking pests one by one, and so forth. Such equipment would be inherently safer, since it simply wouldn't possess the capacity for wholesale destruction. There would still be issues, of course. A manipulator that can snip off a branch could do the same to a finger, and almost anything can be dangerous when near the eyes, but the scale of the threat imposed by smaller machines would be at least an order of magnitude lower, based on their capacity for mechanical force alone.
Additionally, these machines would be making fine-grained decisions, instead of simply running until directed to do otherwise. Each detailed operation would first need to pass a test as to whether it were a good use of the machine's time and available energy, then the motions comprising each operation would be crafted for efficiency and minimal disturbance of the surrounding environment, foliage included. If you're sensing and planning paths around branches and leaves, something as solid as a human will appear as inviolable as a brick wall. Layer on detection and avoidance of warm-blooded animals or vertebrates, and the result should be a very reliable safety regime.
There are other hazards around a farm besides the equipment, but robotics can, and sooner or later will, all but eliminate threats from that source.