A new approach to spraying fertilizer and pesticides onto crops may help farmers reduce the amount of spray needed while also increasing the amount of spray that sticks to its target. The approach reduces runoff - a significant cause of pollution - and saves on costs of expensive chemicals. The technique: placing a fine mesh in between the spray and the intended target.
When spraying fertilizers or pesticides onto crops, the size of the droplets is important. Bigger drops drift less in the wind, allowing them to strike their intended targets more accurately, but smaller droplets are more likely to stick when they land instead of bouncing off. They’re also less likely to damage or weaken certain plants.
The new tactic, developed by a team of MIT researchers, is to make the initial spray consist of larger drops, which are much less affected by breezes and more likely to reach their targets, but to use a mesh screen between the spray and the crops to create much finer droplets just before they reach the surface. The researchers primarily used a commonly available and inexpensive fine stainless steel mesh.
Many kinds of mesh materials would work, the researchers say - what matters is the size of the openings in the mesh and the material’s thickness.
The researchers propose that, after deploying the mesh over the crop, either directly supported by the plant stalks or supported on a framework, a farmer could simply use a conventional sprayer that produces larger drops, which would stay on course even in breezy conditions. Then, as the drops reach the plants, they would be broken up by the mesh into fine droplets, each about a tenth of a millimeter across, which would greatly increase their chances of sticking.
Typically, less that 5% of sprayed liquids actually stick to their intended targets; of the 95 % or more that gets wasted, about half is lost to drift and never even gets there, and the other half bounces away.
The technique also has industrial applications. Atomizers - devices that can spray liquids in the form of droplets so small that they remain suspended in air rather than settling out - are crucial parts of many industrial processes, including painting and coating, spraying fuel into engines or water into cooling towers, and printing with fine droplets of ink.
By using mesh below the spray heads in cooling towers, for example, finer droplets are created; finer droplets are three times more effective at cooling than larger drops, according to the researchers. More effective use of resources lead to cost savings.
