Last week I browsed some agriculture-related journals at the local university and came across a new method for weeding vegetable plants that I thought was promising. The method is called Propelled Abrasive Grits (PAG) Management and the idea is to blast the area around your vegetable plants with a combination of air pressure and "grits" flying out the end of a nozzle. The nozzle gets pointed at the base of your plant so the propelled grits also hit the stalk of your vegetable plant, however, the idea is that certain types of vegetable plants (e.g,. corn, tomatoes, peppers) are demonstrably hardier than the emergent weeds so can survive the PAG onslaught. Frank Forcella is one of the main and early proponents of this technique and has developed the prototype PAG weeder shown below.

Using a PAG weeder to manage the weed load on your vegetable plants can be used as an organic technique for managing a vegetable crop. If you are propelling corn grits through your nozzle then the technique would be considered organic. If propelling conventional fertilizers, then the technique would not be organic.

The corn grits provide the "abrasive" element required to knock out emerging weed seedlings. The technique has been shown to be better than hand weeding for corn, tomatoes, and peppers so far. There is still alot of research to do into what vegetables it can be used for, whether vegetable specific techniques should be used, what types of grits work best, what the grits do for the soil, using grits that also fertilize, how the costs stack up against other weed control techniques, and so on. That being said, I think we'll see this technique leave the lab fairly quickly to be experimented with by small organic farmers using jerry-rigged grit feeders and hoses attached to air compressors.

The case of using propelled corn-grits to manage a corn crop is quite interesting because it begs the question of how much corn to you need to set aside for the purposes of managing weeds on your corn crop and is this cost competitive with buying herbicides to control your weed load? This comparison assumes the issue is only one of economics and not based on considerations of sustainability that a farmer might give more weight to than just the cost aspect. In a corn-grits to manage corn weeds scenario, you are potentially closing the loop, creating a system where and output of the system is fed back into the system as an input. This is a biodynamic loop that is nice to have when it works. Especially for corn when you consider how huge our dependence is on this particular crop for food and bioenergy. The economic and environmental importance of finding more sustainable ways to manage weed load on corn should not be underestimated.

Also interesting is the question of what these grits might be doing to the soil. PAG researchers are experimenting with propelling organic and non-organic forms of fertilizers onto/into the soil and recording what happens in terms of growth. Corn-grits can be considered an organic fertilizer but there are other types of organic grits that might be better in certain situations (see below). I'll end this blog by reproducing the abstract for a recent research paper by Sam Wortman on the PAG technique that looks interesting. Sam is another leading researcher in this area and this paper provides a sense of where the research on this technique is currently at:

Title: Integrating Weed and Vegetable Crop Management with Multifunctional Air-Propelled Abrasive Grits

Author: Sam E. Wortman. Assistant Professor, Department of Crop Sciences, University of Illinois, Urbana, IL.

Abstract

Abrasive weed control is a novel weed management tactic that has great potential to increase the profitability and sustainability of organic vegetable cropping systems. The objective of this study was to determine the effect of air-propelled organic abrasive grits (e.g., organic fertilizers) on weed seedling emergence and growth and vegetable crop growth. A series of thirteen greenhouse trials were conducted to determine the susceptibility of weeds to abrasive weed control with one of six organic materials including: corn cob grits, corn gluten meal, greensand fertilizer, walnut shell grits, soybean meal, and bone meal fertilizer. In addition, crop injury was quantified to determine the potential utility of each organic material as abrasive grits in tomato and pepper cropping systems. Of the six organic materials, corn gluten meal, greensand fertilizer, walnut shell grits, and soybean meal provided the broadest range of POST weed control. For example, one blast of corn gluten meal and greensand fertilizer reduced Palmer amaranth (one-leaf stage) seedling biomass by 95 and 100% and green foxtail (one-leaf stage) biomass by 94 and 87%, respectively. None of the organic materials suppressed weed seedling emergence when applied to the soil surface, suggesting that residual weed control with abrasive grits is unlikely. Tomato and pepper stems were relatively tolerant of abrasive grit applications, though blasting with select materials did increase stem curvature in tomato and reduced biomass (corn cob grit) and relative growth rate (corn gluten meal and greensand) in pepper. Results suggest that organic fertilizers can be effectively used as abrasive grits in vegetable crops, simultaneously providing weed suppression and supplemental crop nutrition. Field studies are needed to identify cultural practices that will increase the profitability of multifunctional abrasive weed control in organic specialty crops.

Link: http://www.bioone.org/doi/abs/10.1614/WT-D-13-00105.1

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