Abrasive grit application for integrated weed and nitrogen management in organic vegetable cropping systems

Abrasive weed control, or weed blasting, uses sand-blasting technology to propel abrasive grits at weeds, physically destroying their emergent structures. This approach has been successfully tested for use in agronomic crops, though research is needed for horticultural cropping systems. This project aimed to determine the efficacy of weed blasting in vegetable crops and to determine if weed blasting can be combined with mulching to increase the overall effectiveness of each strategy. Five abrasive grit treatments (walnut shell grits, soybean meal fertilizer, Suståne© composted turkey litter fertilizer, a weedy control, and a weed-free control) and four supplemental weed management treatments (straw mulch, biodegradable plastic film, polyethylene plastic film, and a bare soil control) were replicated four times in an organic pepper cropping system near Urbana, IL in 2015 and 2016. Soybean meal, turkey litter, and walnut shell grits, used in conjunction with plastic or bioplastic mulch, all decreased total dry biomass of weeds within the crop row by approximately 80% relative to the weedy control. Total nitrogen availability, measured via ion-resin stakes (PRS probes), decreased by 58% and 55% in soybean meal + bare soil and turkey litter + bare soil plots, respectively, in comparison to the weed free control. There were no significant differences between soybean meal, turkey litter, and the weed free control in plastic, bioplastic, and straw plots. There was no significant decrease in yield compared to the weed free control for turkey litter or walnut shell treatments when combined with either bioplastic or polyethylene mulch or for soybean meal + polyethylene plots. Walnut shell + bioplastic had a significant increase in yield compared to the weedy control. There was no significant difference in fruit quality, measured via BRIX, between grit or mulch treatments, and there was no significant difference of percent of diseased tissue between grit treatments. These results suggest that AWM can function as an alternative weed control strategy in organic farming, potentially improving the effectiveness of existing weed management techniques (e.g., plastic mulch). Abrasive weed management (AWM) also has the possibility to serve as a fertilizer application if organic fertilizers are used as abrasive grits. A separate greenhouse experiment aimed to determine the nitrogen mineralization and plant uptake of different organic fertilizers used as abrasive grits. Five abrasive grit treatments (walnut shell grits, soybean meal fertilizer, Suståne© composted turkey litter fertilizer, a weedy control, and a weed-free control), two application rates (400 g/ plot and 800 g/plot), and two tillage treatments (incorporation of top 5cm of soil and no incorporation) were replicated five times in a greenhouse study using Red Russian kale at University of Illinois at Urbana-Champaign's Plant Care Facility in Urbana, IL in 2016 and 2017. The higher N concentrations of turkey litter and soybean meal contributed to higher N mineralization overall in those treatments. The high rate (800 g/plot) of turkey litter, in particular, outperformed the other treatments in tissue N and yield, which was likely due to the higher N mineralization rate. Incorporation of soil amendments significantly affected soil ammonium concentrations and dry yield weight, suggesting that tillage following grit application could contribute to greater soil availability of N and greater plant uptake. Walnut shell, an effective abrasive grit for weed control, was not as effective as a fertilizer in comparison to soybean meal and composted turkey litter. These results suggest that while soybean meal and turkey litter can function as fertilizer amendments when used for abrasive grit application, walnut shell may not provide the same dual benefit