Organic Weed Management Using Propelled Abrasive Grit Management.

Weeds are the number one problem in organic cropping systems. The use of air-propelled abrasive grits aimed at the crop row may provide weed control and an opportunity to simultaneously add slow-release fertilizers to the crop. Five grits, pelletized turkey litter (Sustane 8-2-4, Sustane 4-2-2), corn cob meal, crushed walnut shells (Agra-Grit), pelletized soybean meal (Phytaboost Plant Food 7-1-2) were added at 0, 1200 or 3600 ?g to 1 g of silty clay loam soil at three application timings (1, 2, or 3 applications, with multiple applications 10 d apart starting at 0 d). The soil was maintained at 30% moisture under laboratory conditions. Sampling occurred at 0, 7, 14, 28, 56, 116, 142, 183 d after the initial grit application (DAA) to examine nitrogen release patterns. Soils were extracted with 1M KCL solution with extracts analyzed for NO3--N, and NH4+-N were quantified using a cadmium reduction method (ASTORIA-PACIFIC micro-segmented flow analyzer). NH4+-N release peaked at 14 d into the incubation with 230 ?g N/g soil from the soybean meal grit after two applications. By the 112 d sampling, the NH4+-N levels were similar for all treatments. The NO3ÑN levels were similar in all treatments to the untreated control until 14 d after application. For the three application treatment, the NO3-N mineralized in the soil treated with soybean meal and Sustane 8-2-4 after 14 d was described by the Mitscherlich Equation and by 183 DAA 556 ug NO3 was present in soil treated with soybean meal (r2 = 0.99 ) whereas with a total NO3 of 377 ug NO3 was quantified in the Sustane 8-2-4 (r2 = 0.74 ) treatment. Other grits and application treatments had a maximum of 170 ug of NO3 mineralized. These data indicate that, if chosen carefully and applied often, grits may serve a multiple purpose for weed control and help stimulate soil mineralization or be the supply NO3 to the crop.