Organic Weed Control Grits Affect Uptake of Nitrogen in Corn and Weeds.

The use of air-propelled abrasive grits aimed at the crop row may provide weed control and an opportunity to simultaneously add slow-release nitrogen to the crop, the two biggest challenges for organic corn corps. A randomized complete block split plot field experiment was conducted in 2016 at South Dakota State University to assess the corn yield, weed control and nitrogen uptake of corn and weeds depending on grit treatment. Six main plots were established based on in-row weed control including season long weed checks and four grits: crushed turkey litter (Sustane 8-2-4, Sustane 4-6-4), crushed walnut shells (Agra Grit), and pelletized soybean meal (Phytaboost Plant Food 7-1-2). Subplot experimental treatments were the inter-row treatments of cultivation or flaming, and the season long weedy and weed free checks. 500 kg ha-1 of grit was applied at the V1 and V5 corn growth stages across main plots, while cultivation occurred after the V1 application and then either the cultivation of flaming occurred after the V5 application. In-row and inter-row weed densities were recorded before the first application and 7 d after the second application. Above ground corn and weed biomass, corn stem diameter, relative SPAD chlorophyll meter value, and soil samples down to 15 cm were sampled and recorded at the V12 corn growth stage. Corn was hand harvested at physiological maturity. Inter-row weeds were controlled in all treatments except for season long weedy check, and row weed densities were reduced among all grit treatments after two applications of grit. Soil Nitrogen, corn relative SPAD chlorophyll meter value and grain yield were 220, 10 and 26% greater in the Sustane 8-2-4 treatment compared to all other treatments. Corn grain nitrogen content was 63% in the Sustane 8-2-4 treatment but was not different among in-row weed biomass. The Sustane 8-2-4 grit is able to provide supplement nitrogen and increase corn grain yield while not supplying excess nitrogen to in-row weeds.