**3. Conclusion**

to the weed-free check ranged from 5% to nearly 100%. Maize yields in the SLW, I/B, and BR treatments were almost all lower than the weed-free check. In the SLW vs. weed-free treatments, the percent yield loss was positively correlated with total weed biomass (in-row plus between-row weeds) when examined across all studies (r = 0.93; p = 0.008) (**Figure 1**). Because the I/B and BR treatments had few between row weeds, the yield losses in these treatments were positively correlated with in row weed biomass (r = 0.71; p = 0.001). The slopes of each regression line were similar (m ~ 0.01), which indicated that percent yield loss was about 1%

**Figure 1.** Maize yield loss (% of weed-free control) by total weed biomass at all locations and treatments. Triangles represent the season-long weedy treatments and the regression is shown by the solid black line (r = 0.95; p < 0.01). Circles represent yield loss based on weed biomass compared with the weed-free control plots of the I/B and BR treatments with

Although weeds were present in the row after I/B treatments, maize yields across years and locations were greater than the SLW, except in one case. On average, there was a 30% yield increase in grit application treatments compared within a year and location to its companion SLW treatment. Sustane treatments averaged 44% greater yield than SLW, whereas Agra Grit averaged 14% greater yield (p = 0.1). In addition, maize grain had 16% higher N content than grain from either the SLW or Agra Grit treatments (p<0.003). Sustane appeared to provide some nitrogen to the crop [74], as relative greenness, measured at R4 of maize, was similar to the weed-free check, and averaged 44% (p < 0.01) higher than greenness of plants in the SLW treatment. Agra Grit has a high C/N ratio, and actually slowed soil nitrogen mineralization in laboratory studies [74], although greenness values at R4 were about 30% greater than SLW plants. The BR treatment and I/B treatments averaged over all grits, however, had similar

maize yield increases (23% vs. 30%, respectively; p = 0.63) compared to the SLW.

Soybean yield in weed-free treatments ranged from 1626 (Aurora, 2015) to 4856 (Aurora, 2016) kg ha−1. Yield losses compared to weed-free treatments within location and year ranged from 2 to 43%. However, unlike maize yield losses, which were linearly related to total weed

for each 100 kg ha−1 of weed biomass present at R4.

the regression shown in the dotted line (r = 0.71; p < 0.01).

58 Physical Methods for Stimulation of Plant and Mushroom Development

Weed management using grits was more effect on small broadleaf weeds than larger broadleaf or grass weeds. While the larger weeds and grasses were defoliated with the grit treatment, these regrew and by late season, biomass was similar in-row as the season-long weedy treatment. The in-row treatment, followed by cultivation between rows, tended to increase maize yield compared to no management, and grit with a higher N content tended to increase maize yield and nitrogen content more than a low N grit. Weed control in soybean was more challenging and, due to the size of the weeds even at V1 (one expanded trifoliate leaf), did not control weeds well, and by the second application (V5), weeds were likely too large for meaningful injury. Soybean yield loss was more related to in-row weed biomass than between row weed biomass. Thus, more research is needed to better control in-row weeds in soybean to limit yield loss.
