Organic fertilizer abrasive grits increase soil available nitrogen, plant height, and biomass

Abstract

In organic cropping systems, air-propelled abrasive grits can be used to control in-row weeds. If the applied abrasive grit is an approved organic fertilizer, these applications may serve a dual purpose of weed control and crop fertility. Laboratory soil incubations examined the N mineralization rates of several grit types with differing C/N ratios (Agra Grit [crushed walnut shells, 170:1], corncob grit [91:1], Sustane [composted turkey litter, 5.0:1], Phytaboost Plant Food [crushed and pelletized soybean meal, 5.0:1]). A greenhouse study determined plant wheat (Triticum aestivum L.), kale (Brassica napus pabluaria DC), and velvetleaf (Abutilon theophrasti Medik.) growth response in soils amended with these grits. The N mineralization rates varied by grit type, soil, and application rate. The N mineralized from Phytaboost within 56 d was similar among the amounts of N a whereas the amount of N mineralized from Sustane was inversely related to the amount of N applied. Agra Grit and corncob grit immobilized soil N due to their high C/N ratios. In soils amended with Sustane, plant height and biomass were 15-43% and 34-83% greater than for plants grown in soils with Agra Grit, corncob grit, and the nontreated soil. Applications of organic fertilizer as air-propelled grit may improve crop growth; however, if weed control is imperfect, these grits may increase weed growth. Grits with high C/N ratios may immobilize soil available N but not affect plant growth. Abbreviations: DAP, days after planting. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Abrasive Weeding as a Vehicle for Precision Fertilizer Management in Organic Vegetable Production

“…An orthogonal contrast between the weedy control and both abrasive fertilizer grits at the high application rate showed that weed biomass was reduced by 89% in plots with no compost (P < 0.0001) and by 75% in plots with compost (P < 0.0001). This result is also consistent with that of Carlson et al (2020) because any weed escaping after the abrasive grit applications would benefit from increased soil fertility realized in compost-amended plots. Moreover, overfertilization in organic systems has been shown to benefit weeds more than crops (Little et al, 2015); the combination of compost and high abrasive grit application rates in this study may have resulted in an overabundance of plant available nutrients.…”

“…Taken together, these two studies suggest that the capacity for abrasive weeding to effectively deliver in-season crop nutrition is contingent on the weed efficacy of the technology. This is consistent with the findings of Carlson et al (2020), who reported that organic fertilizer abrasive grits indiscriminately increased the growth of crops and weeds. Because weeds were more effectively controlled during this study than during the study by Braun et al (2019), this is the first study to demonstrate under field conditions that abrasive weeding technology can be used as a vehicle for delivering variable and potentially more precise doses of plant available N to crops during the growing season.…”

“…This may be due, in part, to the reduced weed biomass for broccoli relative to pepper given the differences in the growing season, crop morphology, and crop-weed competition for light (Brainard et al, 2005). Nonetheless, the results are consistent with those of Carlson et al (2020), who demonstrated organic fertilizers as abrasive grits can increase the crop growth rate and biomass if weed competition is reduced. However, the magnitude of this benefit may be crop-specific and influenced by background soil fertility (e.g., compost amendment).…”

“…Any weeds not controlled by the abrasive grit treatment would have competed for plant available N mineralized from the grits, which explained the increased biomass following the high rate of grit applications with S8 for pepper. Consistent with this result, Carlson et al (2020) found that velvetleaf (Abutilon theophrasti) biomass increased in response to the S8 fertilizer delivered at rates typical for abrasive weeding.…”

“…shell grit (Wortman, 2014). Abrasive weeding with organic fertilizers as abrasive grits can increase crop growth, yield, and profitability due to the increased plant available N following mineralization of organic N from the abrasive grits (Braun et al, 2019;Carlson et al, 2020). In-season delivery of N fertilizer via abrasive grits could shift the balance of crop-weed competition by improving the synchrony of soil N availability and peak crop demand (Liebman and Davis, 2000;Wortman et al, 2011).…”