Soil Health Response to Thermal Weed Management in an Organic System.

ABSTRACT

Tillage is the dominant practice for weed control in organic agriculture; however, tillage reduces soil organic carbon and can alter soil properties which lead to soil degradation and erosion. This study evaluated soil health indicators for two alternative thermal weed control practices in row-crop grain production: propane flame and hot water spray. The study also included between-row mowing and a conventional tillage practice of between-row cultivation for comparison. All four weed treatments were integrated into an organic system that included grain crops consisting of corn (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L) in a two year rotation. Other organic practices were utilized for a systematic approach, such as compost application, crimped winter cover crops, and tillage after harvest. The study site was located in central Missouri in Mexico silt loam soil, and indicators analyzed were aggregate stability (AgStab), bulk density (BD), β-glucosidase activity (BG), acid phosphatase activity (AP), phospholipid fatty acid (PLFA) biomass indicators, permanganate oxidizable carbon (POXC), and soil organic matter (SOM). Hot water spray in conjunction with a crimped cover crop had the highest overall soil health indicator values, and with a 15% increase of total PLFA biomass compared to cultivation. Between-row mowing was significant with 70% stable aggregates, and POXC (0.80 g kg soil^-1). Propane flame had decreased soil quality indicator values and was similar to the cultivation treatment values, exceptions are: although not significant, AgStab, AP, fungi community, total PLFA, and SOM. Hot water spray had significant yield results in soybeans (2,098 kg ha^-1) a 22% increase from cultivation, but was not as effective in corn. Propane flame has potential in corn (6,643 kg ha^-1), a 10% decrease compared to conventional cultivation; however, caution must be used for flaming soybeans until improved delivery methods can be employed. Both thermal weed suppressor practices have the potential to sustain soil health when coupled with crimped cover crops and compost.