Biomass yield and soil microbial response to management of perennial intermediate wheatgrass (Thinopyrum intermedium) as grain crop and carbon sink

Abstract

IWG intermediate wheatgrass (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey; IWG) is a perennial grain crop with an extensive root system that could prevent erosion and nutrient leaching, build soil fertility, and potentially sequester atmospheric carbon. Two field experiments were established in southeastern Minnesota, USA to 1) address management strategies for preventing IWG grain yield decline, 2) quantify plant biomass production of IWG relative to other conventional field crops, 3) determine how this perennial grass may alter soil microbial activity and composition to the benefit of soil organic carbon (SOC) accumulation, and 4) investigate the potential for carbon sequestration. Inter-row cultivation using rotary-zone tillage (RZT) as well as herbicide, burning, and mowing at different times were employed for two years, but none effectively prevented grain yield decline. However, the application of herbicide in spring and fall cultivation had positive impacts on grain, straw, and forage yield (relative to other management treatments). IWG can produce significantly more root biomass than annual grain crops, and even more than alfalfa (Medicago sativa). These large root systems, left undisturbed, were likely responsible for an increase in soil fungal biomarkers and overall microbial biomass after three years of growth. Soil respiration rates and microbial biomass-carbon were greater under IWG in the spring and fall seasons when soybean and wheat had either not emerged yet or were already senesced, providing evidence that perennial grasses may alter soil nutrient cycling by expanding and prolonging soil microbial activity. Particularly, changes in nutrient cycling that increase labile carbon pool sizes and promote SOC formation may, in addition to storage in root biomass, support carbon sequestration in agricultural soils.