Return of aboveground nutrients by switchgrass into the surrounding soil during senescence

Abstract

Background: Switchgrass (Panicum virgatum L.) is a crop that holds promise for cellulosic biofuel production. To minimize fertilizer costs, farmers prefer to reduce crop removal of nutrients from the soil when biomass is harvested. The objective of this study was to monitor, from May 2008–November 2009 at Portageville (MO, USA), the nutrient concentration in the soil, switchgrass roots and rhizomes in a 20-year-old switchgrass field. Soil and tissue samples were collected to determine the sink of the nutrients lost in the aboveground biomass during senescence of the plant. Results: Nutrient concentration in switchgrass biomass decreased from July to the end of the season. In general, as switchgrass senesced, the nutrient concentration of the roots did not significantly change, whereas that of the rhizomes increased. Soil test results varied depending on where samples were collected relative to switchgrass root clumps. Generally, soil samples collected from the clump showed the highest evidence of nutrients returning to the soil from the aboveground biomass; however, some of this could be due to root breakage during sampling. Soil ammonium acetate extracted K in the clumps and averaged 218 kg K kg^-1 soil in October, compared with 302 mg K kg^-1 soil in November. Soil NO₃-N content in the clumps in November was 5.5 mg kg^-1 soil, compared with 1.5 mg kg^-1 soil in October. Conclusion: This study provided evidence of nutrient recycling in the field by switchgrass plants and supports the concept of a reverse flow of nutrients to soil at the end of the season. The harvest of switchgrass late in November will help minimize the nutrient removal and maximize biomass yield.

Financial & competing interests disclosure

R Holou is the International Chair of the Sweet Sorghum Ethanol Association and the Chair of the International Service in Agronomy Award Committee. He holds a PhD in Plant, Insect and Microbial Sciences from the University of Missouri (MO, USA) and he is a research scientist at Monsanto. G Stevens is a Faculty at the University of Missouri, and V Kindomihou is a lecturer at the University of Abomey-Calavi (Benin). The Missouri Life Science Research Board and the Missouri Fertilizer and Ag Lime Board funded this research. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.