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ARS Home » Plains Area » Sidney, Montana » Northern Plains Agricultural Research Laboratory » Agricultural Systems Research » Research » Publications at this Location » Publication #337596
Title: Root biomass, root/shoot ratio, and soil water content under perennial grasses with different nitrogen rates

Author
item Sainju, Upendra
item Allen, Brett
item LENSSEN, ANDREW - Iowa State University
item GHIMIRE, RAJAN - New Mexico State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2017
Publication Date: 6/15/2017
Citation: Sainju, U.M., Allen, B.L., Lenssen, A.W., Ghimire, R.P. 2017. Root biomass, root/shoot ratio, and soil water content under perennial grasses with different nitrogen rates. Field Crops Research. 210:183-191. doi:10.1016/j.fcr.2017.05.029.

Interpretive Summary: Perennial grasses, such as ligno-cellulosic feedstock materials, have been shown to be promising crops for bioenergy production. Perennial grasses also produce greater root biomass than cereal crops and provide more carbon inputs for C sequestration. Roots also help in soil water and nutrient uptake and provide support for aboveground biomass. Information on root biomass and root/shoot ratio of bioenergy perennial grasses to estimate carbon inputs from roots is lacking. We examined root biomass, root/shoot ratios, and soil water contents to a depth of 120 cm after grass harvest in the fall for three bioenergy perennial grasses applied with four nitrogen fertilization rates from 2011 to 2013 in the northern Great Plains, USA. Perennial grasses were intermediate wheatgrass, smooth bromegrass, and switchgrass, and N fertilization rates were 0, 28, 56, and 84 kg N ha-1. Root biomass declined with depth and about 60% of the total biomass was located at 0-15 cm where intermediate wheatgrass and switchgrass had higher biomass than smooth bromegrass in 2011. Shoot biomass was greater in intermediate wheatgrass in 2011 and in switchgrass in 2013 than other grasses and increased with increased N rates. Root/shoot ratio was greater in switchgrass than other grasses at 0-120 cm in 2011, but was greater in smooth bromegrass than switchgrass at 0-60, 0-90, and 0-120 cm in 2012 and 2013. Mean root/shoot ratios across N rates and years were not different among grasses and varied from 1.54 at 0-15 cm to 2.54 at 0-120 cm, which were substantially greater than 0.15 and 0.33, respectively, observed for spring wheat. Soil water content increased with depth and was greater under switchgrass than other grasses at 0-120 cm in 2011 and 2013. Water content varied with N rate at various soil depths and years. Root biomass was negatively correlated with soil water content (r = -0.56, P = 0.03, n = 15). Because of greater root and shoot biomass, intermediate wheatgrass reduced soil water content due to increased water uptake and will likely provide more carbon inputs for soil carbon sequestration from belowground biomass compared to smooth bromegrass and spring wheat. As results from successive years showed increased shoot biomass yield with switchgrass than other grasses, more than three years of experiment, however, may be needed to properly evaluate the effects of grass species and nitrogen rates on perennial grass root biomass, root/shoot ratio, and soil water content.

Technical Abstract: Roots help in soil water and nutrient uptake and provide C input for soil C sequestration, but information on root biomass of bioenergy perennial grasses is lacking. Root/shoot ratios are used to estimate crop root biomass and C inputs, but the values for perennial grasses are also scanty. We examined root biomass, root/shoot ratios, and soil water contents to a depth of 120 cm after grass harvest in the fall for three bioenergy perennial grasses applied with four N fertilization rates from 2011 to 2013 in the northern Great Plains, USA. Perennial grasses were intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth and Dewey), smooth bromegrass (Bromus inermis L.), and switchgrass (Panicum virgatum L.), and N fertilization rates were 0, 28, 56, and 84 kg N ha-1. Root biomass declined with depth and about 60% of the total biomass was located at 0-15 cm where intermediate wheatgrass and switchgrass had higher biomass than smooth bromegrass in 2011. Shoot biomass was greater in intermediate wheatgrass in 2011 and in switchgrass in 2013 than other grasses and increased with increased N rates. Root/shoot ratio was greater in switchgrass than other grasses at 0-120 cm in 2011, but was greater in smooth bromegrass than switchgrass at 0-60, 0-90, and 0-120 cm in 2012 and 2013. Mean root/shoot ratios across N rates and years were not different among grasses and varied from 1.54 at 0-15 cm to 2.54 at 0-120 cm, which were substantially greater than 0.15 and 0.33, respectively, observed for spring wheat (Triticum aestivum L.). Soil water content increased with depth and was greater under switchgrass than other grasses at 0-120 cm in 2011 and 2013. Water content varied with N rate at various soil depths and years. Root biomass was negatively correlated with soil water content (r = -0.56, P = 0.03, n = 15). Because of greater root and shoot biomass, intermediate wheatgrass reduced soil water content due to increased water uptake and will likely provide more C inputs for soil C sequestration from belowground biomass compared to smooth bromegrass and spring wheat.