|ASHWORTH, AMANDA - Orise Fellow|
|WEISS, STUART - University Of Virgin Islands, St Croix|
|KEYSER, PATRICK - University Of Tennessee|
|ALLEN, FRED - University Of Tennessee|
|TYLER, DONALD - University Of Tennessee|
|TAYLOR, ADAM - University Of Tennessee|
|BEAMER, KENNETH - University Of Virgin Islands, St Croix|
|WEST, CHARLES - Texas Tech University|
Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2016
Publication Date: 10/10/2016
Citation: Ashworth, A.J., Weiss, S.A., Keyser, P.D., Allen, F.L., Tyler, D.D., Taylor, A., Beamer, K.P., West, C.P., Pote, D.H. 2016. Switchgrass composition and yield response to alternative soil amendments under intensified heat and drought conditions. Agriculture, Ecosystems and Environment. 233:415-424.
Interpretive Summary: Climate change forecasts indicate the southeastern USA could soon be experiencing more tropical or subtropical growing conditions that may include intensified drought and more intense rainfall events, so farmers need cropping systems that can still maintain production in a tropical environment. Switchgrass is a native North American grass that can produce high yields with moderate nitrogen inputs, and it has been successfully intercropped in temperate climates with legume species that can meet the switchgrass nitrogen requirements by depositing atmospheric nitrogen into the soil. Therefore, a research team tested the adaptability of switchgrass using various nitrogen sources (biochar, legume species, and inorganic fertilizer) by comparing yield of switchgrass planted at a tropical site to yield of switchgrass planted at a temperate site and to yield of guinea grass (a near relative of switchgrass) planted at the tropical site. The researchers found that switchgrass was sufficiently adaptable to be competitive and productive in the tropics. This study is of interest to scientists, extension personnel, agricultural producers, and the biomass industry because it indicates that switchgrass production could be continued in the southeastern USA even under tropical growing conditions forecast by climate change models.
Technical Abstract: Switchgrass (Panicum virgatum L.) and guinea grass (Panicum maximum Jacq.) have been proposed as sustainable alternatives to fossil fuels in temperate and tropical environments, respectively; although still requiring non-renewable inputs, notably, fertilizer-nitrogen (N). Furthermore, climate change forecasts suggest southeastern USA may emulate more tropical or subtropical growing conditions resulting in altered N dynamics and plant physiology. Objectives of this study were to determine: i) effects of biochar (1 and 2 Mg ha-1), two intercropped legumes [sunn hemp (Crotalaria juncea L.) and pigeon pea (Cajanus cajan L.) intercrops] versus inorganic N [67 kg ha-1and 0 kg ha-1] on feedstock characteristics, yield, and soil characteristics; ii) feedstock characteristics over three harvest dates; and, iii) switchgrass adaptation to more extreme (tropical) growing conditions. For both species, yield and feedstock composition were influenced by harvest timing (P<0.05), whereas soil amendments influenced these components to a lesser extent (P>0.05). In general, initial harvests had greater digestible 5- and 6-carbon sugars and N, P, and K tissue levels, whereas in subsequent harvests, higher acid- and neutral-detergent fiber levels were observed, suggesting lesser potential fermentability. Desired feedstock characteristics can therefore be manipulated by harvest timing, whereas legume intercropping and soil amendments impact tissue composition to a lesser extent. Yield results suggest pigeon pea and sunn hemp intercrops, and biochar (1 Mg ha-1) may result in equivalent yields as N fertilizer per harvest (P<0.05). However, higher rates of biochar in the tropics adversely impacted yields, perhaps due to N immobilization by biochar. Switchgrass adaptation and competitiveness was moderate (5-30% weed cover) under the intensified climate. Growth can therefore be maintained under a stochastic climate due to its C4 pathway and competitive growth on marginal soils.