Displacing Inorganic Nitrogen in Lignocellulosic Feedstock Production Systems

Abstract

Second‐generation feedstocks such as switchgrass (Panicum virgatum L.) have been proposed as sustainable alternatives to fossil fuels, although they still require nonrenewable inputs, notably, inorganic N. Therefore, our objectives were to determine (i) the effects of biochar (1 and 2 Mg ha−1), three intercropped legumes [red clover (Trifolium pratense L.), partridgepea (Chamaecrista fasciculata [Michx.] Greene), and sunn hemp (Crotalaria juncea L.)] vs. inorganic N [67 kg ha−1 and 0 kg ha−1 (control)] on desired feedstock characteristics, yield, and soil characteristics; and (ii) feedstock alterations and tissue‐nutrient levels for postsenescence (November) and overwintering (February) harvests in a two‐factor randomized block design. Overwintering harvests increased P and K remobilization, ethanol yield, fermentable sugars, and in‐field dry‐down (P ≤ 0.05), although yield losses occurred (22%). November harvests had greater tissue N and fermentable substrates, leading to greater soil nutrient removals. Consequently, harvests manipulated the desired feedstock traits, whereas soil amendments had little effect on feedstock characteristics. Therefore, the results suggest that legume intercrops (partridgepea) and biochar may supply analogous N to synthetic fertilizers (P ≤ 0.05), thereby displacing inorganic N without altering feedstock quality. However, for inorganic N alternatives to be competitive on a break‐even cost basis, greater biomass yields need to be obtained under these management practices.