Legume Addition to Perennial Warm‐Season Grass Swards Increases Harvested Biomass

Abstract

The adoption of perennial warm‐season grass crops for bioenergy production faces significant social, economic, and agronomic challenges. The inclusion of legumes in warm‐season grass swards may increase productivity, reduce weed pressure and the need for fertilizer inputs, and allow farmers greater management flexibility. The objectives of this study were (i) to evaluate whether the overseeding of red clover (Trifolium pratense L.) in warm‐season grass swards can improve biomass yields and reduce weed cover, (ii) to determine if biomass yield gains arise from increased N availability or the biomass production of the legume crop, and (iii) to determine whether switchgrass (Panicum virgatum L.) or big bluestem (Andropogon gerardii Vitman.) accessions respond differently to red clover overseeding. Once established, red clover addition increased biomass yields in unfertilized swards to levels equivalent to fertilization with 112 kg N ha−1 and reduced weed cover by 7%. The yield gains with clover addition were consistent irrespective of the warm‐season grass accession tested and were attributable to the production of biomass by the clover. The incorporation of legumes in mixtures with perennial warm‐season grasses can and should play a part in improving the viability of these cropping systems. Future studies should consider alternative planting, harvesting, and weed control in a long‐term experimental framework to refine management of legume and warm‐season grass mixtures.

Overseeding Eastern Gamagrass with Cool‐Season Annual Grasses or Grass–Legume Mixtures

“…Clover percentage was 20% in cool‐season mixtures containing red clover. Other studies have reported that overseeding red clover into switchgrass decreased weed pressure in the stand in early summer due to relative ground cover (George et al, 1995; Jakubowski et al, 2017). Visual appraisal of canopy cover by desirable forage species was 42 to 62% during the spring–summer transition (Table 4), with the majority of this being eastern gamagrass breaking dormancy during this time period.…”

“…However, this effect was not observed at subsequent grazing events. Other NWSG studies have reported that overseeding red clover into switchgrass improved seasonal distribution of forage growth and decreased weed pressure in the stand in early summer due to relative ground cover (George et al, 1995; Jakubowski et al, 2017).…”

“…The study reported no differences in seasonal Johnsongrass herbage production with or without clover, but clover inclusion increased CP concentration compared with Johnsongrass alone. Jakubowski et al (2017) noted that overseeding red clover into either switchgrass ( Panicum virgatum L.) or big bluestem ( Andropogon gerardii Vitman) increased biomass yields in unfertilized swards to levels equivalent to fertilization with 112 kg N ha −1 . The alkaline soil conditions of the Alabama Black Belt prairie and shrink–swell characteristics of this soil type may have contributed to limited forage production potential (Mitchell et al, 2006).…”

“…Red clover canopy cover was greatest in late spring (P < 0.0001). Jakubowski et al (2017) reported that red clover canopy cover approached 75% in the early summer months, whereas cover was ?25% in the present study (Table 4).…”

Climate Benefits of Increasing Plant Diversity in Perennial Bioenergy Crops

“…Legume addition can substantially increase both the yield of the target grasses and total yield by a factor of 2-3 43,60 or have a positive effect equivalent to mineral N fertilization at 33-150 kg per ha. [61][62][63][64] However, whether legumes can lead to overyielding depends on their complementarity to the target grasses, 65 success of establishment and persistence, 66 and environmental factors such as climate. 67 For example, Ashworth et al 62 tested a variety of legume species and found many could complement switchgrass except for arrowleaf clover due to establishment difficulty.…”