Yield and Botanical Composition of Legume‐Interseeded vs. Nitrogen‐fertilized Switchgrass

Abstract

Switchgrass (Panicum virgatum L.) has a relatively high N requirement for high yields of quality forage. It is not clear what role legumes can play in supplying this N and in improving herbage yield when grown in association with switchgrass. To evaluate cool‐season legume renovation vs. N fertilization of established switchgrass, 10 forage legumes and a legume mixture were compared with 0, 60, 120, and 240 kg N ha−1. Forage yield and botanical composition of basal (<20 cm) and upper (>20 cm) canopy were compared at Ames, IA, on a Webster silty clay loam (mesic Typic Haplaquoll). Legumes were no‐till interseeded in early April; N was applied before mid‐May. Legume renovation did not affect June yield during the establishment year (Yl), but produced 9% greater yields than 0‐N grass in July. N fertilization increased uppercanopy grass yield 2.4‐fold compared with 0 N and legume renovation during Yl. During the second year (Y2) of 1991 seedings, all legume treatments except crownvetch (Coronilla varia L.) produced more totalseason upper‐canopy yield than grass fertilized with 240 kg N. For 1992 seedings, birdsfoot trefoil (Lotus corniculatus L.), Mammoth red clover (Trifolium pratense L.), and trefoil‐red clover mixture had Y2 yields that equaled or exceeded yield for 240 kg N. Mean legume composition of Y2 upper canopy for June, July, and August was 84, 70, and 51%, respectively, in 1991 seedings and 53, 28, and 27% in weather‐damaged stands of 1992 seedings. Y2 yields for interseeded legumes provided significant improvement over 120 or 240 kg ha−1 N, so cool‐season legumes can substitute for N fertilization after the seeding year. Adequate defoliation in early June is important to minimize legume competition to established switchgrass. Livestock producers should renovate only a portion of switchgrass pastures in a single year, because of a shortfall in forage supply during legume establishment compared with that of N‐fertilized grass.

Comparison of Conventional and Minimal Tillage for Low-Input Pasture Improvement

“…7). Although improved fertilizer and grazing management is not an invariable alternative to reseeding (35), for many farmers increased fertilizer use (8,13,44,46,78) might be a more beneficial, and less risky, approach to increasing pasture productivity than reseeding or overseeding.…”

Overseeding Unimproved Warm-Season Pasture with Cool- and Warm-Season Legumes to Enhance Forage Productivity

“…Delay in harvest of cool-season legume in order to encourage seed deposition is likely to increase competition for emerging warm-season legume and regrowing warm-season grass (Posler et al, 1993;George et al, 1995). However, even though warm-season grass output may be reduced by oversowing with cool-season legume the results show that there should be a net benefit of approximately 0.75 kg in combined legume-grass herbage for each 1.0 kg of cool-season legume produced.…”

“…Overseeding to incorporate cool-season forages into existing pasture can increase total annual production and improve seasonal distribution of output, without the level of risk of soil erosion and prolonged production loss associated with crop establishment by clean-tillage (Bartholomew, 2005). Inclusion of cool-season legumes in low-input systems may be of particular interest because of a potential for yield improvement in mixed cropping that may be equivalent to the yield obtained from grass alone with N application of between 100 to 250 kg ha −1 (Evers, 1985;Ocumpaugh, 1990;George et al, 1995). Early season production (Evers, 1985), feed quality (Kalmbacher et al, 1980;Redmon et al, 1998;Mullen et al, 2000) and animal performance (Ocumpaugh, 1990) may all be increased when legumes are grown in mixture with cool-season grasses.…”

“…As the cost of manufactured N increases the introduction of legumes into existing pastures may provide a sustainable and reduced-cost method of maintaining forage productivity on small and resource-limited farms. Legume use is not, however, without problems since early-season growth of legume may prejudice production of warmseason companion grass (George et al, 1995), and lack of persistence of legumes is a widely recognized constraint to their use Laberge et al, 2005). Little attention has been given to the performance and persistence of legumes grown in a low-input and lowproductivity environment where unimproved warm-season grasses are the primary source of forage.…”

N2 Fixation of Common and Hairy Vetches when Intercropped into Switchgrass

“…Experiments with legume-switchgrass mixtures (e.g., red clover (Trifolium pretense L.)) reported yields that exceed those of N-only, even at inorganic-N rates of 240 kg·ha −1 [11]. Similarly, common and hairy vetch are reportedly effective at increasing soil N and can fix N 2 required for a single biomass-cut system [12,13].…”