Establishment and Stand Development of Alfalfa Interseeded into Native Grass Mixture: Cultivar and Row Spacing Effects

Abstract

Interseeding alfalfa (Medicago sativa L.) into native grasslands can enrich forage nutritive value, but successful establishment in semiarid regions is limited by chronic water deficit. The objective was to evaluate establishment and stand development of two upright‐type alfalfa cultivars, ‘WL 440HQ’ (WL), ‘NuMex Bill Melton’ (NM), and prostrate‐type ‘Falcata’–‘Rhizoma’ blend (FR), interseeded into mixtures of four native grass species at 36‐ or 71‐cm row spacing near Lubbock, TX. Average emergence was 265, 216, and 175 seedlings m−2 for WL, NM, and FR, respectively; however, the WL stand declined faster than the FR and NM stands during seedling and crown development stages (P < 0.01). The upright‐type cultivars maintained a greater crown density and ground cover compared with FR at both row spacings (P < 0.05). Alfalfa seedling or crown density fitted against time (d) with exponential models revealed an initial sharp decline followed by a slow rate of decline after establishment. At the end of 3 yr, row‐spacing results converged to similar levels for plant density (6.5 crowns m−2) and alfalfa cover (23.5%). This indicates significant seed cost savings with the wider row spacing at that level of stand establishment. Interseeding adapted, upright‐type cultivars at wide row spacing can produce a desirable level of alfalfa establishment in a semiarid grassland of the southern Great Plains.

Row spacing of alfalfa interseeded into native grass pasture influences soil‐plant‐water relations

“…These results indicate that increased density of alfalfa exacerbates SWD. There was a linear relation between total SWD and observed crown density (Dhakal et al., ) for both years ( P < .05) with r = .59 and .60 in 2017 and 2018, respectively. Treatment effects on soil water storage and depletion varied somewhat between years, in that results for wide spacing were similar to the control in 2017, but more centrally spaced between narrow spacing and the control in 2018.…”

“…In 2017, the wide spacing had relatively few small plants with large inter‐row gaps that were not yet exploited by alfalfa roots. By October 2018, alfalfa crown density at the narrow spacing had declined to a level similar to that of the wide spacing (Dhakal et al., ).…”

“…() reported a positive correlation ( r = .82) between root biomass and the fraction of water at 0‐ to 50‐cm depth that contributed to ET. Counts of alfalfa plant density at the time of root sampling were 26 and 15 crowns m −2 for 36‐ and 71‐cm row spacings, respectively (Dhakal et al., ). Deep‐soil VWC was diminished throughout 2017 and most of 2018 by the narrow‐row spacing (Figure ).…”

“…This indicates that practical improvements in forage yield and quality can be realized at wide spacing with little risk of inducing excessive water deficit stress in the grasses through competition for soil water. By the end of the 2018 season, the row‐spacing treatments were equal in soil water extraction (Figure ) and in alfalfa plant density due to higher alfalfa mortality in narrow‐rows (Dhakal et al., ). This indicates that the wide rows favored conservation of soil water and lower input cost of pasture improvement.…”

“…Multiple forage harvests took place each year between May and October to determine yield: June and September 2016; June, July, August, and October 2017; and May, June, July, August, and October 2018. Alfalfa seedling and crown density (plants m −2 ) were recorded for 3.5 yr at the beginning and end of the growing season, that is, March and October for each of the years from 2016 through 2018 and reported in Dhakal, West, & Villalobos ().…”