Little information is available regarding the relationships of alfalfa (Medicago sativa L.) forage yield with yield components in seed‐established stands grown under dryland conditions. Field experiments that included two cultivars and 15 seeding rates ranging from m 2.2 to 33.6 kg pure live seed ha−1 were established in 1985 at Brookings and Highmore, SD. The objective was to determine seeding rate effects on components of alfalfa forage yield and on plant morphology several years after establishment. In the seeding year, plant density increased linearly with seeding rate at both locations. Yield components were determined in 1988 and 1989. Mean alfalfa yield during 1988 and 1989 was optimum at the 13.4 kg pure live seed ha−1 rate at Brookings, but did not respond to seeding rate at Highmore. Plant density continued to be affected by seeding rate 4 yr after establishment, but greater mortality at high seeding rates caused the response to deviate from linearity. Shoots per plant were negatively correlated with plant density (r = –0.73, P = 0.01). Shoot weight did not respond to seeding rate at Brookings but declined linearly with seeding rate at Highmore. Nevertheless, path analysis suggested that shoot weight was the major influence on alfalfa yield at both locations. Leaf‐to‐stem ratio and shoot length were not affected by seeding rate. Alfalfa yield components are affected similarly by plant density in seed‐established and transplanted stands. Although yield may not be affected by plant density, shoot weight may be affected because of differences in plant competition.
As switchgrass (Panicum virgatum L.) matures, whole plant nutritive value declines. In field studies, ‘Cave‐In‐Rock’, ‘Pathfinder’, and ‘Trailblazer’ switchgrass were seeded into a Blount silt loam soil (fine, illitic, mesic Aeric Ochraqualf) to determine the interaction between morphological components and maturation and its impact on forage quality. Herbage was initially harvested when the flag leaf was just visible with subsequent harvests occurring 14 and 28 d later. Cave‐In‐Rock had higher (25 g kg−1) in vitro dry matter disappearance (IVDMD) and lower (35 g kg−1) neutral detergent fiber (NDF) concentrations than the other cultivars (P < 0.05). Leaf blades, which comprised 47% of total forage at the first harvest and 26% at the last harvest, were highest in N concentration, IVDMD, and extent of NDF digestion for all harvest dates. Leaf sheaths and stems had similar N concentrations, but for IVDMD, NDF, lignin, and extent of cell wall digestion, leaf sheath values were intermediate between blades and stems. Lignin concentration of stems between the first and last harvest increased 38.8 g kg−1, while stem IVDMD and extent of stem NDF digestion declined 210 g kg−1 and 228 g kg−1 NDF, respectively. No significant whole plant cultivar differences were found for either rate or 96‐h extent of NDF digestion (P > 0.05). The in vitro rate constant for stem NDF declined 0.024 h−1 with maturation (P < 0.05), while leaf blade and sheath rate constants did not change. These results indicate that changes in the proportion and composition of the stem fraction and composition of the sheath fraction are the major factors causing a decline in switchgrass herbage quality and rate of NDF digestion with maturation.
Companion crops may compete with alfalfa (Medicago saliva L.) seedlings, but establishment with preemergence herbicides and without a companion crop may enhance the potential for soil erosion. Objectives of this study were to (i) compare alfalfa establishment techniques involving clipping or chemical control of weeds and (ii) determine differences in morphological development of alfalfa grown under several establishment techniques. Experiments were conducted at two locations in eastern South Dakota in 1989. Seven treatments included clipping the oat (Avena sativa L.) companion crop at boot stage, not clipping the oat, two treatments with oat sprayed with sethoxydim (2‐[I‐(ethoxyimino) butyl]‐5‐[2‐(ethylthio) propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one) at either S‐(SES) or 15‐cm (SE15) of oat growth, clear seeding (CS), hand weeding (HW), and a control treatment with no weed control. At Aurora, SD, alfalfa yields were greatest in HW and SE5 treatments. Yields were 24 and 36% less for CS and SE15, respectively, than for SES. At Brookings, SD, yield was also greatest for HW; however, CS had the greatest yield among the conventional establishment techniques. Yield for SES was 15% less than CS. At both locations, alfalfa yield was lowest for the two typical companion crop techniques. For typical companion crop and control treatments, mean tap root length, shoot‐to‐root ratio, and shoot length were reduced compared with other treatments. Subsequent alfalfa yields in 1990 were not affected by establishment technique at either location. Chemical control of an oat companion crop provided greater seedingyear alfalfa yields than typical companion cropping and greater protection from soil erosion than clear seeding.
Factors that influence rumen microbial degradation of switchgrass (Panicum virgatum L.) tissues are not well understood. Our objective was to measure and compare the anatomical degradation of leaf blades, leaf sheaths, and stems by tureen microorganisms. Two field‐grown switchgrass cultivars were harvested when three‐fourths of the inflorescence had emerged. Three‐millimeter portions of blade, sheath, and stem tissue were incubated in buffered rumen fluid for 0, 24, and 48 h, then removed and processed for light microscopy. Tissue composition and microbial degradation within each morphological component were measured with a computer‐based optical image analyzer. No differences in degradation were apparent between cultivars. The largest portion (35.7%) of blade cross‐sectional area was occupied by the mesophyll. After 48 h of incubation in rumen fluid, 32% of this tissue was partially degraded and 68% completely degraded. In contrast, leaf sheath parenchyma tissue was more resistant to complete degradation than that of the blade. In the sheath, 17.2% of tissues in the cross‐sectional area were at least 80% intact after 48 h of incubation; only 4.3% of the cross‐sectional area of the blade was this resistant to degradation. These differences in degradation resulted in lower (101 g kg−1) in vitro dry matter disappearance (IVDMD) in the sheath compared with the blade. Tissues (cortex, xylem, and bundle sheath) in which at least 80% of their area was intact after 48 h of incubation occupied 25.8% of the stem's cross‐sectional area. It is these resistant tissues that appear to cause the stem to have the lowest IVDMD of the three major morphological components of switchgrass. A detailed understanding of differences in degradation of anatomical tissues will result in the development of more digestible cultivars and morefficient forage utilization by livestock.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.