Quantifying Morphological Development of Alfalfa for Studies of Herbage Quality¹

Abstract

A more precise and quantitative method of specifying the morphological development of alfalfa (Medicago sativa L.) is needed for communication among scientists working with the crop and for associating alfalfa phenology and forage quality. A 10‐stage numerical system for individual stems (Stages to 9) was defined, and two procedures for calculating the mean stage of a herbage sample were compared on alfalfa samples grown in the spring, summer, or autumn and representing weekly age increments up to 10 weeks from all seasons. Samples were collected during one growing season from a 3‐year‐old stand of ‘Iroquois’ alfalfa grown in Tompkins County, N.Y. Mean stage by count (MSC) was the average of the individual stages present in the herbage sample, weighted for number of stems in each stage. Mean stage by weight (MSW) was the average of individual stages present, weighted for dry weight of herbage in each stage. Both methods quantified morphological development of alfalfa canopies with the anticipated effects of seasonal temperature, but the MSW procedure was superior in showing greater numerical differentiation and in distinguishing samples of diverse age and stage structure.Linear regression in vitro true digestibility (IVTD) on MSW across seasons and ages of herbage samples was highly significant:IVTD = 92.93−3.98·(MSW), r2 = 0.984, n = 11. Crude protein (CP) was characterized by a highly significant quadratic regression: CP = 40.89−7.38·(MSW) + 0.57 (MSW)2, R2 = 0.995, n = 11. The association of alfalfa quality and MSW has not been sufficiently tested to represent a general prediction model. However, the observed relationship indicates the potential usefulness of MSW in developing such a model.

Nutrient Composition, Forage Parameters, and Antioxidant Capacity of Alfalfa (Medicago sativa, L.) in Response to Saline Irrigation Water

“…For this work, we present data on ionic and nutrient composition at 84 days after seeding (DAS) (2nd harvest, on 15 September 2011) and at 299 DAS (7th harvest, on 17 April 2012). The second harvest was conducted when the control plants were at the early flowering stage, corresponding to morphological stage 5 [21]. The seventh harvest was conducted when the control plants were at a late vegetative stage (due to the absence of flowering).…”

Water-stress effects on forage quality of alfalfa

“…The plants were rated for maturity using the meanstage-by-count method of Kalu and Pick (1981). The leaves from 15 of the 20 sampled stems were removed and the leaf area was measured with a Li-Cor 3000 leaf-area planimeter.…”

“…Plants grown under the greatest water stress had low est maturity ratings (Fig. 7), Water stress, therefore, de layed plant phenological development, as measured by the Kalu and Pick (1981) The effect of water stress in delaying plant development has been demonstrated in work on tropical grasses (Wilson and Ng, 1975;Wilson, 1983b). More recently, Gomez et al (1985) reported a linear increase in maturity of alfalfa with irri gation treatments that allowed more évapotranspiration .. Kalu and Pick (1981) meanstage-by-count method, and X = soil-water content at irriga tion in % of field capacity.…”

“…Their maturity rating was based on the mean-stage-by-count method of Kalu and Pick (1981), and ranged from 1.6 to 6.3.…”

“…The Kalu and Pick (1981) staging method uses stem length as the basis for delineating maturity stages through the late vegetative (0 through 2). Because water stress shortens stem length, this system could underestimate the actual maturity of water-stressed plants.…”