Abstract
AbstractAlfalfa (Medicago sativa L.) can enhance the supply of nutritious forage when interseeded into semiarid native grassland. Alfalfa is a high water‐using species; therefore, a possible trade‐off between soil water depletion and nutritive value merits study. We determined the effects of interseeding three alfalfa cultivars at two densities on crude protein (CP) and digestible organic matter (DOM) accumulations, the water footprint (WF, m3 evapotranspiration kg−1) of CP and DOM accumulation at two row spacings, and the marginal cost (MC) of such trade‐offs. Nutritive values and accumulation of CP and DOM for mixtures with alfalfa planted at 36‐ or 71‐cm row spacing did not differ in 2018 (P > .05), as both spacings reduced the WF over grass only (P < .0001). Alfalfa presence reduced the WF (P < .001) with respect to CP and DOM accumulation from 20.17 and 3.07 m3 kg−1 in the grass‐only control to 10.14 and 2.22 m3 kg−1 in alfalfa–grass mixtures, respectively. Interseeding alfalfa in wide rows had 23 and 26% less MC of revenue increment than interseeding in narrow rows, relative to grass only in Years 2 and 3, respectively (P < .01). Hay‐type cultivars NuMex Bill Melton and WL 440HQ enhanced the forage mixture nutritive value more than the grazing‐type Falcata–Rhizoma blend, mainly driven by greater alfalfa growth. Interseeding alfalfa into native grasses in wide rows can increase the efficiency of water use (lower WF) by enhancing forage nutritive value at low MC, thereby inducing a minimal trade‐off in soil water consumption.
Highlights
Results from water footprint” (WF) calculations were used to describe differences in the amount of water used as ET inherent in a unit mass of Crude protein (CP) and digestible organic matter (DOM) to assess the trade-off between pasture improvement and consumptive use of water
Annual revenue from the pasture was estimated based on forage mass and total digestible nutrients (TDN) accumulation of the mixture according to the USDA Agricultural Marketing Service for each year
Concentrations of CP, acid detergent fiber (ADF), neutral detergent fiber digestibility (NDFD), and acid detergent fiber digestibility (ADFD) were affected by year × cultivar × row spacing interactions (P < .05)
Summary
Alfalfa (Medicago sativa L.) interseeded into native grass pasture increased the total forage mass by 35% and N accumulation by 96% over grass alone in the Texas High Plains (Dhakal, West, Villalobos, Brown, & Green, 2020). Recent studies in the southern High Plains demonstrate that including alfalfa in a semiarid grassland system enhances forage mass, WUE (Dhakal, West, Villalobos, et al, 2020), and forage quality (Baxter, West, Brown, & Green, 2017) at the cost of increased soil water extraction (Dhakal, West, Deb, Villalobos, & Kharel, 2020). The objective was to determine the effects of interseeding diverse types of alfalfa at low and high density into native grass pastures on (a) concentrations of forage nutritive value variables, (b) accumulations and WF of CP and DOM, and (c) the economic benefit associated with changes in cost of production.
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