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.
Livestock productivity of semiarid, native grassland is potentially enhanced by interseeding alfalfa (Medicago sativa L.), but little is known of the impact on forage and N yield and water use. Two hay-type cultivars, 'WL 440HQ' (WL), 'NuMex Bill Melton' (NuMex), and grazing-type 'Falcata'-'Rhizoma' blend (FR) were interseeded into mixtures of four native-grass species in fall of 2015, at 36-and 71-cm row spacing as high-and low-density plantings, respectively. Plots were harvested periodically over 3 yr. Evapotranspiration (ET) was estimated based on rainfall and changes in soil water volume and used to calculate water use efficiency (WUE, kg of forage mass m −3 of ET). Alfalfa-grass mixtures produced 35% more forage mass and 96% greater N yield than the grass-only stands. Narrowrow alfalfa produced greater total forage mass than wide-row for the first 2 yr (P < .05), but no difference between row spacings occurred by Year 3. Cultivars NuMex and WL produced greater forage mass than the short-statured FR, especially at high density (P < .05). Alfalfa-grass mixtures increased WUE by a mean of 25% over the grass-only stands. There was no difference between row spacings for WUE, weed biomass, and weed N mass (P > .05). The alfalfa-grass mixtures reduced weed biomass by 43% over the grass-only stands. Interseeding alfalfa at wide row spacing enhanced forage productivity, WUE, and weed suppression relative to grass-only stands at lower seed cost than at narrow row spacing. Adapted hay-type alfalfa cultivars can be used to improve native-grass pastures in rainfed, semiarid environments.
Cover crops (CC) are versatile and have multifunctional benefits in crop rotations. An understanding of the effect of tillage systems on cover crop (CC) residue decomposition and nitrogen (N) release is essential in cash crop production planning. We investigated the decomposition rate and N release from cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) CC residue in notillage (NT) and reduced-tillage (RT) systems under corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotations. Litterbags were placed in the soil in RT and on soil surface in NT after CC termination in April and collected weekly for 10 wk to measure residue and N retained. Tillage systems did not affect the decomposition rate constant (k) and accumulated N release for both CC. Hairy vetch residue decomposed faster (k = 0.3494) than cereal rye (k = 0.1955) and released a greater amount of N in the soil (hairy vetch vs. cereal rye = 60 vs. 28 kg ha −1), attributable to greater N concentration and narrow C/N ratio compared to cereal rye in 2017 and 2018. Hairy vetch rapidly released N in the soil within 2 wk of termination. Both cover crops had greater decomposition rate constant and accelerated mass loss in 2018 than in 2017, possibly due higher spring temperatures in 2018 than 2017. Hairy vetch CC after terminating greatly enhance N availability in the soil, therefore, alternate management practices like planting green for grain crop following hairy vetch CC might be needed to capture released N.
Interseeding alfalfa (Medicago sativa L.) can improve forage quality of grasslands by adding a high‐protein species, but this runs the risk of accelerating soil water depletion. The objective was to evaluate effects of cultivar and row spacing of alfalfa on soil water balance and plant water potentials (Ψ) of two upright‐type cultivars, NuMex Bill Melton and WL 440HQ, and a prostrate‐type Falcata‐Rhizoma blend, interseeded into native grasses in October 2015 near Lubbock, Texas. Alfalfa was interseeded at 36‐cm (narrow) and 71‐cm (wide) row spacings. Soil volumetric water content (VWC) and midday Ψstem and Ψleaf were measured weekly in 2017 and 2018 growing seasons. Soil VWC was not affected by alfalfa cultivars (P > .05), whereas alfalfa row spacings differed (P < .05). Narrow spacing caused lower (P < .05) VWC than wide spacing relative to the grass‐only control in both the upper 40‐ and 40‐ to 100‐cm layers of the soil. Wide‐row spacing had similar VWC to control in 2017 for both soil layers (P > .05). Soil water depletion increased with alfalfa crown density (r = .60, P < .05) in association with enhanced evapotranspiration and denser root mass below 30‐cm soil depth. Grass and alfalfa Ψstem and Ψleaf were depressed in narrow rows relative to wide rows and control, indicating that presence of alfalfa intensified competition with the grass for soil water. The wide‐row treatment seldom had adverse effects on grass water stress. Wide‐row spacing achieved a favorable compromise between enhanced water use and improved stand productivity.
Core Ideas A noncalibrated PR2 capacitance probe showed significant deviations from actual soil water content. Calibration improved the accuracy and precision of soil moisture monitoring with the PR2. Calibration was necessary for using the PR2 probe for research‐quality soil water measurements. Multi‐depth capacitance sensors are popular to monitor soil water content for scheduling irrigation thanks to their ease of operation and maintenance. The PR2/6 Profile Probe (Delta‐T Devices) measures soil moisture by using either the manufacturer's built‐in equation or a user‐calibrated equation if the soil is high in clay or organic matter. The objectives were to evaluate the performance of the PR2/6 Profile Probe in a perennial grassland and to develop a site‐specific equation to correct probe measurements in Pullman (fine, mixed, superactive, thermic Torrertic Paleustolls) clay loam soils. Permittivity recorded by the profile probe was regressed on the gravimetrically measured soil volumetric water content (VWC). Parameters were optimized to obtain least RMSEs. The default equation provided by the manufacturer estimated VWC with average RMSE and r2 values of 0.053 m3 m–3 and 0.71, respectively. New calibration coefficients were effective in explaining 91% of the variability in soil VWC measurements and reducing RMSE to 0.017 m3 m–3. The results indicate that site‐specific calibration of the capacitance probe is necessary to attain research‐quality accuracy and precision when applied to grasslands in Pullman clay loam and associated clay loam soils.
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