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The recent development of portable X-ray fluorescence spectrometers (PXRF) has created new avenues for rapid plant elemental concentration determination at reduced cost while avoiding hazardous chemicals. A few studies have indicated the potential use of PXRF for homogenous plant tissue analysis. However, there is a lack of information for analysis of heterogeneous plant samples like livestock forage, which consists of a mixture of several species and plant parts, each varying in elemental concentration. Our objective was to evaluate PXRF for forage analysis, specifically the effect of forage particle size and scan time on important elements including P, K, Ca, and Fe determination. Hay samples ( = 42) were oven dried (60°C for 3 days) and ground into three particle sizes (≤0.5 mm, 0.25-0.5 mm and 1-2 mm). Prepared samples were scanned by PXRF using a vacuum (<10 torr) without a filter. Samples were placed in cups over thin prolene X-ray film and scanned for 180 s. A subset ( = 29) were also scanned for 60 and 120 s. PXRF counts for P, K, Ca, and Fe were compared with laboratory Inductively Coupled Plasma Optical Emission Spectroscopy (ICP) determinations, using regression models. Results indicated that these elements could potentially be determined with PXRF ( ≥ 0.70) in heterogeneous forage samples. Relationship strength increased with decreasing particle size, however, the relationship was still strong ( ≥ 0.57) at the largest particle size. Scanning time did not affect the relationship with ICP concentration for any of the particle sizes evaluated. This work demonstrated that with the right sample preparation PXRF can obtain results comparable to acid digestion and ICP regardless of sample composition, and suggests the potential for determinations.

Grassland ecosystems differ in plant and animal species composition and appearance depending on the location and climate [...]

Pasture-based livestock production is impacted by management and weather. In pastures, there is conflict between leaf retention for plant growth and leaf harvest for animal nutrition. Defoliated pastures with low light interception (LI) may have a low forage growth rate (FGR), while excessive growth shades leaves, reducing FGR and resulting in an S-shaped regrowth curve. To optimize production, it is best to keep FGR linear. Three studies were conducted to evaluate the impact of management and weather on FGR. Replicated pastures were used to measure FGR when grazed from 25 to 10 cm and allowed to regrow. The impact of alternative defoliation timings and intensities on FGR were studied using clipped treatments at three recovery intervals and two stubble heights. Variability in FGR was studied using a field validated plant growth model. Of the 24 growth periods studied, two displayed exponential, 12 linear and 10 linear-plateau growth. There was no effect of FM on growth curve form. In May and June, LI increased with canopy height, up to 0.93. Stubble height and days of growth impacted FGR with an interaction. There was no treatment impact on root density. Weather caused variation in FGR. A low FGR risk occurs at high elevations; greater risk occurs east of the plateau.

Fall- or spring-born steers grazed monoculture irrigated birdsfoot trefoil (BFT; Lotus corniculatus L.) or cicer milkvetch (CMV; Astragalus cicer L.) pastures for approximately 12 weeks for 3 years and were compared with steers on concentrate diets. In the 3rd year, an irrigated meadow bromegrass (MBG; Bromus biebersteinii Roem. and Schult.) pasture treatment was added for further comparison. Steer average daily gain (ADG) was 1.31, 0.94, 0.83 and 0.69 kg d−1 on concentrate, ‘Norcen’ BFT, ‘Oberhaunstadter’ BFT, and ‘Monarch’ CMV diets, respectively; ADG on grass pastures was 0.43 kg d−1. The ADG on the concentrate diet was greater than ADG on legume or grass pastures, ADG was greater on BFT than CMV in every year (p < 0.03), and ADG on BFT was greater than ADG on grass (p < 0.03). The rate constant of gas production of an in vitro rumen fermentation demonstrated a slower rate of microbial digestion for CMV than for BFT. The elevated ADG on BFT pastures may be due to greater non-fiber carbohydrate (NFC) concentration and reduced neutral detergent fiber (NDF) concentration combined with condensed tannins that protect proteins in the rumen but do not impede protein digestion in the abomasum and intestines.

Tillage type/timing and herbicide application date may change the amount and timing of N mineralization, altering fertilizer N needs for first‐year corn (Zea mays L.) following glyphosate [N‐(phosphonomethyl)glycine]‐resistant (GR) alfalfa (Medicago sativa L.). Studies were conducted in 2012 and 2013 in Utah. Yield, quality, and economic return of silage corn as affected by five tillage type/timings (fall conventional till, spring conventional till, fall strip‐till, spring strip‐till, and no‐till), three herbicide application dates for alfalfa termination (fall, spring, and in‐crop), and four N rates (0, 56, 112, and 224 kg ha−1) were evaluated. Silage corn yield and quality following GR alfalfa was economically optimized without N fertilization regardless of tillage type/timing and herbicide application date. Thus, N from decomposing alfalfa can provide the full N requirement of first‐year silage corn following GR alfalfa. Estimated animal milk production ha−1 of silage corn was greatest and similar for all herbicide application dates with conventional tillage and spring herbicide application with strip‐till and no‐till (26–38 Mg milk ha−1), whereas an in‐crop herbicide application with strip‐till and no‐till resulted in the lowest estimated milk production (21–29 Mg milk ha−1). Increased economic return for the in‐crop herbicide date by including economics from harvesting the first alfalfa cutting before planting corn mostly offset the reduced economic return of the lower silage corn yield. Therefore, an application of 2,4‐D (2,4‐dichlorophenoxyacetic acid) and dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) in the fall, spring, or in‐crop to control GR alfalfa are good economic options for conventional tillage, strip‐till, and no‐till systems.

Stem dry matter accumulation is correlated with a decline in digestibility in both birdsfoot trefoil (Lotus corniculatus L. [BFT]) and alfalfa (Medicago sativa L.), and the shear force required to harvest mature BFT stems can inhibit BFT grazing by ruminants. Decline in digestibility and increase in shear force are both correlated with increase in stem lignin content. Alfalfa stem development has been well documented, and our objective was to analyze stem development, lignification and tannin in BFT stems using alfalfa as a benchmark. The sixth internode from the base of ten BFT and two alfalfa control plants was sampled from 3 to 15 wk of stem regrowth in midsummer. Lignification occurred primarily in stem secondary xylem and was apparent in the xylary ring of Internode 6 by 5 wk of regrowth. The xylary ring reached maximum thickness by 7.5 wk of regrowth in both BFT and alfalfa but developed at a more rapid rate and to a greater thickness in BFT. Flowering in BFT began at 5.5 wk of regrowth, and full bloom was reached by 6.5 wk of regrowth. The number of cells containing tannin remained constant with stem development, which would decrease stem tannin concentration with internode maturation. Internode 6 of BFT is located 60 to 120 mm from the base of stems, within the recommended cutting height of 75 mm, with sufficient leaves and branches at subtending nodes to support shoot regrowth. These data relate growth and lignification in lower stems of BFT to grazing management recommendations.

(2007, this issue) establish the conceptual basis for herbivore preference for, and benefits of, mixed diets and the possibilities for nutritional and biochemical complementarity of nutrients and toxins in plant species mixtures; abilities of herbivores to learn postingestive consequences of eating behavior; and medicinal values of plant secondary compounds. (2007, this issue) provides an additional overview of factors controlling sheep and cattle ingestive behavioral patterns and diet selection in relation to spatial and temporal heterogeneity within relatively simple grass-clover (Trifolium repens L.) mixtures; reinforces findings that sheep and cattle consume mixed diets when offered choices; and establishes some of the theoretical basis for partial preference for clover.

Received for publication February 7, 2006. Herbage nonstructural carbohydrates (NC) contribute to livestock performance and silage fermentation. Knowledge of the distribution patterns of NC and other nutritional constituents in orchardgrass (Dactylis glomerata L.) swards could support harvest management decisions. Our objective was to determine diurnal and vertical patterns of total NC (TNC), crude protein (CP), and neutral detergent fiber (NDF) concentrations, and in vitro true dry matter digestibility (IVTDMD) and NDF digestibility (NDFD) in orchardgrass swards in October, June, and August. Herbage was sampled at 6-h intervals between 0100 and 1900 h from horizons positioned 40 to 27, 27 to 18, 18 to 12, and 12 to 8 cm above soil surface. Herbage composition varied among horizons in all months, and diurnally only in June and August. In June and August, only TNC with maxima of 109 to 123 g kg-1 at 1900 h exhibited consistent diurnal patterns. Swards harvested to residual heights of 18, 12, or 8 cm exhibited little spatial variation in TNC during June and August, but CP, NDF, and IVTDMD varied with harvest depth on all dates. As swards were harvested to successively greater depths, TNC increased in October, but not in June and August. In contrast, CP and IVTDMD decreased, and NDF increased, for harvests to successively greater depths in all months. For harvests in June and August, manipulation of depth would capture more variation in CP, NDF, and IVTDMD, but manipulation of time of day of harvest would capture more variation in TNC to meet animal performance and silage fermentation requirements.

Herbage soluble carbohydrate (SC) levels vary diurnally and livestock intake can be higher for herbage harvested or allocated to animals in the evening than in the morning. Few assessments of SC and digestibility patterns have been made during sward depletion in rotationally stocked orchardgrass (Dactylis glomerata L.). We tested the hypothesis that simulated evening daily pasture allocation increases 24-h mean herbage SC and digestibility levels relative to morning allocation. Total nonstructural carbohydrate (TNC) and in vitro true dry matter digestibility (IVTDMD) levels were compared during 24-h clipping sequences initiated at 1900 h (PM) and 0700 h (AM). Sward height was progressively reduced from 40 to 8 cm at 6-h intervals in October, June, and August. Successively lower horizons from defoliation sequences and also from control areas that were not under progressive defoliation were analyzed. Digestibility and TNC levels varied diurnally and seasonally, and were often higher for PM sequences, but differences among 24-h means were small. Daily mean TNC levels for defoliation sequences initiated in PM and AM were 138 vs. 132, 93 vs. 88, and 72 vs. 60 g kg(-1) in October, June, and August, respectively. In all periods, digestibility decreased from approximately 920 to 800 to 890 g kg(-1) during sward depletion and displayed similar patterns between defoliation sequences. Patterns of TNC and digestibility during sward depletion may not be represented by those in intact swards, and PM allocation of daily herbage may not increase 24-h mean dietary TNC density relative to AM allocation. Daily quantities of ingested TNC could be higher for PM herbage allocation if livestock consume proportionately more herbage in the PM than we simulated.