Climate models predict, and empirical evidence confirms, that more extreme precipitation regimes are occurring in tandem with warmer atmospheric temperatures. These more extreme rainfall patterns are characterized by increased event size separated by longer within season drought periods and represent novel climatic conditions whose consequences for different ecosystem types are largely unknown. Here, we present results from an experiment in which more extreme rainfall patterns were imposed in three native grassland sites in the Central Plains Region of North America, USA. Along this 600 km precipitation-productivity gradient, there was strong sensitivity of temperate grasslands to more extreme growing season rainfall regimes, with responses of aboveground net primary productivity (ANPP) contingent on mean soil water levels for different grassland types. At the mesic end of the gradient (tallgrass prairie), longer dry intervals between events led to extended periods of below-average soil water content, increased plant water stress and reduced ANPP by 18%. The opposite response occurred at the dry end (semiarid steppe), where a shift to fewer, but larger, events increased periods of above-average soil water content, reduced seasonal plant water stress and resulted in a 30% increase in ANPP. At an intermediate mixed grass prairie site with high plant species richness, ANPP was most sensitive to more extreme rainfall regimes (70% increase). These results highlight the inherent complexity in predicting how terrestrial ecosystems will respond to forecast novel climate conditions as well as the difficulties in extending inferences from single site experiments across biomes. Even with no change in annual precipitation amount, ANPP responses in a relatively uniform physiographic region differed in both magnitude and direction in response to within season changes in rainfall event size/frequency.

Projected global change will increase the level of land-use and environmental stressors such as drought and grazing, particularly in drylands. Still, combined effects of drought and grazing on plant production are poorly understood, thus hampering adequate projections and development of mitigation strategies. We used a large, cross-continental database consisting of 174 long-term datasets from >30 dryland regions to quantify ecosystem responses to drought and grazing with the ultimate goal to increase functional understanding in these responses. Two key aspects of ecosystem stability, resistance to and recovery after a drought, were evaluated based on standardized and normalized aboveground net primary production (ANPP) data. Drought intensity was quantified using the standardized precipitation index. We tested effects of drought intensity, grazing regime (grazed, ungrazed), biome (grassland, shrubland, savanna) or dominant life history (annual, perennial) of the herbaceous layer to assess the relative importance of these factors for ecosystem stability, and to identify predictable relationships between drought intensity and ecosystem resistance and recovery. We found that both components of ecosystem stability were better explained by dominant herbaceous life history than by biome. Increasing drought intensity (quasi-) linearly reduced ecosystem resistance. Even though annual and perennial systems showed the same response rate to increasing drought intensity, they differed in their general magnitude of resistance, with annual systems being ca. 27% less resistant. In contrast, systems with an herbaceous layer dominated by annuals had substantially higher postdrought recovery, particularly when grazed. Combined effects of drought and grazing were not merely additive but modulated by dominant life history of the herbaceous layer. To the best of our knowledge, our study established the first predictive, cross-continental model between drought intensity and drought-related relative losses in ANPP, and suggests that systems with an herbaceous layer dominated by annuals are more prone to ecosystem degradation under future global change regimes.

Based on this idea, greater legume richness and diversity may aid legume contributions to pasture swards used Pastures typically have diverse landscapes, and resulting soil condifor animal production. tions and plant composition can vary within small area units. This study was performed to quantify the spatial variation in legume contri-Information is also lacking that quantifies changes in bution to the plant community when seeded into established perennial legume composition across pasture landscapes, especool-season grass pastures. Pastures were interseeded with an 11cially under grazed conditions. Information regarding legume mixture and divided into three stocking methods (continuous, landscape positions and plant growth mostly involves rotational, and nongrazed), with each stocking method containing five landscape effects on row crop and cereal grain produclandscape positions (summit, backslope, toeslope, opposite backslope,

The most accurate method for determining canopy biomass of pastures for forage availability is by cutting and weighing forage from known areas. Faster methods that require less time and labor would help producers to monitor forage availability in pastures on a daily or weekly basis. Indirect methods rely on calibrations performed on pure or evenly distributed plant compositions to determine forage biomass. However, microclimates developed by varying landscape positions and soil morphological characteristics of pastures may cause uneven plant and species distributions. This study was performed to compare the ability of a modified Robel pole, rising plate meter, canopy height stick, and Li‐Cor LAI 2000 leaf canopy analyzer to determine forage availability in pastures with varying species composition from four areas. Swards consisted of pure warm‐season grass stands, cool‐season grass stands, legume stands, and grass‐legume mixtures. Instrument readings were compared with forage availability determined by clipping and were measured for accuracy, or closeness to clipped weight. For all observations, coefficients of determination (r2), were 0.63, 0.59, 0.55, and 0.32 for the modified Robel pole, rising plate meter, canopy height stick, and leaf canopy analyzer, respectively. For modified Robel pole readings, r2 was highest for observations in red clover (Trifolium pratense L.) (r2 = 0.83), smooth bromegrass (Bromus inermis Leyss.) (r2 = 0.82), and alfalfa (Medicago sativa L. (r2 = 0.76) swards, whereas the rising plate meter r2 values were highest for observations in tall fescue (Festuca arundinacea Schreb.) (r2 = 0.85), alfalfa (r2 = 0.84), and red clover (r2 = 0.73) swards. Grass observations also had their highest r2 values with the modified Robel pole and rising plate meter at 0.63 and 0.59, respectively. The modified Robel pole proved to be the most accurate method used over a variety of species.

Comparisons of stocking rates across sites can be facilitated by calculating grazing pressure. We used peak standing crop and stocking rates from six studies in the North American Great Plains

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small-scale and short-term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long-term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field-scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm-scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM-ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country.

Interseeding annual warm‐season grasses into pastureland dominated by perennial cool‐season grasses may be a strategy to reduce shortage of forage. Field trials were conducted at three Nebraska (Mead, North Platte, and Sidney) and two Kansas (Hays and Mound Valley) locations in 2015–2016 (10 environments) to evaluate forage production responses to six interseeded annual warm‐season grass—corn (Zea mays L.), forage sorghum (Sorghum bicolor [L.] Moench), pearl millet (Pennisetum glaucum [L.] R. Br.), sudangrass (S. bicolor [L.] Moench ssp. drummondii [Nees ex Steud.] de Wet & Harlan), a sorghum–sudangrass hybrid (S. bicolor × S. bicolor var. sudanense), and an unseeded control—and two harvest frequency (once at 90 d and twice at 45 and 90 d after interseeding) treatments. Across environments, total forage accumulation was 146–214% and 100–102% greater in sudangrass and sorghum–sudangrass interseeded than unseeded pastures when harvested once and twice after interseeding, respectively. In smooth bromegrass (Bromus inermis Leyss.) pastures, interseeding sudangrass and sorghum–sudangrass increased forage accumulation in both years at Mead but in only one year at North Platte. In tall fescue (Lolium arundinaceum [Schreb.] Darbysh.) pastures, interseeding forage sorghum and sorghum–sudangrass increased forage accumulation by 103–211% relative to unseeded pastures. Interseeding annual warm‐season grasses presents an effective strategy to increase forage accumulation in humid pasturelands harvested once or twice after interseeding (Mead and Mound Valley). In semiarid pasturelands, forage responses to interseeding will vary from year‐to‐year depending on timing and amount of precipitation, but forage accumulation can be significant.

Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) provide abundant forage for livestock and wildlife during hot summer months when cool‐season grass species may decline in production. Little biomass production for grazing may result during warm‐season grass establishment because of weed competition. Chemical methods of weed control are now limited, because application of atrazine [6‐chloro‐N‐ethyI‐N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] to switchgrass and big bluestem is no longer allowed according to the label. Using corn (Zea mays L.) as a companion crop could provide potential for high biomass production during warm‐season grass establishment, and allow the use of atrazine for weed control. This study investigated the ability of switchgrass and big bluestem to establish in a corn companion crop. The effects of corn hybrid (short‐ vs. long‐season), population density, row spacing, and harvest date on switchgrass and big bluestem stands and on corn production were quantified. Establishment of switchgrass and big bluestem in corn was successful. Switchgrass mean stands were 26.3 plants m−2 in 1995 and 46.4 plants m−2 in 1996. Big bluestem stands were similar to switchgrass in 1995 (31.7 plants m−2), but were much lower in 1996 (5.2 plants m−2). Long‐season corn hybrids and higherdensity corn populations increased corn silage and grain yield without reducing warm‐season grass stands. Within a season, no difference existed between corn grain yields when grown with either switchgrass (6.7 Mg ha−1 in 1995, 5.3 Mg ha−1 in 1996) or big bluestem (6.9 Mg ha−1 in 1995, 5.7 Mg ha−1 in 1996). Silage dry matter yield was not different between corn grown with switchgrass (12.6 Mg ha−1 in 1995, 16.1 Mg ha−1 in 1996) and corn grown with big bluestem (13.1 ha−1 in 1995, and 16.6 Mg ha−1 in 1996) for a given year. Switchgrass and big bluestem grown in corn with atrazine reduced land production losses during the establishment year, yet allowed adequate establishment of these grasses for future forage production.