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.
Abstract:In behavioral studies, cattle within the same pasture are not considered as independent experimental units because of the potential confounding effects of the herd's social interactions. However, evaluating cattle behavior on extensive rangelands is logistically challenging for researchers, and treating individual animals as independent experimental units may be beneficial for answering specific research questions. The objective of this study was to evaluate the association patterns among global positioning system (GPS)-tracked cattle at six different study sites in the western United States. A Half-Weight Index (HWI) association value was calculated for each pair of GPS-tracked cows (i.e., dyad) to determine the proportion of time that cattle were within 75 m and 500 m of each other. Cattle at two study sites exhibited relatively low mean HWI-association values (i.e., less than 0.23 HWI); whereas, cattle at other study sites tended to have greater mean HWI associations (i.e., greater than 0.35 HWI). Distinguishing features between study sites with low and high association values were the management of cattle prior to the study, herd size, pasture size, and the number of watering points. However, at all ranches except one, at least 75% of all dyadic associations had HWI values of less than 0.5 at 500 m, indicating that most of the GPS-tracked cows were greater than 500 m from each other for over 50% of tracking period. While interactions among cattle in the same pasture are often inevitable, our data suggests that under some situations, movement patterns of a sub-set of individual GPS-tracked cows may have levels of independence that are sufficient for analysis as individual experimental units. Understanding the level of independence among GPS-tracked cattle may provide options for analysis of grazing behavior for individual cattle within the same pasture.
Productivity throughout the North American Great Plains grasslands is generally considered to be water limited, with the strength of this limitation increasing as precipitation decreases. We hypothesize that cumulative actual evapotranspiration water loss (AET) from April to July is the precipitation‐related variable most correlated to aboveground net primary production (ANPP) in the U.S. Great Plains (GP). We tested this by evaluating the relationship of ANPP to AET, precipitation, and plant transpiration (Tr). We used multi‐year ANPP data from five sites ranging from semiarid grasslands in Colorado and Wyoming to mesic grasslands in Nebraska and Kansas, mean annual NRCS ANPP, and satellite‐derived normalized difference vegetation index (NDVI) data. Results from the five sites showed that cumulative April‐to‐July AET, precipitation, and Tr were well correlated (R2: 0.54–0.70) to annual changes in ANPP for all but the wettest site. AET and Tr were better correlated to annual changes in ANPP compared to precipitation for the drier sites, and precipitation in August and September had little impact on productivity in drier sites. April‐to‐July cumulative precipitation was best correlated (R2 = 0.63) with interannual variability in ANPP in the most mesic site, while AET and Tr were poorly correlated with ANPP at this site. Cumulative growing season (May‐to‐September) NDVI (iNDVI) was strongly correlated with annual ANPP at the five sites (R2 = 0.90). Using iNDVI as a surrogate for ANPP, we found that county‐level cumulative April–July AET was more strongly correlated to ANPP than precipitation for more than 80% of the GP counties, with precipitation tending to perform better in the eastern more mesic portion of the GP. Including the ratio of AET to potential evapotranspiration (PET) improved the correlation of AET to both iNDVI and mean county‐level NRCS ANPP. Accounting for how different precipitation‐related variables control ANPP (AET in drier portion, precipitation in wetter portion) provides opportunity to develop spatially explicit forecasting of ANPP across the GP for enhancing decision‐making by land managers and use of grassland ANPP for biofuels.
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