P. Nyren

GRAZING INTENSITY AND ECOSYSTEM PROCESSES IN A NORTHERN MIXED-GRASS PRAIRIE, USA

The objective of this study was to evaluate for an 8-yr period the ecosystem-level impacts of no grazing vs. sustained moderate and heavy cattle grazing in terms of: (1) plant species basal cover, density, and composition; (2) aboveground net primary production (ANPP), N content of ANPP (ANPP-N), belowground net primary production (BNPP), and N content of BNPP (BNPP-N); (3) litter and root decomposition and N loss; and (4) soil C, total soil N, and net in situ soil N mineralization. Moderate and heavy grazing treatments were designed to achieve an end-of-the-grazing-season residual vegetation of 50% and 10%, respectively, of the long-term average ANPP of comparable ungrazed sites. The main factor affecting the vegetation response was the increase in precipitation after the drought of 1988; few differences were due to grazing intensity. The total absolute basal cover of grasses increased steadily in all treatments, from an average of 4% during the drought of 1988 to 14% in 1993. Forb density and diversity increased from 51 plants/m2 and 14 species in 1988 to 412 plants/m2 and 36 species in 1995. Grazing, however, increased the relative composition of Poa pratensis and Achillea millefolium, but reduced the relative composition of Bouteloua gracilis and Aster ericoides. ANPP and ANPP-N were correlated with rainfall, but not with grazing intensity. Heavy grazing led to declines in standing dead biomass, litter, peak root biomass and biomass-N, root N concentrations, and in situ net soil N mineralization. There was an increase in root decomposition and N loss with grazing. From this study, we reached the following conclusions about the northern mixed-grass prairie: (1) climatic variations, in particular droughts, control major trends in plant species composition and production, with grazing playing a secondary role; (2) heavy grazing leads to declines in standing dead biomass and biomass-N, litter biomass and biomass-N, peak root biomass and biomass-N, and in situ net soil N mineralization, which may have a significant long-term impact on range condition; and (3) grazing pressures that lead to a removal of 50% of ANPP, however, seem to be sustainable and compatible with the maintenance of range condition.

Effects of Grazing Intensity, Precipitation, and Temperature on Forage Production

Abstract Questions have been raised about whether herbaceous productivity declines linearly with grazing or whether low levels of grazing can increase productivity. This paper reports the response of forage production to cattle grazing on prairie dominated by Kentucky bluegrass (Poa pratensis L.) in south-central North Dakota through the growing season at 5 grazing intensities: no grazing, light grazing (1.3 ± 0.7 animal unit months [AUM] · ha−1), moderate grazing (2.7 ± 1.0 AUM · ha−1), heavy grazing (4.4 ± 1.2 AUM · ha−1), and extreme grazing (6.9 ± 2.1 AUM · ha−1; mean ± SD). Annual herbage production data were collected on silty and overflow range sites from 1989 to 2005. Precipitation and sod temperature were used as covariates in the analysis. On silty range sites, the light treatment produced the most herbage (3 410 kg · ha−1), and production was reduced as the grazing intensity increased. Average total production for the season was 545 kg · ha−1 less on the ungrazed treatment and 909 kg · ha−1 less on the extreme treatment than on the light treatment. On overflow range sites, there were no significant differences between the light (4 131 kg · ha−1), moderate (4 360 kg · ha−1), and heavy treatments (4 362 kg · ha−1; P > 0.05). Total production on overflow range sites interacted with precipitation, and production on the grazed treatments was greater than on the ungrazed treatment when precipitation (from the end of the growing season in the previous year to the end of the grazing season in the current year) was greater than 267.0, 248.4, 262.4, or 531.5 mm on the light, moderate, heavy, and extreme treatments, respectively. However, production on the extreme treatment was less than on the ungrazed treatment if precipitation was less than 315.2 mm. We conclude that low to moderate levels of grazing can increase production over no grazing, but that the level of grazing that maximizes production depends upon the growing conditions of the current year.

Wavelets for Agriculture and Biology: A Tutorial with Applications and Outlook

ABSTRACT Wavelet transforms (WTs) are finding increasing use in the discovery of the scale-specific properties of complex biological data. Although many efforts have been made to explain the main concepts of WT without advanced mathematics, the implicit reliance on digital signal processing terminology is widespread in many popular articles. This may cause some confusion for many biologists who do not have a clear understanding of the computational mechanisms and computer graphics of WTs. In this article we provide a tutorial on WTs for biologists by walking through two carefully selected examples step-by-step, using freely available software as well as a self-developed computer program. Both discrete WT and continuous WT are discussed, and detailed computational instructions, along with thorough interpretations of the computer outputs (or hand-calculated steps), are provided throughout. We conclude by offering a few directions for further study and several ideas on possible new developments in biological sciences using wavelets.

Quantifying root water extraction by rangeland plants through soil water modeling

We used soil water modeling as a tool to quantify water use of non-cultivated plant communities based on easily measured field data of soil water contents, soil hydraulic properties, and leaf area index. The model was applied in the mixed-grass prairie, considering a dynamic and non-uniform root distribution, the effect of soil water stress on plant water uptake, as well as the compensation effect of root water uptake. The simulation was conducted for the 111 days from mid May to early September of 2009. A good agreement between the model simulated and field measured soil water contents was obtained, with a maximum rooting depth estimated within the depth range of 1.3–1.6 m. The results suggest that a reasonable estimate of soil water retention parameters, and especially the use of the root uptake compensation significantly improved both numerical accuracy in predicted soil water dynamics, and the biological importance in the predicted seasonal root water extraction. In particular, the model gave a reasonable simulation of the seasonal progression of the drying zone in the soil profile in the summer of 2009. The method and analyses used in this paper may be useful in a wider context of soil-plant relationships.

Biomass composition of perennial grasses for biofuel production in North Dakota, USA

Background: Successful development of biofuels from biomass feedstocks depends on high yields and acceptable quality. We investigated the chemical composition of ten perennial grasses and mixtures across environments in North Dakota, USA. The contents of neutral detergent fiber (NDF), acid detergent fiber, acid detergent lignin (ADL), hemicellulose (HCE), cellulose (CE) and ash were determined. Results: Biomass chemical composition was affected by environment and species/mixtures, and their interaction. Biomass under drier conditions had higher NDF, ADL and HCE contents but lower CE contents. Tall and intermediate wheatgrass had higher NDF, acid detergent fiber and CE but lower ash contents than the other species and mixtures. Switchgrass and mixtures had higher HCE. Tall wheatgrass and Sunburst switchgrass had the lowest ADL content as compared with other species. Biomass with higher yield had higher cellulose content but lower ash content. Conclusion: Combined with higher yields, tall and intermediate wheatgrass and switchgrass had the optimal chemical compositions for biomass feedstocks production.

Short-term effect of targeted placements of sheep excrement on grassland in inner mongolia on soil and plant parameters

Abstract Grazing animal excrement plays an important role in nutrient cycling and redistribution in grazing ecosystems, due to grazing in large areas and return in small areas. To elucidate the changes to the soil and pasture caused by sheep urine, fresh dung, and compost patches, a short‐term field experiment using artificially placed pats was set up in the autumn of 2003 in the Inner Mongolian steppe. Urine application significantly increased soil pH during the first 32 days in soil layers at depths of both 0–5 cm and 5–15 cm. Rapid hydrolysis of urea gave large amounts of urine‐nitrogen (N) as ammonium (NH4 +) in soil extracts and was followed by apparent nitrification from day 2. Higher inorganic N content in the urine‐treated soil was found throughout the experiment compared with the control. No significant effects of sheep excrement on soil microbial carbon (C) and soil microbial N was found, but microbial activities significantly increased compared with the control after application of sheep excrement. Forty‐six percent of dung‐N and 27% of compost‐N were transferred into vegetation after the experiment. The results from this study suggest that large amounts of nutrients have been lost from the returned excrement patches in the degraded grassland of Inner Mongolia, especially from sheep urine‐N.

Biomass Production in Northern Great Plains of USA – Agronomic Perspective

The development of biofuel is an important measure to meet America’s energy challenges in the future. In the 2007 Energy Independence and Security Act, the U.S. government mandates that 136 billion liters of biofuel will be produced by 2022, of which 60 billion liters will be cellulosic ethanol derived from biomass [1-3]. Currently, ethanol is one of the biofuels that has been developed extensively. In the U.S., initial efforts for ethanol production were focused on fermentation of sugars from grains (especially maize). However, there have been criticisms for ethanol production from maize because of low energy efficiency, high input cost and adverse environmental impacts [4-5]. Biofuels from biomass feedstocks are more attractive because biomass is a domestic, secure and abundant feedstock. There are at least three major benefits for using biofuels. The very first benefit is national energy security. To reduce the reliance of imported oil for transportation, alternative energy options must be developed. Economically, a biofuel industry would create jobs and ensure growing energy supplies to support national and global prosperity. Environmentally, producing and using more biofules will reduce CO2 emission and slow down the pace of global warming and climate change.