159 research outputs found
What Can Iowa Do with 10 Million Acres of Forage?
Iowa\u27s 10 million acres of pasture and forage land can support many more beef cows. The author cites extensive research to show this land can carry anywhere from 1.6 million to 7 million cows
BIRDSFOOT TREFOIL - Brings New Life to Pastures
Thereare over 3 million acres of low yielding open land pastures in Iowa. Birdsfoot trefoil, a high quality, bloat-free forage with persistent stand and ability to withstand continuous grazing might be the answer to developing these low yield pastures
Comparison of Dinitrogen Fixation and Nitrogen Transfer Potentials of Four Red Clover Cultivars
The capacity to fix atmospheric N2 and thus reduce the use of N fertilizer is an important reason for including legumes in forage mixtures. Selection for more efficient N2 fixation could improve red clover (Trifolium prateme L.) (RC) production and its contribution to soil fertility. An isotope dilution study was conducted in two greenhouse experiments to compare the N2 fixation and N transfer potentials of three commercial and one experimental RC cultivars. The experimental cultivar APR-8701 was selected for traits related to increased N2 fixation (rate of acetylene reduction, root size and branch number, and nodule mass). \u27Dawn\u27 orchardgrass (Dactylis glomerata L.) (OG) was used as the grass in mixture and as the reference crop for the isotope dilution study. Four harvests were taken from each of the two experiments.
Herbage was analyzed first for total N and then for isotopic composition by mass spectrometry. Under the conditions of this study, the particular traits selected for in the development of the cultivar APR-8701 resulted in a high N2 fixation rate, ranging from 88.9 to 99.8 %N derived from the atmosphere (%Ndfa) in pure and mixed stands of both experiments, that paralleled the other three cultivars tested (ranging between 86.8 and 99. 9 %Ndfa in pure and mixed stands of both experiments). However, APR-8701 was average when N transfer potentials were compared. Average %N in grass derived from the atmosphere (%Ngdfa) was 32.2 and 46.3% for OG grown with APR-8701 in experiments 1 and 2, respectively, and ranged between 30. 5 and 50.1% for OG grown with the other three cultivars. We conclude that the experimental cultivar APR-8701 showed N2 fixation rates similar to that of other superior, commercially available cultivars, however, APR-8701 only showed average N transfer capability
Order-of-magnitude speedup for steady states and traveling waves via Stokes preconditioning in Channelflow and Openpipeflow
Steady states and traveling waves play a fundamental role in understanding
hydrodynamic problems. Even when unstable, these states provide the
bifurcation-theoretic explanation for the origin of the observed states. In
turbulent wall-bounded shear flows, these states have been hypothesized to be
saddle points organizing the trajectories within a chaotic attractor. These
states must be computed with Newton's method or one of its generalizations,
since time-integration cannot converge to unstable equilibria. The bottleneck
is the solution of linear systems involving the Jacobian of the Navier-Stokes
or Boussinesq equations. Originally such computations were carried out by
constructing and directly inverting the Jacobian, but this is unfeasible for
the matrices arising from three-dimensional hydrodynamic configurations in
large domains. A popular method is to seek states that are invariant under
numerical time integration. Surprisingly, equilibria may also be found by
seeking flows that are invariant under a single very large Backwards-Euler
Forwards-Euler timestep. We show that this method, called Stokes
preconditioning, is 10 to 50 times faster at computing steady states in plane
Couette flow and traveling waves in pipe flow. Moreover, it can be carried out
using Channelflow (by Gibson) and Openpipeflow (by Willis) without any changes
to these popular spectral codes. We explain the convergence rate as a function
of the integration period and Reynolds number by computing the full spectra of
the operators corresponding to the Jacobians of both methods.Comment: in Computational Modelling of Bifurcations and Instabilities in Fluid
Dynamics, ed. Alexander Gelfgat (Springer, 2018
Developing a National Alfalfa Information System
Using state-of-the-art telecommunication technologies, this project is developing a comprehensive knowledge resource for alfalfa (Medicago sativa L.); the National Alfalfa Information System (NAIS). This project will serve as an improved model for Extension educational programs. Alfalfa is the most important forage crop in the USA and grown worldwide for feeding millions of livestock and in many cropping systems. As a legume, it is important in sustaining the environment and the productivity of agriculture. Information needs are present in every state and internationally. The NAIS is being developed through national and international cooperation, putting the best science-based alfalfa information and expertise at the fingertips of producers, consultants, extension workers, instructors, researchers, and users. Collaboratively developed materials will reduce duplication of effort. To make the knowledge easy-to-use, educational design, communication, and information science professionals are working with alfalfa experts in creating a WWW system and Web-aware CD-ROM. To ensure content quality, peer-review by members of multiple professional societies is included. A significant result will be around-the-clock availability of up-to-date, easy-to-use, and peerreviewed information. Shared workload and the peer-review process can influence faculty morale, efficiency, and effectiveness, an adjunct to maximizing the utilization of alfalfa worldwide by making the best information readily available
Grassland productivity limited by multiple nutrients
Terrestrial ecosystem productivity is widely accepted to be nutrient limited1. Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)2,3, the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized4,5,6,7,8. However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μ co-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment
Dynamics of soil organic carbon following land-use change: insights from stable C-isotope analysis in black soil of Northeast China
Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent. Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C4) and from natural vegetation (C3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg−1 on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment. The increase in the percentage of C4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment
Impact of tree species on nutrient and light availability: evidence from a permanent plot study of old-field succession
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