Does diversifying crop rotations suppress weeds? A meta-analysis

Over the past half-century, crop rotations have become increasingly simplified, with whole regions producing only one or two crops in succession. Simplification is problematic from a weed management perspective, because it results in weeds’ repeated exposure to the same set of ecological and agronomic conditions. This can exacerbate weed infestations and promote the evolution of herbicide resistance. Diversifying crop rotations through addition of crop species and their associated managements may suppress weeds and reduce selection pressure for herbicide resistance by altering stress and mortality factors affecting weed dynamics. Here we report the results of a meta-analysis using 298 paired observations from 54 studies across six continents to compare weed responses due to simple and more diverse crop rotations. We found diversifying from simple rotations reduced weed density (49%), but did not have a significant effect on weed biomass. We investigated the effect of management practices, environmental factors, and rotation design on this effect. Diversification that increased the variance around crop planting dates was more effective in suppressing weeds than increasing crop species richness alone. Increasing rotational diversity reduced weed density more under zero-tillage conditions (65%) than tilled conditions (41%), and did so regardless of environmental context and auxiliary herbicide use. Our findings highlight the value of diversifying crop rotations to control weed populations, and support its efficacy under varied environmental conditions and management scenarios

KIPP Middle Schools: Impacts on Achievement and Other Outcomes

The Knowledge Is Power Program (KIPP) is a rapidly expanding network of public charter schools whose mission is to improve the education of low-income children. As of the 2012 -- 2013 school year, 125 KIPP schools are in operation in 20 different states and the District of Columbia (DC). Ultimately, KIPP's goal is to prepare students to enroll and succeed in college.Prior research has suggested that KIPP schools have positive impacts on student achievement, but most of the studies have included only a few KIPP schools or have had methodological limitations. This is the second report of a national evaluation of KIPP middle schools being conducted by Mathematica Policy Research. The evaluation uses experimental and quasi-experimental methods to produce rigorous and comprehensive evidence on the effects of KIPP middle schools across the country.The study's first report, released in 2010, described strong positive achievement impacts in math and reading for the 22 KIPP middle schools for which data were available at the time. For this phase of the study, we nearly doubled the size of the sample, to 43 KIPP middle schools, including all KIPP middle schools that were open at the start of the study in 2010 for which we were able to acquire relevant data from local districts or states. This report estimates achievement impacts for these 43 KIPP middle schools, and includes science and social studies in addition to math and reading. This report also examines additional student outcomes beyond state test scores, including student performance on a nationally norm-referenced test and survey-based measures of student attitudes and behavior

Maize and Prairie Root Contributions to Soil CO2 Emissions in the Field

Increasing soil carbon content via agricultural practices not only enhances the production potential of the land, but also counteracts rising atmospheric CO2 levels. When predicting production systems’ effects on soil carbon, quantifying CO2 efflux derived from live roots is of particular importance as it is a through-flux and does not signify depletion of soil carbon. This field study aimed to measure and compare soil CO2 emissions derived from roots in annual and perennial agroecosystems. We used periodic 48-hour shading over two growing seasons to estimate root growth-derived CO2 in continuously grown maize (CC) with grain and 50% stover harvested each year, unfertilized reconstructed tallgrass prairie (P), and the same prairie grown with spring nitrogen fertilization (PF), both which had biomass harvested post-frost. In CC, P, and PF root-derived CO2 contributed to 28, 31, and 30% of each crop’s respective growing season cumulative CO2 emissions in 2012, and 19, 24, and 28% in 2013, respectively. Season-cumulative root-derived CO2 was not proportional to end-of-season belowground biomass (BGB): P had nearly twice the BGB of PF, but their cumulative root-derived fluxes were not significantly different in either year. A significant proportion of soil CO2 emissions is derived from roots, making it a critical process to consider when comparing or modeling soil emissions of cropped or prairie soils. Using BGB alone may not be a useful proxy for estimating root contributions

Assessing the Psychometric Properties of Both a Global and a Domain-Specific Perceived Quality of Life Measure When Used with Youth Who Have Chronic Conditions

The purpose of this paper was to assess the psychometric properties of the Students’ Life Satisfaction Scale (SLSS) and the Brief Multidimensional Students’ Life Satisfaction Scale (BMSLSS) when used with youth who have chronic conditions. Baseline data from a longitudinal study examining predictors of changes in perceived quality of life (PQOL) for youth with chronic conditions were used. SLSS and BMSLSS data were collected on over 400 youth aged 11–17 using youth self-report and parent proxy-report versions. Internal consistency, convergent validity, and factor structure were examined for both versions. Extent of agreement and magnitude of differences between youth and parent report were evaluated. Finally, gender, age, and condition group differences in youth report scores were examined for the SLSS and BMSLSS. Strong internal consistency was demonstrated for the youth and parent reports of both measures. As with normative samples, a single factor structure was found for youth and parent reports of the BMSLSS. However, both youth and parent reports of the SLSS had a two-factor structure: one consisting of five positively worded items, and the other, two negatively worded items. Youth reported their PQOL to be significantly higher than did their parents. Significant differences in PQOL scores for the youth report were not found by age, gender, or conditions. Findings show that, from a psychometric standpoint, the BMSLSS (both youth and parent report) is a promising measure of PQOL for use in population-based research with youth who have chronic conditions. The SLSS may need to be revised to exclude negative items when used with this population of youth

Snapshot of KIPP Leadership Practices through 2010 -- 2011

As part of the U.S. Department of Education's Investing in Innovation (i3) grant, the Knowledge Is Power Program (KIPP) Foundation commissioned Mathematica to document leadership practices at KIPP schools. This issue brief summarizes notable findings from the study, which focused on identifying leadership practices across diverse areas: leadership structure and transitions, and the selection, development, and evaluation of leaders. Among other notable findings, KIPP combines a tiered sequence of leadership roles at the local level with national staff development programs to generate a pipeline of school leaders. The study also found that KIPP's Leadership Competency Model defines the skills school leaders need and guides development and evaluation

Comparison of Cellulosic Ethanol Yields from Midwestern Maize and Reconstructed Tallgrass Prairie Systems Managed for Bioenergy

Maize- and prairie-based systems were investigated as cellulosic feedstocks by conducting a 9 ha side-by-side comparison on fertile soils in the Midwestern United States. Maize was grown continuously with adequate fertilization over years both with and without a winter rye cover crop, and the 31-species reconstructed prairie was grown with and without spring nitrogen fertilization. Both maize stover and prairie biomass were harvested in the fall. We compared amounts of cellulosic biomass produced and harvested, carbohydrate contents as measured by both dietary and detergent methods, and estimated cellulosic ethanol yields per hectare. From 2009–2013, the cropping system with the largest non-grain biomass yield was fertilized prairie, averaging 10.4 Mg ha−1 year−1 aboveground biomass with average harvest removals of 7.8 Mg ha−1 year−1. The unfertilized prairie produced 7.4 Mg ha−1 year−1 aboveground biomass, with average harvests of 5.3 Mg ha−1 year−1. Lowest cellulosic (non-grain) biomass harvests were obtained from continuous maize systems, averaging 3.5 Mg ha−1 year−1 when grown with, and 3.7 Mg ha−1 year−1 when grown without a winter rye cover crop, respectively. Unfertilized prairie biomass and maize stover had equivalent dietary-determined potential biomass ethanol yields at 330 g ethanol kg−1 dry biomass, but fertilized prairie was lower at 315. The detergent method did not accurately capture these differences. Over the five-year period of the experiment, unfertilized and fertilized prairie systems averaged 810 and 1,790 L potential cellulosic ethanol ha−1 year−1 more than the maize systems, respectively. Differences in harvested biomass accounted for \u3e90 % of ethanol yield variation

Three-year Trajectories of Global Perceived Quality of Life for Youth With Chronic Health Conditions

Purpose Objectives of this longitudinal study were to examine 3-year trajectories of global perceived quality of life (QOL) for youth with chronic health conditions, as obtained from youth and parent reports, and to identify personal and environmental factors associated with the trajectory groups for each perspective. Methods Youth with various chronic conditions aged 11–17 years and one of their parents were recruited from eight children’s treatment centers. Latent class growth analysis was used to investigate perceived QOL trajectories (separately for youth and parent perspectives) over a 3-year period (four data collection time points spaced 12 months apart). Multinomial logistic regression was employed to identify factors associated with these trajectories. Results A total of 439 youth and one of their parents participated at baseline, and 302 (69 %) of those youth/parent dyads completed all four data collection time points. Two QOL trajectories were identified for the youth analysis: ‘high and stable’ (85.7 %) and ‘moderate/low and stable’ (14.3 %), while three trajectories were found for the parent analysis: ‘high and stable’ (35.7 %), ‘moderate and stable’ (46.6 %), and ‘moderate/low and stable’ (17.7 %). Relative to the ‘high and stable’ groups, youth with more reported pain/other physical symptoms, emotional symptoms, and home/community barriers were more likely to be in the ‘moderate and stable’ or ‘moderate/low and stable’ groups. Also, youth with higher reported self-determination, spirituality, family social support, family functioning, school productivity/engagement, and school belongingness/safety were less likely to be in the ‘moderate and stable’ or ‘moderate/low and stable’ groups, compared to the ‘high and stable’ groups. Conclusion Findings suggest that youth with chronic conditions experience stable global perceived QOL across time, but that some individuals maintain stability at moderate to moderate/low levels which is related to ongoing personal and environmental influences. Potential benefits of universal strategies and programs to safeguard resilience for all youth and targeted interventions to optimize certain youths’ global perceived QOL are indicated