Anusuya Rangarajan

Weed Ecology and Nonchemical Management under Strip-Tillage: Implications for Northern U.S. Vegetable Cropping Systems

Abstract In northern U.S. vegetable cropping systems, attempts at no-till (NT) production have generally failed because of poor crop establishment and delayed crop maturity. Strip tillage (ST) minimizes these problems by targeting tillage to the zone where crops are planted while maintaining untilled zones between crop rows, which foster improvements in soil quality. ST has been shown to maintain crop yields while reducing energy use and protecting soils in vegetable crops, including sweet corn, winter squash, snap bean, carrot, and cole crops. Despite potential benefits of ST, weed management remains an important obstacle to widespread adoption. Increased adoption of ST in cropping systems for which effective, low-cost herbicides are either limited (e.g., most vegetable crops) or prohibited (e.g., organic systems) will require integration of multiple cultural, biological, and mechanical approaches targeting weak points in weed life cycles. Weed population dynamics under ST are more complex than under either full-width, conventional tillage (CT) or NT because weed propagules—as well as factors influencing them—can move readily between zones. For example, the untilled zone in ST may provide a refuge for seed predators or a source of slowly mineralized nitrogen, which affects weed seed mortality and germination in the tilled zone. Greater understanding of such interzonal interactions may suggest manipulations to selectively suppress weeds while promoting crop growth in ST systems. Previous studies and recent experiences in ST vegetable cropping systems suggest a need to develop weed management strategies that target distinct zones while balancing crop and soil management tradeoffs. For example, in untilled zones, optimal management may consist of weed-suppressive cover crop mulching, combined with nitrogen exclusion and high-residue cultivation as needed. In contrast, weed management in the tilled zone may benefit from innovations in precision cultivation and flame-weeding technologies. These short-term strategies will benefit from longer-term approaches, including tillage-rotation, crop rotation, and cover cropping strategies, aimed at preventing seed production, promoting seed predation and decay, and preventing buildup of problematic perennial weeds. However, a concerted research effort focused on understanding weed populations as well as testing and refining integrated weed management strategies will be necessary before ST is likely to be widely adopted in vegetable cropping systems without increased reliance on herbicides. Nomenclature: Carrot, Daucus carota L.; cole crops, Brassica spp.; snap bean, Phaseolus vulgaris L.; sweet corn, Zea mays L.; winter squash, Cucurbita moschata Duchesne ex Poir. Resumen En los sistemas de cultivos de vegetales del norte de Estados Unidos, los intentos de producción con cero labranza (NT) generalmente han fallado debido a un establecimiento pobre y madurez tardía del cultivo. El cultivo en bandas (ST) minimiza estos problemas al enfocar la labranza en la zona donde los cultivos son plantados mientras que mantiene zonas sin labrar entre las líneas del cultivo, lo cual mejora la calidad del suelo. ST ha mostrado la capacidad de mantener el rendimiento del cultivo al tiempo que reduce el uso de energía y protege el suelo en cultivos de vegetales, incluyendo maíz dulce, calabacín de invierno, frijol común, zanahoria y coles. A pesar de los beneficios potenciales de ST, el manejo de malezas continúa siendo un obstáculo importante para su mayor adopción. El incremento en la adopción de ST en sistemas de cultivos para los cuales herbicidas efectivos y de bajo costo son, ya sea, limitados (e.g., mayoría de cultivos de vegetales) o prohibidos (e.g., sistemas orgánicos), requerirá la integración de múltiples estrategias culturales, biológicas, y mecánicas dirigidas a los puntos débiles en los ciclos de vida de las malezas. Las dinámicas de poblaciones de las malezas en ST son más complejas que en labranza de cobertura total, labranza convencional (CT) o NT, porque los propágulos de las malezas, además de los factores que los influencian, pueden moverse ampliamente entre zonas. Por ejemplo, la zona no labrada en ST podría proveer refugio para depredadores de semillas o podría ser una fuente de nitrógeno de lenta mineralización, los cuales afectan la mortalidad y la germinación de las semillas de las malezas en la zona labrada. Un mayor entendimiento de tales interacciones entre zonas podría sugerir manipulaciones para suprimir las malezas selectivamente mientras se promueve el crecimiento del cultivo en sistemas ST. Estudios previos y experiencias recientes en sistemas de cultivos de vegetales en ST indican la necesidad de desarrollar estrategias de manejo de malezas que apuntan a zonas específicas mientras balancean los conflictos entre el manejo del cultivo y del suelo. Por ejemplo, en zonas sin labrar, el manejo óptimo podría consistir en usar cultivos de cobertura para la supresión de malezas, en combinación con la exclusión de nitrógeno y el uso del cultivo con altos residuos cuando sea necesario. En contraste, el manejo de malezas en la zona labrada podría beneficiarse de innovaciones en tecnología de cultivadores de precisión y de quemadores de llama. Estas estrategias de corto plazo se beneficiarán de estrategias de largo plazo orientadas a prevenir la producción de semillas, promover la depredación y degradación de semillas, y a prevenir el incremento de malezas perennes problemáticas. Sin embargo, un esfuerzo concertado de investigación enfocado no solo en entender las poblaciones de malezas, sino que en evaluar y refinar las estrategias integradas de malezas, será necesario antes de que ST sea ampliamente adoptada en sistemas de cultivos de vegetales sin una dependencia mayor en herbicidas.

Iron bioavailability from Amaranthus species: 2—Evaluation using haemoglobin repletion in anaemic rats

Initial screening of 46 lines from 12 species of Amaranthus indicated wide variation in total iron (Fe) and small but significant differences in bioavailable Fe when estimated by an in vitro assay. To verify if differences in bioavailable Fe detected by in vitro assay were biologically significant, one line from each species A tricolor, A hypochondriacus and A cruentus was evaluated using a haemoglobin (Hb) repletion assay with anaemic rats. Anaemic rats were fed treatment diets in which almost all Fe was provided by amaranth lines, and Hb gains were compared to those of rats fed control FeSO4 diets. Slope ratio analysis indicated that Fe supplied by A hypochondriacus had a greater relative bioavailability (61%) than from A tricolor (44%), when compared to FeSO4 (100%). However, A tricolor contained a higher concentration of total Fe (690 ppm) in the leaf material. When the same amount of amaranth was added to individual diets (30 g kg−1 diet), analysis of Hb repletion efficiency (HRE) indicated that A tricolor supported the largest Hb gain of the three lines, despite having the lowest relative bioavailability compared to A hypochondriacus and A cruentus. Despite a lack of correlation between total and bioavailable Fe, these results suggest future efforts should focus initially on enhancing total Fe concentration of green leafy vegetables (GLVs), until the forms of bioavailable Fe in these plant materials are identified. Rat bioassay did confirm relative differences in bioavailable Fe estimated by the in vitro assay, supporting use of the in vitro assay in breeding programmes focused on improving Fe nutritional quality of GLVs.

Linking vegetable preferences, health and local food systems through community-supported agriculture.

OBJECTIVE The objective of the present study was to explore the influence of participation in community-supported agriculture (CSA) on vegetable exposure, vegetable intake during and after the CSA season, and preference related to locally produced vegetables acquired directly from CSA growers. DESIGN Quantitative surveys were administered at three time points in two harvest seasons to four groups of CSA participants: new full-paying, returning full-paying, new subsidized and returning subsidized members. Questionnaires included a vegetable frequency measure and measures of new and changed vegetable preference. Comparisons were made between new and returning CSA members and between those receiving subsidies and full-paying members. SETTING The research was conducted in a rural county in New York, USA. SUBJECTS CSA members who agreed to participate in the study. RESULTS Analysis was based on 151 usable questionnaires. CSA participants reported higher intake of eleven different vegetables during the CSA season, with a sustained increase in some winter vegetables. Over half of the respondents reported trying at least one, and up to eleven, new vegetables. Sustained preferences for CSA items were reported. CONCLUSIONS While those who choose to join a CSA may be more likely to acquire new and expanded vegetable preferences than those who do not, the CSA experience has the potential to enhance vegetable exposure, augment vegetable preference and increase overall vegetable consumption. Dietary patterns encouraged through CSA participation can promote preferences and consumer demand that support local production and seasonal availability. Emphasis on fresh and fresh stored locally produced vegetables is consistent with sustainable community-based food systems.