Lesley W. Atwood

Agriculture in 2050: Recalibrating Targets for Sustainable Intensification

http://bioscience.oxfordjournals.org XXXX XXXX / Vol. XX No. X BioScience 1 BioScience XX: 1–6.

Increased productivity of a cover crop mixture is not associated with enhanced agroecosystem services.

Cover crops provide a variety of important agroecological services within cropping systems. Typically these crops are grown as monocultures or simple graminoid-legume bicultures; however, ecological theory and empirical evidence suggest that agroecosystem services could be enhanced by growing cover crops in species-rich mixtures. We examined cover crop productivity, weed suppression, stability, and carryover effects to a subsequent cash crop in an experiment involving a five-species annual cover crop mixture and the component species grown as monocultures in SE New Hampshire, USA in 2011 and 2012. The mean land equivalent ratio (LER) for the mixture exceeded 1.0 in both years, indicating that the mixture over-yielded relative to the monocultures. Despite the apparent over-yielding in the mixture, we observed no enhancement in weed suppression, biomass stability, or productivity of a subsequent oat (Avena sativa L.) cash crop when compared to the best monoculture component crop. These data are some of the first to include application of the LER to an analysis of a cover crop mixture and contribute to the growing literature on the agroecological effects of cover crop diversity in cropping systems.

Soil Functional Zone Management: A Vehicle for Enhancing Production and Soil Ecosystem Services in Row-Crop Agroecosystems.

There is increasing global demand for food, bioenergy feedstocks and a wide variety of bio-based products. In response, agriculture has advanced production, but is increasingly depleting soil regulating and supporting ecosystem services. New production systems have emerged, such as no-tillage, that can enhance soil services but may limit yields. Moving forward, agricultural systems must reduce trade-offs between production and soil services. Soil functional zone management (SFZM) is a novel strategy for developing sustainable production systems that attempts to integrate the benefits of conventional, intensive agriculture, and no-tillage. SFZM creates distinct functional zones within crop row and inter-row spaces. By incorporating decimeter-scale spatial and temporal heterogeneity, SFZM attempts to foster greater soil biodiversity and integrate complementary soil processes at the sub-field level. Such integration maximizes soil services by creating zones of ‘active turnover’, optimized for crop growth and yield (provisioning services); and adjacent zones of ‘soil building’, that promote soil structure development, carbon storage, and moisture regulation (regulating and supporting services). These zones allow SFZM to secure existing agricultural productivity while avoiding or minimizing trade-offs with soil ecosystem services. Moreover, the specific properties of SFZM may enable sustainable increases in provisioning services via temporal intensification (expanding the portion of the year during which harvestable crops are grown). We present a conceptual model of ‘virtuous cycles’, illustrating how increases in crop yields within SFZM systems could create self-reinforcing feedback processes with desirable effects, including mitigation of trade-offs between yield maximization and soil ecosystem services. Through the creation of functionally distinct but interacting zones, SFZM may provide a vehicle for optimizing the delivery of multiple goods and services in agricultural systems, allowing sustainable temporal intensification while protecting and enhancing soil functioning.

Cover-Crop Species as Distinct Biotic Filters in Weed Community Assembly

Abstract Cover crops represent a potentially important biological filter during weed community assembly in agroecosystems. This filtering could be considered directional if different cover-crop species result in weed communities with predictably different species composition. We examined the following four questions related to the potential filtering effects of cover crops in a field experiment involving five cover crops grown in monoculture and mixture: (1) Do cover crops differ in their effect on weed community composition? (2) Is competition more intense between cover crops and weeds that are in the same family or functional group? (3) Is competition more intense across weed functional types in a cover-crop mixture compared with cover crops grown in monocultures? (4) Within a cover-crop mixture, is a higher seeding rate associated with more effective biotic filtering of the weed community? We found some evidence that cover crops differentially filtered weed communities and that at least some of these filtering effects were due to differential biomass production across cover-crop species. Monocultures of buckwheat and sorghum–sudangrass reduced the number of weed species relative to the no-cover-crop control by an average of 36 and 59% (buckwheat) and 25 and 40% (sorghum–sudangrass) in 2011 and 2012, respectively. We found little evidence that competition intensity was dependent upon the family or functional classification of the cover crop or weeds, or that cover-crop mixtures were stronger assembly filters than the most effective monocultures. Although our results do not suggest that annual cover crops exert strong directional filtering during weed community assembly, our methodological framework for detecting such effects could be applied to similar future studies that incorporate a greater number of cover-crop species and are conducted under a greater range of cover-cropping conditions. Nomenclature: Buckwheat, Fagopyrum esculentum Moench; cereal rye, Secale cereal L.; field pea, Pisum sativum L.; hairy vetch, Vicia villosa Roth; mustard, Brassica juncea (L.) Czern.; sorghum–sudangrass, Sorghum bicolor × S. bicolor var. sudanese.

Influence of Seasonal Changes and Shifting Substrate on Survival of Restoration Plantings of Schizachyrium maritimum (Gulf Bluestem) on Santa Rosa Island, Florida

ABSTRACT Miller, D.L.; Thetford, M.; Dupree, J., and Atwood, L., 2014. Influence of seasonal changes and shifting substrate on survival of restoration plantings of Schizachyrium maritimum (Gulf bluestem) on Santa Rosa Island, Florida. Environmental gradients on barrier islands are modified by the loss of dunes as a result of hurricane overwash. The success of restoration plantings in posthurricane landscapes is determined by abiotic conditions, including seasonal and spatial gradients of wind speed and substrate transport encountered before dune redevelopment. The response of Schizachyrium maritimum, a dominant, sand-trapping, dune-forming grass of the northern Gulf Coast to month of planting, sand manipulation, and plant spacing was investigated on Santa Rosa Island, Florida. This grass is also a valuable food for endangered beach mice. Seasonal plantings were initiated in 4 months (November 2005, February 2006, June 2006, and August 2006) at each of six sites. For each site and each planting date, plots were split by plant spacing (30 or 45 cm between plants) and again by two sand manipulation regimes (natural sand accumulation or sand level at 3 cm). Sand surface levels were determined and manipulated every 2 weeks. Plant survival and growth were recorded September 2006 and July 2007. Plant survival and growth were greatest for summer plantings, particularly June plantings. Sand burial by natural accumulation did not result in plant death. Most plant death, particularly for November and February plantings, was associated with root exposure and sand loss around transplants. Closer spacing appeared to slow sand loss and plant death for November plantings. Planting of S. maritimum should be restricted to summer months, preferably June, and where sand loss can be minimized by use of mulch or other sand stabilizing methods.

Effect of Polyacrylamide Gel on Woody Plant Establishment in Barrier Island Swales

ABSTRACT: Increased hurricane frequency and intensity and residential and commercial development are contributing to loss of maritime forests, coastal hammocks, and scrub dunes. Barriers to natural regeneration necessitate active restoration. We evaluated the survival of woody species planted in ephemeral barrier island swales on Santa Rosa Island, Florida, in an effort to restore barrier island scrub and pine forest lost in recent hurricanes. Contractors planted sand live oak (Quercus geminata) on swale ridges, inkberry (Ilex glabra) on swale mid-slopes, and slash pine (Pinus elliottii) in swale depressions. Polyacrylamide gels are often used to increase transplant survival in the drought-prone, sandy environments. To assist us in evaluating the efficacy of these gels, contractors planted 10 plants with gel and 10 without for each swale, position, and woody species. We followed plant survival for 21 months and measured changes in plant height after one year. Polyacrylamide gel did not significantly affect survival of slash pine or sand live oak. Less than 25% of slash pine and sand live oak survived after 21 months. We found initial survival of inkberry was greater with than without gel, but plant death continued; and after eight weeks, we found no difference in survival for inkberry planted with and without gel. Inkberry survival declined to < 5% at the last evaluation. Changes in plant height were also not affected by Polyacrylamide gel. We do not recommend the use of Polyacrylamide gel to replace supplemental water or to replace the planting of deeply rooted plants on barrier islands.