Advancing the Sustainability of US Agriculture through Long-Term Research.

Agriculture in the United States must respond to escalating demands for productivity and efficiency, as well as pressures to improve its stewardship of natural resources. Growing global population and changing diets, combined with a greater societal awareness of agriculture's role in delivering ecosystem services beyond food, feed, fiber, and energy production, require a comprehensive perspective on where and how US agriculture can be sustainably intensified, that is, made more productive without exacerbating local and off-site environmental concerns. The USDA's Long-Term Agroecosystem Research (LTAR) network is composed of 18 locations distributed across the contiguous United States working together to integrate national and local agricultural priorities and advance the sustainable intensification of US agriculture. We explore here the concept of sustainable intensification as a framework for defining strategies to enhance production, environmental, and rural prosperity outcomes from agricultural systems. We also elucidate the diversity of factors that have shaped the past and present conditions of cropland, rangeland, and pastureland agroecosystems represented by the LTAR network and identify priorities for research in the areas of production, resource conservation and environmental quality, and rural prosperity. Ultimately, integrated long-term research on sustainable intensification at the national scale is critical to developing practices and programs that can anticipate and address challenges before they become crises.

Simulated Soil Organic Carbon Changes in Maryland Are Affected by Tillage, Climate Change, and Crop Yield.

The impact of climate change on soil organic C (SOC) stocks in no-till (NT) and conventionally tilled (CT) agricultural systems is poorly understood. The objective of this study was to simulate the impact of projected climate change on SOC to 50-cm soil depth for grain cropping systems in the southern Mid-Atlantic region of the United States. We used SOC and other data from the long-term Farming Systems Project in Beltsville, MD, and CQESTR, a process-based soil C model, to predict the impact of cropping systems and climate (air temperature and precipitation) on SOC for a 40-yr period (2012-2052). Since future crop yields are uncertain, we simulated five scenarios with differing yield levels (crop yields from 1996-2014, and at 10 or 30% greater or lesser than these yields). Without change in climate or crop yields (baseline conditions) CQESTR predicted an increase in SOC of 0.014 and 0.021 Mg ha yr in CT and NT, respectively. Predicted climate change alone resulted in an SOC increase of only 0.002 Mg ha yr in NT and a decrease of 0.017 Mg ha yr in CT. Crop yield declines of 10 and 30% led to SOC decreases between 2 and 8% compared with 2012 levels. Increasing crop yield by 10 and 30% was sufficient to raise SOC 2 and 7%, respectively, above the climate-only scenario under both CT and NT between 2012 and 2052. Results indicate that under these simulated conditions, the negative impact of climate change on SOC levels could be mitigated by crop yield increases.

Autonomic response characteristics of porcine airway smooth muscle in vivo.

We studied the autonomic response characteristics of airways in 65 swine in vivo. Tracheal smooth muscle response was measured isometrically in situ; bronchial response was measured simultaneously as change in airway resistance and dynamic compliance. To determine the optimal resting length at which maximal tracheal contraction was obtained, length-tension studies were generated in four animals using maximal electrical stimulation of the vagus nerves determined from stimulus-response characteristics in eight other swine. Pharmacological studies were performed in 25 animals to determine the relative potency and intrinsic activity of agonists (acetylcholine greater than histamine much greater than norepinephrine) causing contraction of trachea and bronchial airways. In 13 swine, the effects of autonomic stimulation were studied by intravenous administration of dimethylphenylpiperazinium (DMPP) after muscarinic blockade with 1.5 mg/kg iv atropine. Tracheal contraction caused by topical application of 3.4 X 10(-4) mol histamine (13.4 +/- 1.54 g/cm) was 96 +/- 7.2% blocked by 25 micrograms/kg iv DMPP in adrenal-intact animals; minimal relaxation was demonstrated in adrenalectomized animals, indicating absence of substantial sympathetic innervation to porcine trachea. Nonadrenergic innervation was not demonstrated. After beta-adrenergic blockade, sympathetic stimulation caused alpha-adrenergic contraction in bronchial airways but not in trachea. These data define the unique response characteristics of the airways of swine and demonstrate their utility for acute experimental study of airway responses in vivo.