• Authors:
    • Munoz-Carpena, R.
    • Gabriel, J. L.
    • Quemada, M.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 155
  • Year: 2012
  • Summary: Using cover crops (CC) in semiarid irrigated areas is often limited by low nutrient and water-use efficiency. This work was conducted over 3.5 years to determine the effect on NO 3- leaching, water balance and soil mineral N accumulation of replacing fallow with CC in irrigated systems. Treatments studied during the maize ( Zea mays L.) intercrop period were: barley ( Hordeum vulgare L.), vetch ( Vicia villosa L.) and fallow. Soil water content was monitored daily to a depth of 1.3 m and used with the numerical model WAVE to describe the water balance. Determination of crop canopy parameters was based on digital image analysis, and root depth in capacitance sensor readings. Nitrate leaching was calculated multiplying drainage by the soil solution nitrate concentration. Soil mineral N was determined before sowing CC and maize. Over the study, cumulative nitrate leaching in the fallow, vetch, and barley was 346, 245, and 129 kg N-NO 3- ha -1, respectively; occurring more than 77% during the intercrop period. In dry winters, NO 3- accumulated in the topsoil, and CC controlled the NO 3- leaching during the initial maize growth stages. Vetch was less efficient than barley at controlling leaching, but enhanced soil N retention. The CC controlled NO 3- leaching and recycled N inside the cropping system.
  • Authors:
    • Stewart, J. S.
    • Menge, B. A.
    • Gouhier, T. C.
    • Iles, A. C.
    • Haupt, A. J.
    • Lynch, M. C.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 2
  • Year: 2012
  • Summary: Eastern boundary current systems are among the most productive and lucrative ecosystems on Earth because they benefit from upwelling currents. Upwelling currents subsidize the base of the coastal food web by bringing deep, cold and nutrient-rich water to the surface. As upwelling is driven by large-scale atmospheric patterns, global climate change has the potential to affect a wide range of significant ecological processes through changes in water chemistry, water temperature, and the transport processes that influence species dispersal and recruitment. We examined long-term trends in the frequency, duration, and strength of continuous upwelling events for the Oregon and California regions of the California Current System in the eastern Pacific Ocean. We then associated event-scale upwelling with up to 21 years of barnacle and mussel recruitment, and water temperature data measured at rocky intertidal field sites along the Oregon coast. Our analyses suggest that upwelling events are changing in ways that are consistent with climate change predictions: upwelling events are becoming less frequent, stronger, and longer in duration. In addition, upwelling events have a quasi-instantaneous and cumulative effect on rocky intertidal water temperatures, with longer events leading to colder temperatures. Longer, more persistent upwelling events were negatively associated with barnacle recruitment but positively associated with mussel recruitment. However, since barnacles facilitate mussel recruitment by providing attachment sites, increased upwelling persistence could have indirect negative impacts on mussel populations. Overall, our results indicate that changes in coastal upwelling that are consistent with climate change predictions are altering the tempo and the mode of environmental forcing in near-shore ecosystems, with potentially severe and discontinuous ramifications for ecosystem structure and functioning.
  • Authors:
    • Roy-Macauley, H.
    • Jalloh, A.
    • Sereme, P.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 157
  • Year: 2012
  • Summary: The West and Central Africa (WCA) sub region covers a total area of over 11.5 million km 2 with a population of over 318 million. Most of the rural population in WCA are poor and food insecure and about 70% of the people in the region depends on agriculture, which accounts for over 35% of Gross Domestic Product (GDP) and over 40% of its export. The agroecological zones of WCA are closely related to the agro climatic zones of the region with rainfall decreasing from the southern coast in the forest region to the sub humid and semi arid Sahelian region in the north. The major agroecosystems of WCA include the semi arid, sub humid, humid forest, and swamp. Growing populations, inappropriate agricultural practices and changing climate in the region are influencing the composition and ability of agroecosystems in providing much needed ecosystem services. Coordinating efforts to tackle these challenges and leverage opportunities for sustainable agricultural production while ensuring conservation of the diverse ecosystems in the region is therefore a major preoccupation of the West and Central African Council for Agricultural Research and Development (CORAF/WECARD).
  • Authors:
    • Alves, B. J. R.
    • Follett, R. F.
    • Halvorson, A. D.
    • Jantalia, C. P.
    • Polidoro, J. C.
    • Urquiaga, S.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 6
  • Year: 2012
  • Summary: Ammonia (NH 3) volatilization is one of the main pathways of N loss from agricultural cropping systems. This study evaluated the NH 3-N loss from four urea-based N sources (urea, urea-ammonium nitrate [UAN], SuperU, and ESN [polymer-coated urea]) surface band applied at a rate of 200 kg N ha -1 to irrigated, strip-till corn production systems for 2 yr using semi-static chambers (semi-open and open) to measure NH 3-N loss. The efficiency of the semi-static chambers in estimating NH 3-N loss under field conditions was determined using 15N labeled urea applied at rates of 50, 100, and 200 kg N ha -1. Both chamber types had similar NH 3-N recoveries and calibration factors. Immediate irrigation with 16 to 19 mm of water 1 d after N fertilization probably limited NH 3-N volatilization from surface-applied N fertilizers to a range of 0.1 to 4.0% of total N applied. SuperU, which contains a urease inhibitor, had the lowest level of NH 3-N loss when compared to the other N sources. Analyzed across years, estimated NH 3-N losses for the N sources were in the order: ESN=UAN > urea > SuperU. Both years the results showed that measurement time may need to be increased to evaluate NH 3-N volatilization from polymer-coated urea N sources such as ESN. The open-chamber method was a viable, low cost method for estimating NH 3-N loss from small field plot N studies.
  • Authors:
    • Moyo, B. H.
    • Chirwa, P. W.
    • Khumalo, S.
    • Syampungani, S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 157
  • Year: 2012
  • Summary: This paper reviews the agroecosystems and agricultural biodiversity in Southern Africa and highlights the importance of the agricultural landscape in biodiversity conservation and the important role that the traditional farming systems play in conserving biodiversity. The review established that agrobiodiversity is of great importance to both small scale and large commercial farmers in Southern Africa through its provision of ecosystem services. The paper also highlights the significant loss of agrobiodiversity as a result of human population pressure and the transition from traditional mixed farming systems which is characterized with high agrobiodiversity, to modern monoculture farming resulting in decline of species diversity. Although concerted efforts are being made to promote the sustainable use and management of this agrobiodiversity, there need to have a multi-stakeholder approach so that conservation efforts are successful, a role that is currently played by the SADC Plant Genetic Resources Centre in Southern African conservation of agrobiodiversity.
  • Authors:
    • Ippolito, J. A.
    • Lentz, R. D.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Carbon-rich biochar derived from the pyrolysis of biomass can sequester atmospheric CO 2, mitigate climate change, and potentially increase crop productivity. However, research is needed to confirm the suitability and sustainability of biochar application to different soils. To an irrigated calcareous soil, we applied stockpiled dairy manure (42 Mg ha -1 dry wt) and hardwood-derived biochar (22.4 Mg ha -1), singly and in combination with manure, along with a control, yielding four treatments. Nitrogen fertilizer was applied when needed (based on preseason soil test N and crop requirements) in all plots and years, with N mineralized from added manure included in this determination. Available soil nutrients (NH 4-N; NO 3-N; Olsen P; and diethylenetriaminepentaacetic acid-extractable K, Mg, Na, Cu, Mn, Zn, and Fe), total C (TC), total N (TN), total organic C (TOC), and pH were evaluated annually, and silage corn nutrient concentration, yield, and uptake were measured over two growing seasons. Biochar treatment resulted in a 1.5-fold increase in available soil Mn and a 1.4-fold increase in TC and TOC, whereas manure produced a 1.2- to 1.7-fold increase in available nutrients (except Fe), compared with controls. In 2009 biochar increased corn silage B concentration but produced no yield increase; in 2010 biochar decreased corn silage TN (33%), S (7%) concentrations, and yield (36%) relative to controls. Manure produced a 1.3-fold increase in corn silage Cu, Mn, S, Mg, K, and TN concentrations and yield compared with the control in 2010. The combined biochar-manure effects were not synergistic except in the case of available soil Mn. In these calcareous soils, biochar did not alter pH or availability of P and cations, as is typically observed for acidic soils. If the second year results are representative, they suggest that biochar applications to calcareous soils may lead to reduced N availability, requiring additional soil N inputs to maintain yield targets.
  • Authors:
    • Kunkel, K.
    • Reddy, K. R.
    • Gao, W.
    • Xu, M.
    • Liang, X. Z.
    • Schmoldt, D. L.
    • Samel, A. N.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Climate variability and changes affect crop yields by causing climatic stresses during various stages of the plant life cycle. A crop growth model must be able to capture the observed relationships between crop yields and climate stresses before its credible use as a prediction tool. This study evaluated the ability of the geographically distributed cotton growth model redeveloped from GOSSYM in simulating U.S. cotton ( Gossypium hirsutum L.) yields and their responses to climate stresses during 1979 to 2005. Driven by realistic climate conditions, the model reproduced long-term mean cotton yields within 10% of observations at the 30-km model resolution across virtually the entire U.S. Cotton Belt and correctly captured the critical dependence of their geographic distributions on regional climate characteristics. Significant correlations between simulated and observed interannual variations were found across 87% of the total harvest grids. The model also faithfully represented the predictive role of July to August air temperature and August to September soil temperature anomalies on interannual cotton yield changes on unirrigated lands, with a similar but weaker predictive signal for irrigated lands as observed. The modeled cotton yields exhibited large, positive correlations with July to August leaf area index. These results indicate the model's ability to depict the regional impact of climate stresses on cotton yields and suggest the potential predictive value of satellite retrievals. They also provide a baseline reference for further model improvements and applications in the future study of climate-cotton interactions.
  • Authors:
    • Termansen, M.
    • Boix-Fayos, C.
    • Vente, J. de
    • Nainggolan, D.
    • Hubacek, K.
    • Reed, M. S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 159
  • Year: 2012
  • Summary: An understanding of land use change and its drivers in semi-arid Mediterranean agro-ecosystems is important for informing ways to facilitate adaptation to future environmental and socioeconomic pressures. In this paper, we mapped and quantified land use changes in the semi-arid Mediterranean agro-ecosystem of Torrealvilla catchment between 1956 and 2008. Subsequently, we detected signs of landscape fragmentation and examined the relationship between land use change trajectories and a set of biophysical factors using Generalized Additive Models (GAMs). Finally, we qualitatively evaluated the role of socioeconomic drivers on the land use change trajectories. The study provides accounts of multidirectional land use trajectories in semi-arid Mediterranean landscapes. Our analysis shows that more than 72% of the study area has undergone significant changes over the past five decades with pronounced effects on landscape composition and structure. Both biophysical and socioeconomic factors are strongly related to the observed spatial and temporal changes in land use. Three major trajectories were observed. Firstly, rain-fed agriculture is becoming less dominant; future abandonment of rain-fed agriculture should be anticipated. Secondly, expansion of forested areas is evident in higher altitudes. The trend is still likely to continue given the possibility of further abandonment of rain-fed farming and existing subsidies for reforestation of arable land. Thirdly, intensification has been observed which has occurred mainly in lower parts of the landscape on flat to gentle slopes and near main roads. Further intensification is likely to be subject to market drivers, irrigation water availability, and future rural development and agricultural policy. Overall, the study shows that even within a given locality, contrasting land use trajectories can emerge as a result of local responses to multiple drivers of change and these need to be carefully taken into account in future policy development.
  • Authors:
    • White, J. W.
    • Kimball, B. A.
    • Ottman, M. J.
    • Wall, G. W.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 1
  • Year: 2012
  • Summary: Possible future increases in atmospheric temperature may threaten wheat (Triticum aestivum L.) production and food security. The purpose of this research is to determine the response of wheat growth to supplemental heating and to seasonal air temperature from an unusually wide range of planting dates. A field study was conducted at Maricopa, AZ, where wheat was planted from September to May over a 2-yr period for a total of 12 planting dates. Supplemental heating was provided for 6 of the 12 planting dates using infrared heaters placed above the crop which increased canopy temperature by 1.3°C during the day and 2.7°C during the night. Grain yield declined 42 g m -2 (6.9%) per 1°C increase in seasonal temperature above 16.3°C. Supplemental heating had no effect on grain yield for plantings in winter (Dec./Jan.) since temperatures were near optimum (14.9°C). However, in spring (Mar.) plantings where temperature (22.2°C) was above optimum, supplemental heating decreased grain yield from 510 to 368 g m -2. Supplemental heating had the greatest effect in the early fall plantings (Sept./Oct.) when temperature was slightly below optimum (13.8°C) and mid-season frost limited the yield of unheated plots to only 3 g m -2 whereas yield of heated plots was 435 g m -2. Thus, possible future increases in temperature may decrease wheat yield for late plantings and shift optimum planting windows to earlier dates in areas of the world similar to the desert southwest of the United States.
  • Authors:
    • Lecain, D.
    • Prihodko, L.
    • Grosso, S. del
    • Smith, D.
    • Morgan, J.
    • Parton, W.
    • Kelly, R.
    • Lutz, S.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 3
  • Year: 2012
  • Summary: Net ecosystem productivity (NEP) was measured on shortgrass steppe (SGS) vegetation at the USDA Central Plains Experimental Range in northeastern Colorado from 2001 to 2003. Large year-to-year differences were observed in annual NEP, with >95% of the net carbon uptake occurring during May and June. Low precipitation during the 2002 April to June time period greatly reduced annual net carbon uptake. Large precipitation events (>10 mm day -1) promoted carbon uptake, while small precipitation events (5 mm having a similar increase in respiration (>3.00 g m Cm -2 day -1). In addition, the size of the heterotrophic respiration pulse is independent of both the amount of time since the last rainfall event and the time of occurrence during the growing season.