11. Social change, spatial change: evolution of the Limari irrigation system (Chile).; Transformations sociales, transformations spatiales: l'evolution du systeme d'irrigation du Limari (Chili).

• Authors:
  • Reyes Serrano, H. F.
  • Alvarez Latorre, P.
  • Poncet, Y.
• Source: Sécheresse
• Volume: 22
• Issue: 4
• Year: 2011
• Summary: The Coquimbo region, in Chile, receives a rainfall of 110 mm (annual mean), winter rains, which allow only small scale cereal cropping and pastures for goat and sheep raising. However, thanks to subtle irrigation processes, practiced for centuries, the region used to export high value agricultural products up to mining and transportation workers and facilities settled in the northern arid area of the country. The history of ground occupation and soil uses, throughout the colonial era then in an independent Chile, designed not only the land property modalities, but also the sharing of rights of water usage. During the last sixty years, this system has changed considerably, with both technical causes (artificial lakes to stock water, cheap electric energy in rural areas) and with political and social causes (agrarian reform, agricultural foreign capital). The scientific research program " Suivi de la desertification, connaissance des systemes d'elevage caprin, gestion de la ressource en eau: trois aspects pour la definition d'une politique environnementale incluant la participation des populations dans la IVeregion du Chili ( ECOS-Conicyt)" studied theses changes and their consequences, in order to anticipate consequences and foresee negative ones: the "Limari model" is frequently given as an example of successful economic development and is to be copied in other arid valleys. The irrigation graphic scheme of the valley of Limari is hereafter presented in four dynamic figures, as one of the multidisciplinary supports for research into the well-known problems of geographic and economic balance between rural and urban development, between irrigated and arid areas, and upon the long range effects of the disconnection between land rights and water rights. The new social and economic order will be effected as a consequence of the relationship between new technical applications and new laws and rights. This graphic demonstration is contrived to organise and discuss available information about water, energy, irrigated areas and regulation by law.

12. Using maize as a reference plant material and natural 13C for field assays of soil carbon dynamics.

• Authors:
  • Balesdent, J.
  • Munoz, C.
  • Vidal, I.
  • Zagal, E.
• Source: Proceedings of the 19th World Congress of Soil Science: Soil solutions for a changing world
• Year: 2010
• Summary: Sustainable agriculture should maintain soil organic carbon to prevent soil degradation and erosion, but soil C management still requires basic data on soil C dynamics under many climates, soil types and land uses. We applied a simple field method for the measurement of soil carbon dynamics, based on the natural 13C labelling technique of carbon inputs. The method implies the addition of locally produced maize material into the soil with C3 crops, in a simple, light and cost-effective design, and the kinetic analysis of soil 13C/ 12C. In Chile the approach was applied on a nine years fertility experiment with no till conditions sustaining a wheat-oat rotation, and followed thereafter for 5 years. The experimental site is located in the Andes pre-mountain (36degrees55′S, 71degrees53′O). The soil is of volcanic origin (medial, amorphic, mesic, Typic Haploxerands) and the crop rotation wheat-oat. The labeling technique showed that a very low amount (about 1 t ha -1) was incorporated to the soil (new C) during the time-period of the experiment (4 years). The ratio of remaining C/ added C after 4 years was very low (0.03) suggesting that the high carbon content of the soil can therefore be considered as due to a large amount of passive carbon, or to ancient carbon inputs, that have saturated the sorption capacity.

13. The history of herbicide-resistant weeds in Chile.

• Authors:
  • Prado A., R. del
  • Diaz S., J.
  • Espinoza N., N.
• Source: XVII Congreso de la Asociación Latinoamericana de Malezas (ALAM) I Congreso Iberoamericano de Ciencia de las Malezas, IV Congreso Nacional de Ciencia de Malezas, Matanzas, Cuba, 8 al 11 de noviembre del 2005, pp. 326
• Year: 2005
• Summary: Eight biotypes of herbicide-resistant weeds have been described in Chile. All belong to grass weeds, specifically wild oat ( Avena fatua), ryegrass ( Lolium rigidum), Italian ryegrass ( L. multiflorum) and crested dogtailgrass ( Cynosurus echinatus), which are the most common in the main wheat, barley, oats, lupin and canola producing area (36degreesS to 39degreesS). The biotypes have shown resistance to ACCasa, ALS and EPSP inhibitors. Most biotypes have appeared in farm fields subjected to intensive land use, with annual crops, with a trend to wheat monoculture in some cases, and with intense use of no-till and herbicides with similar mode of action. Herbicides most frequently used have been glyphosate (EPSP), diclofop-methyl and clodinafop-propargyl (ACCasa). Cross-resistance to ACCasa was found in some biotypes of wild oat and ryegrass, with greater resistance to aryloxyphenoxypropionates than to cyclohexanediones. All ACCasaresistant biotypes were susceptible to iodosulfuron and flucarbazone Na (ALS). These two herbicides are recommended for wheat and began to be used just recently in the country. Two biotypes of Italian ryegrass were found resistant to glyphosate. One of these biotypes showed, in addition, resistance to ALS; that is to say, showed multiple resistance. Also the crested dogtailgrass biotype showed multiple resistance to ACCasa and ALS.

14. Meeting cereal demand while protecting natural resources and improving environmental quality

• Authors:
  • Yang, H.
  • Walters, D. T.
  • Dobermann, A.
  • Cassman, K. G.
• Source: Annual Review of Environment and Resources
• Volume: 28
• Issue: 1
• Year: 2003
• Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.

15. Weed Management in Conservation Tillage Systems for Wheat Production in North and South-America

• Authors:
  • Lindwall, C. W.
  • Roman, E. S.
  • Moyer, J. R.
  • Blackshaw, R. E.
• Source: Crop Protection
• Volume: 13
• Issue: 4
• Year: 1994
• Summary: Soil erosion by wind or water is a serious problem in North and South America. When no-till or reduced tillage is used to control erosion, the density of certain annual and perennial weeds can increase and new weed control techniques are usually required. The effects of conservation tillage on annual and perennial weeds, weeds that are spread by wind, plants from rangelands and pasture as weeds and volunteer plants as weeds arc reviewed. Current weed control methods with minimum tillage, herbicides, cover crops and other cultural practices in conservation tillage systems in North and South America are described. Some producers are successfully controlling weeds in continuous summer cropping systems in North America and in double cropping systems that include wheat in the winter and soybean or corn in the summer in Brazil, Argentina and southeastern United States. Successful conservation tillage systems usually involve cropping sequences of three or more crop types and several herbicides. In these cropping sequences, the ground is covered with a crop during most of the period in which the climate is favourable for weed growth. Perennial weeds are a problem in all tillage systems and there is a general dependence on glyphosate for perennial weed control. In successful conservation tillage systems, the amount and cost of herbicides used is similar to that for herbicides used in conventional tillage systems.