Progrès dans la science et la technologie des cultures

Abstrait

Improvements in Alfalfa (Medicago sativa L.) Seed Production with Warming Climatic Conditions on the Northern Altiplano of La Paz, Bolivia

Mario Coca Morante and Zoia Coronado Lira

Alfalfa (Medicago sativa L.) has been cultivated since 1948 on the Northern Altiplano of La Paz, Bolivia. It is grown largely for forage rather than seed since the cold negatively affects fruit production. During the 2001/2002 season, an experimental plot with a complete random block design (5 × 2 m) and four replicates, was established at the Estación Experimental Belén (the Belén Research Station) on the Northern Altiplano at an altitude of 3824 m, in which 11 varieties of alfalfa were planted with the aim of examining their seed-producing potential. These crops were left uncut between sprouting (August) and harvest. Maximum and minimum and mean daily temperatures were recorded over the growing season, and compared to those recorded for 1949/50 (just after alfalfa was first introduced). All the varieties showed good percentage flowering rates (mean 80%). In May 2002, 1 m² samples were harvested from each experimental unit and air dried in the normal environment. The seeds were separated out by threshing, weighed, and the percentage able to germinate determined in the laboratory. The variety Valador produced the greatest seed yield (76 kgha^-1) followed by Ranger (51 kg.ha^-1). Historical records show no alfalfa seed to have been produced in the late 1940s/early 1950s. The variety UMSS produced the seeds that most often germinated (57%); those of the other varieties were commonly hard or immature. The temperatures recorded for the 2001/2002 season were notably warmer than those for 1949/50; temperature is known to influence alfalfa seedproducing capacity. The present results show that alfalfa seed can now be produced on the Northern Altiplano. This might be due to the higher temperatures currently recorded in the region, which might increase the presence of pollinating insects as well as improve plant and seed metabolism.