THE EFFECTS OF WATER AND NUTRIENT ADDITION ON ANNUAL ABOVEGROUND BIOMASS PRODUCTION OF CHENOPODIUM PETIOLARE HBK (CHENOPODIACEAE) IN A NORTH-CENTRAL CHILEAN OLD FIELD

The effects of water and nutrient supplementation on the annual aboveg round biomass production of Chenopodium petiolare H.B.K. were measured in an old field of north-central Chile by simulating rainfall events of 5 mm per month and by adding fertilizers to experimental quadrats i n two years with different precipitation levels. In irrigated quadrats , the biomass of C. petiolare was higher than in non-irrigated quadrat s. In the nutrient supplementation experiment, the only fertilizer tha t elicited a plant response was nitrogen. Biomass yield in the nitroge n-supplemented quadrats was over twice that in the control quadrats. A s expected from experimental results, biomass in the wet year (1991) w as twice as high as the biomass yield during the dry year (1990). Obse rvations on the spatial distribution of C. petiolare elsewhere support our experimental results.