Abstract

We investigated the effects of water and macronutrient (N, P, K, Ca, and Mg) on the above-ground dry biomass production of annual plants in an old field from a coastal desert site in North-Central Chile. Field experiments were conducted in two 1-ha plots located on a marine terrace at 30006'S. Experimental plots differed in soil characteristics (E.C., O.M., N, P, K, and Ca), in the depth of a calcareous hardpan layer ("tertel"), which varied between 30 cm (Plot 1) to > 1 m (Plot 2), and in species composition. In Plot 1, only two species out of five, Erodium malacoides and Oxalis micrantha, had higher biomass in the watered quadrats. In Plot 2, 7 out of 10 species, Adesmia tenella, Calandrinia trifida, Cryptantha glomerata, Cryptantha glomerulifera, Oenothera coquimbensis, Oxalis micrantha, and Plantago hispidula had higher biomass in watered quadrats. In Plot 1, except for Erodium malacoides, species had higher biomass in nitrogen amended quadrats. In Plot 2, 4 species, Calandrinia trifida, Camissonia dentata, Cryptantha glomerulifera, and Schismus arabicus had significantly higher biomass in nitrogen amended quadrats. In both plots, annual species did not responded to P, K, Ca, Mg and ground tertel addition. Whereas in Plot 1 no interaction effects of water and fertilizer were detected, in Plot 2 Calandrinia trifida and Schismus arabicus showed a significant combined effect of water and nitrogen. We suggest that species responses to water and nitrogen may be related to the depth of the tertel layer, since moisture stays longer at the surface in shallower soils. In contrast, infiltration reduces water availability for the plants in soils where tertel is deep. This could explain why more species responded to artificial irrigation in Plot 2 than in Plot 1. By stimulating plant growth, irrigation and rainfall have forced more species to encounter limiting nitrogen levels in Plot 1.