SOIL DEPTH, WATER AVAILABILITY AND WHEAT YIELD IN THE AUSTRAL PAMPA OF ARGENTINA

Resumen

The influence of soil depth (SD) on the content of available water at sowing (AWS), in November (AWN) and crop yield (YLD) was studied in a wheat monoculture under no-till in the semi-arid region of Buenos Aires province, Argentina. The objectives were to set and rank relationships between variables such as SD, precipitation and soil water availability on YLD under zero tillage and to establish a critical SD value for less random economic returns. At 15 points selected annually in a commercial field, AWS, AWN and YLD were measured during seven years. Relative yields (RYLD) were calculated and simple regression and classification-regression tree procedures were used. Minimum and maximum absolute yields were 870 and 5900 kg ha-1. Significant relationships were observed between SD and YLD in six of the seven years. A critical SD of 0.52 m was established for an RYLD value of 0.68, which corresponds to a production range between 1500 and 4000 kg grain ha-1. All years showed relationship between SD and AWS (R2> 0.31, p<0.06), and six of them with AWN (R2> 0.34, p<0.02). In turn, soil water content influenced crop yield: AWS in five years (R2> 0.41, p<0.01), and AWN in six (R2> 0.23, p<0.07). Although there was a relationship between these variables and rainfall, no significant correlations could be established. Classification-regression tree selected SD as the first determinant variable for wheat RYLD, followed by rainfall during the crop cycle and rainfall in November for the shallower soils. Rainfall during crop cycle and during fallow was the determinant variable for the deeper ones. Results indicate that site-specific nutrient management is possible based on SD.