Soil organic matter and wheat productivity in the semiarid argentinian pampas

DÍAZ-ZORITA, MARTÍN; BUSCHIAZZO, DANIEL E; PEINEMANN, NORMAN

AGRONOMY JOURNAL

American Society of Agronomy

Lugar: Madison, WI; Año: 1999 vol. 91 p. 276 - 279

0002-1962

Crop productivity under dryland conditions is largely limited by soil water availability. Soil organic matter (SOM) contents have been found to be a reliable index of crop productivity in semiarid regions because it positively affects soil water-holding capacity. Our objectives were to explain differences in wheat (Triticum aestivum L.) yields in response to SOM levels and related properties and to quantify the contribution of a unit increment of SOM content to soil productivity during 1991,1992, and 1994 on a total of 134 production fields in the semiarid Argentine Pampas. Wheat yields were related to both soil water retention and total organic C (TOC) contents in the top layers (0–20 cm) in years with low moisture availability (1992 [r = 0.51, P < 0.01] and 1994 [r = 0.59, P < 0.01]), and were related to both total N and available P contents in a year without water deficit stress (1991 [r = 0.58, P < 0.01]). Wheat yields over all years were linearly related to TOC (r = 0.68, P < 0.01) when these contents were <17.5 g kg–. Dependence of wheat yields on soil water retention and on TOC contents under water deficit was related to the positive effect of these soil components on plant-available water. In the absence of water deficit (1991), nutrient availability was the limiting factor. Losses of 1 Mg SOM ha– were associated with a decrease in wheat yield of approximately 40 kg ha–. These results demonstrate the importance of using cultural practices that minimize losses of soil organic C in the semiarid Argentine Pampas.