Comparative behavior of wheat and barley associated with field release and grain weight determination

Double-cropping using the wheat-soybean sequence is a common practice in Argentina to promote the intensification of crops within rotations. However, the late release of the fields by a delayed harvest time in wheat determines soybean yield penalizations. In this context, barley could represent a better option than wheat preceding soybean in the crop rotation since there is some evidence that finishes its cycle earlier than wheat. However, it is not clear which period of barley shortens crop cycle allowing an earlier field release than wheat. The objectives of this study were to compare wheat and barley in terms of [i] field release and [ii] grain weight determination through the analysis of their physiological mechanisms. Field experiments during two consecutive growing seasons testing five different environments [three sowing dates in 2007 and two in 2008] were carried out to analyze the duration of different ontogenic periods and the attributes [dry matter and water dynamics] determining grain weight during the grain-filling period in wheat and barley. Early flowering time was the main cause of the early field release by barley as the grain filling and drying period were similar in both species. A strong relationship was found between dry matter and water dynamics in both species. Barley reached a higher maximum water content than wheat and also achieved physiological maturity with higher moisture concentration than wheat [48 and 39 percent, respectively]. Barley showed a slight increase in grain weight, respect to wheat, due to a source:sink ratio enhancement [4 percent and 9 percent for wheat and barley, respectively]. These data show an opposite response to that of Mediterranean, Australian and UK environments, where barley was under stronger sink limitation than wheat during the grain-filling period.