In central Oklahoma continuous wheat is the predominant cropping system. However, nowadays it is not rare to find fields with summer crops. Full season summer crops such as corn, soybean and sorghum are usually planted from late March to early May and harvested in late August to September. Afterwards, winter wheat is usually planted. At this moment we usually have the dilemma whether this following winter wheat will have lower yields compared to wheat after fallow, due to starting with drier soil profile.
In a study that compares the adoption of several crop species in 2-yr cropping systems, we have observed that the soil profile after full season crops is considerably drier than a soil profile coming from a fallow period (about 4 months in the typical continuous wheat systems of central Oklahoma). Nonetheless, at this point wheat does not require much water. Wheat water needs may be satisfied by few fall precipitation events that recharge the first 30-40 cm, even when the rest of the soil profile remains dry.
Later measurements of plant available water at the beginning of April did not show significant differences between these cropping systems. Winter wheat grain yield after grain sorghum and corn was similar than wheat after a follow period. This shows that initial water content may not play an important role as it does precipitation distribution according to crop needs.
