Telleraga Station, a 2,400 ha property in northern NSW, Australia has been growing cotton since 1979. The black cracking clay soil is subject to compaction by farm machinery, particularly when the cotton is picked (harvested) with soil wet from rain. Flood irrigation is used.
Wheat was grown in Field 16 at Telleraga in 1985, prior to growing cotton in the 1986-87 season. The graph shows the full and refill points from the 1985 cotton crop, together with moisture readings taken after growing wheat.
The deficit, the difference between full and refill, has increased from ?? to ??.
It has been found that rotation with wheat breaks up the soil profile, with a subsequent increase in water availability to cotton in following seasons. This allows for less frequent irrigations (each irrigation reduces yield from waterlogging), and more flexibility with irrigation scheduling as there is less yield reduction if a crop is not irrigated by its refill point.
What is also of interest is that if a soil sample at 60 cm depth had been examined before and after the wheat was grown it would (presumably) have shown no difference in visible structure. Yet before the wheat was grown the cotton crop was stressed at 43% VSW, and after the wheat it was stressed at 39%. And yet it was the same soil.