Diagnosing the cause of symptoms seen in crops can be helped by sampling soils and plant tissues during the growing season. Where patches of poor growth are seen, either soil or plant tissue samples from within the good and poor patches can be taken and sent for analysis.
For plant tissue samples, cut around 100 youngest fully expanded leaves to send away. This is the minimum amount required to do the testing at the laboratory. For soil samples, take the top 10 cm in the good and bad areas, keep them separate and send them for testing.
|The shapes of the good and poor patches can often help with diagnosis. For example, if the good patches are on last years crop windrows and the poor patches between the windrows, then potassium deficiency could be suspected. On the other hand, if the good patches are between the windrows, then tie up from the crop residue might be limiting nitrogen supply. Poor spreading patterns can also be indicated by strips across paddocks.|
If the patterns are occurring in patches they may correspond to subsoil limitations, such as low pH, high levels of salinity, high boron or high sodicity that is closer to the soil surface where gilgais have been smoothed off over the years. Iron and manganese deficiencies can also show up where limestone is close to the surface.
Article by Rob Norton, IPNI with technical input from Abigail Jenkins, NSW DPI & James Easton, CSBP. Photo courtesy of IPNI.