Reefinating rocky areas of paddocks has increased the arable areas of many farms, but what might be the implications for fertiliser requirements?
CSBP is collaborating with the farm consulting group Consult Ag who have GRDC funding to find some answers.
Our contribution is a barley trial near Piesseville in the Great Southern, where we are investigating the need for phosphorus (P) and trace elements - copper (Cu), zinc (Zn) and manganese (Mn).
Soil tests after reefinating indicated good P reserves (Colwell P 45 mg/kg, PBI 60) – probably due to low historic yields and removal rates. Soil pH is ideal (6.0 in 0-10cm increasing to 6.5 in 20-30cm).
Unfortunately, additional testing highlighted other constraints - water repellence in the surface gravelly sand and sodicity in the clay below 30cm.
The trial design features four rates of P (0, 6, 12 and 18 kg P/ha) using Agflow , the addition of Mn (3.2 kg Mn/ha using Agflow Manganese) and the addition of liquid Cu and Zn oxides banded below the seed with Flexi-N at seeding (2.0 kg of each/ha).
So, what are we seeing so far?
Patchy establishment – no surprise given the water repellence. A soil wetter may have been beneficial.
There’s a good response to P and plant tissue testing confirmed Mn deficiency which was corrected where Agflow Manganese was applied (Table 1). Without Mn, the responses to P are likely to be less than what they could have been.
The tissue test results also showed increased Cu and Zn levels where they were applied, but levels are more than adequate where they weren’t.
It’s only one trial, and every situation will be different.
Other reefinated paddocks may have different nutritional requirements - so it's important to test them.
Table 1. Manganese concentrations in barley whole tops (2 July).