Comparable $ savings
Economic assessment of the results shows that there are considerable savings to be made by better targeting phosphorous application rates to meet crop needs and site conditions.
Fertiliser P rates in use at the eight non-responsive sites that fell within the >310 µg/L zone were in the range 66 to 114 kg P/ha. Results show that replacement P rates would be sufficient at these sites, equating to P application rates in the order of 11 to 40 kg P/ha.
An example from one of the sites in the Riverland that had a high starting soil DGT-P of 717 µg/L (Colwell-92, Olsen-48 and Bray-417 mg/kg) showed that the application rate in use by the grower was 88 kg P/ha (400 kg MAP/ha). At a targeted replacement rate of 32 kg/ha, the grower can save 56 kg/ha of P fertiliser, equating to 255 kg of MAP at a cost of $178.50 per hectare (Table 1). Even still, the results show that at a site with such a high starting soil P level, the return on investment (ROI) for every dollar spent on MAP would only be $2.76 (Table 1); once the costs for transport, handling and spreading are taken into consideration, the returns would be minimal.
Table 1. Non-responsive site | 0 kg P/ha | Current farmer rate – 88 kg P/ha | Recommended rate – 32 kg P/ha | |
---|---|---|---|---|
Yield t/ha | 56 | 57 | 57 | |
Income $/ha @ $280/t (Fresh) | $ 15,680 | $ 15,960 | $ 15,960 | |
Additional income $/ha | $ – | $ 280 | $ 280 | |
MAP required kg/ha (22% P) | 0 kg | 400 kg | 145 kg | |
Cost of P @ $700/t | $ – | $ 280 | $ 102 | |
$ return for every $1 invested | $ – | $ 1.00 | $ 2.76 | |
36 Ha Pivot – MAP | $ – | 14.4 t | 5.2 t | |
Transport $20/t | $ – | $ 288 | $ 104 | |
Fertiliser + Transport cost – ROI | $ – | $ 0.49 | $1.36 |
Similarly, savings can also be made at P responsive sites with better targeted P application rates. An example from a site in the South East shows savings of $161/ha (230 kg MAP) and a substantial increase in ROI from $9.26 to $21.43 for every dollar invested (Table 2), based on trial results. In the case of a 36 ha pivot, this equates to a total saving of $5,796 that otherwise would have been invested prior to the crop being planted.
Table 2. P fertiliser responsive site | 0 kg P/ha | Current farmer rate – 110 kg P/ha | Recommended rate – 60 kg P/ha | |
---|---|---|---|---|
Yield t/ha | 67 | 79 | 82 | |
Income $/ha @ $270/t (Processing) | $ 18,090 | $ 21,330 | $ 22,140 | |
Additional income $/ha | $ – | $ 3,240 | $ 4,050 | |
MAP required kg/ha (22% P) | 0 kg | 500 kg | 270 kg | |
Cost of P @ $700/t | $ – | $ 350 | $ 189 | |
$ return for every $1 invested | $ – | $ 9.26 | $ 21.43 | |
36 Ha Pivot – MAP | $ – | 18 t | 9.7 t | |
Transport $20/t | $ – | $ 360 | $ 194 | |
Fertiliser + Transport cost – ROI | $ – | $ 4.56 | $ 10.57 |