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Sharon Taylor, Central West Farming Systems - Greg Brooke, NSW Agriculture, Nyngan
Take Home Messages:
- It was difficult in this trial to see the carryover of residual P into 2003 as some plots were affected by crown rot.
- The maximum wheat yield was achieved when 5 kg P/ha was applied in 2003 on top of 11 kg P/ha in 2002
INTRODUCTION
Previous work conducted on the carryover of phosphorous (P) from a drought year into a recovery year suggests that a certain amount of residual P from a drought year is available in the recovery year. This provides a question - "Can fertiliser rates be reduced after a drought year to allow for the use of residual P?"
The Nyngan regional site group conducted a trial in, what we hoped would be the recovery year, 2003 to test what fertiliser recovery there may have been following the drought, and failed crops, of 2002.
METHOD
The trial was located at 'Coreen' on the main Nyngan Regional Site trial site. In 2002 the trial site had a variety by fertiliser trial, which failed during the drought and was not harvested. The varieties used in the 2002 trial were Strezlecki, Sunmist, Cunningham, Sunbrook and Sunstate, whilst the fertiliser rates were 60 kg/ha, 100 kg/ha and 130 kg/ha of DAP sulphur (16:17.8:11.7), which gave 11, 18 and 23 kg P/ha respectively. In 2003 the trial was sown to Strezlecki with 3 rates of Trifos fertiliser (0:20.7:1.3) - 0, 25 and 50 kg/ha, which gave 0, 5 and 10 kg P/ha respectively. The trial was sown on 2nd May with 50 cm of subsoil moisture. The rainfall figures for the Nyngan site can be seen in Figure 1.
RESULTS
The wheat yields in 2003 with varying fertiliser rates in 2002 and 2003 can be seen in Figure 2. In these results there was no interaction between wheat yields in 2003 and the fertiliser rates of 2002 and 2003.
DISCUSSION
The residual effect of P from 2002 on 2003 wheat yields is not clear in this trial. It is difficult to determine the carryover of P from 2002 onto 2003 as areas of the trial were affected by crown rot. The crown rot was the worst in some of the plots which had 0 kg P/ha in 2003, but not all of them. This may explain the high yields when there was 0 kg P/ha in 2003 and 18 kg P/ha in 2002. These plots may not have been affected by crown rot and the residual P may have allow the crop to achieve a yield of 1.51 t/ha. But it is difficult to determine if this is the case. Without the crown rot problem would the 0 kg P/ha in 2003 treatment on 11 and 23 kg P/ha in 2002 treatments been similar to 1.51 t/ha - indicating a carryover of P?
From these results, however, it can be concluded that the maximum yield was achieved when 5 kg P/ha was applied in 2003 on top of 11 kg P/ha in 2002, whilst the lowest yield was achieved when no P was applied in 2003 on top of 11 kg P/ha in 2002.
ACKNOWLEDGEMENT
On behalf of the Nyngan Regional Site group we would like to thank Will & Steven Carter, Tom Fitzgerald, Daryl Reardon, Jim Priestly, Tim McNee and Cath Evans. Your support and help with this trial was greatly appreciated.
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