HISTORICAL Wellington rainfall records which have averaged 50 millimetres a month for the past 200 years have changed within the past 25 years to drier autumns and wetter summers.
Wellington farmer, Peter Knowles, who is cropping a little more than 400 hectares this winter at Argyle Park, says rainfall patterns have changed drastically.
"For 200 years the average has been consistent at 50mm per month, give or take two or three mils," Mr Knowles said.
"But my studies show that in the past 25 years at least, the rainfall average in April has dropped to 32mm and 38mm in May while in November the year's highest average is now 70mm.
"We are trying to sow our winter crops in April and May in the two lowest rainfall months and then try and harvest in November/December in the two wettest months."
"When you take that into account it is critical that November/December rain is stored in your soil," he said.
As a cropping-only enterprise, Peter and wife Fay, don't run stock, however, he suggests to mixed-farmers to limit stock grazing on cropped cereal stubbles as that stubble protects and stores the much-needed moisture over summer for next season.
"We need to keep as much moisture stored under as much ground-cover as possible and leave it," he said.
"This way and with a little luck you have some good stored moisture come March to go sowing on with a bit of confidence."
Mr Knowles said the use of disc seeders allowed operators to dry-sow a lot easier in stubble than with a tyne machine.
"If you can jag 15mm or 20mm of rain on April 1 you can sow on Anzac Day with confidence your crop is going to germinate. Plants sown by disc are a bit slower to get established and come out of the ground than if sown by tyne, so, with a disc you can sow a week earlier than the window says.
"You push the window forward and instead of sowing on Anzac Day, you can sow from April 15 which I did this year."
With the change in rainfalls Mr Knowles said he had given summer cropping serious consideration and even tried it.
"But there is so much irregularity in that summer rainfall," he said. There are years of big variations in January alone from 116mm to 7mm in the past 25 years.
"Inevitably, if you sow a summer crop in October it's flowering around Christmas/early January, and you also get those days of 40 degree centigrade heat which knocks the blazes out of any potential yield."
March rain sets winter crop sowing window
LATE-March rain tallying 78 millimetres set Peter Knowles up for winter crop sowing after a useful 2018 season.
Mr Knowles and wife, Fay, run a cropping-only enterprise on Argyle Park, Wellington, and are sowing 400 hectares of canola, wheat and barley with field peas to follow next week..
"We picked up 78 mils in the last two weeks of March setting us up for a mid-April canola sowing," Mr Knowles said. He checked paddocks with a soil probe and found insertion relatively easy.
"The rain had topped-up what moisture was held over from summer's November and December falls.
With no rain in April so sowing with a Daybreak disc seeder unit trailed by a home-made air seeder was set to work on April 15 and 16 with Hyola 559TT sown at two kilograms/ha with 50kg/ha of monoammonium phosphate (MAP) at a depth of 25cm.
Crop rotations used to be fixed - wheat, barley, canola, wheat, and probably a pulse, however, in recent years of relatively extreme seasons, Mr Knowles has looked more towards sowing canola into paddocks with more ground cover and cereals into barer paddocks without breaking the rotation too drastically.
"We vary it a bit now," he said.
"Last year was a classic example of what I'd say was a high-risk cropping year.
"We chose barley because of its later sowing window and its ability to finish in a dry year and good rain in October saw it turn into a handy crop."
This year, Mr Knowles said he was paying the penalty for not having a crop in a lot of his country last year as ground cover is low over most of it. This country has been sown to cereals.
He's sowing 140ha wheat, 130ha canola, 80ha barley and 50ha of field peas.