FERTILISERS like DAP or MAP placed with canola seed at sowing can cause seed germination losses of 60 per cent or more. That can represent a loss in seed of over $50 a hectare or over a $12,500 on a typical 250ha canola sowing.
Not only is seed wasted, but control of plant population is lost, and crop yield can suffer dramatically or re-sowing may be required. Although canola has a great capacity to compensate for lost plants, that can only go so far, and in some cases potential yield is not realised when plant density low.
Several years of research, including recent droughts, conducted by Grain Orana Alliance (GOA), led by Maurie Street and Ben O'Brien, have comprehensively assessed fertiliser placement options in canola growing. GOA, with major funding from GRDC, has conducted trials on farmers properties over five years across the Central West, including Nyngan, Jemalong, Gilgandra, Curban, Wellington, Canowindra to Geurie.
While reliable yield response from phosphorus fertilisers, like MAP and DAP, came from placement (about 4cm) below seed, similar responses also often occurred when fertiliser was spread on the soil surface before or after sowing. The difference was plant establishments were largely not negatively impacted as compared to when fertiliser was placed with the seed.
Ben O'Brien and Maurie Street say responses from surface applied phosphorus was interesting as many of the trials were conducted in dry years, even record droughts. One would expect little phosphorus would have been available as top-soil would have been dry over most of the growing season. But crops often responded to traditional application methods.
It seems canola can tap into surface applied phosphorus at the slightest opportunity given even light post sowing rains. In wetter years expect greater movement down the soil profile of water soluble phosphorus, as most of it is in MAP type products. Other research of phosphorus fertiliser placement in cereal crops is showing good results from deep soil placement, with residual responses common for several years, given a suitable pre-sowing application rate prior to the first crop. Canola research via this GOA project has, in almost every trial over five years, shown phosphorus fertiliser response to fertiliser broadcast pre or post sowing or placed below the seed, to be equal to, or be the highest yielding of any placement treatment.
MORE READING:
Ben O'Brien says there can be a lot of germination problems with canola when fertiliser phosphorus is placed directly with seed, even at relatively low rates. Decades of research has shown crops like wheat take up most of their fertiliser phosphorus early in the plant's life. With cereals, germination issues are not so obvious or expensive compared to hybrid canola. However GOA trials show as much as 60pc reduction in plant density can occur in canola from phosphorus fertiliser placed with seed.
That loss of plant population can be equivalent to over $50/ha loss of seed. Even more critical is the loss of plant population. In cases where one is aiming for a minimalist plant population (minimising seed costs or marginal growing conditions) and sows a low seed rate, a big reduction in establishment could lead to big potential yield losses.
Looking to the future both researchers are keen to continue testing strategies of applying some phosphorus fertiliser by topdressing, and a smaller amount with the seed where germination problems are minimised. Having some fertiliser with seed should help cater for immediate crop needs, perhaps sufficient for a 'dry year', and provide time for the crop to access fertiliser applied via topdressing particularly if the season turns favourable.
Mr Street says another plus for this strategy, provided it results in yield responses close to those of where fertiliser is applied with the seed, is logistic advantages. Applying most fertiliser phosphorus needs ahead of sowing allows large areas to be sown between fertiliser and seed refills at sowing. More area can be sown on a given day, plus risk of fertiliser seedling burn is reduced with lower rates being applied in direct contact with seed.
Gain research can from GOA or GRDC web sites.
Next week: Assessing good from bad advice. Base it on science where possible.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
Love agricultural news? Sign up for The Land's free daily newsletter