To investigating if applying fertiliser according to productivity zones is more profitable than blanket applications of fertiliser across the whole paddock. We aimed to design trials to demonstrate to growers that matching fertiliser inputs to productivity zones will increase whole paddock profitability compared to blanket applications of fertiliser. We also aimed to use off the shelf tools (Silverfox/Sky Plan, Nulogic etc) that growers could access to enable them to follow our procedures to adopt VRT across the whole farm.

VRT Performance

Matching fertiliser inputs to productivity zones (VRT) was rarely the most profitable strategy. Table 1 summarises the 9 successful trials undertaken in 2006 and 2007. These were above 5 average production years for the Corrigin area. It is assumed that the low, medium or high fertiliser treatments were blanketed across the whole paddock. The VRT treatment involved apply low inputs to the poor productivity zone, medium inputs to the average productivity zone and high inputs to the good productivity zone. This summary shows that in 8 of the 9 trials a blanket application of low or medium fertiliser rates was the most profitable way to fertilise the paddocks. High inputs were never the most profitable approach. The VRT approach was only most profitable in 1 of the 9 trials. The high input treatment was the least profitable strategy in 6 of the 9 trials.

Phosphate responses

Many of the paddocks where we had our trials were un responsive to phosphate. Our research has shown that many soils now have sufficient levels of phosphate that crops either don’t respond to additional applied phosphate or the responses are very small. The WA wheat belt has been in a phosphate building phase since clearing. Many farms now have sufficient phosphate levels. Fertiliser regimes could now be reduced to a maintenance regime. This would offer significant savings to growers especially given that the price of phosphate has tripled in the past two years. There would also be some significant environmental benefits to preventing over fertilising.

Best Fit for VRT

We feel that in the Corrigin area the most economic use of VRT will be for patching out potassium on responsive soil types as well as ameliorating soil with applications of lime or gypsum in the areas which have the highest requirement, rather than blanket applications on areas that do not require amelioration. VRT could also be used for tactical applications of nitrogen. Where the paddock is blanketed with N and P for and average production season. In an above average season additional nitrogen should be applied to the high productivity zones where the demand for additional nitrogen is likely to be highest.

W & M Baker

The findings from this trial support previous research that indicates that lupins are less responsive to applied phosphate than cereals where soil phosphate levels are sound. Adopting VRT in an unresponsive situation will be un-economical. The blanket application of high inputs was the least profitable treatment generating a loss of $2,630 across the paddock compared to the blanketing of low inputs. Although the lupin yield in this trial was slightly below average it can still give growers confidence that successful lupin crops can be grown with minimal applications of phosphate where soil phosphate levels are sound and reactive iron levels are low. This trial was repeated in 2007 on the same plots. This allowed an evaluation of the compounding effects of multiple applications of each treatment (low, medium, high) over repeated years.

P & A Groves

Blanket applications of medium inputs (5 kg P and 15 kg N) were the most profitable way to fertilise the paddock. Unfortunately if the paddock had been fertilised with VRT applying the high inputs to the best area of the paddock and the low inputs to the poor area of the paddock it would have returned $4,500 less than the blanket treatment of medium inputs.

This trial generated some very interesting data and showed that the soil phosphate bank can be drawn upon to supply a crops phosphate requirement where the soil phosphate levels are sound and the phosphate retention is low.

While we would not advocate wide scale sowing of crops with nil phosphate fertiliser, this data gives growers confidence to reduce rates in difficult times (when soil testing is undertaken) and know that the yield penalty will be low even in good producing seasons.

This trial was replicated in 2007 (see next page) to investigate the compounding effect of low fertiliser inputs over two seasons.

I & H Lee

Unfortunately there was an error with this trial at seeding time.

Instead of each treatment plot being sown 4 air seeder widths wide, it was only sown 2 air seeder widths wide. This resulted in a concertina effect of the trial and the treatments were not overlaid over the same treatments in previous years (2003 and 2004).

This has made the trial invalid and it is not possible to draw any strong conclusions from the data produced because the residual fertiliser from the previous treatments will have influenced the response to the 2006 treatments. However average treatment yields and quality results have been included for the average and good production zones.

N & G Turner

2006 was a high production year with yields ranging from 2 t to 3.9 t/ha from the poor productivity zone to the high productivity zone.

The season allowed for efficient use of applied and soil nutrients, with minimal leaching events, yet adequate rainfall to allow the crops to finish well and achieve above average yields in all productivity zones.

In 2006, there would have been a net benefit of $2,693 in this paddock from matching fertiliser inputs to productivity zones (VRT) compared to applying a blanket rate across the whole paddock. This represents an increase in returns of 5 per cent.

If the whole paddock was blanketed with the high input treatments there would only be a $740 benefit compared to the medium input in 2006. This is a small additional return given the extra financial risk associated with spending an extra $37/ha on fertiliser. In an average or poor season the high input treatment would be highly unprofitable.

This trial will be repeated in 2007 to investigate the compounding effects of the previous season’s fertiliser regime on each plot.

S. Wallwork

2006 was a dry season at east Corrigin, especially for canola on heavy clay soil types.

Plant establishment and survival in the poor and average productivity zones was to low to justify harvesting for trial purposes.

The trial was repeated in 2007 with a cereal crop (see next page for results). The low, medium and high input treatments were repeated over the same sites to evaluate the compounding effects of the previous season’s fertiliser treatments.

W & M Baker

At this trial site in 2007 and in previous seasons there has been a poor economic return from using VRT technology to fertilise crops. In most situations blanket applications of either medium or low inputs have been the most profitable way to fertilise the paddock.

The high input treatments rarely give large enough yield responses to cover the additional cost of the fertiliser, even in the high productive zones.

Our research shows that farmers should fertilise for the average season on paddocks with sound phosphate levels (above 25 ppm) and low phosphate binding. In favourable seasons where the yield potential is high the soil has the ability to supply the additional nutrients.

P & A Groves

This trial site has generated a great deal of exciting information over the two trial years.

In soils with high P levels and low reactive iron levels there is scope for growers to reduce P rates with no loss in yield over a 1-2 year period.

Two wheat crops in a row achieved over 2 t yields with no applied phosphate. In most cases the slight reduction in yield was not severe enough to limit profitability, with the nil treatment being the most profitable treatment in one zone and the second most profitable treatment across the whole paddock.

The most profitable treatment in the paddock was a blanket application of medium input (returning $51,200), the VRT treatment was second ($48,800) and the blanket low input treatment (nil P) was third ($48,400). The poorest performing treatment was the blanket application of high inputs ($41,900).

An area for future research could focus on optimum soil phosphate levels for a given soil phosphate retention. This means growers could draw on the soil phosphate bank in difficult times by only applying maintenance rates of phosphate.

WA soils are naturally phosphate deficient. Since clearing, growers have been applying phosphate to crops and pastures to maintain growth and build up soil levels. Our trial results indicate that in some situations the soil phosphate levels are now at high levels and growers can look at fertilising to maintain phosphate levels rather than building up soil levels.

I & H Lee

The results from this trial show that VRT can be profitable provided that the performance of each zone can be predicted and is consistent through time. In this trial the biomass image analysis was a poor predictor of zone performance making VRT less profitable.

Profitable crops can be grown without phosphate (in short term) where soil phosphate levels are high (> 40 ppm) and reactive irons are low to medium. While sowing crops with nil phosphate is extreme and not recommended in most situations it should give growers confidence to at least reduce rates in these situations.

Where a change in farming system or farmer, historical biomass maps can be a poor predictor of zone performance in this example knife points and early sowing enabled the historically poor performing area to be the top performing zone of the paddock due to overcoming waterlogging.

N & G Turner

2007 was a high yielding season with an average yield across the trial of 2.88 t/ha and a range from 2.1 t to 3.5 t/ha, all treatment plots made A. Soft grade.

The rainfall pattern in 2007 allowed for efficient use of applied and soil nutrients which enabled treatments to optimise yield.

The results from this trial suggest that there is unlikely to be large efficiency gains by matching fertiliser inputs to productivity through variable rate technology (VRT). In 2007, there would have been a net loss of $2,700 in this paddock from matching fertiliser inputs to productivity zones (VRT) compared to applying a blanket rate of medium inputs across the whole paddock.

If the whole paddock was blanketed with the high input treatments there would have been a $5700 loss compared to the medium input in 2007. There was a minimal yield response to the additional fertiliser (even in an above average season) and it failed to cover the additional cost of fertiliser.

Blanket applications of medium inputs (8 kg P, 65 kg N and 5 kg K) was the most profitable treatment of the trial which was surprising given the paddock has light soil, high yield and was the third cereal in a row.

These results show that growers need to take care not to over fertilise crops above realistic target yields and that fertilising for the average season is a sound strategy as the soil can usually supply the additional required phosphate if reactive irons levels are low and there is sound phosphate levels in the soil.

Wallwork

2007 was a dry season at east Corrigin and crops failed to achieve maximum potential.

The site proved unresponsive to fertiliser, with treatments of low fertiliser input generating the greatest returns.

The most profitable way to fertilise the paddock was with a blanket application of low or medium inputs. The high inputs and variable rate treatments generated the lowest paddock returns.

The trial was repeated in 2006 and 2007 with low medium and high inputs repeated on the same sites.

These results are consistent with our previous findings in over 6 trials undertaken in low and high yielding seasons.