One of the four key areas within the Future Proofing Vegetable Production project aims to improve the accuracy of fertiliser applied. This work is part of the MPI Sustainable Farming Fund “Future Proofing Vegetable Production” project, co-funded by Horizons Regional Council, Potatoes NZ, Gisborne District Council, Ballance AgriNutrients and LandWISE.

Growers were invited to participate in having their equipment assessed. Equipment was tested with growers in both Horowhenua and Gisborne. Ten fertiliser applicators have been assessed through working with eight growers. Multiple settings or products were tested for some equipment.

Performance assessment of fertiliser application equipment provides information on actual rates applied and the evenness of application. Ensuring that fertiliser is applied evenly minimises the risk of leaching if over application occurs, or the risk of yield penalties if under application occurs where nutrient availability is limiting plant growth. Growers were confident their equipment was spreading evenly, however the assessment results show there is room for improvement.

Fertiliser application equipment measured can be split into two main categories:

1. Broadcast fertiliser spreaders (spinning disc, oscillating spout)
2. Direct placement machines (banders, side dressers and planters)

Methodologies

Different methodologies are appropriate for broadcast versus direct placement equipment.

• Broadcast fertiliser spreaders were tested according to the FertSpread Protocol: see www.fertspread.nz
• Power take off driven placement equipment (banders or adapted oscillating spouts) were assessed by placing buckets under the outlets and collecting fertiliser for a measured time (~30 – 60 Seconds). By determining travel speed the application rate can be calculated.
• Ground driven equipment (most side dressers and planters) were assessed by collecting fertiliser from outlets over a set distance in-field or from 20-wheel rotations in static testing.

Tests were repeated twice, however where results between tests appeared quite different, the test was repeated up to six times. For some machines multiple settings or fertiliser products were tested.

Direct placement machines were assessed using a calibration calculator that has been developed over the period of testing this equipment as there is currently no industry accepted assessment calculator available.

The draft fertiliser calibration calculator for the assessment of direct application machines is included in the supporting documentation. This spreadsheet calculates and reports a wide range of statistics to assess performance.

Three key performance indicators are suggested:

1. Target application rate vs. actual rate applied
2. Variation between outlets/spouts
3. Variation between test runs

Results

The application variability of the direct placement equipment tested varied quite markedly; from 0.4% CV to 26.4% CV.  A summary of the test results for direct application equipment is provided in Table 1.

All but one of the machines tested are within the SpreadMark accepted performance for broadcast spreaders applying nitrogen-based fertilisers.

The actual rates of fertiliser applied varied from the target rates. In one case the actual average rate applied was 48% of the target rate, the greatest over application was 152% of the target rate.  

Fewer broadcast spreaders were assessed as direct placement machines are more commonly used in intensive vegetable production systems. Table 2 provides a summary of the two broadcast spreaders assessed.

Figure 2 gives a snapshot of part of the report produced through the FertSpread website. In this example, if the grower reduced their bout width from 22.5m to 19m, the machine performance would be within the acceptable level for nitrogen and non-nitrogen fertilisers.

Discussion

Assessments have been completed on a range of fertiliser application equipment in both Levin and Gisborne. Most of the equipment tested has been direct application (banders, planters and side dressers), rather than broadcast spreaders. Fertiliser applications for vegetable production are predominantly applied as banded strips along the bed or scarified during planting or as a side dressing. There is currently no accepted protocol for the assessment of this type of equipment.

Direct fertiliser application (banders, side dressers)

To enable the assessments to be completed within the project, a draft protocol and fertiliser calibration calculator for direct applicators has been developed and is being refined. This is currently in an Excel spreadsheet which has been developed as we have been testing equipment. The number of tests required and the statistical analysis to report the suggested three key indicators is still to be discussed and agreed upon. This concept and draft calculator will be taken to the annual Fertiliser and Lime Research Centre conference in February 2019 for advice from leading experts. The acceptable level of equipment performance and report outputs provided to growers will be discussed.

It is currently accepted for broadcast fertiliser spreaders that the coefficient of variation, CV, should not exceed 15% for nitrogen fertilisers and 25% for non-nitrogen fertilisers. The method of calibrating fertiliser rates applied ‘through the spout’ to achieve target rates are accepted, however a different statistical analysis is required for an assessment to be completed and best practice or acceptable levels of variation need to be defined. It is suggested that a CV of 15% for nitrogen or even non-nitrogen fertilisers is well below the capability of these direct placement applicators. Machinery in good working order should achieve a CV of much lower than this, but an acceptable CV is not currently defined.

This has opened discussion around how the acceptable CV is determined and if this is applicable in vegetable production systems. Our understanding is that accepted variance is based largely on pasture value and response curves, we query what values are appropriate for high value vegetable crops. Excess fertiliser increases leaching risk, insufficient fertiliser can make a crop unsaleable through quality loss. This is another area that it is felt important and worth further investigation.

The results of the tests carried out on direct placement equipment highlighted several key areas to address:

• The target rate is not often achieved, the results showed machines are both over and underapplying, which have implications for leaching risk and potential marketable yield penalties or decrease nutrient use efficiency.
• In some cases, the outlets are not applying fertiliser at equal rates. The cause of this is different for each machine. However, the growers were keen to investigate why one outlet was applying a lower rate. In one case the grower was able to fix the equipment and significantly reduce the variation between outlets.
• One machine resulted in different rates being applied in each test. This is a greater concern for older equipment that is worn and manually operated hoppers.  
• The amount of the fertiliser in the hopper appeared to affect the rate of fertiliser applied. This suggests that as the hopper empties that rate applied to the beds decreases. This also appeared to change significantly with the bulk density of the fertiliser product. More testing is required to investigate this further. There may be a minimum amount of fertiliser (product/bulk density dependent) required to be in the hopper to achieve an even application.

The interest and engagement of growers through testing their equipment has built awareness. Once a protocol is developed, the spreadsheet will then be developed into a tool for growers. Prior to next season, workshops demonstrating how to calibrate equipment, use the tool and interpret the report will be run in Gisborne and Levin, with the possibility of visiting additional regions. Conversations with growers during visits have shown there is good support for an event.

Broadcast fertiliser spreaders

Broadcast spreaders are less commonly used, and only two-disc spreaders were assessed. The results showed that at the current bout width used neither machine was achieving an acceptable CV for nitrogen fertilisers. One of the two was on the limit of acceptable for non-nitrogen fertiliser products. This suggests that the growers need to change either settings and/or bout width to achieve an acceptable CV.

Reports are generated for all equipment we tested and distributed to growers. Some growers have requested that we re-test their equipment after they have made adjustments or prior to next season.