Broadcast spinner spreaders are one of the most common and widely used application equipment for lime and granular fertilizer. The importance of proper spreader calibration for accurate fertilizer applications has been emphasized many times and it is always good to see growers putting the time and effort into performing a calibration on their spreaders. However, there are also some other considerations for fertilizer applications with broadcast spreaders that may not be talked about much but are equally important. Like any other operation, mistakes during application with broadcast spreaders are also common and sometimes also unavoidable. However, it is important to be aware of them and avoid them because any application mistake can be very costly, especially with the high fertilizer prices in recent years. Listed below are some of the common mistakes that I have encountered while helping troubleshoot application issues with broadcast spreaders over the years. I have also made some of these mistakes myself as it is easy to get in a hurry and not think about making simple changes or adjustments in between applications or at the beginning of the season.
1. Spreader settings not changed between lime and granular fertilizer: This is one of the most common mistakes that occur during applications with spinner spreaders. Lime is usually applied earlier in the year or before granular pre-plant dry fertilizer and at a much higher rate (tons/ac) than granular fertilizer. It is easy to forget about changing the spreader settings such as feed gate height or flow divider position when changing from lime to granular applications.
2. Gate height set too low or too high: Even if the spreader settings are changed between lime and granular fertilizer, sometimes the feed gate height is set too low or too high. Too high can be easily noticed from the pulsing of the conveyor chain which affects both rate and spread pattern. Setting the gate height too low makes the conveyor chain to turn too fast which again causes application issues. Using the rate chart provided by the spreader manufacturer to determine the correct height (based on product density and application rate) can help avoid this mistake.
3. Material flow divider position: This is one of the most important settings on broadcast spreaders for obtaining a uniform spread pattern. The correct position of the flow divider is determined through proper spreader calibration and varies by the product type, rate and spread width. On most spreaders, it is not hard to tell when the flow divider hasn’t been moved between different products for years or since the spreader was purchased. Some general recommendations for flow divider position for different products/blends are also provided in the spreader operators manual which is always a good starting point and then use the pan test to fine tune the position.
4. Spread swath too wide: Most new high-clearance spinner spreaders can spread up to a width of 70 ft or more but that doesn’t necessarily mean that every product should be applied at those wider spread widths. The chances of non-uniform fertilizer application and even segregation for blended fertilizers are tremendously higher at these wider swaths. It is also common to not change the spread width between single and blended fertilizers whereas an effective spread width through proper calibration should be determined for each product/blend before application.
5. Spreader settings not entered correctly in the controller/display: For spreaders equipped with rate control technology (which is common on most new spreaders), the controller requires the operator to manually enter the spreader settings such as gate height and spread width to maintain the target application rate. These settings again change between product types (especially lime and granular fertilizer) and are easy to forget to be updated in the controller/display before application.
6. Incorrect fertilizer density in the controller/display: Similar to spreader settings, the rate controller also utilizes product density to calculate the amount of material to dispense (cubic feet per revolution) for a target application rate (lbs/ac). The product density differs considerably between different single and blended fertilizer products, and being unable to measure and/or change this value results in under or over-application.
7. Incorrect GPS and equipment offset: This is another setup mistake that is less common but again easy to miss or have incorrect values entered during initial controller installation and setup. Incorrect GPS and equipment settings in the rate controller result in the spreader coming on and off either too early or too late in the field or during rate transitions when implementing a variable-rate fertilizer prescription. This is also more common on pull-behind spreaders than on large high-clearance spreaders.
8. Improper spreader calibration: While every operator agrees with and understands the importance of proper spreader calibration, more often it is done in a quick and dirty manner. Collecting fertilizer in the pans spaced 5 to 10 ft apart and looking at the spread pattern in tubes that comes with most spread pattern kits do not provide any information about the applied rate (lbs/ac) and at very best provides a very rough estimation of spread uniformity. The proper calibration involves weighing fertilizer in each pan/tube separately to determine the actual application rate (in lbs/ac) and plotting all these weights to assess the spread pattern.
9. Too many rates in the prescription map: One of the common mistakes when creating variable-rate prescription maps is not considering the capabilities and limitations of application technology on fertilizer spreaders and how accurately it can implement the target application rates within small areas or zones. Having too many rates in the prescription map, especially for smaller areas in the field is not a good practice as the rate controller is then constantly chasing a target rate than attaining and maintaining it within that area. Generally, it is a good practice to merge those smaller areas or zones with adjacent areas to ensure smooth transitions and an efficient application.
10. Unreliable as-applied data: Currently, unlike seed counters on the planter row-units or a flow meter on the sprayer, there are no sensors on the broadcast spinner-spreaders that are measuring the actual applied fertilizer rate and spread width in real-time during application. Most of the rate calculations and mapping in the controller/display are based on the spreader and product settings entered by the operator during calibration, hence the as-applied data is as good as the controller setup and calibration. A common mistake is to use that data to check what rates were applied within the fields or assess spreader application performance without considering if all the equipment and product setup information was initially entered correctly into the controller.