By: Dan Kaiser, Extension nutrient management specialist
University of Minnesota Extension
Increases in fertilizer prices and talk of tight supplies have led to questions about options for the upcoming growing season to reduce costs. Starter fertilizer does provide growers with some options to reduce the need for broadcast fertilizer, especially for phosphorus. If you are looking to use starter more effectively, there are some things that should be considered.
1. Watch your starter fertilizer rate for corn to limit the risk of reduced germination
Salt and nitrogen (N) in starters could reduce seed germination if the rates applied to corn are too high. Low-salt fertilizers are available but balancing the cost of the product versus what you are getting for nutrients with the starter application can be tricky. For phosphorus (P), one of the best products to use is 10-34-0 due to its higher analysis of P2O5. However, 10-34-0 is not a low-salt product, which can cause some concerns depending on how much you apply. The main decision that needs to be made is: how much fertilizer do I actually need? The best way to figure this out is by taking a soil sample.
2. Know your current soil test values before you make a decision
For starter fertilizers, like other fertilizer sources, knowing how much to apply to supply the right amount of nutrients is critical. Research has shown that in-furrow starter fertilizer alone is not enough to maximize corn yields if soils test low or very low in phosphorus. In one recent study, upwards of 7.5 gallons of 10-34-0 was applied to corn, supplying 30 lbs P2O5 crop. However, yield was still less with the starter alone versus broadcast P when soils tested low to very low in P. The best option for a starter-only strategy would be for soils testing medium or higher in P. We found no difference in yield with a 2.5 to 5 gallon rate of 10-34-0 versus a two-year corn-soybean rotation removal rate of P2O5 applied ahead of corn. A combination of broadcasting P2O5 at a lower rate (accounting for the P in the starter in low and very low testing areas) and an in-furrow starter-only strategy in medium to high testing areas can work if you are trying to reduce the need for broadcast P fertilizer.
3. What about applying potassium and zinc in-furrow for corn?
The primary issue with potassium (K) in starter is whether the rate you can apply in-furrow will be enough for the crop. Research suggests that the likelihood of getting a response to K on high clay soils decreases significantly around 200 ppm K in the soil. Most liquid starters have very low concentrations of K2O and do not supply large amounts of K to the crop. Even though banding K is more efficient than broadcast, soils testing too low in K are unlikely to receive enough K for a high-yielding corn crop. When it comes to zinc, there are deficiency situations where a blanket application of zinc chelate across all acres is likely not needed. However, zinc is the micronutrient most likely to be deficient for corn in Minnesota, so if you are trying to reduce costs, the full micronutrient package could be omitted from your starter program and you could just apply zinc.
4. What about new in-furrow technologies?
I have had a few questions related to newer technologies like Precision Planting’s FurrowJet that is designed to split the starter band into multiple bands, some away from the seed. Typically, placement with at least one inch of soil between the seed furrow and starter band is sufficient to reduce the risk of seedling damage. If we get another dry spring next year, the risk for damage increases even if the fertilizer is placed away from but near the seed. I have not evaluated the FurrowJet technology, so I cannot speak to whether it is safer than traditional in-furrow applications. My general view is that you should not apply high rates of starter fertilizer to the corn seed. Instead, supply only what is needed to get the crop off to a faster start in the spring.
5. If starter fertilizer benefits corn, can it be used for other crops?
It depends. Crops vary in their tolerance to in-furrow fertilizer. I would avoid application of any traditional starter fertilizer containing N, P, or K on soybean due to the crop’s greater sensitivity to seedling damage. Products like Soygreen or other iron chelates are the exception, as data has shown that they can be applied directly on the soybean seed. Data has shown that in-furrow P applied to sugarbeet can be as good or better than broadcast application. Knowing your crop’s level of tolerance to starter fertilizer is key when deciding whether to apply fertilizer in-furrow.
While starter fertilizer can be a viable, cost-saving alternative to broadcast applications with high fertilizer prices, it is important to remember that the chance for a response to P or K declines substantially when soils test high in either nutrient. Not applying fertilizer will likely result in a decline in soil test values over time, so, if you are looking to reduce application rates, it may be beneficial to sample your soil sooner than common four to five year cycles. More frequent soil sampling can help you monitor how your soils are trending and whether reductions in fertilizer application rates are warranted.