If you could ask an expert about soil fertility, what would you ask? Participants in a virtual session with Matt Clover, a Pioneer agronomist and soil fertility specialist, got that opportunity.

Here are questions farmers asked:

Can we apply so much P and K that we harm the soil and make it toxic for plants? For phosphorus, you don’t need to worry about toxicity, but you should consider potential environmental impacts. If you have soils testing high or very high in phosphate, be responsible in considering further applications. High phosphorus levels may impede uptake of certain micronutrients if those levels are low.  For potassium, in most situations, you won’t damage the soil. Plant injury due to high salt content is possible if you apply too much too close to young roots.

Are land-grant universities keeping pace with upping recommendations to match higher yields? There is a wide variation in how recently university recommendations have been updated. When they’re updated, they scrutinize phosphorus levels closely due to environmental concerns.

At Pioneer, we’ve seen that as we reach higher yields, we also remove more nutrients. We’ve come from 100 bushel per acre yields and are heading to 300 bushels per acre yields, so we’ll need to apply more P and K to keep up. Studies we’ve done across the Corn Belt over the past three or four years tend to indicate the P and K soil test levels are dropping — farmers tend to underestimate how many nutrients are being removed.

I’ve applied enough potash to build soil test levels, but I’m not seeing higher soil test levels everywhere. Is this unusual? No, it happens. Potassium can be a frustrating nutrient. Soils with lots of clay particles can fix potassium and hold it tight. It seems to have the ability to bind up tight within clay particles, and soil test re-agents won’t always pull it out. If it’s dry when you pull soil tests, you’re also likely to see lower K levels than you expect.

Should I sample in the spring or the fall? Choose either one that works best, but once you choose, be consistent. Sample at the same time of year each time. That way you can make better comparisons over time. There will be differences in numbers between spring and fall.

I haven’t paid much attention to soil fertility but want to intensify my efforts. Where should I start? Start with the big players. Get pH, nitrogen, phosphorus and potassium taken care of first.

Then you can pay attention to sulfur, then micronutrients, including zinc, boron and manganese. As you move yield goals higher, you will want to pay more attention to these, and you may want to do more soil testing and tissue testing. But get the big guys in order first!

Does it make sense to approach owned land and rented land differently? You must make that decision and it may depend upon how long a lease you have on rented land. When we asked farmers on our webinar, there was a slight trend to soil sample less often or not at all on rented land vs. owned land. If you haven’t soil sampled a field at all, consider at least taking a couple soil samples to get a base line.