Q: Why should growers be cautious about using compost and/or manure?
A: I tell growers who have severe excess levels of phosphorus or potassium not to use compost or manure until we can get those levels down.
Any time a grower can use compost or manure and has access to it, I want them to use it as much as possible, as long as it’s not hurting them instead of helping them. But when you drive the P and K up with compost and manure, it ties up other vital nutrients.
When you get to 7.5 percent potassium in your soil, you start tying up boron, which is what gives the size to the seed. And once the sodium plus potassium totals above 10 percent, it starts blocking manganese. Even if you have excellent manganese levels in the soil, you can’t get enough manganese into the plant. If you have a manganese deficiency, if it’s below 40 parts per million, soybeans will show it right away. But corn doesn’t generally show it until you get down to about 33 parts per million. You can tell because it always makes shorter corn.
