Field Notes from Kip Cullers

Question: Since you don't use soybean inoculant, how much fertilizer nitrogen do you apply and when? Why don't you use soybean inoculant? Are trying to reserve the sugars produced by photosynthesis for the plant rather than the rhizobium?

Kip: It's a little hard to know how much N is actually available to our soybean crop since some of it is supplied as "slow release" poultry litter in the fall. The N release from this source plus the supplemental N in our ammonium sulfate fertigations should supply most of the crop N need. We don't use soybean inoculants because we get excellent nodulation just from the existing soil bacteria population. We don't really want to encourage extra nodulation since it will remove some energy from the plant in the form of carbohydrates to feed the rhyzobium in the nodules.

Question: Do you variable rate seed your corn or soybeans? I am beginning to think we haven't been pushing our populations enough for top-end yields on our best bottom ground, currently we drop everything 30,136, and I know some areas we are too thick, yet all of our bottoms could stand more and produce more with a few more thousand plants. What are your thoughts?

Kip: On our contest plots we do not use variable seeding rates, since these locations are chosen for their high yield potential. For a normal planting we use 60,000 seeds per acre for corn and 250,000 for soybean. Hopefully this will give us final stands of 56,000 and 220,000 plants per acre. This year the Easter freeze took out a few corn plants so we ended up with 38,000 plants per acre there and about 210,000 in the soybean plots. For our normal production acres we generally plant a uniform seeding rate, but somewhat lower than in the contest fields. For dryland fields we do plant a lower population than in our irrigated fields, for the reasons you mentioned. We push populations even in our commercial acres, such as 34,000 in dryland fields and 40,000 with irrigation. We were blessed with ample rainfall this year so we are glad we had the higher populations. They helped us take advantage of the very high yield potential on the dryland acres this year.