This is not your father’s corn hybrid. Today’s hybrids produce more corn yield per unit of nitrogen (N). A new Purdue study confirms exactly how much more efficient they really are.

Flower power is more than a shopworn phrase from the 1960s. Corn flowering and the period from two weeks before and after is the peak biomass production time (when water is not limiting). When silks emerge and pollination occurs (R1 stage), the corn plant should already have optimum N levels, because that will help insure high kernel number establishment and growth, along with continuing to absorb the necessary N, phosphorus (P), potassium (K) and sulfur, say lead Purdue study authors and agronomy researchers Ignacio Ciampitti and Tony Vyn. In fact, between flowering and maturity stages, modern hybrids can take up from 30% to 40% of their total N, over 50% of their total P and over 40% of their total sulfur at maturity. Slightly higher proportions of all four nutrients are taken up before flowering at higher plant densities (e.g., up to 42,000 plants/acre).

Modern hybrids absorb more than half of their final kernel N content after flowering, Vyn says. In fact, they absorb 27% more total N from the soil after flowering than hybrids grown between 1950 and 1990. In the newly released study by Ciampitti and Vyn, today’s hybrids absorb more grain-N during grain fill, as opposed to N being remobilized from plant leaves and stems. The higher amount and duration of N uptake contributed to better grain yields, even as actual grain N concentrations decline; hybrids are much more efficient. But as corn plants increase N use, they increase their uptake of other nutrients.

Optimum N levels increases plants' abilities to absorb P, K and sulfur. Having enough N results in progressively higher percentages of total plant P, K and sulfur in the grain at harvest, Vyn says. In fact, with sufficient N, up to 83% of P, 33% of K and 66% of sulfur in the whole above-ground plant at maturity ended up in the grain fraction.

Do you need any further reason to fine-tune your sidedressing program (supplemental N application at V5-V8 so as to deliver nutrients when corn most needs it)?

Today’s corn hybrids could potentially benefit more from sidedress N application than did pre-1990s hybrids, Vyn confirms. “I would expect current hybrids to be more responsive to typical sidedress timing (V5-V8), as well as to even later applications (e.g., V10 –V12) of a portion of the total plant N requirements. But we don’t have all the answers yet.”

Depending on sidedressed N completely increases your weather risk, he adds. “For example, in 2010 and 2011, we had higher yields with a majority of N sidedressed than with 100% preplant and at-planting (with starter N applied with the planter at 18 lbs. N/acre),” Vyn says. “But in 2012, our preplant N approach (either 130 lbs. or 180 lbs. of N/acre) yielded more than the all-sidedress approach because of persistent drought after sidedress application. In the long run, an ideal N efficiency approach is multiple N application timings.”

The ideal proportion of preplant to sidedress N varies with precipitation timing and amount, inherent soil mineral N availability and sidedress timing relative to corn development stage, Vyn says.

Vyn reminds growers that although total plant K uptake is proportionately faster than any other macronutrient from about the V5-V15 stage, about 10% of K uptake still occurs after the flowering stage. And recognize that proportionally more P than K uptake can occur later in modern corn hybrids, he says.

But all nutrient uptake rates depend on the specific interactions of hybrids with their environment and management factors like plant density and soil nutrient availability, Vyn says.