New research shows that irrigation on North Carolina's black soils can raise corn yields and boost nitrogen (N)-use efficiency.

As corn production costs increase, North Carolina corn growers face increasing risks due to the amount of money invested and the potential impact of dry weather in reducing corn yield. One way to reduce risk is to use irrigation to decrease the likelihood of poor grain yield.

While there is evidence that irrigation systems are cost effective in the Coastal Plain, there is little information on how much impact irrigation would have on organic or mineral organic soils in the blackland regions of North Carolina.

A 2009 research project looked at how much irrigation could increase corn yields on North Carolina's black soils and what management practices would enhance the value of irrigation on these soils.

The study was done at 3B Farms near Washington, NC, on fine, loamy soils. Four seeding rates and four N treatments were tested in irrigated and non-irrigated fields.

Seeding rates were 23,000, 28,000, 33,000 and 43,000 seeds/acre. All plots received a uniform broadcast application of blended fertilizer containing 25 lbs. N/acre, plus a uniform application of 30 gal./acre of 30% UAN, providing a base N rate of 124 lbs./acre. At growth stage V6-V7, a 30% UAN solution was applied in a dribbled band at four rates: 0, 50, 150 and 250 lbs. N/acre.

Irrigation increased corn yield by 100 bu./acre. Average yield on the non-irrigated treatments was 128.8 bu./acre, compared to 229 bu./acre on the irrigated treatments. There was adequate rainfall in May, but a dry period in late June at tassel emergence reduced yields in the non-irrigated fields.

In addition, the study found that irrigation increased both the optimum N rate and the optimum corn plant population.

IN THE NON-IRRIGATED plots, there were no yield differences among the four N rates. But in the irrigated plots, corn yield responded to higher N rates. An N rate of 274 lbs./acre added an average of 13 bu./acre, compared to the non-irrigated plots.

Plant populations were also influenced by irrigation. Without irrigation, there were no significant yield differences at seeding rates of 28,000 and 33,000 seeds/acre, and yields fell at 43,000 seeds/acre.

By contrast, in the irrigated plots, corn yields increased at all four seeding rates. At a seeding rate of 43,000, the irrigated plots produced an additional 25 bu./acre over the non-irrigated plot average.

This study highlights the importance of selecting corn management practices that increase the value of irrigation. It is especially interesting to consider N-use efficiency under irrigation compared to the same soil without irrigation. When the base rate of 124 lbs. of N was applied with-out irrigation, N-use efficiency was 0.97 lb. N/bu. of corn. At the optimum N rate of 174 lbs./acre under irrigation, N-use efficiency improved to 0.77 lb. N/bu. of corn.

In short, irrigation produced more corn with less N per bushel.

Ron Heiniger is an Extension crops specialist at North Carolina State University's Vernon James Research and Extension Center. His research activities include global positioning systems and geographic information systems in managing crop product-ion in North Carolina.