Nitrogen Response in the USA and Argentina of Corn Populations with Different Proportions of Flint and Dent Germplasm

While N is widely used in the USA for yellow dent corn ( Zea mays L.) production, N is rarely used in the Argentine hard flint Corn Belt. Response to N fertilization is common in the USA but usually low and inconsistent in Argentina. To determine the importance of germplasm type on N response in the USA and Argentina, 50 S 2 's each from corn populations with 100, 75, 50, and 25% of Argentine flint germplasm, respectively, were crossed to a flint and a dent inbred tester. These testcrosses were evaluated under 0 and 280 kg N ha −1 at Champaign, IL and 20 and 300 kg N ha −1 at Havana, IL during 1985 and under 0 and 200 kg N ha −1 in three locations in Argentina during 1986. The relative N response for yield was 15% of the yield at the low N level in both countries. Nitrogen response was not affected by proportion of dent germplasm. Grain yield response per unit N applied also was similar in both countries. Testcross means in both countries for yield at low and high N levels and average yield increased as the proportion of dent germplasm in the population increased. Means for the dent tester were higher than those of the flint tester. Within a country, genetic variances of these populations did not differ significantly for any trait. Unlike results in Argentina, genetic variance for N response was significant in the USA and genetic variances for yield at high and low N levels differed. In both countries, selection in high‐N environments resulted in higher predicted gains in N response and in average performance over both N levels than selection in lower N environments. These results suggests use of higher N levels for selection.