In-Season Nitrogen Fertilization to Improve Nutrient Use Efficiency in Maize.
M. A. Al-ali and Thomas Morris. Univ of Connecticut, 1376 Storrs Rd; U-4067, Plant Science, Storrs, CT 06269
Much of the Nitrogen (N) that is lost from maize fields occurs in the spring and early summer when rainfall leaches nitrate from the root zone. Much of the nitrate lost is from N fertilizer applied before planting. Application of N fertilizer to maize fields during the growing season should reduce the amount of N lost to the environment and improve the efficiency of N use in maize production. Delaying N applications, however, could reduce the yield of maize especially on fields with no history of manure applications and a low capacity for N mineralization. In this study we evaluated the effect of delayed N applications on the yield of silage corn at 5 sites in 2003 and 5 in 2004. Eight of the sites were on farmers' fields and two of the sites were at a research station. Six of the sites had no history of manure applications for at least 15 years, three of the sites had a long-term history of manure applications and one site had no history of manure but manure applied in the year of the experiment. Ammonium nitrate fertilizer was applied by hand to plots 4.57 m wide by 9.14 m long at four times: at planting at rates of 0, 56, 112 and 224 kg N/ha; at the V7 and V14 growth stages at rates of 56, 112, and 224 kg N/ha; and at the Silk stage at 56 and 112 kg N/ha. Each treatment was replicated three times. Rainfall in 2003 was much greater than normal for the growing season (April to Sept total of 733 mm) and rainfall for 2004 was near normal for the growing season (586 mm). There was a significant increase in maize yield from 56 kg N/ha at all ten sites when N was applied at planting, with three of the sites showing a significant yield increase from 112 kg N/ha. Four of the sites in 2003, including two with long-term histories of manure applications, had a significant decrease in yield when N was delayed to the V7 growth stage compared with N applied at planting. In 2004, two of the three sites with no history of manure applications had a significant decrease in yield when N was delayed to the V7 growth stage. There was no advantage to applying greater than 56 kg N/ha when the N was applied at the V7 stage. These results suggest that delaying N until the V7 stage can significantly reduce yields when a large amount of rainfall occurs between planting and the V7 stage or when the field has a low capacity for N mineralization. Most efficient use of N will probably require application of small amounts of N at planting, except on fields with long-term histories of manure, with additional N applied at the normal time of sidedressing, which is the V4 to V8 stage of growth.