Comparison of Foliar and Preplant Applied Nitrogen Fertilizer for Sugar Beet

Leaf canopies of sugar beet ( Beta vulgaris L.) grown in the Red River Valley of Minnesota and North Dakota sometimes display midseason (July) symptoms of N deficiency. The influence of in‐season foliar N applications on sugar beet grown under non‐irrigated conditions on a Wheatville loam (coarse silty over clayey, frigid Aeric Calciaquoll) with low and medium levels of soil N fertility was studied for 3 yr. A combination of eight soil and foliar treatments were investigated. The soil treatments were (i) soil NO − 3 −N in the 0– to 60– cm depth of soil in the previous autumn (45 kg ha −1 in the 1986 and 1987 experiments, and 78 kg ha −1 in the 1988 experiment), and (ii) the above soil NO − 3 −N levels plus sufficient fall‐applied urea‐N to give the equivalent of 157 kg N ha −1 . In‐season foliar‐N treatments, using an urea‐NH 4 NO 3 solution (28‐0‐0), were applied in 22 kg N −1 increments on 1 July, 15 July, and 1 August to give total foliar‐N treatments of 0, 22, 44, and 66 kg N ha −1 at both levels of soil‐N fertility. Overall, the use of foliar N application did not effect root yield and extractable sugar per hectare in 2 of the 3 yr. In one year, 1986, it did increase root yield by 5.2 Mg ha −1 and extractable sugar by 0.9 Mg ha‐t under N deficient conditions with no differences occurring under adequate N nutritional levels. There was a significant increase in both root yield and extractable sugar per hectare in 1986 and 1987 as a result of fall applied fertilizer N but not in 1988. If soil moisture conditions are favorable for plant growth such as in 1986, the use of a mid season foliar N application may be beneficial in N deficient situations.