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 mid-season (Jul y) symptoms of N deficiency. The influence of in-season foliar N appli cations on sugar beet grown under non-irrigated conditions on a Wheatv ille loam (coarse silty over clayey, frigid Aeric Calciaquoll) with lo w and medium levels of soil N fertility was studied for 3 yr. A combin ation of eight soil and foliar treatments were investigated. The soil treatments were (i) soil NO3--N in the 0- to 60-cm depth of soil in th e 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 NO3--N level s plus sufficient fall-applied urea-N to give the equivalent of 157 kg N ha-1. In-season foliar-N treatments, using an urea-NH4NO3 solution (28-0-0), were applied in 22 kg N ha-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 hec tare in 2 of the 3 yr. In one year, 1986, it did increase root yield b y 5.2 Mg ha-1 and extractable sugar by 0.9 Mg ha-1 under N deficient c onditions with no differences occurring under adequate N nutritional l evels. There was a significant increase in both root yield and extract able sugar per hectare in 1986 and 1987 as a result of fall applied fe rtilizer 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 app lication may be beneficial in N deficient situations.