DETERMINING THE EFFICIENCY OF NITROGEN FERTILIZERS ON MAIZE USING ISOTOPE METHODS AT DIFFERENT IRRIGATION LEVELS

The isotope technique can be used to improve and develop land management systems, including the effective and efficient use of nutrients and water to increase crop productivity. The study aimed to obtain information on nutrient uptake by maize and the efficiency of nitrogen fertilizers at some irrigation water levels in sub-optimal land. This study was conducted at the Research Station of Taman Bogo, East Lampung, Indonesia. The study used a split-plot design in a randomized group with three replications. The main plots consisted of water levels 100%, 80%, and 60% based on FAO’s recommendation, whereas the sub-plots were N fertilizer in the form of urea 15N labels with the rates 0, 100, and 135 kg N ha-1. The results showed that the average grain yield of maize (8.0 t ha-1) was the highest for 135 kg N ha-1 and 80% irrigation water. The application of 100 kg N ha-1 with 80% irrigation water was sufficient for increasing N uptake in grain and biomass. The highest efficiency (15.7–16.7%) of N fertilizer on maize was shown by treatments of 135 kg N ha-1with 100% irrigation water and 100 kg N ha-1 with 80% irrigation water. With the isotope method, the N efficiency from fertilizers can be traced