USE OF DRAINAGE LYSIMETERS TO EVALUATE NITROGEN AND IRRIGATION MANAGEMENT STRATEGIES TO MINIMIZE NITRATE LEACHING IN MAIZE PRODUCTION

Increasing public awareness of nitrate contamination of groundwater has caused agriculturalists to focus their attention on nitrogen recommendations and management strategies. In Michigan the problem of nitrate contamination of groundwater is pervasive. Using drainage lysimeters placed in a grower's field, a conventional nitrogen fertilizer and irrigation strategy was compared with a conservative research strategy for impact on yield and nitrate leaching in maize (Zea mays L.) production. The conventional nitrogen fertilizer strategy was to apply 178 kg N ha-1 preplant as anhydrous ammonia and then some additional N in the starter fertilizer. Irrigation water applications for the conventional strategy were based on an irrigation scheduling program and the physical limitations of the existing center pivot system. The research strategy was to use split applications of nitrogen fertilizer and to apply irrigation water based on daily crop requirements. The research plot was outside of the influence of the grower's irrigation system and had its own dedicated irrigation system which provided flexibility in the timing and amount of water applied. The two strategies resulted in similar yields for two seasons. However, the conventional plot received an additional 89 kg N/ha-1 (preplant) in the first year due to operator error. During the first 24 months, the total drainage from the conventional strategy was 190 mm more than the research strategy and the nitrate leached was 170 kg N ha-1 more. In the third year of the study, the preplant application of the conventional strategy was deleted and only 9 kg N ha-1 was applied in the starter fertilizer. This was done to study the ability of maize to mine the soil nitrogen and reduce nitrate leaching. The research strategy was continued as in years past. Though only 9 kg N ha-1 of nitrogen were applied to the conventional plot, the grain yield was 4445 kg ha-1 and the nitrate leaching was reduced to 43 kg N ha-1 over an eight-month period. That represented a reduction in nitrate leaching of 60% as compared to the same time period in the previous year. This study has shown the usefulness of drainage lysimeters in evaluating nitrogen and irrigation management strategies in respect to soil water drainage and nitrate leaching. Additionally, the collection of data throughout the year provides greater insight into non-growing season drainage, showing that most nitrate loss occurs between the harvest date and the subsequent planting date.