NITROGEN AND WATER MANAGEMENT STRATEGIES TO REDUCE NITRATE LEACHING UNDER IRRIGATED MAIZE

Cropping systems that fail to integrate nitrogen (N) water management are frequently associated with elevated concentrations of nitrate-N in soil and groundwater. Examples of poorly integrated management practi ces are abundant, especially where irrigation is used to minimize the effects of drought and N fertilizer is inexpensive. Two maize fields u nder improved water and N management practices at the Nebraska Managem ent Systems Evaluation Area (MSEA) project were compared with an adjac ent field under conventional furrow irrigation that followed managemen t guidelines mandated by the local Natural Resources District. Surge-f low furrow irrigation with laser grading and a runoff-water recovery s ystem reduced water application by 45-69% compared to conventional fur row irrigation over the three years of this study. Center-pivot sprink ler irrigation reduced water application by 60-72% compared to convent ional furrow irrigation. Uniformity of water application was improved with the surge-flow and sprinkler irrigation systems, which made it re asonable to consider adding fertilizer N in the water (fertigation) to meet crop needs. The spoon-feeding strategy, based on chlorophyll met er readings to schedule fertigation, saved 168 kg ha(-1) N the first y ear and 105 kg ha(-1) N the second year without reducing yields. Near total reliance of fertigation to meet crop N needs resulted in a 15% y ield reduction the second year because spatial variability in soil N s tatus made it difficult to collect representative chlorophyll meter da ta. Plot studies showed chlorophyll meter readings and yields were con sistently higher for maize following soybean than where maize was grow n in monoculture.