Nitrogen fertilisation of irrigated maize under Mediterranean conditions

Nitrogen fertilisation of maize (Zea mays L.) has become an important economic and environmental issue, especially in high-yielding irrigated Mediterranean areas. Producers have traditionally applied more IN fertiliser than required and, as a result, some environmental problems have appeared in recent decades. A 4-year study (2002-2005) was conducted and six N rates (0, 100. 150,200, 250 and 300 kg IN ha(-1) year(-1)) were compared. Before planting 50 kg Nha(-1) were applied. The rest of the N was applied in two sidedresses, the first at V3-V4 developing stage and the second at V5-V6. Yield, biomass, grain N uptake. plant N uptake and SPAD-units were greatly influenced by both N fertilisation rate and soil NO3--N content before planting and fertilising [Nini (0-90 cm)]. At the beginning of the experiment, Nini was very high (290 kg NO3--N ha(-1)) and there was therefore no yield response to N fertilisation in 2002. In 2003, 2004 and 2005, maximum grain yields were achieved with 96, 153 and 159 kg Nha(-1), respectively. Results showed that N fertilisation recommendations based only on plant N uptake were not correct and that Nini should always be taken into account. On the other hand, the minimum amount of IN available for the crop [N applied with fertilisation plus Nini (0-90 cm)] necessary to achieve maximum grain yields was 258 kg N ha(-1). This value was similar to plant N uptake, suggesting that available N was able to predict IN maize requirements and Could be an interesting tool for improving maize IN fertilisation. (C) 2008 Elsevier B.V. All rights reserved.