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Nitrogen (N) fertiliser use in Mozambique is very low, but blanket recommendations on higher fertiliser application rates may not be appropriate for small-scale rainfed farms in different edaphic and climate regions of the country. Data from field experiments with two water levels, three tillage methods (only one tillage method was used in the present study) and two fertiliser N application rates to maize (Zea mays L.) were used to calibrate and validate the Agricultural Production System Simulator (APSIM) model. The model was subsequently used to simulate multiple-season scenarios (25 years) and determine adequate fertiliser rates for rainfed and supplemental irrigation conditions on sandy loam soil in Southern Mozambique. For this, APSIM was configured to simulate long-term maize response to varying N application (0-120 kg ha(-1)) and planting density (1, 4.2 and 8.4 plants m(-2)) in a rainfed or supplemental irrigation system.

The APSIM maize model proved capable of producing fairly accurate predictions of observed trends in soil moisture under rainfed and irrigation conditions in a semi-arid region. The model was also able to predict maize grain and biomass yield well.

Multiple-season analysis of grain yield revealed that, compared with the medium (recommended) plant density (4.2 plants m(-2)), in rainfed conditions low plant density and high plant density (8.4 plants m(-2)) reduced overall grain yield by 1281 kg ha(-1) (40%) and 242 kg ha(-1) (8%), respectively. With high plant density, grain yield was below 1000 kg ha(-1) in 20% of simulated years, whereas with low planting density the lowest grain yield was around 500 kg ha(-1) (4% of simulated years). Irrigation stabilised grain yield in most simulated years, except in some years with high planting density.

Fertiliser and supplemental irrigation increased yield for all scenarios except those with low plant density. The optimal N fertiliser rate was identified as 33-102 kg ha(-1) in the rainfed system and 38-86 kg ha(-1) in the supplemental irrigation system, compared with the national blanket recommendation of 120 kg N ha(-1). The simulation results suggested that the national recommended rate is only appropriate for years and regions with adequate rainfall distribution (> 300 mm per cropping season). (C) 2017 Elsevier B.V. All rights reserved.