Effects of reduced irrigation dose and slow release fertiliser on nitrogen use efficiency and crop yield in a semi-arid loamy sand

- Nitrogen use efficiency (NUE) tended to be higher at 75% than at 100% irrigation level.
- Slow-release nitrogen fertiliser did not give higher NUE than quick-release nitrogen fertiliser.
- Furrow irrigation tended to give higher NUE and maize yield than drip irrigation.

Quantification of the interactive effects of irrigation water and nitrogen (N) fertiliser on nitrogen use efficiency (NUE) provides an important insight for more effective water and N management. This study evaluated the effects of different irrigation and N fertiliser management options on water flux, N uptake, NUE and maize grain yield in a semi-arid loamy sand in Mozambique. The experiments were carried out in field plots in two consecutive cropping periods (CP's) representing contrasting growing seasons: a hot-wet season (CP-1) and a cold-dry season (CP-2). The treatments included two irrigation methods (furrow and drip), two irrigation levels (75 and 100% of the crop water requirement), and two distinct N fertiliser types (a quick-release and slow-release urea) arranged in a randomised complete block design. In both CP-1 and CP-2, NUE tended to be higher for the 75% irrigation level, regardless of irrigation method and N fertiliser type. Higher NUE was generally observed in CP-2 than in CP-1. The highest grain NUE (41.6 kg kg−1 N) was observed in CP-2 under furrow irrigation combined with 75% irrigation level and quick-release N fertiliser. Slow-release N fertiliser did not improve N uptake, NUE or maize yield. Potential N losses were assumed to be higher in CP-1 than in CP-2, associated with higher estimated deep percolation volumes in CP-1 (mean 127 mm) than in CP-2 (mean 12 mm). In CP-1, deep percolation events mainly coincided with high rainfall events. Furrow irrigation tended to give higher NUE than drip irrigation, especially in CP-2. Reducing of irrigation level by 25% tended to increase N uptake, NUE and maize yield for both CP-1 and CP-2. The effects of slow-release N fertiliser and drip irrigation were inconclusive.