Response of maize root growth to irrigation and nitrogen management strategies in semi-arid loamy sandy soil

• Irrigation method explained the variation in root density (RD) and maximum rooting depth (MR).
• Slow-release N fertiliser gave higher RD than quick-release N fertiliser in cold-dry seasons.
• Interactions between irrigation method, irrigation level and N fertiliser type did not explain the variation in RD or MR.
• Higher RD tended to result in higher maize grain yield.

Strategies to promote dense, deep root systems are important for the efficient use of water and nitrogen fertilisers in subtropical loamy sandy soil. This study assessed the effect of interactions between irrigation method (drip and furrow), irrigation level (full and reduced), and nitrogen fertiliser type (quick-release and slow-release) on root growth of maize (Zea mays L.) and the associated effect on grain yield, aboveground biomass and leaf area index. Factorial field experiments on semi-arid loamy sandy soil in Mozambique was carried out in four cropping periods (two in the hot-wet season, two in the cold-dry season). The response to the management factors at three growing stages of coarse (≥0.7 mm diameter) and fine (<0.7 mm diameter) root density (RD) (two cropping periods) and maximum rooting depth (four cropping periods) were measured in situ by modified profile wall method. The interactions between management factors did not explain the variation in maize RD or maximum rooting depth. However, seasonal variation between the cropping periods affected the distribution of coarse RD. Drip irrigation gave 33–153% higher coarse RD and 26–55% higher fine RD than furrow irrigation in deeper layers (16–64 cm), whereas furrow irrigation gave 21–40% higher coarse RD than drip at a shallow depth (0–16 cm). Irrigation level had little effect on RD, whereas slow-release fertilisation resulted in overall higher RD, aboveground biomass and grain yield than quick-release fertilisation in the cold-dry season. RD or maximum rooting depth showed few significant correlations with grain yield, biomass and leaf area index, respectively, but higher RD generally tended to result in higher yield. Overall, drip irrigation combined with reduced irrigation and slow-release N fertiliser appeared to be the most promising strategy to promote maize rooting and increase yield, especially in the cold-dry season.