Epsilon Open Archive

Abstract

Understanding water and nitrogen redistribution in the soil profile is important to improve water and nitrogen use efficiency for sustainable agriculture. This thesis evaluates the interactions between water and fertiliser management factors affecting water and nitrogen use efficiency, based on field experiments on a semi-arid loamy sandy soil. The impact on maize (Zea mays L.) yield and other crop properties was also assessed. Cropping periods in two hot-wet seasons and two cold-dry seasons were compared. The treatments involved two irrigation methods (furrow and drip), two irrigation levels (full and reduced) and two top dressing nitrogen fertiliser types (quick-release and slow-release).

Overall, there were trends for better nitrogen uptake, water and nitrogen use efficiency and grain yield in the cold-dry than in the hot-wet season, especially under reduced irrigation. Furrow irrigation with reduced irrigation level tended to give higher grain and dry matter nitrogen use efficiency in both hot-wet and cold-dry cropping periods. Soil moisture distribution, water flow direction and deep percolation were primarily affected by irrigation method and irrigation level in the cold-dry season and by a combined effect of irrigation level and rainfall events in the hot-wet season. In both seasons, full irrigation level with quick-release nitrogen fertiliser was found to induce more net downward redistribution of water and nitrogen in the soil profile, irrespective of irrigation method. Reduced irrigation, particularly in the hot-wet season, resulted in less deep percolation. In the cold-dry cropping period, reduced irrigation combined with slow-release nitrogen fertiliser, resulted in longer nitrogen residence time at 30 and 60 cm depth, irrespective of irrigation method. Drip irrigation resulted in a moister soil profile overall in both seasons, and thus allowed better growth and elongation of coarse and fine roots, which were denser in the uppermost 56 cm of soil and reached a maximum depth of 80 cm.

These results indicate that reduced irrigation should be considered as a potential irrigation management option for semi-arid loamy sandy soil in both hot-wet and cold-dry seasons. Drip irrigation and slow-release nitrogen fertiliser may be suitable options for the cold-dry season.