Technologies for improved water use efficiency in small-scale maize production in a semi-arid region
Sammanfattning: Alternative technologies to increase grain maize production under rainfed systems are urgently needed, considering the low grain yield in small-scale farming in countries such as Mozambique. Supplemental irrigation, fertiliser application and tillage methods are valuable available farming technologies. This thesis examined the impact of supplemental irrigation, fertiliser application and three tillage methods (hand hoeing, strip tillage, disc tillage) on maize grain yield. Studies on belowground biomass showed that most roots were concentrated in the upper 20 cm of the soil. Root abundance decreased down the soil profile, which can be genetically derived but also attributable to higher penetration resistance at greater depth. Tillage had a great effect on soil penetration resistance, but little effect on root growth and a limited effect on yield. Root to shoot ratio was high under rainfed conditions, due to low allocation of assimilates to aboveground traits under water stress. Degrees above canopy threshold (DACT, a water stress index) varied from 0 °C (no stress) to 17.1 °C (high stress). It was mainly affected by water supply and was negatively correlated with soil moisture, grain yield, thousand-grain weight and water use efficiency. Water use efficiency ranged from 0.16-0.60 kg m-3 (rainfed) to 0.45-1.09 kg m-3 (irrigated) and was negatively correlated with DACT in both seasons studied. Supplemental irrigation alone resulted in an average maize yield increase of 161% compared with rainfed maize and increased water use efficiency by 79%. Application of 48 kg ha-1 of nitrogen fertiliser alone increased grain yield by 31% compared with no fertiliser and increased water use efficiency by 18%. Crop modelling results suggested that the recommended nitrogen fertiliser rate (120 kg ha-1) for maize in Mozambique is only suitable for irrigated maize or for regions with high, uniform rainfall. Overall, the work in this thesis reveals scope for improving crop water use efficiency in semi-arid regions through better soil and water management practices.
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