Water and nutrient balances under selected soil and water conservation practices in semi-arid Ruzizi plain, Eastern Democratic Republic of Congo

Soil water deficit is a major production-limiting factor in the predominantly rainfed agriculture of the Ruzizi plain, eastern Democratic Republic of Congo (DRC). Appropriate soil and water conservation (SWC) practices would be a valuable option for maximizing water uptake by plants in the context of water demand and supply unbalance. This study assessed the efficiency of selected SWC practices in improving water and nutrient (nitrogen and phosphorus) balances along the slope gradients in Ruzizi plain using a three-season field experiment. The SWC practices, tied ridges and Zai pits, improved the cumulative soil water balance by 148.7 and 21.1%, respectively, compared to conventional tillage. In the same order, the maize (Zea mays L.) yield performance significantly varied with SWC practices: tied ridges (2.16 t ha-1) out performed the Zai pits (1.48 t ha-1) and conventional tillage (1.58 t ha-1).  Besides, the tied ridges reduced the total nitrogen losses by 34.4–49.8%, compared to conventional tillage. However, SWC practices were only reliable when daily rainfall amounts were at reasonable threshold (>10 mm) and on low slope gradients (<8%). Therefore, tied ridges provide an opportunity as a component of an integrated soil water and nutrient management strategy to sustain the rainfed maize production in Ruzizi plain. Key words: Tied ridges, Zai pits, rainfall variability, slope gradient, dryland, Zea mays L.