Rectangular zaï pit Lengths and Fertilisation Effects on Soil Fertility in the Sudano-Sahelian Zone of Burkina Faso

Abstract

Approximately 65% of agricultural land in the Sudano-Sahelian zone of Burkina Faso consists of degraded bare soils requiring urgent restoration. Although zaï technology is widely adopted, the influence of pit dimensions and their interaction with organic and mineral fertilisation on soil restoration remain insufficiently understood. A split-plot design was installed in 2019 on two contrasting bare soils: Toyendé (moderately acidic lixisol, Sudano-Sahelian) and Gouéré (near-neutral plinthosol, Sahelian). The main factor comprised four rectangular zaï pit lengths (30, 35, 40, 45 cm) and one circular pit (30 cm), all 20 cm deep in order to compare the performance of the two types of zaï in terms of water collection and the trapping of plant residues in the pits. The sub-factor comprised four fertilisation regimes: no input, compost (250–500 g/pit), NPK (6.5 g/pit) and compost + NPK. After two cropping seasons (2019–2020), soil samples (0–10 cm) were analysed for pH, organic carbon, total nitrogen, available phosphorus and available potassium using standard methods. Soil responses were strongly site-dependent. At Gouéré, compost in 30 cm rectangular pits increased soil organic carbon by 106% and available potassium by 153%, while compost in 35 cm pits increased total nitrogen by 25%. At Toyendé, circular zaï without fertilisation enhanced available phosphorus by 372%, whereas 40 cm rectangular pits without amendments increased available potassium by 412%. Compost in 45 cm pits produced the highest pH increase (39%). Rectangular zaï improved soil restoration more effectively than circular zaï by enhancing runoff harvesting and sediment retention. However, optimal pit dimensions and fertilisation strategies must be tailored to the initial soil fertility status to maximise long-term restoration while preventing yield-driven nutrient depletion.