Effect of Supplemental Irrigation and Organic Fertilization Rates on Soil Fertility and Contamination

Abstract

Objective: To determine the combined effect of compost and different irrigation regimes on soil chemical and biological properties as well as pesticide sequestration, in a rain-fed tomato farming context. Experimental Set-up: The experimental set-up adopted was a split plotarrangement in a Randomised Completely Block Design (RCBD) with four replications and nine treatments. Location and Duration: The experiment took place at the IPD-AOS site in Wayalgin, Ouagadougou (Sudano-Sahelian zone), during two consecutive wet seasons. Methodology: The primary factor corresponded to three irrigation levels (100%, 75% and 50% of tomato water requirements), equivalent respectively to 36, 24 and 12 liters of water per furrow (3, 2 and 1 watering cans). The secondary factor involved three doses of compost: 0, 5 and 10 t/ha, i.e. 0, 2 and 4 kg per sub-plot. Each block comprised three main plots (for irrigation doses), subdivided into three sub-plots according to compost doses, making a total of 36 sub-plots. Results: Results showed that composting at 10 t/ha significantly increased carbon and organic matter contents at all irrigation levels (D50%, D75%, D100%), with respective increases of 43%, 79% and 23%. Similarly, doses of 5 and 10 t/ha increased nitrogen content by 50%, 125% and 62%, depending on the irrigation level. Potassium content also increased, albeit unevenly. On the other hand, the sum of exchangeable bases increased by around 40% and cation exchange capacity by 32%, regardless of treatment. Finally, although the effect of compost amendments on soil biological activity was mixed, pesticide residues were detected only in the amended soils, suggesting a possible scavenging effect of the compost Conclusion: These treatments durably improved soil fertility while reducing the risk of groundwater contamination.