Soil Fertility and Pollution Risk Assessment of Irrigated Agricultural Lands Along the Kubanni River, Zaria, Nigeria

Abstract

Soil quality plays a pivotal role in supporting agricultural productivity and maintaining environmental 
integrity. Healthy soils not only supply essential nutrients to crops but also regulate water, sequester 
carbon, and support biodiversity. This study investigated the physicochemical characteristics of soils 
from farmlands irrigated with water from the Kubanni River in Tudun Wada, Zaria, Kaduna State, 
Nigeria, with the aim of assessing spatial variation in soil quality as influenced by proximity to the river. 
A total of 15 soil samples were systematically collected. Twelve samples were obtained from cultivated 
plots located at incremental distances of 20 ft, 40 ft, 60 ft, and 80 ft from the river, representing 
areas subjected to varying intensities of irrigation and potential sediment deposition. An additional 
three samples were collected from a control site situated approximately 20 km away on virgin land within 
the Ahmadu Bello University (ABU) campus. This control site, untouched by irrigation or cultivation, 
provided a reference point for assessing the extent of anthropogenic influence on soil quality in the 
irrigated areas. All laboratory analyses were conducted at the Soil Science Laboratory, Institute for 
Agricultural Research, ABU, Zaria. The following soil parameters were analyzed: pH, organic matter 
(OM), available phosphorus (P), exchangeable bases (potassium [K], sodium [Na], calcium [Ca], and 
magnesium [Mg]), cation exchange capacity (CEC), exchangeable acidity, and particle size distribution. 
These parameters were chosen due to their critical role in determining soil fertility and overall health. 
The results revealed a discernible gradient in soil quality, with higher values of pH, organic carbon, and 
essential nutrients recorded in plots closer to the river. This trend is likely driven by the deposition of 
nutrient-rich sediments and the continuous input of irrigation water, which may enhance nutrient cycling 
and soil biological activity. In contrast, soils from the control site exhibited significantly lower levels 
of fertility-related parameters, reflecting the undisturbed and less managed nature of the virgin land. 
Textural analysis showed that soils in the irrigated plots ranged from sandy loam to silty loam, textures 
generally favorable for cultivation due to their balanced water retention and drainage capabilities. 
Furthermore, moderate to high CEC values observed in these soils suggest a strong ability to retain and 
exchange nutrients, which is beneficial for sustaining crop growth under intensive agricultural use. 
These findings underscore the positive impact of river-based irrigation on soil fertility enhancement. 
However, they also highlight the need for regular soil monitoring to prevent potential long-term 
degradation, such as salinization, nutrient imbalances, or contamination from upstream sources. 
Maintaining soil health is essential for ensuring the sustainability of agricultural systems and achieving 
food security in the region. Future research should expand on these findings by investigating potential 
risks associated with irrigation, including heavy metal accumulation, pesticide residues, and changes in 
microbial communities. Such comprehensive assessments are crucial for developing integrated soil 
management strategies that balance productivity with environmental stewardship.