Spatial Variability and Mapping of Soil Structural Stability: The Interplay of Texture and Organic Matter at Jibia Irrigation Project, Semi-Arid Zone of Nigeria

Abstract

The study assessed the spatial variability and mapping of soil structural stability in relation to texture and organic matter in Sector F1 of the Jibia Irrigation Project, Katsina State, Nigeria. The area lies in a semi-arid zone with predominantly sandy soils and low organic matter, contributing to poor aggregation and a low structural stability index (SI), which increases erosion risk. A total of 144 georeferenced soil samples were analyzed for texture, SOM, and aggregate stability indicators such as dry and wet mean weight diameter (MWD) and SI. Descriptive statistics showed moderate variability in sand and high variability in silt, clay, and aggregate indices.  Semivariogram analysis revealed strong spatial dependence for sand, silt, clay, and dry MWD; moderate for SI; and weak for SOM and wet MWD. Clay had the widest spatial range (8.5 m), indicating stronger intrinsic control than sand (3.24 m) and silt (2.93 m). SOM showed weak spatial structure, likely influenced by land-use practices. The results show that sandy soils with low organic matter content have poor aggregation and weak structural stability, making them susceptible to erosion. Fine-textured components, such as clay and silt, and OM significantly enhance SSI, while high sand content undermines it. Organic matter and fine particles were key to improving soil aggregation and stability. The study highlights the importance of managing soil texture and organic inputs to improve aggregation, moisture retention, and productivity in semi-arid soils. Recommendations include increasing organic inputs, reducing tillage, and adopting targeted irrigation. The exponential model best fitted most semivariograms.