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Soil Composition

Definition

Soil composition describes the proportions of mineral particles (sand, silt, clay), organic matter, water, air, and dissolved nutrients that make up soil. Texture controls water holding and aeration; organic matter drives fertility and structure; minerals and pH regulate nutrient availability. In GIS, composition is represented by maps of texture classes, organic carbon, cation exchange capacity, and micronutrients derived from field samples, spectroscopy, and predictive soil mapping. Composition changes with land management, climate, and parent material, so time series and uncertainty are important.

Application

Farmers tailor irrigation and fertilizer to composition, reducing waste. Engineers evaluate bearing capacity and swelling risk. Ecologists map habitat quality and carbon sequestration potential. Public health tracks heavy metals near industry. Restoration projects design amendments that rebuild structure and microbiomes.

FAQ

How do laboratory and proximal sensing methods complement each other?

Labs provide precise benchmarks for nutrients and texture, while proximal sensors (EMI, Vis‑NIR) rapidly estimate properties over large areas. Calibrating sensors with lab samples enables cost‑effective mapping with quantified error.

What role does organic matter play in drought resilience?

Organic matter increases water holding and aggregation, reducing runoff and improving infiltration. Fields with higher carbon maintain plant-available water longer, stabilizing yields during dry spells.

How do you harmonize legacy soil surveys with modern digital soil maps?

Reconcile class definitions, resample to common grids, and use pedo‑transfer functions to translate between categorical and continuous properties. Keep lineage so users can trace values back to sources.

When should managers update composition maps?

After major land‑use change, irrigation shifts, or amendments. For intensive agriculture, revisit key layers every 3–5 years; for stable rangelands, longer intervals may suffice.