Relationships Between Soil Fertility Indicators and Maize Productivity Across Contrasting Soil Units Under Low-Input Management

Soil fertility is a major factor associated with maize productivity in low-input farming systems. This study evaluated relationships between soil physical and agrochemical properties and maize yield across six contrasting soil units in the Domașnea hilly region of southwestern Romania during the 2024 growing season. Soil properties were determined from samples collected at 0–30 cm depth, and maize grain yield was assessed from 66 individual spatial yield determinations distributed across the six soil units. We analyzed data using ANOVA, Pearson correlations, simple linear regressions, principal component analysis (PCA), and hierarchical cluster analysis (HCA). Mean maize yield ranged from 2.59 to 6.03 t·ha−1 across the six soil units. At the soil-unit level (n = 6), exploratory analysis showed positive associations of yield with humus content (r = 0.83; p = 0.043) and the Nitrogen Index (NI) (r = 0.88; p = 0.021), representing the strongest positive associations with yield among the agrochemical indicators analyzed. Multivariate analyses revealed soil-unit structuring by exchange-complex properties, organic matter status, nutrient availability, and maize yield. These relationships should be interpreted as site- and season-specific exploratory associations, as the study was conducted during a single growing season characterized by pronounced summer heat and water stress.