SPATIAL ASSESSMENT OF SOIL FERTILITY HETEROGENEITY FOR PRECISION NUTRIENT MANAGEMENT IN THREE SUB-HUMID SMALLHOLDER TOBACCO AGRO-ECOSYSTEMS OF ZIMBABWE.

Abstract

Conventional fertilizer recommendations for tobacco production in Zimbabwe have historically emphasized NPK formulations based on blanket guidelines developed in the 1980s. However, changing soil fertility conditions, intensified cropping, and increasing yield demands require a reassessment of these standards. A survey of 165 farmers was conducted in three flue-cured tobacco-growing areas (Beatrice, Wedza, and Trelawney) and 291 soil samples were collected from these farmers for chemical analysis. Yield showed a significant positive linear relationship with both basal and nitrogen top-dressing fertilizer application rates, with maize being the predominant rotational crop. Soils across all sites were strongly acidic, with Beatrice recording a significantly lower pH (4.79) than Wedza (5.17) and Trelawney (5.23) (P ≤ 0.05). Initial mineral nitrogen (IMN) was significantly low in Beatrice and Wedza but adequate (>31 mg kg⁻¹) in Trelawney. Phosphorus was marginally deficient across all areas, with no significant differences (P > 0.05). Potassium levels were generally adequate, though significantly lower (P ≤ 0.05) in Beatrice. Significant variability (P ≤ 0.05) was observed in other macro- and micronutrients. Calcium was acutely deficient in all areas, while magnesium was deficient in Trelawney and acutely deficient in Beatrice and Wedza. Zinc levels ranged from low to adequate. The marked spatial variability in soil nutrient status highlights the need for systematic soil mapping, revision of blanket fertilizer recommendations, and development of area-specific formulations addressing key deficiencies, particularly Ca and Mg. Site-specific nutrient management is essential to ameliorate soil acidity, improve nutrient use efficiency, and enhance tobacco yields and profitability.