Organic Versus Mineral Fertilization Regimes in Relation to Potato Brown Rot Suppression and Crop Production

The effect of different fertilization regimes on bacterial wilt, caused by Ralstonia solanacearum was evaluated in four different naturally infested districts in two successive years. The effect of different fertilization components on disease suppression and potato yield varied from place to another according to different edaphic factors. Area 1 (Manyl-Arus) with clay soil was characterized by high C/N ratio (13) and low electric conductivity EC (0.06 ds/m). Area 2 (Ganoub El-Tahrir) with sandy soil was characterized by low C/N ratio (5) and low organic matter (OM). Area 3 (Talia area) with clay soil was characterized by high EC (0.37 ds/m), high OM (2.2%) and high total organic carbon (TOC) (0.99%). While, area 4 (Wardan area) with sandy soil was characterized by high pH (8.8) and low TOC (0.04%). NPK showed a remarkable disease suppression that was most clear under high alkalinity at area 4. NPK improved potato yield with a reasonable increase in amino acids in root exudates. Replacing potassium with magnesium (NPMg) suppressed the disease at different areas and decreased Peroxidase (PO), Polyphenol oxidase (PPO)with a remarkable increase in Tyrosin ammonia lyase (TAL) activities. Apparent vegetative growth and/or potato yield were recognized in this treatment. Disease suppression by replacing potassium with calcium (NPCa) was correlated with decrease in PO, PPO and an increase in Catalase (CAT) activities. Composted chicken manure suppressed the disease only in soil of area 1 and plant rhizosphere of area 4. The disease decline in area 1 was correlated to the decreased activity of PO & PPO and increased ones in TAL (similar to NPMg treatment). High ammonium and low content of variety of amino acids were shown in potato root exudates with dominance of glycine, proline, serine and threonine. Plant-animal compost complex suppressed the disease at area 1 and area 4 area but not at area 3. The complex treatment showed an increase in both amino acids and NH4⁺ as compared to untreated control. High ratio of aspartic (acidic) and arginine (basic) was recorded. Plant-animal compost complex showed a remarkable decrease in soil organic matter which was associated with a narrow C/N ratio and limited N and K plant uptake at Talia area.