message: Farm and Paddy Field: +1 food with Chemistry instead of Biology
diff: <ImprovementUpgrade/>
  <TechYieldChanges>
  <TechYieldChange>
  - <PrereqTech>TECH_BIOLOGY</PrereqTech>
  + <PrereqTech>TECH_CHEMISTRY</PrereqTech>
  <TechYields>
  <iYield>1</iYield>
  </TechYields>
  <ImprovementUpgrade/>
  <TechYieldChanges>
  <TechYieldChange>
  - <PrereqTech>TECH_BIOLOGY</PrereqTech>
  + <PrereqTech>TECH_CHEMISTRY</PrereqTech>
  <TechYields>
  <iYield>1</iYield>
  </TechYields>
  