连续多年种植蔬菜的老菜区，土壤环境恶化，会造成蔬菜病虫害日趋严重，大片死亡。土壤恶化的表现：一是线虫、病菌、残留毒素增多。蔬菜连作造成病菌及毒素在土壤积累，根系因受害而腐烂，甚至全株死亡。线虫危害也会加重。二是土壤板（。，有机质匾乏。由于大量施用二锐复合 For many years vegetable growing old vegetable area, deteriorating soil environment, vegetable diseases and pests will cause more serious, large-scale death. The performance of soil deterioration: First, nematodes, germs, residual toxins increased. Vegetable continuous cropping causes bacteria and toxins to accumulate in the soil. The root system is decayed by the victimization and even the entire plant dies. Nematode hazards will increase. Second, the soil plate (organic plaque lack, due to heavy application of two sharp composite