In reality some intensive agricultural area are using a lot of chemicals to the plants and soil especially on vegetable production area. The effect of chemical fertilizer, pesticides, fungicides, weedicides, sticker and many others will dissolve and accumulate in the soil that able to kill most of the microorganism and beneficial predators. I have seen some vegetable growing area very hard to find any flying or crawling insects due to the pesticide application. If you have take soil sample and sent to the lab may be the result of microbial content is worsen. I always advice the farmers to improve soil fertility by various ways that is proven, cheap, applicable, simple and the most important practical.
The decline can take 20 to 30 years to reach the point that most of the natural controls are finally lost and disease runs rampant. The speed with which the "edge" is reached depends on the amount of soil organic matter that was in the soil when it was first plowed, how often the soil was plowed and how much residue was added back. Additionally, how much variety was added back, and the inoculum base for the disease are also important. Certain diseases don't occur in some places because the disease hasn't reached them yet. But the instant the disease does arrive, it goes throughout he fields like a wildfire, because there are few natural competitors to stop it in the soil .
This article I hope give us some idea how important to know the soil fertility sustainability in our Malaysian farms. The record from DOA shown that the use of more organic fertilizer and reducing chemical application in a continuous campaign in Good Agriculture Practices (GAP). A standard certification program called SALM (Skim Amalan Ladang Baik Malaysia) and SOM (Skim Organik Malaysia) introduced for commercial food crop growers to ensure a high quality and safe produce for domestic and export market. Thanks . . .