Japanese-style soil disinfection adopted by farmers

Giving the soil a "summer break"

Nhuong, a farmer in Hoi Thinh Commune, Phu Tho Province, explained that growing leafy brassica vegetables is subject to significant pest pressure, particularly from diamondback moths and flea beetles. While biological crop protection products can be used to manage diamondback moths, flea beetles are much more difficult to control.

In the past, farmers followed traditional practices passed down through generations. After harvesting a crop, they would plow the field and flood it for 15 to 20 days to suppress flea beetle populations.

However, once the water was drained, the soil dried, beds were prepared, and a new crop was planted, flea beetles would quickly reappear.

"Since adopting the new technique of covering and treating the soil for a month during the summer, we have not seen the problem return," Nhuong said. "It seems that not only the adult flea beetles but also their eggs are eliminated by the process."

Kieu Thi Hue, Director of the Vinh Phuc Safe Vegetable Cooperative in Tam Duong District, Phu Tho Province, said that soil disinfection and rejuvenation, also known as solar soil treatment, is a technical method introduced to the cooperative in 2018 through a project supported by the Japan International Cooperation Agency (JICA).

The technique is applied between May and August, the hottest months of the year. When the ambient temperature reaches 35°C, the temperature within the treated soil must rise to 60-65°C. At this level, weed seeds decay and lose their ability to germinate, while many soil-borne pathogens and pests are eliminated. Beneficial microorganisms, however, can survive and continue developing under these conditions.

The process involves four main steps: 

Step 1, fertilizer is applied before plowing to ensure it is incorporated deeply and distributed evenly throughout the soil, providing sufficient nutrients for the entire growing season. While NPK fertilizer may be used, properly treated livestock manure is an essential component.

Step 2, the soil is thoroughly tilled and formed into raised beds so that the next crop can be planted immediately after treatment without requiring additional land preparation. Soil moisture should be maintained at approximately 60% to help increase soil temperature during plastic covering.

Step 3, white plastic sheeting is used to trap solar heat. The plastic must cover the entire soil surface, including the furrows between beds, and be securely sealed around the edges to prevent heat loss.

Step 4, after at least 20 days, the plastic can be removed and the field prepared for planting. However, because soil temperatures remain extremely high immediately after the covering is removed, farmers should allow the soil to cool for about one day before sowing seeds or transplanting crops.

Eight years of commitment to a single technique

Hue's cooperative does not own a large production area. Instead, it maintains only a small plot for testing new varieties and cultivation techniques. As a result, the cooperative relies entirely on production partnerships with local farmers. It currently works with 15 households, cultivating a total of 11 hectares.

At the beginning of each season, the cooperative develops production plans based on customer demand for volume and crop varieties, provides guidance on planting schedules, and assigns technical staff to monitor and supervise production practices. Of the 11 hectares under cooperative management, 8 have been certified to VietGAP standards, while the remaining 3 have yet to receive certification due to land documentation issues rather than any shortcomings in farming practices.

Nguyen Van Nhuong, who cultivates one hectare of land, began partnering with the cooperative in 2018 and has applied the soil treatment technique ever since. Early each year, he grows two to three successive crops of leafy mustard greens before pausing production to treat the soil and allow it to "rest" for one month during the summer. He then resumes cultivation for subsequent crop cycles.

Nguyen Van Hao has had a similar experience. Farming two hectares of land, he has also partnered with the cooperative since 2018. While he initially cultivated a variety of vegetables, in recent years, he has shifted most of his production area to sweet leaf bush (Sauropus androgynus).

Today, Vinh Phuc Safe Vegetable Cooperative supplies its produce to the WinMart supermarket chain as well as schools and industrial kitchens in the area.

In addition to conducting regular product testing, customers have become increasingly attentive to food safety standards. From time to time, they visit the cooperative's production sites to observe firsthand how farmers carry out cultivation practices.

By strictly adhering to VietGAP standards and incorporating the soil treatment technique as a preventive measure against pests and diseases, the cooperative has operated for 12 years without a single food safety incident. This has helped provide consumers with hundreds of thousands of safe and reliable meals.