SITE-SPECIFIC NUTRIENT MANAGEMENT (SSNM)

Northern Vietnam

Red River Delta and Nearby Regions

Team Leader

Dr. Tran Thuc Son

Vice Director and Soil Scientist

National Institute for Soils & Fertilizers

Hanoi

Email: tsonnisfacvn@hn.vnn.vn

Partner Institutions

§         National Institute for Soils & Fertilizers

§         Plant Protection Department

Site Characteristics

The Red River Delta (RRD) accounts for about 20% of the national rice production in Vietnam and rice produced there is mainly used for local consumption. In 2002, the total harvested rice area in the RRD was about 1.2 million hectares, mostly found in the lowlands along the Red River and in coastal regions. The total rice production was 6.7 million tons, which corresponds to an average yield of 5.6 t ha⁻¹.

There are two rice-growing seasons per year:

§    Spring season (early rice) from February to June. This is the high-yielding season and rice is established by transplanting.

§    Summer season (late rice) from June to September. Yield in this season is usually lower because the crop is often affected by heavy rainfall or storms. Farmers usually grow short-duration varieties to be able to grow a nonrice winter crop (i.e., maize or soybean) after summer rice.

The climate in the RRD is subtropical, characterized by a cool winter season and a hot and humid summer. Rainfall averages about 1700 mm per year, mostly occurring from May to September.

The major soil types in the RRD are alluvial, acid sulfate, alluvial gley, degraded, and marine saline.

Research and Training Sites

Development of SSNM recommendation based on soil type (1998-2004)

SSNM evaluation and nutrient omission plot trials were conducted in five soil types in five different provinces of the RRD (Fig.1).

Fig. 1. Map showing the locations (provinces) for SSNM evaluation and nutrient omission plot trials for developing recommendations based on soil type, 1998–2004.

Wider-scale evaluation and promotion of SSNM (2005 onward)

Wider-scale evaluation and promotion of SSNM started in 2005, with the addition of more sites (provinces) extending even beyond the RRD (Fig. 2).  In eight of eleven provinces, activities in 2005 included both research (LCC demonstration, nutrient omission plots) and training of trainers (TOT). In three provinces, activities focused only on TOT.

Fig. 2. Map showing the provinces for wide-scale evaluation and promotion of SSNM in 2005.

Research Results

Attainable yield and nutrient deficits (2003–04)

Attainable yield with full fertilization and nutrient-limited yields were determined from nutrient omission plots. The results by soil type and rice cultivar in 2003–04 are shown in Tables 1 (spring) and 2 (summer).

Rice grain yield in plots fully fertilized with N, P, and K provided an estimate of the attainable yield target, which was higher in the spring than summer season. The yield of rice not fertilized with N but fertilized with other nutrients was used to determine N-limited yield. Similarly, the yield of rice not fertilized with P but receiving other nutrients indicated P-limited yield; and the yield of rice not fertilized with K but receiving other nutrients indicated K-limited yield. The difference between the yield target and a nutrient-limited yield indicated the crop response to the nutrient.

Yield response to P averaged ≤1 t ha⁻¹ for most of the soils in both seasons. Yield response to K averaged >1 t ha⁻¹ in shallow alluvial and degraded soils in both seasons (Tables 1 and 2), and in alluvial gley soil in spring season (Table 1); it was ≤1 t ha⁻¹ in acid sulfate and alluvial soils in both seasons (Tables 1 and 2).

Table 1. Rice yields obtained in the spring season with the nutrient omission plot technique in farmers’ fields in five soil types in the Red River Delta, Vietnam, 2003–04. Values shown are means of 12 replicates.

Table 2. Rice yields obtained in the summer season with the nutrient omission plot technique in farmers’ fields in five soil types in the Red River Delta, Vietnam, 2003–04. Values shown are means of 12 replicates.

SSNM-based nutrient requirements for rice in five soil types (five provinces) in the Red River Delta

Total fertilizer P₂O₅ and K₂O were estimated from attainable yield target, P-limited yield, and K-limited yield (Tables 1 and 2) using the nutrient decision support system (NuDSS). Straw input was estimated as 0.5 t ha⁻¹ in summer. There is no straw input in the spring season. The economical rates of K₂O fertilizer were determined from economic benefit analysis of the different K₂O rates used in 2004.  

Table 3. Fertilizer N, P₂O₅, and K₂O requirements estimated from results with the nutrient omission plot technique in five soil types in the Red River Delta, Vietnam, 2003-04. Values shown are the means and standard deviation of 12 replicates per soil type.

* Economical rates as determined from economic benefit analysis of different K₂O rates used in 2004. 

On-farm evaluation of SSNM in five soil types located in five provinces of the Red River Delta, Vietnam

In SSNM, fertilizer N is applied several times during the season based on crop needs as determined by the leaf color chart (LCC). Fertilizer P is all applied within 14 days after transplanting (DAT); and fertilizer K is applied twice about 50% before 14 DAT and 50% at early panicle initiation. Rice yields averaged for 12 farmers’ fields per soil type in 1998-01 and for six farmers’ fields in 2003-04 were higher with SSNM compared to the farmers’ fertilizer practice (FFP) (Fig. 3). Tables 4 and 5, respectively, show the total amount of fertilizer N, P₂O₅, and K₂O applied per season in 2003-04 with FFP and SSNM.

Fig. 3. Performance of SSNM as compared to the farmers’ fertilizer practice (FFP) in the Red River Delta, Vietnam. * indicates a significant difference between the two treatments at P<0.05 in a given year.

Table 4. Total amount of fertilizer N, P₂O₅, and K₂O applied to rice per season with the farmers’ fertilizer practice (FFP) in the Red River Delta, Vietnam, 2003-04. Values shown are the means and standard deviation of 12 replicates per soil type.