Central Vietnam 

Team Leader

Ms. Tran Thi Thu Ha

Hue University of Agriculture and Forestry

Hue City

Email: hatranhue@gmail.com  

Partner Institution

Hue University of Agriculture and Forestry

Site Characteristics

There are two rice-growing seasons per year in Central Vietnam:

§    Spring season from December to April

§    Summer season from May to early September

Research Sites

Development of SSNM recommendation (2005 onward)

Activities, including the use of nutrient omission plot trials, to develop SSNM recommendations began in 2005 on different soil types in Thua Thien-Hue and Quang Nam Provinces. In 2006, activities expanded to Quang Tri, Quang Ngai, Binh Dinh, and Phu Yen Provinces (Fig. 1).

Fig. 1. Map showing the locations (provinces) for developing SSNM recommendations in Central Vietnam.

Research Results

Attainable yield and nutrient deficits (2005)

Attainable yield with full fertilization and nutrient-limited yields were determined from nutrient omission plots conducted in 2005 in five farmers’ fields per soil type. The results by soil textural class 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 slightly higher in the summer than spring 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.

In Thua Thien-Hue, yield response to P averaged <1 t ha⁻¹ for all soils in spring (Table 1) and >1 t ha⁻¹ in summer (Table 2). Yield response to K averaged ≥1 t ha⁻¹ in clay loam and loam soils in spring (Table 1) and in all soils in summer (Table 2); yield response was higher in summer than in spring.

In Quang Nam, data were collected only in the spring season. For both clay loam and sandy loam soils, the yield response to P was ³ 2 t ha⁻¹, while the yield response to K was >1 t ha⁻¹ (Table 1).

Table 1. Rice yields obtained in spring 2005 with the nutrient omission plot technique in farmers’ fields in two provinces with different soil types in Central Vietnam. Values shown are means of 5 replicates.

Table 2. Rice yields obtained in summer 2005 with the nutrient omission plot technique in farmers’ fields in Thua Thien-Hue Province with different soil types. Values shown are means of 5 replicates.

SSNM-based nutrient requirements for rice in Thua Thien-Hue and Quang Nam, central Vietnam

The SSNM approach was used to estimate fertilizer N, P₂O₅, and K₂O requirements based on the results in Tables 1 and 2. Total fertilizer N required for rice (Table 3) was estimated from the measured response to N (Tables 1 and 2) and an assumed target agronomic efficiency of N (kg yield increase kg fertilizer N⁻¹) of 20 for both spring and summer. See N management for more details.

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 2 t ha⁻¹ per cropping season. 

Table 3. Fertilizer N, P₂O₅, and K₂O requirements estimated from results with the nutrient omission plot technique in Thua Thien-Hue and Quang Nam, central Vietnam, 2005. Values shown are the means and standard deviation of 5 replicates per soil type.

 * These low estimated fertilizer N rates are the result of high yields without fertilizer N in farmers’ fields selected in 2005. Fertilizer N rates would be higher in fields with lower N fertility.

Locally Adapted Recommendation for Thua Thien-Hue and Quang Nam

Results obtained with the nutrient omission plot technique and interviews of farmers were used to develop locally adapted recommendations for managing N, P, and K. These tentative recommendations assume an attainable target yield of 6 to 6.5 t ha⁻¹ in both spring and summer seasons. They provide two options for N management. A relatively low application of fertilizer N is recommended for fields with relatively fertile soil and low response (≤1.5 t ha⁻¹) to fertilizer N, and a relatively higher application of fertilizer N is recommended for fields with relatively lower soil fertility and high response (≥2 t ha⁻¹) to fertilizer N. In 2005, all trial sites in Quang Nam had high response to fertilizer N, whereas sites in Thua Thien-Hue varied with both high and low response to fertilizer N (Tables 1 and 2).

Tentative recommendations for the spring and summer seasons are provided at the links below. Field-testing to evaluate and refine these recommendations started in 2006.

SSNM recommendation for wet-seeded rice in spring

Version 1 [PDF 151kb]

SSNM recommendation for wet-seeded rice in summer

Version 1 [PDF 149kb]

CVN summer rice version 1.0 (www.irri.org/irrc/ssnm)

Site Specific Nutrient Management