SITE-SPECIFIC NUTRIENT MANAGEMENT (SSNM)

Team Leader

Ms. Greta Gabinete

Assistant Professor

College of Agriculture and Forestry

West Visayas State University, Lambunao, Iloilo

Email: gggabinete1@yahoo.com

Partner Institution

West Visayas State University

Site Characteristics

The Province of Iloilo occupies the southern and northeastern portion of Panay Island. It has a total land area of 466,342 hectares, of which 74% is classified as agricultural lands. Iloilo is the largest rice producing province in the Western Visayas region, which ranks second in rice production in the country. In 2005, the total land area cropped to rice was 230,000 ha, of which about 54% is irrigated. The average yield for irrigated areas was 3.3 t ha⁻¹ in 2005.

The Province has two pronounced seasons; a dry season from November to April and a wet season during the rest of the year. The mean annual rainfall is about 1600 mm. Generally, two rice crops are grown in the irrigated areas of the province:

§         First crop (wet season): April/May to August/September (high yielding season)

§         Second crop (dry season): September/October to December/January (low yielding season)

Both direct seeding and transplanting are practiced in both seasons.

Development and Evaluation of SSNM Strategies

Research on the development of an SSNM recommendation was conducted in 2005−06 with 56 farmer cooperators on Sta. Rita and Alimodian soils. The nutrient omission plot technique was used in the farmers’ fields to determine the attainable and nutrient-limited yields for both the wet and dry season. A preliminary evaluation of an SSNM recommendation was conducted in the dry season with 14 farmers to compare the SSNM performance with farmers’ practice.

Research Results

Attainable yields and nutrient-limited yields

The omission plot technique was used to determine the attainable yield target and nutrient-limited yields on Sta. Rita and Alimodian soils. Table 1 shows the rice yields from the nutrient omission plot study in the wet season (2005). The attainable yield target on Sta. Rita averaged 5.5 t ha⁻¹, which was higher than on Alimodian soil. Likewise, the N, P, and K-limited yields in Sta. Rita soil were higher than on Alimodian soil. Yield responses for Sta. Rita soil were 1.7 t ha⁻¹ for N, 0.7 t ha⁻¹ for P, and 0.5 t ha⁻¹ for K. Yield responses for Alimodian soil were 1.2 t ha⁻¹ for N, 0.7 t ha⁻¹ for P, and 0.4 t ha⁻¹ for K.

Table 1. Rice yields obtained with the nutrient omission plot technique in farmers’ fields in five municipalities in Iloilo Province, Philippines, in the 2005 wet season.

SD= standard deviation; n= number of replicated plots

Table 2 shows the yields obtained with the nutrient omission plot technique during the dry season. Attainable yields averaged 5.2 t ha⁻¹ on Sta. Rita soil and 4.3 t ha⁻¹ on Alimodian soil. N-limited yields were 3.6 t ha⁻¹ on Sta. Rita soil and 2.9 t ha⁻¹ on Alimodian soil. Yield responses for Sta. Rita soil were 1.5 t ha⁻¹ for N, 0.7 t ha⁻¹ for P, and 0.7 t ha⁻¹ for K. Yield responses for Alimodian soil were 1.6 t ha⁻¹ for N, 0.4 t ha⁻¹ for P, and 0.4 t ha⁻¹ for K.

Table 2. Rice yields obtained with the nutrient omission plot technique in farmers’ fields in five municipalities in Iloilo Province, Philippines, in the 2005−06 dry season.

SD= standard deviation; n= number of replicated plots

SSNM-based nutrients requirements

The rates of fertilizer N, P₂O₅, and K₂O were determined using the SSNM approach. Data shown in Table 1 and 2 were used to calculate the SSNM recommendation. Fertilizer N rate was estimated by dividing the N-response by the target agronomic efficiency for N (AE_N), which was 20 for the wet season and 18 for the dry season. The rates of P₂O₅ and K₂O fertilizers were estimated from attainable yield targets, and P and K-limited yields using the Nutrient Decision Support System (NuDSS), assuming a medium straw input of 2.5 t ha⁻¹ for both seasons.

Table 3. Fertilizer N, P₂O₅, and K₂O requirements estimated from the nutrient omission plot technique in five municipalities in Iloilo Province, Philippines, in 2005−06.

CY= crop year; SD= standard deviation; n= number of replicated plots

On-farm evaluation of SSNM

The SSNM recommendation was tested in 14 farmers’ fields during the dry season using improved seed rate (100−120 kg ha⁻¹) and farmers’ seed rate (110−200 kg ha⁻¹). The SSNM recommendation included early application of 28 N, 28 kg P₂O₅, and 28 kg K₂O ha⁻¹. The succeeding N fertilizer applications at 20−25 days after sowing (DAS) and 35−40 DAS were based on leaf color chart (LCC) readings. Additional K (30 kg K₂O ha⁻¹) was applied at panicle initiation to assess whether it increased yield. The yields in the SSNM plots were compared with the yields in the farmers’ fields.

Results show that with improved seed rate of 100−120 kg ha⁻¹, SSNM significantly yielded almost 1.0 ton ha⁻¹ higher than did farmers’ practice on Sta. Rita soil (Table 4). Yield difference between using SSNM with improved seed rate and farmers’ seed rate was significant at 0.7 ton ha⁻¹.

Table 4. Grain yield (t ha⁻¹) in SSNM and farmers’ practice fields.

*Improved seed rate= 100−120 kg ha⁻¹; **Farmers; seed rate= 110−200 kg ha⁻¹

Values in a column followed by different letters are significantly different (P<0.05).

Locally Adapted Recommendation

Results from the nutrient omission plot trials and evaluation of N management options were used to formulate locally adapted recommendations for managing N, P, and K. Recommendation for direct wet-seeded rice on Sta Rita soil is available at the link below.

Iloilo, western Visayas, Philippines SSNM version 1.0 (www.irri.org/irrc/ssnm)

Site Specific Nutrient Management