Site-Specific Nutrient Management (SSNM) for Wet-Seeded Rice in Nueva Ecija Province, Central Luzon, Philippines

N management: Real time 

SSNM is a plant-based approach for ‘feeding’ a rice crop with nutrients as needed. SSNM includes the following features:

§         Apply sufficient P and K within 21 days after sowing (DAS) to meet crop needs.

§         Apply only a moderate amount of fertilizer N within 21 DAS.

§         Apply fertilizer N at tillering and later growth stages based on the needs of the crop for supplemental N as determined with a leaf color chart (LCC).

§         Apply fertilizer K at panicle initiation based on crop needs.

§         Use micronutrients based on local recommendations. (For details, consult with the local Agriculture Technician.)

Real-time N management is one of two equally effective options for applying fertilizer N based on crop needs as determined with the LCC. In this option, farmers monitor the color of rice leaves at regular intervals of about 7 to 10 days and then apply fertilizer N whenever the leaves become more yellowish-green than the critical threshold value indicated on the LCC. It typically requires four to six visits by the farmer to the field for monitoring leaf color.

Target for recommendation

This recommendation was developed based on attainable yield targets and rice responses to fertilizer N, P, and K typically observed for irrigated rice in farmers’ fields in Nueva Ecija. They are summarized in the table below, and they represent the features of rice fields to which this SSNM recommendation can be targeted for inbred rice.

* For hybrid rice the attainable yield target is 7 to 8 t ha⁻¹ and the yield response to N is about 3.5 to 4 t ha⁻¹.

SSNM recommendation using real-time N management

This recommendation involves the following steps:

1)     Apply the first (early) application of N, P, and K within 21 DAS.  Do not use the LCC with this early N application.

In the dry season apply:

§         30 kg N ha⁻¹. Reduce this amount when high quality organic material is applied.

§         30 to 35 kg P₂O₅ ha⁻¹.

§         30 to 40 kg K₂O ha⁻¹ to all soils.

In the wet season apply:

§         20 kg N ha⁻¹. Reduce this amount when high quality organic material is applied.

§         20 to 25 kg P₂O₅ ha⁻¹.

§         15 to 20 kg K₂O ha⁻¹ to all soils.

2)     Take LCC readings every 7−10 days starting from about 30 DAS and continue until booting for inbred rice or early heading for hybrid rice.

3)  Apply N when the LCC reading is below 3 in the period up to 65 DAS:

§         In the dry season apply 2 bags of urea per hectare (45 kg N ha⁻¹).

§         In the wet season apply 1 bag of urea per hectare (23 kg N ha⁻¹).

4)     If the LCC reading is 3 or above, do not apply N. Wait 3−5 days and repeat the LCC reading.

5)     Apply K at panicle initiation (about 55−60 DAS) for soils with low to moderate indigenous K supply.

§         In the dry season apply 30−40 kg K₂O ha⁻¹.

§         In the wet season apply 15−20 kg K₂O ha⁻¹.

6)     Apply N during booting (70−75 DAS) if the LCC reading is below 3.

In the dry season:

§         For hybrid rice, apply 1.5 bags of urea per hectare (35 kg N ha⁻¹).

§         For inbred rice, apply 1 bag urea per hectare (23 kg N ha⁻¹).

In the wet season:

§         Do not apply N in the typical season.

§         Apply 1 bag of urea per hectare (23 kg N ha⁻¹) when climate is exceptionally good and potential yield is high.

7)     Apply 1 bag of urea per hectare (23 kg N ha⁻¹) at early heading for hybrid rice in the dry season, if the LCC reading is below 3.

The recommendation is illustrated for the dry season (Fig. 1) and the wet season (Fig. 2). Rates of P₂O₅ and K₂O and rates of early N are given in kg per hectare. Either compound (NPK) or single element fertilizers can be used in the early application to obtain the desired amounts of N, P₂O₅, and K₂O at the lowest cost. Fertilizer N doses at tillering and later are given in bags of urea (1 bag = 50 kg).

This recommendation is specifically developed for rice varieties with growth duration from seed to seed of 115−120 days, which is common in Nueva Ecija Province. The timing of fertilizer applications at panicle initiation and heading and the timing of leaf color monitoring with the LCC should be adjusted accordingly for varieties with longer or shorter growth duration.

Fig. 1. Real-time N management with LCC for wet-seeded rice in the dry season.
 

Fig. 2. Real-time N management with LCC for wet-seeded rice in the wet season.

Nueva Ecija (Philippines) WSR-RTN version 1.0 (www.irri.org/irrc/ssnm)

Site Specific Nutrient Management