Site-Specific Nutrient Management (SSNM) for Transplanted Rice in Java, Indonesia

N management: Real time

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

§      Applying sufficient P and K within 14 days after transplanting (DAT) to meet crop needs.

§      Applying only a moderate amount of fertilizer N within 14 DAT.

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

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

§      Using micronutrients based on local recommendations. (For details, consult your local agricultural extension representative.)

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 7–10 days, 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 to monitor leaf color.

Target for recommendation

This recommendation was developed based on attainable yield targets and approximate responses of rice to fertilizer N, P, and K typically observed for irrigated rice in farmers’ fields in Java. The approximations summarized in the table below represent the features of rice fields targeted by this SSNM recommendation. All yields are expressed on dry grain (about 14% moisture) basis.

SSNM recommendations for transplanted rice

Guidelines for farmers on implementing improved management practices tailored to their specific fields are given below as a series of steps at critical crop growth stages. These guidelines are based on the following premises:

• The historical application of >30 kg P₂O₅ ha⁻¹ per crop in the past five seasons is sufficient to build soil P status to a level where fertilizer P₂O₅ is only required to maintain soil P fertility.
• Rice ‘straw’ refers to the portion of the rice biomass cut and removed with the panicles for threshing. Straw is considered ‘removed’ when biomass removed with the harvested panicles is not returned to the field; it is considered ‘retained’ when this harvested biomass is returned to the field. Rice biomass remaining in the field after cutting the crop at harvest (i.e. rice stubble) is presumed to be retained in the field in all cases.

Early growth stage: Apply N, P, K, and S as needed

Within 14 DAT, apply fertilizer based on an identified yield target as shown in Table 1. The steps in the process of estimating fertilizer needs for a specific location are

• Step 1. Select a yield target from the four options of 5, 6, 7, or 8 t ha⁻¹ expressed at 14% moisture content.
• Step 2. Select a fertilizer N rate from Table 1 based on yield target.
• Step 3. Identify whether the historical level of fertilizer P₂O₅ application is above or below 30 kg ha⁻¹ per season in the past five seasons.
• Step 4. Select a fertilizer P₂O₅ rate from Table 1 based on yield target and past fertilizer P₂O₅ use.
• Step 5. Identify whether rice straw is historically removed or returned to the field.
• Step 6. Select a fertilizer K₂O rate from Table 1 based on yield target, straw management, and knowledge of relative soil K supplying capacity (low or high) in a geographical location.
• Step 7. For rice-growing areas where fertilizer S is recommended, select an ammonium sulfate rate from Table 1 based on yield target.

Either single-element fertilizers or compound (NPK) fertilizers can be used to obtain the desired amounts of N, P₂O₅, and K₂O at the lowest cost. Fertilizer N can be supplied as urea, ammonium sulfate, or NPK fertilizer.

Table 1. Guidelines for early application of fertilizer N, P₂O₅, K₂O, and S within 14 days after transplanting (DAT) rice in Indonesia.

Vegetative growth stage: Topdress fertilizer N using real-time N management with LCC

Apply fertilizer N several times during the growing season to ensure that the N supply matches the crop need for N as determined with the LCC, and as shown in the figure below. 

Real-time N management from active tillering to booting using LCC involves the following steps:

1.   Take LCC readings every 7–10 days starting from about 25 DAT and continue until booting (50 DAT).

2.   Apply N when the LCC reading falls below the critical value of 4 (value is about 3.5 or midway between 3 and 4):

a.   In locations with very high response to fertilizer N, apply 125 kg urea ha⁻¹ (58 kg N ha⁻¹).

b.   In locations with high response to fertilizer N, apply 100 kg urea ha⁻¹ (45 kg N ha⁻¹).

c.   In locations with medium response to fertilizer N, apply 75 kg urea ha⁻¹ (35 kg N ha⁻¹).

d.   In locations with low response to fertilizer N, apply 50 kg urea ha⁻¹ (23 kg N ha⁻¹).

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

4.    Apply 1 bag of urea ha⁻¹ (23 kg N ha⁻¹) at early heading (55–65 DAT) for hybrid or new-plant type (NPT) rice, if the LCC reading falls below 4 (value is midway between 3 and 4).

Recommendations for applying fertilizer N using the real-time N management with LCC are illustrated in the figure below. This recommendation is specifically developed for rice varieties with a growth duration from seed to harvest of 115–120 days. 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.

The critical value for the LCC should be selected such that there are two applications of fertilizer N from tillering to booting for seasons in which the attained yield matches the yield target. The applications of fertilizer N from tillering to booting should increase to three for seasons in which climate and management enable yield to exceed the yield target, whereas fertilizer N applications should decrease to one for seasons in which climate and management prevent yield from reaching the yield target.

Real-time N management with LCC for transplanted rice with growth duration of 115-120 days.

Panicle initiation: Apply fertilizer K₂O at targeted locations

For optimal grain filling and yield at locations with low supply of plant-available K, apply fertilizer K₂O at panicle initiation based on an identified yield target as shown in Table 2. The steps in the process of targeting fertilizer K₂O to specific locations are

• Step 1. Select a yield target from the three options of 5, 6, 7, or 8 t ha⁻¹ expressed at 14% moisture content.
• Step 2. Identify whether rice straw is historically removed or returned to the field.
• Step 3. Select a fertilizer K₂O rate from Table 2 based on yield target, straw management, and geographical location.
• Step 4. Encourage the farmer to apply the recommended fertilizer K₂O to a small plot at panicle initiation, then compare grain yield and grain filling between the plot with additional K₂O and an adjacent field without additional K₂O.

Table 2. Guidelines for application of fertilizer K₂O at panicle initiation.

Indonesia Java RTN version 2.0  (www.irri.org/irrc/ssnm)

Site Specific Nutrient Management