Site-Specific Nutrient Management (SSNM) for Direct, Wet-Seeded Rice in Hunan Province, China

Single rice: 130−140 days growth duration (from seed to harvest)

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 21 days after sowing (DAS) to meet crop needs.

§      Applying only a moderate amount of fertilizer N before 21 DAS.

§      Applying 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).

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

§      Using micronutrients based on local recommendations.

Target for recommendation

Cultivars with 130−140 days growth duration from seed to harvest are common for the single rice cropping system with wet-seeded rice in Hunan Province. This recommendation was developed based on attainable yield targets and approximate responses of rice to fertilizer N, P, and K typically observed for such rice cultivars in farmers’ fields in Hunan Province. The approximations summarized in the table below represent the features of irrigated rice fields targeted by this SSNM recommendation. All yields are expressed on dry grain (about 14% moisture) basis.

 ^a Responses to P and K tend to be higher at higher attainable yield targets.

SSNM recommendation

This recommendation involves the following steps:

1.   Apply basal N, P, and K fertilizer before 20 DAS.

a.   3 kg P₂O₅ mu⁻¹ (1 mu = 667 m²), which is equivalent to 45 kg P₂O₅ ha⁻¹.

b.   2.4 kg K₂O mu⁻¹, which is equivalent to 4 kg KCl mu⁻¹ (36 kg K₂O ha⁻¹).

c.   3.2 kg N mu⁻¹ (48 kg N ha⁻¹). This corresponds to about 19 kg ammonium bicarbonate mu⁻¹ or 7 kg urea mu⁻¹.

2.   Take LCC readings at about 30−35 DAS. Adjust the rate of N (urea) application based on the LCC reading, as shown in the figure below.

a.   If the LCC reading is below 3.5, apply 5 kg urea mu⁻¹ (35 kg N ha⁻¹).

b.   If the LCC reading is between 3.5−4, apply 4 kg urea mu⁻¹ (28 kg N ha⁻¹).

c.   If the LCC reading is ≥4, apply 3 kg urea mu⁻¹ (21 kg N ha⁻¹).

3.    Take LCC readings at panicle initiation, about 60−70 DAS. Adjust the rate of urea application based on the LCC reading, as shown in the figure below.

a.   If the LCC reading is below 3.5, apply 8 kg urea mu⁻¹ (55 kg N ha⁻¹).

b.   If the LCC reading is between 3.5−4, apply 6 kg urea mu⁻¹ (41 kg N ha⁻¹).

c.   If the LCC reading is ≥4, apply 3 kg urea mu⁻¹ (21 kg N ha⁻¹).

4.    Apply 4 kg KCl mu⁻¹ (36 kg K₂O ha⁻¹) with the third N application at panicle initiation.

5.    At early heading (90–100 DAS), apply 3 kg urea mu⁻¹ (21 kg N ha⁻¹) if the LCC reading is below 4.

Use either compound (NPK) or single-element fertilizers for basal application to obtain the desired amounts of N, P₂O₅, and K₂O at the lowest cost. Recommendations for applying N, P, and K fertilizers are illustrated in the figure below. Fertilizer rates are given in kg mu⁻¹ (1 mu = 667 m²).

This recommendation is specifically developed for rice cultivars with growth duration from seed to harvest of 130−140 days, and with a seed rate of about 1.5 kg seed mu⁻¹ for hybrid rice, and about 3 kg mu⁻¹ for inbred rice. The timing of fertilizer applications at tillering and panicle initiation should be adjusted accordingly for cultivars with longer or shorter growth duration. The optimal critical LCC reading and distribution of fertilizer N could change for higher seed rates.

The K₂O recommendation presumes that half or more of the rice residue is returned to the field. If most residue from the previous crop is removed from the field, then each of the two K₂O applications should be increased from 4 to 5 kg KCl mu⁻¹.

Recommended fertilizer application for wet-seeded rice with growth duration of 130−140 days.

Hunan WSR single rice version 1.0 (www.irri.org/irrc/ssnm)

Site Specific Nutrient Management