Crop Guide: Rice Cultivation - Mineral Fertilizers

Element	Soil test method	Critical value
Phosphorus	NaHCO3	6 ppm PO4-P(In cold years, may be as high as 9 ppm)
Potassium	NH4Ac	60 ppm K
Zinc	DTPA	0.5 ppm Zn

Field research has established the critical concentrations of P, K, and Zn in the soil by correlating soil test values of these mineral nutrients and rice plant performance. The presence of critical or subcritical values (Table 6.2) of a given nutrient will generally result in a reduction of 10% or more of growth and grain yield. When soil test values are near or below the critical level, application of the deficient nutrient will usually prevent this reduction. Therefore, proper soil sampling, chemical analysis and interpretation help avoid plant nutrient deficiencies and are valuable guides in soil fertility management.

 

 

6.1.2 Leaf analysis

Whereas soil analysis provides insight to preplant fertilizer needs, plant tissue analysis is valuable as a way of diagnosing the nutritional status of the growing crop. Tissue analysis serves as a guide for mid-season N application and for anticipating the need for N, P, and K applications for subsequent rice crops. The value of tissue analysis depends on representative sampling, selection of the proper plant part, generally- the most recently matured whole leaf blade, also known as the “Y-leaf”, (Figure 6.1), drying and handling of samples, analytical procedure used, and the correct interpretation of the relationship between the nutrient levels and crop growth and yield.

 

Figure 6.1: The "Y-leaf," the most recently fully expanded leaf of the rice plant, is the correct leaf to sample for tissue analysis.

 

Table 6.2: Adequate and critical values of nutrients for leaf-analyses of rice plants of short statured varieties

 

Plant growth stage*	Nitrogen(% total N)		Phosphorus (ppm extractable PO4-P)		Potassium(% extractable K)		Zinc (% in whole seedling plant)
	critical	adequate	critical	adequate	critical	adequate	critical	adequate
Mid-tillering	4.6	4.6 - 5.2	1,000	1,000-1,800	1.4	1.4 - 2.8	20	22 - 80
Maximum tillering	4.0	4.0 - 4.6	1,000	1,000-1,800	1.2	1.2 - 2.4	–	–
Panicle initiation	3.3	3.3 - 3.8	800	800-1,800	1.0	1.2 - 2.4	–	–
Flag leaf	2.6	2.6 - 3.2	800	800-1,800	1.0	1.2 - 2.2	–	–

* Analysis on dry weight basis of most recently matured leaves for Kjeldahl N, 2% HAc extractable PO₄ and K

 

6.2 Soil N-P-K applications

Nitrogen

Optimal application rate of N fertilizer depends mainly on the variety and soil type. Therefore, the range of total N is wide (Figure 6.2). There are two application approaches:

• A single pre-flood application, where the entire N rate is applied at once. Such a treatment is not recommended for certain varieties, and under poor water management conditions.
• Split applications, whereby the total amount of N fertilizer can be split into three applications with an early N application of about 20-30 % of the total requirement. The remaining 70 to 80% is split into two applications based on the needs of the crop, as determined by leaf color by using the leaf color chart (Figure 6.3).

Figure 6.2: Example of split applications of recommended nitrogen

 

 

Apply high N rate	Apply baseline N rate	Apply little or no N

 

Table 6.3: Nitrogen application rates by soil type and cultivar characters

Cultivars	Total N(kg/ha)	Pre-flood(kg/ha)	Mid-Season(kg/ha)
Clay
Normal varieties	200	150-185	50-15
Semi-dwarf		135-175	65-25
Lodging-susceptible		100-135	65-100
Silt-loam
Normal varieties	185	145-160	40-25
Semi-dwarf		135	50
Lodging-susceptible		100	85

 

Phosphorus

Phosphorus fertilizer application timing of is a critical factor affecting the P nutritional status of the rice crop. P fertilizer should be applied pre-flood on P deficient soils, because P uptake for biomass production takes place during the entire growth season. As rice crop will remove 0.35 kg of P₂O₅ per 50 kg rice grain, the following application rates apply for soils testing between lower than 35 and over 55 kg/ha of P. These recommendations take into account the said removal factor.

 

Table 6.4: Phosphorus recommendations for rice based on "Mehlich 3" soil test:

 

Soil pH	Soil test P (kg/ha)*	Recommended P2O5 (kg/ha)
6.5	≤ 35	20
	> 35	0
> 6.5	≤ 35	70
	35-55	45
	> 55	0

* In the event the soil test results in higher extractable P contents, Table 6.6 will provide more accurate recommendations.

 

Potassium

Table 6.5: Potassium recommendations for rice, based on the "Mehlich 3" soil test:

Soil test K (kg/ha)	≤ 140	140 - 200	>200
Recommended K2O (kg/ha)	100	65	0

These recommendations are based on the assumption that the straw will be recycled into the soil after the harvest. However, if the straw is removed from the field, K₂O requirements for a yield of 6.5 t/ha and of 5.5 t/ha are 153 and 121 kg/ha, respectively.

Potassium application is recommended before rice shows K deficiency symptoms as only low yield benefit, if any, is obtained from K fertilizer application to deficient rice in the mid-to-late boot stage. K fertilizer added at this time probably has little benefit for the current rice crop, but will remain in the soil for the future crops.

Silt and sandy loam soils have a very low buffering capacity and soil test K can decline rapidly if K fertilizer is omitted for several consecutive crops.

 

It is recommended to apply all potassium rates by broadcasting and incorporating before planting in both water-seeded and dry-seeded rice. If potassium fertilizers could not be applied pre-plant, they can be applied before establishing the permanent flood. Split application is also common in some areas.

 

Table 6.6: Phosphorus (P2O5) and potassium (K2O) fertilizer recommendations for grain yield goal of 8.5 t/ha

 

Soil pH	P Soil test level			Soil test K level
				Very low		Low	Medium		Optimum	High
				61 ppm		62-90 ppm	91-130 ppm		131-175 ppm	>175 ppm
				137 kg/ha		137-200 kg/ha	201-290 kg/ha		291-390 kg/ha	>391 kg/ha
Level	ppm	lbs/A	P2O5- K2O  (kg/ha)
> 6.5	Very Low	16	36	100-135	100-100		100-70	100-0		100-0
	Low	16-25	36-55	70-135	70-100		70-70	70-0		70-0
	Medium	26-35	56-80	55-135	55-100		55-70	55-0		55-0
	Optimum	36-50	81-110	0-135	0-100		0-70	0-0		0-0
	High	>50	>110	0-135	0-100		0-70	0-0		0-0
6.5	Very Low	16	36	55-135	55-100		55-70	55-0		55-0
	Low	16-25	36-55	35-135	35-100		35-70	35-0		35-0
	Medium	26-35	56-80	0-135	0-100		0-70	0-0		0-0
	Optimum	36-50	81-110	0-135	0-100		0-70	0-0		0-0
	High	>50	>110	0-135	0-100		0-70	0-0		0-0

 

 

6.3 Controlled release fertilizer - CoteN™

6.3.1  What are Multicote™ and CoteN™?

Multicote™ is a polymer-coated controlled release fertilizer that releases plant nutrients slowly and continuously throughout the crop growth cycle. Multicote™ is available in a wide range of formulas, and with release longevities of 2 to 16 months (at soil temperature of 21^oC).  CoteN™ is the most suitable polymer-coated controlled release fertilizer for rice since it is a polymer coated urea with 4-month release longevity. One base-dressing application ofCoteN™ enables avoiding top-dressing application and prevents nitrogen loses by leaching.

 

Haifa produces a special non-floating CoteN™ for paddy rice (Figure 6.4). This special fertilizer is heavier than the regular CoteN™ which settles in the water on the flooded soil surface and will not be washed away with water current that may occur in a paddy field. It gradually releases available nitrogen to the rice plant. This controlled release procedure, prevents nitrogen loses and increases the uptake efficiency by the plant.

 

Figure 6.4: Standard CoteN™ (left) and non-floating CoteN™ (right)

 

 

6.3.2 CoteN™ recommended application

1. CoteN™ is suitable for base-dressing application. Continuous release of nitrogen from the encapsulated urea, ensures the supply of nitrogen according to plant growth and developing needs. CoteN™ be applied as a part of the total recommended N, by blending it with the regular fertilizers or by using it as the sole source of the recommended nitrogen rate. Scientific research demonstrated that the continuous supply and reduced loses of nitrogen derived from CoteN™, enable a considerable reduction (20%) in the application rate of nitrogen. This will save on the fertilization costs and reduce the groundwater pollution. 
2. Non-floating CoteN™ is suitable especially when side-dressing is required. The higher specific weight of this special product will ensure that the product granules will remain on the bottom of the rice paddy and will continuously release nitrogen in accordance with the rate needed by the crop, preventing the need for a second top-dressing application.

 

6.4 Foliar feeding

Foliar Feeding is a fast and highly effective method of supplementing and enriching plant nutrients when needed. Foliar application of Haifa Bonus water soluble fertilizer provides the exact composition of plant nutrients for optimal development of rice crop, when absorption of nutrients from the soil is disturbed. Precision-timed foliar sprays are a fast-acting and effective method for treating nutrient deficiencies.

 

Haifa Bonus, a high-K foliar fertilizer contains a special adjuvant, which improves the adhesion of the fertilizer to the leaf surface and creates fertilizer clusters that release nutrients over a prolonged period of time. Foliar application of the correct Haifa Bonus nutrients, in relatively low concentrations at critical rice development stages, contributes significantly to higher yields and improved quality.

 

Selecting the right Haifa Bonus fertilizer

Haifa Bonus fertilizers are available in various N-P-K-Mg-Zn ratios. The fully water soluble high K and chloride-free fertilizer, is suitable for rice crop wherever it is grown. Careful soil- and leaf analyses will help selecting the optimal Haifa Bonus formula.

 

Determine safe foliar applied rate:

To verify the safe rate under local conditions, it is advisable to spray recommended rate of Haifa Bonus on a few rice plants then, 3 to 4 days later, check the treated rice plants for scorching symptoms.

 

Preparation of tank-mix

Dissolve the entire required Haifa Bonus massin water, at about double of the Haifa Bonus mass. Add this solution to the spray tank when it is half full with water. When tank-mixing with crop-protection agents, addition of wetting agents is not necessary. To ensure inter-compatibility of the two (or more) tank-mix components, a small-scale spray test should be performed on few rice plans several days prior to the commercial application.

Application rate of Haifa Bonus
Concentration	grams per 8 liter sprayer*	grams per 16 liter sprayer **
2 %	160 g	320 g
3 %	240 g	480 g