Nutrient Management

Organic manuring

Apply organic manure in the form of farmyard manure or compost or green leaf @ of 5 t/ha and incorporate into the soil while ploughing. Vermicompost or Coirpith compost @2.5 t/ha can be substituted for 5 t/ha FYM in Onattukara region. The entire quantity of phosphatic fertilizers may be applied along with the organic manures.

Use of biofertilizers

Azospirillum is suitable for both upland and wetland conditions and is available as carrier-based inoculum. It fixes about 20-25 kg N per ha under ideal conditions, thereby effecting a reduction of 25 per cent in the quantity of N fertilizers required. Treatment with Azospirillum also induces better root formation in inoculated plants. The isolates of Azospirillum brasilense strains AZR 15 and AZR 37 from Kuttanad soils are highly effective for rice.

Mix 2 kg of culture in 60 litres of water and soak the seeds required for 1 ha (60 kg) for 24 hours before sowing. At the time of transplanting, dip the roots of seedlings for 15-20 minutes in the culture slurry prepared by mixing 2 kg inoculum with 40 litres of water. This slurry can be used for treating seedlings required for 1 ha. Another 2 kg culture may be applied in the field along with FYM or compost.

Blue green algae (BGA) is mainly recommended for wetland rice cultivation. It is available as carrier-based inoculum and it fixes about 25-30 kg N per ha under ideal conditions. However, the use of this biofertilizer is not feasible in acidic soils with pH below 6.0. It can be broadcasted in the rice fields at the rate of 10 kg/ha one week after transplanting.

Azolla is suitable for wetland rice cultivation. The required quantity of azolla will have to be raised in the farmers field itself. Fixes about 25 to 30 kg N per ha. Fresh azolla can be applied at the rate of 10 t/ha at the time of ploughing.

Green Crop Manuring

Cowpea may be raised as an intercrop in dry seeded low land (semi-dry) rice by sowing 12.5 kg seed/ha along with rice to serve as a source of green manure. When the rice field gets submerged with the onset of southwest monsoon, cowpea at the age of about six weeks and at active vegetative stage decays and gets self-incorporated in the soil adding substantial quantity of green manure. Such a system of concurrent growing of cowpea also reduces weed pressure in semi-dry rice.

Concurrent growing of cowpea/daincha

A. Dry seeded rice :When there is an undue delay in the onset of monsoon, concurrently grown cowpea in rice fields can be incorporated by spraying 2,4 –D @ 1.0 kg/ha at 30-40 days after sowing without affecting the yield with a substantial reduction on weed incidence.

B. Wet seeded rice: In wet seeded rice, daincha can be raised as an intercrop by sowing 20 kg seed of daincha/ha along with rice (seed rate 60 kg/ha) to serve as a source of green manure. Daincha can be incorporated by spraying 2, 4–D @ 1.0 kg/ha at 30 days after sowing thereby adding substantial quantity of green manure. System of concurrent growing of daincha can also reduce the weed pressure in wet seeded rice.

Fertilizer application

*Location specific recommendations. Strict surveillance of pests and diseases is a must under such situations.

**Wherever the soil K status is medium to high based on soil test data and also where incorporation of straw is a practice and tidal contribution of the nutrient is significant. 

Stages of fertilizer application in rice

BA = Basal application; AT = At tillering; API = At panicle initiation; HY = High yielding;
DAP = Days after planting; DAS = Days after seeding

For modan cultivation (upland crop) and direct seeded crop in wet lands, apply nitrogen in three equal split doses, first as basal dressing, second at tillering stage (three weeks after seeding) and the third at panicle initiation stage (about thirty days before flowering). Apply the full dose of P₂O₅ at the time of land preparation as basal dressing. Apply K₂O either in a single dose as basal or in two split doses half as basal and half at the panicle initiation stage.

In Kuttanad region, wherever wet broadcasting (direct seeding) is adopted, give the first basal application of the N at the time of letting in water after drying the field. Water soluble phosphorus can be recommended for application in two split doses in Kuttanad region, as basal and at maximum tillering stage.

The general principle to be followed is that in light soils as well as in soils with high leaching, N may be applied in three or four split doses according to the duration of the variety.

For typical Onattukara region, where soil is sandy loam and with iron toxicity problem, apply 5 tonnes of organic matter or vermicompost 2.5 tonnes and 67.5 kg K₂O/ha.

During the first crop season, when basal application of N is not possible due to incessant rains, basal dose can be shifted to 15 days after transplanting.

In coarse sandy loam soils with high percolation as in Onattukara region, nitrogen and potash fertilizers may be applied in five equal splits given at planting, 15^th, 38^th, 53^rd and 70^th day for medium duration varieties, which coincide with the stages of early tillering, neck node differentiation, early reduction division and heading stages respectively in the case of medium duration varieties.

For Thiruvananthapuram and Malappuram districts, Phosphorous application is essential for increasing rice yields. Rock phosphate may be substituted for super phosphate. Basal dose of nitrogen may be postponed to initial tillering phase of rice crop, especially during the rainy season. Split application of potash @ 50 per cent basal, 25 per cent at tillering and 25per cent at panicle initiation stage is recommended for this region. In sequential cropping of rice, application of 50 per cent of the nutrient requirement (on nitrogen equivalent basis) as organics (FYM, rice straw, green manure) and 50 per cent as fertilizers during kharif season and the entire dose of nutrients as fertilizers in rabi season enhances the grain and straw yield. The organics may be incorporated 3 weeks before transplanting. Application of 25 per cent of the nutrient requirement as organics and 75 per cent as fertilizers during kharif season and reducing the fertilizer dose of rabi by 25 per cent gives comparable yield with full POP recommendation during both seasons.

Specific dose of fertilizer for Koottumundakan system

A fertilizer dose of (N:P₂O₅:K₂O) @ 20:10:10 kg/ha for the first crop and 30:15:15 kg/ha for the second crop is recommended for high yield in Koottumundakan system. N and K₂O may be applied in two equal parts for the first crop, one as basal and other at panicle initiation stage. P₂O₅ may be applied fully as basal. The fertilizer for second crop may be applied as a single dose immediately after the harvest of the first crop (ad hoc recommendation).

Fertilizers (N:P₂O₅:K₂O) @ 40:20:20 kg/ha for virippu and 20:10:10 kg/ha for the photosensitive mundakan  crop are recommended as economic dose for the northern region under koottumundakan practice.

Methods of fertilizer application

For pre-planting application, apply the fertilizers at the final ploughing. In areas where availability of water is assured, temporarily draining the field one day prior to application and re-flooding after twelve hours is recommended for top dressing of fertilizer.

For increasing the efficiency of urea for top dressing, mix urea with six times its weight of slightly moist soil and apply to the field 24-28 hours after mixing. Oil seed cakes such as punna and neem cakes can also be mixed with urea (1 part of oil cake + 5 parts of urea by weight) for increasing fertilizer efficiency. This method is particularly useful for basal application of N. Under special conditions of drought and waterlogging, apply N as foliar spray. Urea may be applied as a low volume spray at 15% concentration using power sprayer or at 5% concentration using a high volume sprayer, the quantity applied in one application being limited to 15 kg/ha.

When zinc deficiency is noticed, apply zinc sulphate @ 20 kg/ha. Early stages of zinc deficiency are evidenced by interveinal chlorosis, bleaching of midribs and light yellow colouration of the leaf. Older leaves develop brown rusty spots and are extremely brittle. Zinc sulphate and potash should not be applied on the same day. The effect of zinc application can persist up to 5 years depending on the soil cropping pattern. Hence soil application is not required for every season. Soil zinc status should be monitored before application to avoid accumilating toxic concentrations of zinc. To treat zinc deficiency, apply 20kg ZnSO₄.7H₂O per ha. Foliar spray of 0.5% ZnSO₄ solution,( 1kg ZnSO₄ + ½ kg lime to avoid phytotoxicity in 200 L water/ha ie. 5g ZnSO₄ + 2.5g lime per litre of water) for emergency treatment of Zn deficiency in growing plants. Apply at tillering (25–30 DAT), and give two or three repeat applications at intervals of 10–14 days.

Split application of water soluble phosphatic fertilizers in two equal splits as basal and at maximum tillering stage is effective in giving higher grain and straw yield than the full dose as basal dressing under certain situations.

Application of chemical fertilizers can be dispensed for Vyttila-1 and Vyttila-2 in pokkali rice fields.

When the soil has less than 10 ppm of calcium chloride extractable sulphur or 15 ppm of phosphate extractable sulphur, substitute urea with ammonium phosphate sulphate to correct sulphur deficiency. For medium duration rice grown in brown hydromorphic soils ammonium phosphate sulphate may be used to supply 25 kg sulphur per hectare to protect the crop from sulphur deficiency (ad hoc recommendations).

Application of magnesium as basal dose in the form of magnesium sulphate (16 per cent MgO) or magnesite (40 per cent MgO ) or dolomite (10 per cent MgO) @ 20 kg MgO/ha is effective in giving a significant increase in grain and straw yield of rice in magnesium deficient soils. In nondeficient soils, a marginal increase in grain and straw yield is also obtained. On per unit MgO basis, magnesite is more concentrated and cheaper than magnesium sulphate.

In iron toxic laterite soils of Kerala, application of 120 kg potash/ha + lime 150 kg/ha + silica 100 kg/ha (as sodium silicate 250 kg/ha or fine silica 100 kg/ha or rice husk ash 500 kg/ha) is recommended for higher yields.

Liming

In general, addition of lime is absolutely necessary when the pH is lower than 5.5 and it is advisable when pH varies between 5.5 and 6.5.

Apply lime @ 600 kg/ha in two split doses, the first dose of 350 kg/ha as basal dressing at the time of first ploughing and the second dose of 250 kg/ha as top dressing about one month after sowing.

For Pokkali areas, apply lime @ 1000 kg/ha, 50% at the time of preparation of mounds and the rest at the time of dismantling the mounds.

A time lag of one week should be given between application of lime and fertilizers. For top dressing, lime may be applied one week prior to the application of fertilizers.

Top