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30-35% water savings over traditional transplantation route pushes up demand for herbicide-resistant paddy varieties/hybrids from IARI and Savannah Seeds

For basmati paddy grower Satyavan Sehrawat, the two biggest challenges are water and labour.

The traditional method of cultivating the cereal grain crop – by puddling (flooding the field and tilling repeatedly to break down soil clods, plug large pores and create a soft seedbed) and transplantation (of seedlings initially raised in nurseries) – is highly water-intensive.

“Puddling itself consumes water equivalent to three irrigations. For the first three weeks after transplanting, the field has to be irrigated every second day to maintain a standing water depth of 4-5 cm. You need to irrigate even thereafter once a week,” said the 56-year-old Sehrawat, who farms basmati on 50 out of his 54-acre holding in Delhi’s Daryapur Kalan village.

Depending on the crop’s duration (115-120 days from seed to grain for Pusa Basmati-1509 and 140-145 days for Pusa Basmati-1121), and also how much it rains, the total irrigations can be anywhere between 20 and 30. Each irrigation uses over 200,000 litres of water per acre.

Those calculations matter, especially in an El Niño year, with rainfall across India being 24.1 per cent below-normal in the current monsoon season (June-September) till July 5.

But it isn’t water alone. Transplanting paddy seedlings in puddled fields requires labour, which is getting increasingly scarce. “I pay Rs 4,000 per acre to the transplanting workers, plus arrange for their chai-paani (refreshments) and LPG cylinder or firewood. Smaller farmers who cannot provide these have to shell out Rs 5,000 per acre,” noted Sehrawat.

Direct seeding advantage

That’s where DSR or direct-seeded rice technology comes in. It dispenses with preparation of nurseries (where paddy seeds are sown and grown into young plantlets over 25-30 days) and uprooting of the seedlings for transplanting in the main field (ten times the nursery area). Nor is there need for puddling and flooding of fields.

In DSR, the paddy seeds are directly sown in the main field, just like wheat. In transplanted paddy fields, the standing water acts as a natural herbicide, depriving weeds of oxygen and sunlight for their seeds to germinate or already-emerged seedlings to survive. Continuous flooding is necessary to prevent weed growth, especially during the crop’s early stage.

DSR basically replaces water with chemical herbicides. It means growing paddy varieties or hybrids that can “tolerate” their application – in this case, of Imazethapyr, a herbicide that controls a wide spectrum of grassy and broadleaf weeds.

The normal Pusa-1509 and Pusa-1121 varieties Sehrawat cultivates cannot “tolerate” Imazethapyr, as the chemical does not distinguish the crop from the weeds and ends up killing both. What he’s, however, growing now are Pusa Basmati-1985 and Pusa Basmati-1979. These are the Imazethapyr herbicide-tolerant (HT) versions of the same popular basmati varieties bred by the Indian Agricultural Research Institute (IARI) in New Delhi.

The HT varieties have been developed through non-genetically modified mutation breeding, involving altering the ALS (acetolactate synthase) gene. This is a gene naturally present in rice plants and not introduced from soil bacteria and other unrelated species (as with genetically-modified Bt cotton or hybrid mustard).

“The ALS gene codes for an enzyme responsible for the synthesis of leucine, isoleucine and valine, which are essential amino acids for plant growth and development. Imazethapyr sprayed on normal paddy binds itself to the ALS enzyme, inhibiting the production of these amino acids,” explained A.K. Singh, former IARI director.

The two HT basmati varieties bred by him and fellow IARI scientists contain a mutated ALS gene whose DNA sequence has been altered. While amino acid synthesis isn’t inhibited, the ALS enzyme no longer has binding sites for Imazethapyr. The paddy plants can then “tolerate” the herbicide, which will only kill the weeds.

An inflection year

Last year, Sehrawat tried out Pusa Basmati-1985 and Pusa Basmati-1979 on one-acre land each. The results were good enough for him to expand DSR to 20 acres this year: 16 acres under the first and four under second HT variety.

“There’s no paneeri (nursery preparation) here or labour required for ropai (transplanting). And I’m saving 30-35 per cent water, as the field does not have to be flooded. Irrigation is given sirf nami barkarar rakhne ko (to retain moistness),” he pointed out.

Sehrawat completed the DSR sowing of his 20 acres between May 27 and June 8: “I had to only plough my field once and use a laser land leveler (for ensuring uniform placement of seeds and fertilisers as well as distribution of water) before sowing”.

Source : indianexpress