Tread with caution on direct seeding of rice

Surinder S Kukal

PADDY is considered to be a water-guzzler, requiring 4,000-5,000 cubic metres of water per acre. No wonder Punjab’s groundwater has been declining very fast both in terms of quantity and quality. Scientists have been making efforts to develop water-saving techniques for paddy. One such water-saving technique developed by Punjab Agricultural University (PAU) is direct seeding of rice (DSR); it is also labour-efficient. DSR was initially aimed at coping with the shortage of labour for paddy transplantation; later, it started being promoted as a water-saver as well. The extension personnel of the state Department of Agriculture and PAU have been trying to promote this technology among the farmers of the state for the past several years, but with little success. Despite tall claims of more than 5 lakh hectares of paddy area under DSR during 2020 and 2021 by the state government, no reduction in electricity consumption in the agricultural sector was observed during the paddy season of these years. Still, to effectively promote this technology, the state government recently announced a subsidy/bonus of Rs 1,500 per acre to the farmers who will opt for DSR during 2022.

Why puddling in paddy fields?

Puddling is a practice of tilling the soil in standing water so as to break down the soil aggregates into primary particles. After puddling, the soil particles settle down with differential speed, with sand particles settling first and clay particles doing so last, leading to the formation of a ‘clay skin’. This clay skin results in a reduction in the infiltration rate of water into the soil and ensures that applied irrigation water remains on the surface of the soil for a longer period of time. Perhaps this practice evolved because of the behaviour of paddy plants, which are accustomed to grow under anaerobic (wet) conditions. Paddy is the only crop where the plant roots breathe through the aerial parts — the stem of the plant being hollow from inside. Under wet conditions, the ammoniacal nitrogen prevails in the soil, which is easily taken up by the paddy plants, in contrast to other plants which do not take up this form of nitrogen. Also, puddling leads to ease of transplanting by the farmers.

As per PAU’s Package of Practices, DSR is recommended only in medium to fine textured soils, where the laser-levelled fields are irrigated before being tilled. Under workable moisture conditions, these fields are to be shallow-cultivated and planked twice during evening hours, followed by immediate sowing of seeds. The herbicides are also required to be sprayed immediately after sowing. The first irrigation after sowing is recommended to be applied 21 days after sowing and thereafter irrigation is to be applied at 5-7 days’ interval. In contrast, in the traditional method of growing paddy, the puddled fields are required to be irrigated so as to maintain flooding for two weeks after transplanting and thereafter irrigation is recommended at an interval of 2-3 days after complete disappearance of water from the fields, which means an irrigation interval of 4-5 days. However, the farmers have not been following this recommendation for the puddled transplanted paddy crop, despite efforts made through live demonstrations by the state government and PAU.

Points to ponder

• Farmers believe that it is important to irrigate their fields 3-4 days prior to puddling for so-called cooling of the soil — this is a myth. It should require only one irrigation (of course heavy, 8-10 cm) for the puddling process, provided the transplanting of seedlings is done in time.
• The farmer keeps water standing in the paddy fields for 60-75 days against the PAU recommendation of only 15 days after transplanting. This leads to higher consumption and hence greater extraction of groundwater. A similar mindset if followed in DSR fields could prove counter-productive to the claims of this technique being water-saving. It is, thus, important to strictly follow the irrigation schedule recommended by PAU; otherwise, DSR may consume higher irrigation water than a puddled system.
• In puddled fields, the residence time of water on the soil surface (being wetter) is lesser than in DSR fields, where the soil surface is rougher. Coupled with lower infiltration rate of puddled fields than DSR ones, it leads to higher amount of irrigation water per irrigation in DSR (7.5-8 cm) compared to puddled fields (3-4 cm). It is advisable that while estimating water consumption in DSR fields, the amount of irrigation water gives a real picture rather than simply counting the number of irrigations.
• Studies at PAU have shown evapotranspiration losses to be similar in both systems, rather higher in DSR. Any reduction in evapotranspiration losses leads to real water-saving; otherwise, it is more of energy saving.
• Experiments at PAU and Borlaug Institute for South Asia have shown lower yields of DSR. This could be due to soil type, weed intensity and diversity. Studies at PAU have shown a decline in crop yields in DSR fields in subsequent years. Farmers must alternate DSR and puddled transplanted paddy in the fields so as to check the development of a weed seed bank, which competes with the main crop for water and nutrients.

It is commendable that the state government is trying to popularise water-saving technologies in paddy fields. But it is also important for the state agencies to ensure that irrigation practices in DSR fields are followed strictly as per the recommendations of PAU. Otherwise, DSR fields may end up consuming more irrigation water than in the puddled system.

The author is Member,

Punjab Water Regulation & Development Authority