The Hindu Business Line : December, not March, to decide wheat output

Crop watch
The key variable to watch this time is minimum temperatures in the second half of December.
1degree increase in average minimum temperature above normal levels leads to a yield loss of 315 kg/ha.

Karnal , Sept. 11

For wheat-watchers, the variable seen as most critical in determining the size of the crop in the country is the average temperatures prevailing during March. In recent years, abrupt rise in the mercury at this crucial grain-filling stage has led to premature ripening of the crop and significant reduction in harvested yields.

But this time, things could turn out different. A favourable moisture regime conferred by prolonged monsoon rains across the northern plains is likely to see farmers go in for large-scale early sowing of wheat — well before the recommended November 25 deadline.

The Ides of March, then, may not really cause concern, as the crop would by then have attained a minimum threshold growth, giving ample time to complete its normal 140-145 days duration before the first half of April.

The key variable to watch this time, scientists say, is not mean temperatures at grain-filling time in March, but minimum temperatures in the second half of December when the crop is at the tillering stage.

Yield loss

An analysis by the Directorate of Wheat Research (DWR) here reveals that every one degree increase in average minimum temperature above normal levels during the second half of December leads to a yield loss of about 315 kg per hectare.

This is, in fact, more than the 290-kg hectare loss arising from the same phenomenon in the second half of March, according to Dr Jagdish Rane, Senior Scientist (Plant Physiology), who carried out the study based on the last nine years' experimental data. "December is when tillers (stems) are formed. If temperatures rule high, you will have fewer tillers produced per plant and the signalling system in the crop induces early ear-head emergence and flowering. The crop records less horizontal and premature vertical growth," he explains.

Low production

This was precisely what happened in 2004-05, when temperatures in the second fortnight of December averaged roughly four degrees above normal. Subsequently though, things cooled down and an extended winter resulted in ideal conditions for grain filling in March. But this could not undo the initial damage from lowering tillering and the country ended up harvesting only 68.64 million tonnes (mt). In 2005-06, December was fine, but in March, temperatures were at least five degrees above normal. So, production was again low at 69.48 mt.

Good result

The last time when both December and March were good for wheat was 1999-2000, with output touching an all-time high of 76.37 mt. It is difficult to say now how 2006-07 will be. But given the low possibility of damage during March — courtesy early plantings by farmers — one could hazard a realistic guess by end-December, when both acreages and tillering performance will be known.