By Bruce Barker
The market dictates price, and the market says that as seed size increases for kabuli chickpea varieties
The market dictates price, and the market says that as seed size increases for kabuli chickpea varieties, so does price. Kabuli seeds equal to or greater than nine millimetres in diameter get the extra price, so increases in the proportion of these seeds in the seed lot increase the overall economic returns.
Yantai Gan, a researcher at Agriculture and Agri-Food Canada at Swift Current, Saskatchewan, says that while seed size is a genetically controlled trait, the seed size distribution in the harvested seed lot is strongly influenced by several factors, including the growing season environment. To help guide chickpea growers on the best agronomic practices for growing bigger seed, he conducted a field experiment from 2004 to 2006 with plots located at Swift Current and Shaunavon, Saskatchewan.
“Yes, we know that seed size is partially determined by the variety, but for a given variety, we wanted to find out what the influence of different factors were on seed size,” explains Gan.
The study received financial support from Saskatchewan Pulse Growers, Saskatchewan Agricultural Development Fund and Agriculture Agri-Food Canada Matching Investment Initiative. It examined the effect of environmental conditions, preceding stubble type, and fertility/ inoculation management regimes on seed size distribution of two kabuli chickpea varieties, CDC Frontier and CDC Xena.
Two genetically different varieties were compared, the large seed-sized variety CDC Xena and medium-sized variety CDC Frontier. They were grown on wheat and barley stubble, and
conventional summerfallow under each of the eight different rhizobium inoculation and nitrogen (N) fertilizer management regimes. Yields and seed size were analyzed.
Not surprisingly, during three years, the highest percentage of nine millimetre diameter and greater seeds was obtained with the large-seeded variety, CDC Xena. Averaged across the six site years, CDC Xena produced 59 percent of seed with nine millimetre diameter and greater seed, of which 22 percent was greater than 10 millimetres and 37 percent was between nine and 10 millimetres in diameter. Over the same period, 24 percent of the seed for CDC Frontier was nine millimetre diameter or greater, with 50 percent between eight to nine millimetres, and the rest in the seven to eight millimetre category. Drought conditions in 2006 shortened the period of seed filling, resulting in smaller seed size for both varieties.
Preceding crop type also influenced seed size distribution for both CDC Frontier and CDC Xena. CDC Xena grown on barley stubble produced |59 percent of seeds nine millimetre
or greater, which was six percent higher than if CDC Xena was grown on wheat stubble. However, Gan explains that this difference was mainly due to 2004 when the two stubble types were in adjacent fields.
“The year of 2004 was wet with growing season precipitation about 40 percent greater than normal and in that year we had a difference in seed size between barley and wheat stubble. The two stubble types were in separate, adjacent fields, though, but they had the same level of residual soil N and water. However, during the last two years (normal to dry years), the two stubble types were in the same field and we didn’t see any difference. So, there is a need to determine whether the differences observed in 2004 were due to wet conditions or due to other factors. In general, I wouldn’t be too concerned about wheat or barley stubble selection,” explains Gan.
Advantages of growing kabuli chickpea on conventional summerfallow were realized only in the dry year of 2006, when the fallow-grown CDC Xena produced 60 percent of nine millimetre or greater seeds, significantly higher than when grown on barley, at 35 percent, or wheat stubble at 31 percent.
Granular inoculation important
The use of rhizobium granular inoculant increased the proportion of nine millimetre or greater diameter seed for CDC Frontier by six percent compared to treatments that received fertilizer or no-N/no-inoculant. Similar trends were found for CDC Xena where use of rhizobium or high level of N-fertilizer increases the proportion of seed greater than nine millimetres.
The results of the study show that while the weather has a lot to do with the harvested seed size, growers can influence seed size to a certain extent. The biggest factor appears to be ensuring adequate N fertility through successful inoculation.