Features Inoculants Seed & Chemical
Manage chickpea maturity with fertilizer

Think back to the disastrous 2004 chickpea season, which had a long wet fall
that delayed chickpea maturity for many growers. With poor quality and a high
proportion of green seeds in the harvested bins, the chickpea crop was disappointing
for many. But research at Agriculture and Agri-Food Canada (AAFC) may help growers
improve chickpea maturity to help reduce the probability of a crop wreck.

Managing N fertility can help manage maturity risk. Photo Courtesy Of Saskatchewan Pulse Growers.

The research is looking at using nitrogen (N) fertilizer as a risk management
tool. The theory is that under good growing conditions, the N fertilized crop
will grow vigorously in the early growing season, will run out of fertility
later on, and obtain a timely maturity. On the other hand, a well inoculated
crop may continue growing if favourable conditions are available for continuous
N fixation activity within the crop. When N is not restricted, the crop will
have a delayed maturity.

"The fertilizer approach would be used as a risk management tool to help
growers manipulate maturity. It's not to save money on inputs or provide the
highest yield, but it can allow a grower to harvest a crop sooner to avoid a
frost," explains Yantai Gan, a research scientist at AAFC Swift Current,
Saskatchewan.

"The maturity problem with chickpeas is that they have a strong indeterminate
growth habit. When conditions are favourable, the plants continue their vegetative
growth, which delays maturity. But with nitrogen fertilizer, the plants develop
a more vigorous vegetative growth early in the season, which depletes applied
nutrients and soil water, promoting earlier maturity."

Gan conducted three years of field experiments at Swift Current and Shaunavon,
Saskatchewan from 2004 to 2006, with funding from the Saskatchewan Pulse Growers
Association, the Saskatchewan Agricultural Development Fund, and the AAFC Federal
MII. Gan has summarized the results of the first two years, while the final
year of data is being analyzed. However, Gan says the trends in the first two
years are evident in the 2006 data as well.

Where nitrogen fertilizer was used, chickpea maturity was significantly improved
compared to the crops where non-inoculant and non-fertilizer N were used or
only rhizobial inoculant was used. Cultivars with later maturity responded to
the fertilization more significantly than the relatively earlier maturing cultivars.

Figure 1. 2004 and 2005 chickpea yields. SC = Swift Current SH = Shaunavon. Source: Gan, AAFC Swift Current.

"As a risk management tool, using nitrogen fertilizer looks very promising,"
says Gan. "In some years, if you used nitrogen fertilizer, it improved
maturity by up to 24 days."

The 2004 trials had very large differences between treatments, with the biggest
difference in maturity between treatments at 20 to 24 days. In 2005, the difference
at Swift Current was relatively small at seven to eight days, while the Shaunavon
site was similar to 2004, with much earlier maturity with the nitrogen treatments.
Swift Current has a medium texture soil, which may have hastened maturity more
than the heavier textured soil at Shaunavon.

In 2006, Gan says differences were relatively small, because precipitation
in July and August was very low, and all crops matured quickly.

In addition, chickpeas grown on conventional summer fallow either did not mature
by a killing frost (in 2004) or delayed maturity (in 2005) compared to wheat
or barley stubble. Chickpeas grown on barley stubble matured earlier than those
on wheat stubble.

The 2005 growing season was near long-term normal, with harvest approximately
one month earlier than the 2004 season. Most chickpea treatments matured normally
in 2005, with good quality seed. 2006 was earlier yet, than 2005.

Fertility effect on seed yield and green seed
Gan says that while the inoculant treatments often produced higher yields, they
had to be balanced off with the risk of delayed maturity. In 2004, seed yield
increased with increased N rates from zero to 112kg/ha (100lb/ac). Plots that
received inoculant only produce similar seed yields as plots that received 84kg/ha
(75lb/ac) of N, but inoculant only treatments produced the highest (52 percent)
proportion of green seeds due to delayed maturity.

In 2005 there were lower differences in yield between treatments at both Shaunavon
and Swift Current, although Shaunavon treatments were still significantly different
and yields were similar to 2004. Yields at Swift Current in 2005 were significantly
less.

To use nitrogen fertilizer as a maturity risk strategy, Gan says producers
should carefully select the field. He explains that a field that has a low residual
soil N is a good choice for chickpeas. The field that had a crop with very high
yield the previous year, such as a durum, canola or barley crop, would be good
for chickpeas to follow this year because this land has low soil residual nitrogen.
Conversely, summerfallow fields usually have very high residual nitrogen, along
with the fields that had poor crops the previous year due to poor growing conditions,
or the field that shows high fertility levels in a soil test are not good candidates
for chickpeas. Gan says that fields with 50 to 60 pounds per acre of available
N would not be suitable for this strategy.

"On fields with lower residual fertility, the nitrogen fertilizer applied
at seeding is picked up quickly during the early seedling stages, resulting
in vigorous vegetative growth which will be the foundation for pod production
later on. Later in the season, the soil will run out of nitrogen-supplying power,
and the chickpeas vegetative growth will shut down and seed set will start,"
explains Gan. But if there is high soil residual N, it will allow plants to
continue to grow because the residual soil nitrogen will be released gradually
from the soil, and it may last for the entire growing season."

Once the 2006 data is crunched, Gan will be summarizing the research and providing
more specific recommendations. Economically, should the final results be similar,
growers would have to balance off the reduced risk of frost and improvement
in grade with the increased cost of production from fertilizer. In the end,
the economics may come down to each individual grower's personal risk aversion.