Chickpeas in 2010: Low temperature effects in 2009

| Date: 11 May 2010

Kevin Moore1, Leigh Jenkins1, Kathi Hertel1, and Graeme Callaghan2
1NSWI&I, and 2Graeme Callaghan & Associates, Dubbo
Take home message
·         Low temperatures and frost caused losses up to 100% in many 2009 chickpea crops
·         Chickpeas won’t hold a pod until average daily temperature reaches15C
·         Temperature records in the canopy can explain why flowers and pods abort
·         Plant at the optimum time to maximize WUE and yield and minimise frost damage
·         Early planting can lead to excessive biomass, reduced WUE and increased frost damage
What happened in 2009 – where did my pods go?
In 2009, many chickpea crops in northern NSW, especially in the Parkes, Dubbo, Gilgandra, Curban, Coonamble region, had missing (aborted) or ghosted (empty) pods. We believe this was caused by periods of low temperatures during flowering i.e. from about mid-August and pod set i.e. from about 2nd week September. 
 
These low temperature effects on chickpea reproduction were exacerbated by frosts on 28 Sep and (in some places) 8 Oct 09. These frosts caused widespread damage to chickpeas (and wheat, barley and canola), with losses ranging from 100% in the Peak Hill-Tomingley area to less than 25% in crops on red soil and on higher ground. In one “fortunate” case east of the Castlereagh highway, chickpeas with 100% frost damage when inspected on 8 Oct 09, got some rain, re-flowered and went 0.4t/ha (yield estimated on 8 Oct without frost 1.7t/ha). Frost damage is the result of cell contents freezing and the resulting ice crystals damaging cell contents and cell walls.   Low temperature works differently (see next section).
Chickpea physiology
The three major factors affecting chickpea growth and reproduction are temperature, day-length and available soil water. Unlike other winter growing legume crops, chickpeas are very susceptible to cold conditions, especially at flowering. As a general guide, the first chickpea flower is found around the eighth node on the main stem. However, experiments have shown that it is the average daily temperature i.e. (max+min)/2, that is critical for flowering and pod set, rather than any specific effects of maximum or minimum temperatures. The critical mean, or average daily temperature, for abortion of flowers in most current varieties, is below 15°C. Abortion occurs below this temperature because the pollen becomes sterile and reproductive structures do not develop. Flowers may develop below this temperature (pseudo-flowers), but they contain infertile pollen.
 
Once the flowers are produced, a period of cool weather can cause flower or pod abortion to varying degrees. If flowering starts before average daily temperatures reach 15°C, then flowers will continue to abort until temperatures increase beyond this critical temperature. Examining daily temperatures will help explain what you are seeing in your chickpea crop. The best records are those collected in the crop canopy – temperature profiles at airports are often different (usually a few degrees warmer) than in a chickpea canopy.
A Case Study: 2009 PBA HatTrickpbrlogo vs. Yorkerpbrlogo
Interactions between varietal maturity, low temperatures and frost damage can be illustrated by following the progress of Yorkerpbrlogo and PBA HatTrickpbrlogo chickpeas grown on the same farm east of Armatree. The Yorkerpbrlogo was sown @ 60kg/ha on 11 May 09 into a paddock with black soil in the lower end changing to red soil at the higher (northern) end. The HatTrickpbrlogo was sown @ 60kg/ha 18 May 09 into an adjoining paddock of mostly black soil but with some red soil in the north east corner.
 
When first inspected on 18 Aug, the HatTrickpbrlogo was more advanced than the Yorkerpbrlogo with flowers on 2-3 nodes compared with Yorker just starting to flower. The closest temperature records to these crops were captured about 20km to the south near Gilgandra.
 
Figure 1: Daily temperature, Gilgandra July – October 2009
 
Figure 1 indicates those first flowers would have been pseudo flowers or would have aborted because the average temps for 11-15 Aug were below 15C slightly above on 16 Aug and then dropped below for the next few days.  This pattern repeats itself from 24 Aug to 12 Sep.
The second inspection on 10 Sep 09 revealed 2-4 pods on HatTrickpbrlogo (with the higher number where plants were stressed i.e. north eastern end of paddock) and 1-2 pods on Yorkerpbrlogo . Fig 1 suggests some of these pods would have aborted as average temperatures from 3-11 Sep were below 15C. 
 
On 18 Sep the HatTrickpbrlogo had 3-4 green pods (some of the ones seen on 10 Sep had aborted) and the Yorkerpbrlogo had 0-1 green pods (some earlier ones also aborted). Both varieties would have continued to set and hold pods until about 23 Sep, when the mean dropped (again) below 15C and stayed that way till 30 Sep. However, the grower recorded a minus 2C in the canopy on 28 Sep (also visible in Fig 1) and this would have knocked a few pods and flowers. There were 6-7 days after the frost when the mean >15C, but then it dropped back till about 10 Oct, including a second frost on 8 Oct (minus 2.5C). Apart from 15 – 18 Oct and 26 Oct, the mean temperature stayed above 15C for the rest of the season.
On 30 Oct, both varieties had stopped podding: the HatTrickpbrlogo had fewer pods than the Yorkerpbrlogo . The HatTrickpbrlogo went 1.2t/ha and the Yorkerpbrlogo 1.66t/ha.
We believe what we saw in these two crops was primarily flower and pod abortion caused by mean temperatures below 15C with secondary effects of frost. This was more severe in the HatTrickpbrlogo , either because (i) it started flowering earlier, (ii) it was on heavier soil and remained fresher that the Yorker pbrlogo(which had more red soil), or (iii) it may be more sensitive to low temperature stress/frost than Yorkerpbrlogo
Maximising yield and minimising low temperature and frost risk
Selection of sowing date is a trade-off between sowing early with high yield potential in those years with a warmer spring, versus lower yield potentials from delayed sowing, to ensure flowering occurs in temperatures closer to 15°C in cooler springs.
If sowing date occurs significantly before average daily temperatures reach 15°C, then the crop will continue to grow vegetatively, and will use soil moisture in the process. Water Use Efficiency (WUE) may decline under these circumstances.
Observations in 2009 indicated that plants that were well hydrated sustained less frost damage. Improving fallow efficiency may help reduce risk of frost damage.
Conclusions
·         Low temperatures and frost caused losses up 100% in many 2009 chickpea crops
·         Chickpeas don’t form fertile flowers and keep pods until average daily temperature reaches15C
·         Temperature readings, preferably collected in the canopy, can be used to explain why flowers and pods abort
·         Planting at the optimum time maximises WUE and yield and can minimise frost damage
·         Early planting can lead to excessive biomass, reduced WUE and increased frost damage
Contact details
Kevin Moore,
NSW Department Industry & Investment
Tamworth Agricultural Institute,
4 Marsden Park Rd, Calala, NSW, 2340
Tel: 02 6763 1133,
Mob: 0488 251 866,
Fax: 02 6763 1222,

Reference
Certified Chickpea Agronomy Course Manual (2007) “Module 1 – Growth Stages & Development” Pulse Australia, NSW DPI and QLD DPI