Actually..the original cardinal temperatures used for maize were Tb=8, Topt=34 and Tmax=44. But when models were developed usng this they failed to capture continued leaf development and progress to physiological maturity of maize in temperate climates. This is usually because the base temperature is derived from extrapolation of of a linear regression through a dataset that is not close to the base temperature -and the original work came from continental US in the development of Ceres-Maize by Ritchie et al. This was the basis for the APSIM mazie model and is still commonly used. However, when that model was applied to carefully collected datasets from New Zealand it was apparent that development did not stop at 8 C. Thus, at the point 18,10 a new relationship was developed that is linear from this point down to zero zero. Effectively the two lines are now describing the curvilinear response of development to temperature and accounting for the observed development below the previously defined Tb of 8C. The error is common in defintiion of Tb and has been well covered by Bonhomme in EJA 2000 13 1-10 with the original paper by Wilson et al. in FCR 1995. 43 1-18 foir maize.

Regarding the climate of the geographic origin of Maize, the minimum growing temperature for original genetic lines should have been at least 12 degrees. Modern hybrids have 10°C as minimum. What the genetic breeding has contributed is in increasing cold tolerance but not lowering minimum temperature much more the original threshold

Gracias! I did find evidence that optimum growth temperatures take thousands of years to change - but phenological development temperatures change much more rapidly.

A good answer deserves another question.

I have a time series of historic cold-tolerance from the Germany Crop Variety Office, but it is in index form - so what about the temperature (and duration) at which a maize crop incurs permanent damage?

Very nice cuestion. In my opinion doesn't exist one general minimun temperature at which maize will growth. In many literature about maize crop are using 8 ºC as the base temperature for maize, but this values is not the real one. Generally, this value change according to the latitude where the experiment take place. You can read Birch et al., 1998. Field crop research 55 93-107 and you will understand about it. In the north of Europe people are using low values that you coment.

Currently I am busy on samilar type of suitability reaerch. I sereach many liberaries journals. I found out one research which is not published digitally, one of my advisory commitee submitted to me that has been performed in Thailand under the topic of qualitative land evaluation. the following are the requirenemnts indicated for corn.

Diagnostic Factor Unit S1 S2 S3 N

Annual Rainfall mm 500-800 400-500 300-400 35

20-23 16-19 46

1500

Slope ? 0-2 20-Dec 20-35 >35

Soil Depth Cm >100 50-100 25-50 8.4

Organic mater % >1.2 >0.8

Actually..the original cardinal temperatures used for maize were Tb=8, Topt=34 and Tmax=44. But when models were developed usng this they failed to capture continued leaf development and progress to physiological maturity of maize in temperate climates. This is usually because the base temperature is derived from extrapolation of of a linear regression through a dataset that is not close to the base temperature -and the original work came from continental US in the development of Ceres-Maize by Ritchie et al. This was the basis for the APSIM mazie model and is still commonly used. However, when that model was applied to carefully collected datasets from New Zealand it was apparent that development did not stop at 8 C. Thus, at the point 18,10 a new relationship was developed that is linear from this point down to zero zero. Effectively the two lines are now describing the curvilinear response of development to temperature and accounting for the observed development below the previously defined Tb of 8C. The error is common in defintiion of Tb and has been well covered by Bonhomme in EJA 2000 13 1-10 with the original paper by Wilson et al. in FCR 1995. 43 1-18 foir maize.

Great tip! Bonhomme states that"...at temperatures below approximately 10°C there is no growth in maize." And explains that what appears to be growth at lower temperatures at higher latitudes is actually due to temperature fluctuation throughout the day - so that an average daily temperature of 5° C actually affords several hours above 10°C. Further, photoperiod sensitivity also masks this effect as more equatorial cultivars require longer days which are highly correlated with temperatures. That nonlinerar relationship between temp. and development at low temperatures is the key, so it becomes a matter of how your plant growth model is coded!

Don't forget that Maize and sugar cane are both C-4 plants and therefore adapted to higher daytime temperatures and the resulting water-stress than are most other grasses, like Rice, which is a C-3 plant. C-4 plants have a unique anatomy that enables them to avoid the high rates of photorespiration that would normally take place in C-3 plants at high temperatures. So it makes sense that they have an adaptive advantage at higher temperatures. At lower temperatures, when Rubisco doesn't bind Oxygen as well, the more common C-3 pathway has an advantage.

Just thought I would mention it as a reminder.

And to deal with the fluctuations during the day Jones and Kiniry developed a 3 x 8 hour model for calculating mean temperatures -that is what is used in the Ceres models and AFRCWHEAT -important for crops that grow on the shoulders of a growing season and for winter wheat and in my case pastures in temperate zones that spend some of each day in winter above and some below Tb.

Note, in the recent excellent ACIAR/GRDC publiation "Crop yields and global food security -Will yield increase continue to feed the world?" Fischer et al. quotes values of 8 for Tb of both vegetative and reproductive growth of maize but comment the reproductive value may actually be 0 C. They don't suport this comment but do refer to John Porter pers comm. stating cardinal values may be 6 and 31  - this comes from his 2014 publication

"Temperatures and the growth and development of maize

and rice: a review" - in Global Change Biology 20 408-417 where the leaf initiation value is about 6 but there is no evidence for a lower value for grain filling.  

Excellent discussion and thanks to all participants. I would like to point that we are not differentiating temperature responses in terms of growth or development. They do not necessarily match. The original question by Phillip was about the minimum temperature for growth. Fernando said that modern hybrids have 10 °C as the minimum. It looks quite high. A day with a Tmin of 10 °C may have many daytime hours above that minimum. In addition we should consider if the low temperature is early in the season (i.e. seedling growth) or late in the season (i.e. grain filling depending on photosynthesis and/or remobilization). How low temperatures would affect each of these processes? In terms of temperature effect on development, there is a nice paper by Kumudini et al (2014) in AJ reviewing a number of temperature functions for maize development. Also we are completing a couple of papers for FCR looking more into the other extreme of temperatures (i.e. heat stress). We collected field data and complemented with greenhouse data in three locations over three years. For development, we found excellent results with the simplified beta function (Yan & Hunt, 1999, Ann Bot). Toptimum was 30 and 25 for the vegetative and reproductive phases and Tmax was around 47 for both phases.

Jon you are right, in a day with 10 ° C minimum temperature there may be many hours above this temperature. For this reason it is not advisable to take the daily minimum as the basis for a model of growth and development (ideally it is better to take hourly temperatures for it). We have experimental data showing that there is actually growth between 8 and 10 ° C, but keeping temperatures below 10 ° C for many days tends to slow down (stop) growth. We have not seen this phenomenon above 10 ° C.

Indeed very fruitful discussion! Thanks, some issues are much clearer to me now.

I always wondered why the French heat sum model from AGPM predicting harvest dates for maize (see below) is using a base temperatur of only 6°C while having literature such as the Global Change Biology publication Mr Moot mentioned in mind. Despite daily fluctuations, I think 6°C base temp is still very low, as heat sum is rising very quickly over the vegetation period as a consequence.

However, a hourly model would be indeed much more accurate.

ASSOCIATION GÉNÉRALE DES PRODUCTEURS DE MAIS (2000): Besoins en degrés-jours des variétés de mais. Reactualisation 2000. Info No. 266.

I was on my turn searching for the base temperature of maize and found that it is not so much documented. Thus, it seems that 8°C is normally considered as the base temperature except in Europe where 6°C is generally used. I had never thought about this question for maize but I know a beautiful story. Once upon a time, in 1947 in fact, André Cauderon a young maize breeder at INRA, France was asked to work on the development of suitable varieties for the northern part of France. Very luckily, he was awarded of the existence of a farmer’s landrace able to complete its life cycle in a mountainous village in the south of France, initially created from only two ears. He grew this landrace in Versailles and derived two famous lines from it, F2 and F7, know for their adaptation to low mean temperature. All the current European hybrids are related with these two lines. Could it be that one farmer detected a mutation that decreased by 2 degrees the base temperature? I don’t have yet the answer. Let’s ask if someone have it?