The influence of temperature on plant productivity in agriculture: Accumulated temperature

Accumulated temperature is a weather parameter that directly influences the productivity of agricultural plants. All biological and chemical processes taking place in the soil are connected with air temperature. The heat supply of crops is characterised by a sum of average daily air temperatures that are higher than a biological minimum during a vegetation period. Both too-high and too-low temperatures spoil the course of biochemical processes in cells, and irreversible changes can be caused that lead to a stoppage of growth and the death of plants.    

Temperature limits of growth

The growth of plants is possible within comparatively broad temperature limits. There are three distinct fundamental temperature points of growth: minimal temperature, which is enough for growth to start; the optimal one, which is the most advantageous for growth processes; and the maximum one, where growth stops. Minimal temperatures of growth are usually a little bit higher than a point where tissue freezes, while maximum temperatures are several degrees lower than an index of thermic death. Along with that, the fundamental temperature points of growth vary depending on temperature adaptation, the development stage, the season and the time of day.  

For each plant species, due to its peculiarities and mainly owing to its geographical origin, there are specific temperature limits within which the plants are able to reproduce. For a major part of the vegetative world, a rise in temperature up to 25–28°C increases the activity of photosynthesis, and with a further increase (higher than 30°C) photorespiration starts to prevail over photosynthesis significantly. This can lead to a reduction in the weight of a plant, to a slowdown, and even to a total end to the reproduction process. There is a supposition according to which, at temperatures above 30°C, some matter necessary for growth decays quickly or is not produced in the required amounts. There are even genes in many living creatures that are “sensitive to temperature”.                 

The division of plants into thermophilic and cold-resistant  

Thermophilic plants (corn, cucumber, melon, pumpkin, etc.) have their fundamental temperature points of growth increased. There are plants whose maximum temperature point of growth can exceed 50°C. And cold-resistant plants successfully grow even at temperatures below 0°C.      

The influence of temperature mode on particular parts of a plant 

For the growth of different parts of a plant, optimal temperatures can vary for one and the same plant. Generally, the optimal temperature for root growth is lower than for the other parts of a plant. Low (below 5°C) and high (above 30°C) soil temperatures cause the root to be in a shallow position, which notably reduces its growth and activity. The majority of plants develop a strong, branchy root system when the soil temperature ranges from 20°C to 25°C.    

The maturing of the productive parts of a plant needs its own temperature range, while flowering is induced in another, quite narrow, temperature interval; and the development of flowers takes place at other temperatures. The temperature affects seed sprouting in a dual manner. On the one hand, the temperature defines the speed of sprouting; and on the other hand, thermal influence can make a plant dormant.

Obviously, the temperature requirement is different for various plant species, and it changes during the course of the plant’s life span or during a season; it even varies for specific parts of a plant.

That is why, when planning a crop yield, there is not only the matter of choosing a suitable climatic area – the choice of a location for sowing within the borders of a region is also of great importance. For example, a poorly chosen place for settling a vineyard 50km from an area with the required climate can severely impact a crop yield. This issue is more vivid when considering such sensitive plants as salads.

In this situation, the importance of timely acquisition of accurate and visual data is hard to overestimate. OpenWeatherMap is happy to announce our new API for accumulated temperature data based on historical data. This index is determined as a sum of average daily air and soil temperatures that exceeds a defined threshold of 0°C, 5°C or 10°C, or a biological minimum temperature level that is crucial for some specific plant.