Accumulated temperature is a weather parameter which directly influences productivity of agricultural plants. All biological and chemical processes taking place in the soil are connected with air temperature. Heat supply of crops is characterized 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 a course of biochemical processes in cells, and irreversible changes can be caused that lead to a stop of growth and death of plants.
Temperature limits of growth
Growth of plants is possible within comparatively broad temperature limits. There are distinguished 3 fundamental temperature points of growth: minimal temperature which is enough for a start of growth, optimal one which is the most advantageous for growth processes and maximum one when growth stops. Minimal temperatures of growth are usually a little bit higher than a point of tissue freezing, while maximum temperatures are several degrees lower than an index of thermic death. Along with that, fundamental temperature points of growth vary depending on temperature adaptation, a development stage, a season and a part of the day.
For each plant species due to its peculiarities and mainly owing to its geographical origin, there exist specific temperature limits within which these plants are able to reproduce. For a major part of vegetative world a rise in temperature up to 25-28C increases activity of photosynthesis, and by its further increase (higher than 30C) photorespiration starts to prevail over photosynthesis significantly. This leads to a reduction in the weight of a plant, to a slowdown and even to a total stop of a reproduction process. There is a supposition according to which at temperatures above 30C some matter necessary for growth is being decayed fast or is not produced in 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 shifted to a side of higher temperatures. There are plants whose maximum temperature point of growth can exceed 50C. And cold-resistant plants successfully grow even at temperatures below zero degrees.
The influence of temperature mode on particular parts of a plant
For growth of different parts of a plant optimal temperatures can vary for one and the same plant. Generally, optimal temperature for root growth is lower than for the rest parts of a plant. Low (below 5C) and high (above 30C) temperatures of soil cause a shallow position of a root what notably reduces root growth and activity. A major part of plants develop a strong branchy root system when the temperature of soil ranges from 20 to 25C.
Maturing of productive parts of a plant needs its own temperature range, while flowering is induced in another, quite narrow temperature interval, and development of flowers takes place at different from those temperatures. Temperature affects seed sprouting in a dual manner. On the one hand, temperature defines a speed of sprouting, and on the other hand, thermal influence can shift a state of rest.
Obviously, a temperature requirement is different for various plant species, and it changes in the course of a life span of a plant, of a season, and it varies even for specific parts of a plant.
That is why when planning a crop yield there is not only a choice of a proper climatic area, but a choice of a right place for sowing within borders of one region is of great importance. For example, a mistakenly chosen place for settling of a vineyard in 50km from an area with proper climate can severely influence a crop yield. This case is more vivid when speaking about such sensitive plant as salad.
In this situation, importance of timely obtaining 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 which exceeds a definite threshold of 0, 5, 10 degrees or a biological minimum of a temperature level which is crucial for some specific plant.