Climatic elements as factors of crop growth
The climatic factors are abiotic or non-living components of the environmental factors (outside of genetic factors) that affect plant growth and development. They are elements of climate. There are other abiotic environmental factors, that is, topography and soil, which are treated in a separate page. Under favorable conditions, gene expression is maximized. Ultimately, enhanced growth and development translates into high crop yields.
Light plays an important part in photosynthesis activity in plants. The time required by a crop to achieve maturity is a function of the length of the day (photo period) and, therefore, preference for a variety is judged by its maximum utilization of light energy.
In general, a crop planted in the winter season requires more calendar days to mature than the same crop planted later. In cloudy areas, cloud cover often reduces the amount of light available. This has great significance in regions where ripening of crops and their harvesting in dry condition are often in doubt. Cloud cover and excessive rainfall also prevent double cropping.
Water is an essential requisite to life. Some organisms can live without oxygen (called anaerobic), but these organisms and all others including all plants and animals inclusive of humans will perish without it. Rainfall is the most common form of precipitation and source of water to plants. It is the falling of water in droplets on the surface of the Earth from clouds. The amount and regularity of rainfall vary with location and climate types and affect the dominance of certain types of vegetation as well as crop growth and yield.
The crops to be grown, the agricultural operations and agricultural patterns are closely influenced by the prevailing temperature conditions of the region. The agricultural scientists have proved that each crop has a specific zero below which it cannot grow. There is also an optimal temperature in which the crop is at its. Greatest vigour. For each of the functions of crop life, weather germination, foliation, blossoming or fructification a specific zero and optimum can be observed in the temperature.
The impact of temperature on agricultural patterns may be seen from the fact that the northern limit of the regions in which the date- palm bears ripe fruit coincides almost exactly with the mean annual isotherm of 19° C. The essential factor in the limit of grape orchards seems to be the temperature in summer, for the grape ripens only in those countries in which the mean temperature from April to October exceeds 15° C. Similarly, it has been calculated that maize ripens at the period of the year when the sum of the daily maximum temperatures has reached 2500° C.
In general, crops like barley, rye, oats and winter wheat perform well when the mean daily temperature ranges between 15° C and 25° C. Contrarily, tropical crops like cacao, coffee, spices, squash, dates, rubber, and tobacco require high temperature throughout the year, while crops like peas, gram, lentil, wheat, potato, mustard, rapeseed, linseed, lucern and bar seem require relatively warm temperatures during the growing and ripening periods and low temperatures (around 20° C) during the growth and development stage.
Frost is also an important factor which restricts the cultivation of crops at higher latitudes and altitudes. The sowing dates, germination, emergence of seeds, dates of budding, flowering, ripening and dates of harvest are all affected by frost free period in a given region. The phenomenon of frost, however, does not occur in the lowlands of the equatorial and tropical regions. Frost free period is progressively shorter with increasing latitudes.
In the areas of frost occurrence, frost kills the standing crops. Many a time, the damage may be disastrous over larger areas. The occurrence of frost during the earlier stages of plant growth before plants have made the necessary physiological adjustments may be hazardous. In the tropical; latitudes the citrus orchards are highly vulnerable to frost. Germinating seeds are not often affected by surface frost, but young seedlings may be damaged or killed unless they are frost hardy varieties.
Crops like tomatoes, potatoes, melon, cucumber and musk-melon are highly frost sensitive right upto their maturity. The flowering stage of all cereals and orchard crops is also critically vulnerable to frost. The quality and quantity of all crops including the orchard crops are adversely affected under frost conditions. Fruits affected by frost are less tasty and have little market value. Frost resistant crops are grown in areas susceptible to frequent frost.
All crops need water. They take water and moisture from the soil. This moisture may be available from rains or from surface or underground irrigation systems. Within wide temperature limits, moisture is more important than any other environmental factor in crop production. There are optimum moisture conditions for crop development just as there are optimum temperature conditions. Plants obtain their water supplies primarily through their root system. The maintenance of soil moisture is, therefore, the most compelling problem of agriculture.
The excessive amount of water in the soil alters various chemical and biological processes, limiting the amount of oxygen and increasing the formation of compounds that are toxic to plant roots. The excess of water in the soil, therefore, leads to stunted growth of plants. The problem of inadequate oxygen in the soil can be solved by drainage practices in an ill-drained tract.
Rain is the cheapest source of water provided it is timely and adequate in quantity. But rainfall in the greater parts of the world is uncertain and highly unevenly distributed. Failure of rains or excessive rainfall in a short period has brought repeated crop failures and famines in many parts of the world. Indian farmers like others have often suffered on account of the failure of rains or fury of floods.
Drought has devastating consequences on the crops and land use of a region. Soil drought has been described as a condition in which the amount of water needed for transpiration and direct evaporation exceeds the amount available in the soil. Drought damages the crops when plants are inadequately supplied with moisture from the soil. Land use practices which tend to increase run off decrease vital soil moisture storage accordingly.
In addition to temperature and moisture conditions in a region, winds’ direction and their intensity also have an influence on the cropping pattern and agricultural productivity of the region. The cold and dry severe winds in the northern plains of China, for example, restrict the growth of certain crops which otherwise could have been grown there. In the arid and semiarid areas, hot winds do great damage to agriculture and, therefore, in the hot deserts, growing of crops is confined only to the tiny patches of oases.
Winds have both the direct and indirect effects on crops. Direct winds result into the breaking of plant structures, dislodging of cereals, fodder and cash crops and shattering of the seed-heads. Fruit and nut crops may be stripped from the trees in high winds. Small plants are sometimes completely covered by wind-blown dust or sand. The indirect winds transport moisture and heat in the air. The movement of winds increases evaporate.
Snowfall is also an important climatic constraint in the agricultural operations. It results into hardship to livestock and damage to the crops. Hill sheep farming in Scottish highlands and Welsh mountains is adapted to snow conditions and the sheep are moved to safer areas when snowfall is severe. Sheep can live for two weeks or so in snow drifts but rescue operations are arduous and losses are heavy. In plain areas of higher latitudes fodder crops are damaged, leading to fodder shortages.