(b) Climate

Of all the physical factors, climate is one of the most significant determinant of agricultural land use and cropping patterns.

(i) Temperature The crops to be grown, their patterns and combinations are closely controlled by the prevailing temperature and precipitation conditions. The agricultural scientists have proved that each crop has a specific zero temperature below which it can not be grown. There is also an optimal temperature in which the crop is at its greatest vigour. For each stage of crop life, i.e. germination, foliation, blossoming or fructification a specific zero and optimum can be observed in temperature.

The upper limit of temperature for plants growth is 60°C under high temperature conditions, i.e. at over 40°C, crops dry up, if the moisture supply is inadequate. In contrast to this, the chilling and freezing temperatures have a great adverse effect on the germination, growth and ripening of crops. Crops like rice, sugarcane, jute, cotton, chilli and tomatoes are killed or damaged at the occurrence of frost. The minimum temperature for wheat and barley is 5°C, maize 10°C, and rice 20°C.

The impact of temperature on cropping patterns may be seen from the fact that the northern limit of the regions in which date-palm bear ripe fruit coincides almost exacdy with the mean annual temperature of 19°C. The essential factor in the limit of grape orchards seem to be temperature. Grapes ripen only in those countries in which the mean temperature from April to October exceeds 15° C. Crops like winter wheat and barley perform well when the mean daily temperature ranges between 15°C and 25°C. Contrary to this, tropical crops like cocoa, coffee, spices, squash, rubber and tobacco require over 18° C temperature even in the coldest months, while crops like wheat, gram, peas, lentil, potato, mustard, and rapeseed require a temprature of about 20°C during the growth and development, stage and relatively higher (over 25°C) during the sowing and harvesting periods.

(ii) Moisture All crops need moisture. They take water and moisture from the soil. This moisture may be available from the rains or from irrigation systems. Within wide temperature limits, moisture is more important than any other climatic factor in crop production. There are optimal moisture conditions for crop development just as there are optimal temperature conditions. 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.

Heavy rainfall may directly damage plants or interfere with flowering and pollination. Cereal crops are often lodged by rain and this makes harvest difficult and promotes spoilage and diseases. Heavy rainfall at the maturity of wheat, gram, millets, oilseeds, and mustards cause loss of grains and fodder. Indian farmers all over the country have often suffered on account of failure of rains or fury of floods.

(iii) Drought Drought has devastating consequences on the crops, their yields and production. Soil drought has been described as a condition in which the amount of water needed for transpiration and direct evaporation exceeds the amount of water available in the soil. Drought damages the crops when plants are inadequately supplied with moisture from the soil.

1 he drought prone areas of India lie in the states of Rajasthan, Gujarat, Madhya Pradesh, Chhattisgarh, Jharkhand, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Odisha, Bundelkhand (U.P.), Uttarakhand, H.P., J&K, south-west Punjab and Haryana. In the areas where the average annual rainfall is less than 75 cm, agriculture is considered a gamble on monsoon. In 2009, the erratic monsoon resulted into drought in more than 200 districts of the country.

The incidence of drought and its intensity can be determined from the annual, seasonal and diurnal distribution of rainfall. Moreover, different plants have different moisture requirements. In the drought prone areas of India, dry farming is practiced, while in the more rainfall recording regions, intensive agriculture of paddy crop is a common practice.

(iv) Snow The occurrence of snow reduces the ground temperature which hinders the germination and growth of crops. Land under snow cannot be prepared for sowing because of permafrost. Melting of snow may cause hazardous floods in the summer season, affecting the crops, livestock, and land property adversely.

(v)WindB Winds have both, direct and indirect effects on crops. Direct winds result in the breaking of plant structure, dislodging of cereals, fodder and cash crops and shattering of 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 effect of winds are in the form of transport of moisture and heat in the air. In fact, the movement of winds increases evaporation and transpiration.