Crop Weather Related Point Wise Notes For Competitive Exam

• In northern latitude, day length starts increasing from January onwards and reaches a peak in June and subsequently decreases up to December.

• The photoperiodic effect is realized only when optimum temperature prevails.

• Because of the phasic changes taking place due to the influence of both temperature and photoperiod, it is better to calculate photothermal units (PTU) instead of heat units for accurate prediction of flowering and maturity.

• The optimum date of sowing can be arrived by estimating PTU from climatological data.

• Rice requires 2,200 PTU for high yield.

• By calculating PTU for different dates of sowing, the best date of sowing can be determined.

• Number of leaves produced is less with decrease and increase in photoperiod with short and long day plants respectively.

• Tillering and plant height decrease under extreme photoperiod.

• Leaf number increases with increase in temperature.

• Increase in duration of light (for long-day plants) and temperature decreases different stages of crop, especially during vegetative phase.

• A short-day plant, when exposed to short-days earlier, produces less number of leaves thus source is less.

• If short-day plants are subjected to short days at very late stage, more foliage is developed and increases duration of the crop without increasing the yield.

• In rice, wheat etc. source is not limited but yield potential is less due to less number of storage organs.

• In sink-limited crops, amount of solar radiation in sufficient quantities is necessary during the period of formation of storage organs i.e., from panicle initiation to flowering.

• In some crops, source is limited, hence solar radiation is critical during grain-filling stage, low solar radiation during this period causes large number of unfilled grains.

• Mean temperature is average of maximum and minimum temperature.

• For each species of plants, there are upper (maximum) and lower (minimum) limits of temperature at which growth is nil or negligible and optimum temperature at which growth is maximum.

• Most of the crop plants grow best at 15 to 30 °C.

• Many crop plants die at a temperature of 45 to 55 °C.

• The minimum, maximum and optimum temperatures of a crop are known as cardinal temperatures.

• The crops which grow best in cool weather period are called cool season crops and are generally grown in winter season (November to February).

• Most of the cool season crops cease to grow at an average temperature of 30 to 38 oC.

• Cool season crops are wheat, barley, potato, oats etc.

• Cool season crops are called temperate crops because they are mostly grown in temperate regions.

• The cardinal temperatures for cool season crops are Maximum temperature: 30-38 °C Minimum temperature: 0 to 5 °C Optimum temperature: 25 to 30 °C

• Warm season crops are rice, sorghum, maize, sugarcane, pearl millet, groundnut, redgram, cowpea etc.

• Warm season crops are also called tropical crops.

• Tropical crops are generally grown in monsoon season and some also in summer season.

• The cardinal temperatures of warm season crops are Maximum temperature: 45-50 °C Minimum temperature: 15-20 °C Optimum temperature: 30-38 °C

• The rates of biochemical processes are affected mainly by temperature.

• Any chemical reaction increases with increase in temperature.

• The rate of reaction may double or even be more for every 10 °C increase in temperature.

• The heat unit or growing degree-day concept was proposed to explain the relationship between growth duration and temperature.

• Growing degree-day concept assumes a direct and linear relationship between growth and temperature.

• Base temperature (Tb) is the lowest temperature at which there is no growth.

• Base temperature of wheat is 4.5 °C.

• Base temperature of wheat, maize and pearl millet is 10.0 °C.

• Degree-days are useful for predicting harvesting dates and to select optimum date of planting.

• Day and night length is one of the basic factors controlling the period of vegetative growth for photosensitive varieties of crops.

• Mere accumulation of heat units do not predict developmental stages and maturity in photosensitive varieties. Therefore, photothermal units are proposed, wherein the degree-days are multiplied by length of night in case of short-day plants and length of the day for long-day plants.

• Flowering is hastened as the length of night increases in short-day plants, while flowering is delayed as the length of night increases in long-day plants.

• High temperature increases amino acid concentration in roots and shoots.

• Low temperature stress results in accumulation of abscisic acid.

• Abscisic acid production and breakdown of complex products are important mechanisms of temperature stress.

• If the rainfall receive is more than 2.5 mm on any particular day, it is called a rainy day.