Soil Physics & Water Relations

The critical oxygen diffusion rate (ODR) below which root elongation in maize is significantly inhibited is 30 x 10^-8 g cm-2 min-1.

• 40 x 10^-8: High critical threshold characteristic of highly oxygen-demanding vegetable crops like tomato or pea.
• 22.9 x 10^-8: Below the minimum threshold for healthy root respiration in maize.
• 30 x 10^-8: For maize (Zea mays), an ODR value of 30 x 10^-8 g cm-2 min-1 represents the critical boundary below which root growth ceases and aeration deficiency occurs.
• 25.9 x 10^-8: A sub-optimal aeration level resulting in root stress.

• 530 x 10^6 kcal is lower than the heat required at normal ambient temperatures.
• 560 x 10^6 kcal is lower than standard latent heat value at 20°C.
• hectare = 10^8 cm2. A 1 cm depth of water over 1 ha equals 10^8 cm3 of water, which weighs 10^8 grams (100,000 kg). The latent heat of vaporization of water at ambient temperature (~20°C) is approximately 580 cal/g (0.58 kcal/kg). Total energy absorbed = 10^8 g x 580 cal/g = 5.8 x 10^10 cal = 58 x 10^6 kcal. Note: The question options contain a 10-fold unit error (printing 580 x 10^6 kcal instead of 58 x 10^6 kcal), and RPSC officially designated Option (C) [580 x 10^6 kcal] as the keyed answer.
• 610 x 10^6 kcal exceeds the latent heat of vaporization at ambient temperature.