The soil environment and sowing

Temperature

• Seed will germinate at low temperature, but germination rate decline as temperature moves away from optimum.
• Poor establishment at low temperatures is a result of slow seed germination and extended period of time during which germinated seedlings can be attacked by soil fauna.
• At high temperature, poor establishment is more usually associated with declining soil moisture levels.

Water and oxygen

• The soil moisture must be adequate to first allow the germination process to proceed and second to support the continued growth of the seedlings.
• Excess water cause depleting oxygen supply and creating anaerobic conditions.
• Under anaerobic respiration, the seed accumulates toxic metabolites ( Acetic acid and ethylene) and eventually the seedlings dies.

Physical structure

• Poor soil physical structure and loss of aggregate stability increases large pore space, increases bulk density, and increases the risk of pores becoming water filled, thus obstructing oxygen diffusion to the seed.