Question

LET'S OBSERVE
1. What has happened to the fields here?
(waterlogging/leaching/ crop rotation)
2. Which of these would happen that will affect the roots here? LO 3
a. Lack of air in soil b. Lack of nitrogen in soil
C. Lack of seeds in soil
​

Answer 1

Answer:

Waterlogging occurs when roots cannot respire due to excess water in the soil profile.

• Water does not have to appear on the surface for waterlogging to be a potential problem.
• Improving drainage from the inundated paddock can decrease the period at which the crop roots are subjected to anaerobic conditions.
• While raised beds (see Raised Bed Cropping fact sheet) are the most intensive management strategy, they are also the most effective at improving drainage.
• Waterlogged soils release increased amounts of nitrous oxide (N2O), a particularly damaging greenhouse gas.

Background

1. Waterlogging occurs whenever the soil is so wet that there is insufficient oxygen in the pore space for plant roots to be able to adequately respire. Other gases detrimental to root growth, such as carbon dioxide and ethylene, also accumulate in the root zone and affect the plants.
2. Plants differ in their demand for oxygen. There is no universal level of soil oxygen that can identify waterlogged conditions for all plants. In addition, a plant’s demand for oxygen in its root zone will vary with its stage of growth.

Symptoms and causes

• Lack of oxygen in the root zone of plants causes their root tissues to decompose. Usually this occurs from the tips of roots, and this causes roots to appear as if they have been pruned. The consequence is that the plant’s growth and development is stalled. If the anaerobic circumstances continue for a considerable time the plant eventually dies.
• Most often, waterlogged conditions do not last long enough for the plant to die. Once a waterlogging event has passed, plants recommence respiring. As long as soil conditions are moist, the older roots close to the surface allow the plant to survive. However, further waterlogging-induced root pruning and/or dry conditions may weaken the plant to the extent that it will be very poorly productive and may eventually die.
• Many farmers do not realise that a site is waterlogged until water appears on the soil surface (figure 1). However, by this stage, plant roots may already be damaged and yield potential severely affected.