Root Implications in Wet Soils

February 2024

Although there appears to be something of a north south divide this year, most places in the UK have experienced higher than average rainfall, meaning that some crops, especially where later drilling is practiced, will not be looking as good as planned. Even earlier drilled and therefore better-established crops may not perform the same this year due to the level of rainfall experienced and the generally wet soil conditions.

Poor and backward wheat crops will clearly have a restricted root growth, easily identifiable by the low level of above ground biomass. However, even the more well-established crops may have a less effective root system if soils have been saturated for a period of time. It has been reported previously that waterlogging can decrease the root:shoot ratio by half, reflecting the stronger decrease of root dry mass (up to 62%) compared with shoot (up to 33%).

The implications for nutrition on these soils is twofold:

• Firstly, the availability of nutrients may be reduced (particularly the mobile nutrients) which may have been leached. This will particularly affect nitrogen, but also sulphur and on light soils, potassium. Further to leaching, where soil erosion has occurred, this will also have removed nutrients from the field that are adsorbed onto the soil particles, such as phosphate.
• Secondly, the crops’ ability to explore the soil for nutrients is diminished where the root system is restricted. For phosphate and potash nutrition, the principle has always been to maintain an adequate level of nutrients in the top of the soil profile to provide enough to match daily demand in the spring, which for potash, can be up to 10kg/ha/day. Although crops with a lower yield potential will not require so much phosphate and potash, these crops could still be limited by the roots ability to access sufficient levels of nutrition from the soil.

Maintaining soil indices is the best remedy for these situations, however, most soils, especially those that are below the target index, are likely to benefit from fresh applications this spring. Whether through organic manures or fertiliser applications, these crops are likely to require some additional TLC to help pull them through…