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WESTCOUNTRY FARMER: Soil needs time to recover

By Western Morning News  |  Posted: March 19, 2014

WESTCOUNTRY FARMER: Soil needs time to recover

Highly saturated grass fields will take time to restore soil fertility.

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After long wet periods there is a tendency to hope that once the sun comes out and temperatures start to rise then the saturated field issues will naturally self-rectify.

To some extent they will, however much of the damage that is likely to have occurred will be less obvious and take longer to correct.

The obvious water damage to crops and pastures will be complete plant death caused by prolonged flooding and loss of top-soil by soil erosion (effects pictured). Obviously only practical actions will overcome these issues, both now and in the future.

Less obvious damaging effects to soil productivity will range from surface compaction, through to leaching of soil nutrients, loss of soil structure and importantly, a decrease in microbial activity. Highly saturated and waterlogged grass fields will take time to recover optimum soil fertility. However, by taking these damage factors into account when planning soil and plant nutrition programmes it will be possible to restore full potential forage production far sooner.

Continuous saturation of the soil means that the natural soil pores are filled with water and thereby force out the oxygen which is required by both the plant roots and soil microorganisms to supply good nutrition to the plants

In comparison to many crops, grass is fairly resilient to soil saturation and can recover relatively well, by comparison to say cereal crops. However, the grass sward still regresses when saturated and livestock producers increasingly rely on forage crops to provide the profitability for the business, we need to consider how best to ensure its return to full potential productivity just as soon as possible.

Waterlogging results in oxygen being depleted in the root zone, therefore normal aerobic conditions become anaerobic and several processes can occur:

Grass roots cannot respire, resulting in dieback, manifesting itself above ground by leaf yellowing, early senescence of older leaves and lack of plant tillering. Other gases detrimental to root growth, such as carbon dioxide and ethylene, also accumulate in the root zone and negatively affect the plants.

Anerobic condition adversely affects microorganisms while harmful organisms can proliferate and restrict plant growth.

Soil nutrients become less available to the plant as poorer root systems restricts uptake, vital soil microorganisms are inactivated and the anaerobic conditions favour microbes that denitrify and reduce sulphate in the soil. Waterlogged soils also release increased amounts of the greenhouse gas nitrous oxide (N2O).

An example of bacteria in the normal soil processes that make nitrogen available to grass plants.

The grass sward damage is not limited to period of waterlogging but is also likely to affect the subsequent growing season. For instance, it is common to observe plants that have experienced waterlogging to be especially sensitive to hot temperatures and to display nitrogen and phosphorus deficiencies later in the season due to restricted root development. Therefore it is important to provide the grass sward with its best opportunity for recovery once conditions improve.

When soils do start to dry out again the grass plants are likely to be weakened and there will be reduced, and possibly imbalanced, levels of soil nutrients. The application of a chemical fertiliser will have a limited effect on sward thickening and quality grass growth until the balance of soils activity and pH is corrected.

Soil tests should then be utilised to inform us about not only the soil nutrient content but also importantly the pH and the Cation Exchange Capacity (CEC). This will provide us with information not just on how the nutrients may have been affected, but also the ability of the grass plants to access the nutrients that are available. Then recommendations can be made for specific fertilisers types that will provide a more efficient nutrient usage and cost effective approach to more quickly restore the equilibrium and forage productivity from the previously waterlogged soils.

If you have concerns about the productivity of your saturated land once the conditions improve then Mole Valley Forage Services are able to provide technical background to a range of high quality fertilisers that both provide for the nutrient requirements of the grass plants and also the vital microbial content of the soil.

For further information call Mole Valley Forage Services on 01769 576405.

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