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Fertilisation

How to Manage Crops in Waterlogged Soils

Dealing with waterlogged soils is an all-too-familiar challenge for many farmers – especially in light of more frequent extreme weather events, caused by climate change.

This blog provides practical advice on managing cereal, grass, and oilseed rape crops in waterlogged conditions, to help protect yields. It covers decision-making on crop varieties, sowing strategies, plus pest and disease management.

This blog also offers guidance on how to ensure a crop’s nutritional needs are met while balancing the increased risk of nitrogen leaching, through targeted fertiliser applications.

Understanding the impact on crop performance

Waterlogging can seriously impact the performance of cereal, grass, and oilseed rape crops, which each respond differently to excess moisture.

Cereals

Cereal crops, like wheat and barley, are particularly sensitive to waterlogging. Excess water can hinder root development, reduce oxygen availability, and lead to nutrient deficiencies. This can result in stunted growth, poor yield, and increased vulnerability to diseases.

Grass

For grass crops, waterlogging can cause root damage and reduce the availability of essential nutrients. This can lead to reduced growth rates and lower nutritional value, impacting livestock grazing or forage quality.

Oilseed rape

Oilseed rape can be more tolerant to waterlogged conditions than cereals, but prolonged waterlogging still poses risks. It can lead to reduced growth, root diseases, and eventual yield loss.

Advice on managing crops growing in waterlogged soils

Managing crops in waterlogged soils is a complex challenge that requires a multipronged approach.

By understanding the specific needs of different crops, adopting effective soil and crop management strategies, and being mindful of nitrogen fertiliser use, farmers can mitigate the adverse effects of waterlogging and sustain crop performance.

The following list sets out key areas of practical guidance for growers:

  1. Soil assessment and drainage

The first step in managing waterlogged fields is to thoroughly assess the soil structure, which affects water infiltration and retention.

Start with looking for signs of soil compaction, indicated by a hard soil surface, slow water infiltration, and poor root development. Also observe how quickly water dissipates from the soil after rainfall or irrigation.

To better understand key metrics that influence soil drainage capacity, including soil texture, compaction levels, pH, and organic matter content further, soil testing can be undertaken to help identify specific contributing factors.

As a solution, implementing effective surface or subsurface drainage systems can help remove excess water and prevent waterlogging. You could also consider subsoiling to break up compacted layers that impede drainage.

  1. Choice of crop varieties

When considering cereal, grass, or oilseed rape seed varieties, consider which are best known for their tolerance to waterlogged conditions.

Varieties with robust and deep root systems are generally better at coping with waterlogged conditions. A strong root system enables the plant to access oxygen and nutrients even when surface soil layers are saturated.

For the following crops look out for key variety qualities including:

  • Cereals: In areas prone to waterlogging, early maturing cereal varieties can be advantageous. They complete their growth cycle before the worst waterlogging conditions typically set in.
  • Grass: Varieties with deeper and denser root systems can better withstand prolonged periods of water saturation. Species such as tall fescue and reed canary grass are known for their tolerance to wet conditions.
  • Oil seed rape: Varieties that establish quickly and exhibit vigorous early growth can better withstand early-season waterlogging by developing a more robust root system early on.

Consult your agronomist or trusted adviser to help with choosing the varieties best suited to your farm’s particular conditions.

  1. Sowing strategies

To avoid poor seed germination and establishment in crops grown in waterlogged soils, it is advised to delay sowing until the soil has adequately dried. Choosing the right sowing depth is equally important, as seeds sown too deep in wet conditions may struggle to emerge.

Implementing direct drilling or minimum tillage practices can help in preserving soil structure, reducing compaction, and promoting better water infiltration.

Additionally, sowing cover crops or under-sowing with species that can tolerate or even thrive in wetter conditions can protect the soil surface from water and wind erosion, enhance soil organic matter, and improve overall soil structure, therefore increasing the soil’s resilience to waterlogging.

  1. Nitrogen fertiliser use

The application of nitrogen fertiliser in waterlogged conditions requires careful consideration. Excess nitrogen can easily leach into the soil and move into watercourses, especially when the crop’s ability to uptake nutrients is compromised. However it remains important to meet the crop’s nutritional needs for growth.

To maximise the efficacy of fertiliser applications, consider:

  • Timing: Applying nitrogen fertilisers should be delayed until the soil has sufficiently drained and begun to dry. Fertiliser application should coincide with signs of crop recovery and new growth, indicating that the plants are ready to uptake nutrients effectively.
  • Rate: The rate of application should be adjusted to account for the reduced nutrient uptake capacity of waterlogged crops. Conducting soil tests to determine the existing nutrient levels can help in deciding the appropriate application rate.
  1. Crop rotation and diversification

Implementing a diverse crop rotation system can improve soil health and structure, enhancing resilience against waterlogging.

Different crops have varying root structures and depths. Some crops, like deep-rooted legumes, can help break up compacted layers of soil, thereby improving soil aeration and drainage.

This variety in root systems helps in creating a more porous soil structure, which can improve water infiltration and reduce the likelihood of waterlogging.

It is advised to tailor your rotation pattern based on local climate conditions, soil types, and the history of waterlogging in the area.

  1. Pest and disease management

Waterlogged conditions can encourage the growth of pests and diseases.

For example, root rot and other fungal diseases are more prevalent in waterlogged soils because the excessive moisture creates an ideal environment for fungal spores to germinate and infect plants.

Similarly, pests like snails and slugs, are attracted to moist environments. In waterlogged fields, they can cause extensive damage to seedlings and young plants, severely impacting crop yields.

Vigilant monitoring helps with detecting early signs of infestation or disease. It is crucial to act promptly to prevent pest or disease spreading, however, in waterlogged conditions, where the movement of chemicals can be unpredictable, it is especially important to be judicious with the application of chemical control measures.

Preventing nitrogen leaching in waterlogged fields

Preventing nitrogen leaching is vital for maintaining soil fertility, ensuring crop health, and protecting water quality.

It is especially crucial in waterlogged conditions, where the risk of nutrient loss is heightened due to excessive moisture.

The following guidance can help reduce the risk of nitrogen leaching in waterlogged cereal, grass or oilseed rape growing fields.

  1. Establish cover crops between cash crops

Cover crops, such as clover, rye, or vetch, help absorb available nitrogen from the soil, which might otherwise leach into groundwater, especially in waterlogged conditions.

Some cover crops, particularly legumes, have the ability to fix atmospheric nitrogen, enriching the soil with this vital nutrient when decomposing.

The root systems of cover crops also enhance soil structure, improving water infiltration and drainage, which helps reduce waterlogging and the associated risk of nitrogen leaching.

  1. Add organic matter to soils

Adding organic matter like manure or green manure increases the soil’s organic matter content, which improves its water-holding capacity and nutrient retention ability.

Also, organic matter slowly releases nutrients over time, which aligns better with the crop’s uptake needs, reducing the likelihood of nutrient leaching.

Furthermore, organic matter fosters increased biological activity in the soil, such as earthworms and beneficial microbes. These organisms play a key role in maintaining soil structure and nutrient dynamics, further mitigating nitrogen leaching risks.

  1. Use precision farming techniques

Advanced technologies like GPS, soil sensors, and variable rate technology (VRT) enable farmers to apply fertilisers more efficiently and accurately. This approach ensures that fertilisers are applied in the right amounts, at the right place, and at the right time, minimising excess application.

Precision farming also enables site-specific management of fields. Farmers can identify areas more prone to waterlogging and adjust fertiliser applications accordingly to prevent leaching. Precision agriculture tools often come with data recording and analysis capabilities. Keeping detailed records of fertiliser applications and comparing them with crop performance and environmental conditions can help in fine-tuning application strategies over time.

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