Farm Ireland

Monday 20 November 2017

Digging deep with management for soil fertility

Soil sampling is an important task for tillage farmers ahead of the 2015 growing season
Soil sampling is an important task for tillage farmers ahead of the 2015 growing season

Mark Plunkett and David Wall

Putting a proper soil management plan in place now will help maximise yields in 2015. The winter cereal harvest is almost complete with spring cereals near the finish line. Over the past month the oncoming cropping year will have been discussed and decisions made about the 2015 cropping plan on winter and spring cereal farms.

These decisions must consider factors such as greening and crop diversification measures under CAP along with variety selection and seeding rates. Soil fertility is also a key factor at this stage and requires both short and long-term management strategies.

The short-term plan must ensure the correct supply of nutrients for the current growing season.

Long-term management may involve a plan to build soil phosphorus (P) and potassium (K) levels and maintain soil pH in the optimum range.

Depending on crop type and rotational position, there will be different soil fertility requirements within the cropping cycle. For example, oats are tolerant of soil pHs as low as 5.5, while barley requires a soil pH 6.5.

Reviewing soil fertility information for each field prior to planting is essential in making the best and most informed nutrient management decisions.

Over the coming weeks and months the following factors need to be considered for both spring or winter cereal cropping systems. This will develop the most suitable plans based on soil information.

1 Soil Testing

Also Read

The first principle in good 
nutrient management is to check soil test results.

This will provide field specific information to identify and address problems such as low soil pH, P or K levels in advance of crop planting. It will also aid in selecting suitable fertilisers to address crop nutrient supply shortfalls and to correct soil P and K balance prior to key crop growth stages.

Where soil test results are not available, or more than five years old, fields should be sampled over the next two months once crops are harvested.

2 Check soil pH and lime 

Optimum soil pH status is an essential - think of it as the equivalent to topping up the oil level in an engine -it maximises performance for longer.

For Irish soils to function to their maximum, it is essential to maintain soil pH close to the optimum range for each crop in the rotation (see table opposite).

Lime should be applied 
before the most sensitive crop in the rotation. Soil test results indicate that approximately 55pc of tillage soils are below a target soil pH 6.5 for cereal crops.

September can be a good month for liming in order to correct soil pH for either spring or winter cereal crops. Lime can be applied to stubble ground or applied to ploughed soils and worked into the seedbed with cultivation prior to sowing.

3 Correct soil P & K levels

Tillage crops tend to remove significant levels of both P and K at harvest time with the majority of the P removed in the grain and K in the straw. To maintain soil P and K levels the nutrients removed need to be replaced annually.

Phosphorus is required in the early stages of crop 
development as it is the key driver of both rooting and tillering. Potassium is required at later growth stages and its peak demand by the crop is after the tillering phase.

Fields low in either P or K, or both, should receive 
additional P and K for building up to the target outlined in the accompanying table (opposite page).

Building soil fertility is a slow process with P levels generally slower to increase compared to K levels, but this is dependent on soil type.

Options to improve soil P and K include organic 
manures where available such as farmyard manure (FYM), Spent Mushroom Compost (SMC) and cattle or pig 
slurry, all of which are valuable sources of P and K.

Fertilisers such as 0-10-20 or 0-7-30 are also suitable while Muriate of Potash (MOP) (50pc K) is an effective fertiliser to replenish soils.

Now is a good time to identify low fertility fields and decide on a programme to deliver the correct level of P and K to meet crop nutrient requirements throughout the growing season.

Remember K fertilisers can be applied at any time of the year as its use is not restricted under Nitrates legislation.

4 Organic Fertilisers

Organic manures are a 
valuable source of major and minor nutrients and are a cost- effective route to supplying or replenishing soil nutrients.

Intensive livestock farmers may require additional lands to apply slurry in order to keep within the legislative limits.

Intensive tillage soils could benefit from an application of organic manures on a rotational basis. This would help control fertiliser costs and build soil fertility levels over a number of years.

It is important that liquid manures (slurry) are well agitated and evenly spread across the field to avoid problems such as crop lodging later in the season.

5 Soil Structure

Good structure has a key role to play in nutrient availability, soil drainage and crop rooting. Assess the soil structure by digging a soil test pit with a spade and looking for evidence of soil compaction in the top 30cm of soil.

For example, where a plough pan is present it may be removed by ploughing a little deeper to remove it.

If soil layers are compacted at deeper levels it may be best to minimise heavy trafficking with machinery especially during periods when soils are wet.

Often the natural soil 
wetting and drying cycle processes will rectify these problems over time. If compaction is more severe, sub-soiling may be necessary.

It is critical only to operate sub-soilers when soil conditions are suitable (when soils have low moisture levels and shatter easily).

Operate the cultivation equipment 2.5-5cm below the compacted layer.

Cross-compliance checklist

Grass weed control with a non-selective herbicide is permitted on 25pc of cereal land after 
October 15 with no requirement to re-establish a green cover.

A 2m uncultivated margin is required along all surface waters identified on a 6" OSI map.

lSoil samples every five years.

The last date that chemical fertilisers can be applied this year is September 14.

Complete farm records for 2014

Mark Plunkett and David Wall are soil science specialists with Teagasc at Johnstown Castle, Co Wexford

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