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Time to Soil Sample

Time to Soil Sample

With fertiliser prices at all-time highs now is a good time to take the first step to controlling fertiliser costs in 2023. Mark Plunkett, Soil & Plant Nutrition Specialist, Teagasc, talks about soil sampling and what to look out for.

Over the coming weeks assess soil fertility levels on farm through taking fresh soil samples. Soil analysis is a small cost at €1.25/ha/yr for a standard soil sample (pH, LR, P & K). This is a very worthwhile investment and will allow time to plan crop nutrient requirements for the year ahead.

Take Fresh Soil Samples

In 2023, up to date soil samples will be required to apply phosphorus (P) where no sample are taken P index 4 must be assumed.  The Teagasc soils database indicates that 19% and 38% of tillage soils are Index 4 for P (>10mg/l) and K (>150mg/l) offering an opportunity to omit nutrient applications.  For example take a crop of winter wheat yielding 10t/ha and where a maintenance K rate is applied at Index 4 offers a saving ~€200/ha (100kg K/ha x €2/kg).  Now is a great time to get up to take fresh soil samples and check soil fertility changes especially where P or K’s were omitted in 2022.

Lime & Soil pH

The Teagasc soils database indicates that ~ 40% of tillage soils require lime. Optimum soil pH is the basis to nutrient availability and efficiency for such major nutrients as N, P, K, Mg, Ca & S. Apply recommended lime rates based on recent soil analysis. Ground limestone is the most cost effective route to correcting and maintaining soil pH in the long term. Where soil magnesium is low apply Magnesium limestone to build soil Mg levels.   

Straw Incorporation

Approximately 52,000 ha of straw chopped in 2022 resulting in retention of more P and K in cereal / OSR fields.   Straw contains approx. 10% and 50% of total crop P and K, respectively. For example the straw from a 10t/ha grain crop of winter wheat will return ~4kg P & 50kg K/ha. This offers significant savings of ~€120/ha in P & K’s. Adjust fertiliser advice to take account of nutrients returned in chopped straw.

Protected Urea v CAN

Currently markets reflect that CAN (€3.25/kg N) is more expensive per kilo of N compared to protected urea (€2.25/kg N). This offers a large saving by selecting protected Urea (46% N) over CAN (27% N) in the coming year.  Field trials show that protected urea delivers similar grain yield performance to CAN. At present urea is ~45% cheaper than CAN, therefore for every 100kgN/ha applied as protected urea makes a saving of €100/ha over CAN. Urea can be more difficult to spread but with good quality product (granule size 2 to 4mm) and good spreader set up, good spreading can be achieved across a range of bout widths.

Winter Cereals and P & K Advice

Apply P and K on very low to low fertility soils (P & K Index 1 and 2). Aim to incorporate or combine drill 0-10-20 at 100 to 200 kg/ha (0.8 to 1.6 bags/ac) at sowing time. Placing phosphorus (P) will increase the availability of the P in the seedbed. Building soil P and K Index to Index 3 is essential for top grain yields in winter cereals and improving plant N efficiency. A recent trial from Oak Park  (see figure 1) shows that increasing soil P index from Index 1 to 3 increased winter wheat grain yield by 1.5t/ha. This trial shows that building soil P index has the largest effect on grain yield potential in winter wheat. With current high fertiliser prices consider alternative P & K sources such as organic manures (FYM / Cattle slurry / Mushroom compost) as cost effective source to build optimum soil fertility levels.

More information on Soil & Soil Fertility is available here
Find out more information and advice from the Teagasc Crops team here. Find your local Teagasc office here