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Tillage Update 25th March 2021

In the weeks and months ahead cereal and other crops will receive the most of their N, P, K & S requirements to build and develop grain yield potential. This Water Quality week Teagasc advises efficient use of applied nutrients to reduce loss to the environment. Mark Plunkett talks about the 4 Rs

The 4 'R's

Using applied nutrients as efficiently as possible delivers a double dividend in protecting the environment and increasing overall farm profitability.  Targeting applied nutrients based on soil fertility status and crop nutrient requirements is the starting point. Preparing a farm fertiliser plan and consulting it on a regular basis provides the basis for using all applied nutrients at the right rate, at right time, selecting the right product and in the right place ( 4 R’s).

Correct Soil pH

Lime is a key nutrient in correcting soil pH to increase nutrient efficiency (esp. N & P). Maintaining optimum soil pH firstly increases the availability of soil nutrients and secondly increases plant use efficiency of applied nutrients in manures & fertilisers.  Aim to maintain soil pH 6.5 to 6.8 depending on the crop rotation. For spring crops apply lime as recommended on the soil test report and work into the seedbed prior to sowing.

P & K Index 3

Building soil P and K levels to agronomic optimum P (> 6.1mg/l) & K (>101 mg/l) Index 3 will further increase N efficiency and build grain yield potential. For spring barley select a suitable fertiliser blend and adjust application rates based on soil P & K Indexes. Supplying a good balance of N, P & K at establishment will be critical to getting the crop off to a good start. The first 3 to 6 weeks are critical for rapid root and tiller development, the foundation for building yield potential.  Plus it will ensure the crop has the ability to utilise applied nutrients (N & S) thereafter.  Aim to apply all P & K at sowing time and supply ~25 to 30% of the crops total N requirements at this stage.  

Calculate Crop N

To determine the crops N requirements take the average grain yield for the last 3 years.  For every 1 t/ha grain yield above the base yield of 6.5t/ha increase or decrease by 20kgN/ha. For example where continuous feeding spring barley (Soil N Index 1) has yielded an av. of 7.5t/ha (3t/ac) this crop will require 155kgN/ha (135 +20). Adjust crop total N for seedbed N, therefore top dress the remaining ~110 to 115kg N/ha (85 to 90 units/ac) from early to mid tillering stage. This can be applied in a single application or alternatively a split application (70:30).  Splitting the application increases the N use efficiency while reducing the risk of N losses through either leaching or volatilization.  Where the above crop is grown after beans (Soil N Index 2) the total crop N requirements can be reduced by 35kgN/ha (28 units/ac) to take account of the N fixed by the previous spring bean crop. This crop will require a total N of 120kgN/ha (96 units/ac) after beans.

Organic Fertilisers

Where organic manures such as cattle or pig slurry have been applied adjust crop nutrient advice to take account of N, P & K in manures.  Table 1 shows available N, P & K values per 1,000gals.  For example take an application of 2,000gals/ac of pig slurry will supply ~ 38 units N/ac, 14 units P/ac & 40 units K/ac. This can reduce a spring barley crops N requirement by 30% and supply a proportion of the P & K requirements. Where possible have organic manures tested to determine actual nutrient values.

To maximise the use of organic manures ensure manures are well agitated and applied evenly.  For maximum N recovery apply with low emission techniques such as the trailing shoe and plough in within 3 to 6 hours. Organic manures bring the advantage of adding soil organic matter which will help feed soil biology, help build soil organic matter & improve soil health.

Other Nutrients

Cereals have a sulphur (S) requirement of 15kg S/ha.  Sulphur increases plant N efficiency and aim to apply S with main N topdressings.  Similarly for magnesium (Mg) cereals have a low requirement and in general Irish soils have a good Mg supply. Trials would indicate that it is very difficult to find a yield response to Mg in cereal crops.

Cereals have a requirement for trace elements such as copper, manganese and zinc. Where soil test results show low levels (Index 1 or 2) or where there is a history of a deficiency, ensure good seedbed preparation and consolidation to improve root to contact and nutrient availability. Apply trace elements at the 2 to 4 leaf stage and repeat where necessary. 

Balancing major and minor soil and plant nutrient requirements during the growing season will improve the efficiency of all N sources from the soil to organic manures to applied fertilisers. This week is water quality week, take time to tune into short videos on how to use N efficiently during the growing season to improve both air and water while reducing farm costs.

For more information see Water Quality Week 

Also see Tillage Month for updates on Agronomy webinars