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Tillage Update - 20th January 2022

In this week's tillage update Mark Plunkett, Teagasc Crops Specialist discusses Cereal Crops P & K Requirements. He focuses on the role of P and K, the strategy to adopt for Soil P and K Index in 2022, and he has P & K advice for the different cereal crops.

Role of P & K

Phosphorus and potassium have many roles in cereal crop nutrition from rooting to N use efficiency. To maximise the return from applied N it is very important to ensure the crop has a balanced supply of major (P, K & S) and minor nutrients (Cu, Mn & Zn).  For example, P is very important for rooting and tillering (see figure 1)especially in spring cereals while K is very important for straw strength and plant tolerance to such diseases as powdery mildew.

Figure 1:- The impact of combine drilling P on Index 1 soils (very low P supply) on crop root and tiller development.

Soil P & K Index Strategy in 2022

It will be very tempting to reduce or omit P and K’s in 2022 to control production costs. It will be prudent to tailor P and K rates based on soil test results.

Soils at Index 1 & 2 will be most responsive to applied P & K and have a very low to low P and K supply.  These soils will have higher P and K requirements as soil supply will be lower.  For spring cereals where possible combine drill P at sowing time to increase the efficiency of applied P fertiliser.  It will be important to fertilise these soils to their expected grain yield in potential.  Therefore, in order to control fertiliser costs omit additional P & K application for soil fertility build-up in 2022.  

Soils at Index 3 have a good nutrient supply, aim to replace P, and K removed at harvest time to maintain soil fertility in the optimum range (Index 3).  Again, it is important to fertiliser to crop yield potential to maintain soil fertility levels.  These crops will use N most efficiently and produce the largest grain yields annually.  Omitting P and K will result in soil P and K levels declining thus reducing grain yield potential in the years ahead.  For higher yielding crops such as winter wheat maintaining higher soil indexes produce higher grain yields.   

Soils at Index 4 are very fertile and have a good supply of P and K to meet crop requirements during the growing season.  Up to date soil analysis will help identify these soils on the farm as they don’t have a P and K requirement.  The Teagasc soils database shows that 31% of tillage soils are at Index 4 for P & K in 2020 offering a major saving on P & K applications in 2022. 

P & K Advice

Over the last number of year’s soil fertility levels have improved on tillage farms resulting in higher grain yields.  To maintain profitable grain yields and hold soil fertility levels at their current levels it is recommended to fertilise crops to their grain yield potential.  For example, take the average yield over the last 3 years to form the basis for calculating P and K requirements in 2022.

Table 1 below shows the P and K off takes for a range of cereal crops.  Note the P removed is similar for all cereals while the K levels differ depending on crop type.  See example showing how to calculate the P and K removed for a crop of spring barley.


Table 2 below shows the P and K advice for different cereal crops based on average expected grain yields.  In addition, suggested fertiliser products and rates are shown to deliver sufficient P and K.

National Tillage Conference

The 2022 National Tillage Conference will take place virtually, split over two days. The first session took place on Thursday, 13 January and the second session will take place on Thursday, 27 January. The podcast here covers the excellent question and answer sections which cover the main topics from the webinar on Thursday, 13 January.

You can watch the webinar in full here  For more episodes and information from the Tillage Edge podcast go to: www.teagasc.ie/thetillageedge

To register for the National Tillage Conference Part 2 webinar and for other webinars as part of Tillage Month, go to: www.teagasc.ie/tillagemonth/

Find out more information and advice from the Teagasc Crops team here.   The Teagasc Crops Specialists issue an article on a topic of interest to tillage farmers every Thursday on Teagasc Daily