Chemical phosphorus rules anger and frustrate farmers. More specifically, it’s the inability of farmers to legally spread enough bag Phosphorus (P) that angers a lot of dairy farmers.

For the last number of years, phosphorus rules have come in for mostly negative comment from farmers who feel they are disadvantaged by regulations from growing more grass.

Farmers on both heavy and dry soils, irrespective of rainfall levels, suggest it is next to impossible to lift P index levels on grassland given the restrictions on artificial P spreading. Monitor farmers in high rainfall areas have soil test results showing consistent falls in P content from one year to the next despite good management.

Table 1 shows the current breakdown of the index system used to measure the amount of phosphorus in soil. For example, on grassland soils, index one is classified as having 0 to 3mg/litre of P on the Morgans scale. If your P soil sample result came back at 3.1mg/l, then your soil could be classified as index two and you are allowed to spread less P.

I have talked to many farmers over recent years who have got soil test results back at 5.2/5.3 mg/l, the low end of Index 3. They feel they are very limited on how much P they can spread compared to index one and two soils yet they are just outside the index two threshold.

In summary, what farmers are saying is that the index method of classifying soils is a very crude instrument to say the least. If sticking with the index system, some suggest why not have a five-index system? That way at least it would be a bit more specific.

Another one of the frustrating issues is a farmer just stocked over 170kg of organic nitrogen per hectare (two cows/ha) can spread almost the same amount of P as a farmer stocked just under 250kg of organic nitrogen per hectare (2.9 cows/ha). This in essence is central to the problem - probably 80% of farmers have more than enough phosphorus for their stocking rate but highly stocked (mostly dairy farms) are short on the amount of P fertiliser they can spread.

Table 2 outlines the maximum P application rates on grassland at different soil indexes. There is only a difference of 5kg of P/ha in allowance for a farmer stocked at 2.1 cows/ha and a farmer stocked close to 2.9 cows/ha. Yet ideally the higher-stocked farmer needs to grow at least 3t to 4t of grass dry matter extra per hectare while at the same time the drain (outflow in meat and milk) of nutrients from each hectare is probably up 25% to 30% higher on the higher-stocked farm.

The history

Back in 1973 when agriculture was developing in Ireland, over 90,000t of P were spread and this figure fell to an all-time low of 20,000t in 2009. It is fair to say that since 2006, intensive dairy farmers have been restricted on what they can spread. Research has shown a clear trend to increasing meal usage and declining fertiliser usage on higher-stocked dairy farms. Effectively, those Irish dairy farmers are losing their competitive advantage. We have to protect our environment but at the same time not disadvantage a production system that has care of the environment at the core of its existence.

However, the rules are not all to blame for declining soil fertility. Recent research shows lime is important for P uptake and the usage of lime has also decreased significantly for the last number of years. There is a clear requirement for phosphorus to be replaced when taking off crops of first- and second-cut silage. Results show just to replace the P taken off in low yields of first- and second-cut that 32kg of P/ha needs to be replaced and almost 200kg/ha of potash. Many farmers take big cuts of silage and don’t replace the nutrients.

As our understanding and management of soil fertility improves, it is becoming more apparent that the most limiting factor to grass growth can vary from paddock to paddock and even if all the rest of the nutrients are in place the most limiting nutrient can reduce output.

Farmers need to change also in how they manage the grassland crop. Up to now it is fair to say soil analysis was done by necessity for schemes in the main. The best grassland farmers are now taking a soil sample every year to track changes. They are then using the amount of bag phosphorus available for spreading on those paddocks that need a lift. The day of blanket-spreading 10:10:20 or some other compound across the farm should be gone. A tailored nutrition package for each paddock is now the order of the day. This includes targeting slurry at paddocks that are low in P and K.

A focus on lime must also return. We know getting the pH up to 6.3 is optimum for most soils and we also know lime can help the availability of other nutrients. Often phosphorus and potash get lumped into the same box when we talk about rules and regulations. However, artificial potassium is not restricted under the Nitrate directive, nor is lime.

The other focus area that needs attention is drainage. Farmers should if at all possible fix drainage problems and infrastructure before attempting to fix soil fertility problems. In order to utilise extra grass grown, you need to be able to graze or cut paddocks without damaging soil.

  • The inability of farmers to legally spread enough bag phosphorus (P) angers a lot of dairy farmers.
  • The Index method of classifying soils is a very crude instrument to say the least.
  • There is only a difference of 5kg of P/ha in allowance for a farmer stocked at 2.1 cows/ha and a farmer stocked close to 2.9 cows/ha.
  • In 1973, over 90,000t of P were spread and this figure fell to 20,000t in 2009.
  • On silage paddocks after first- and second-cut, just to replace lost nutrients, 32kg of P and almost 200 kg/ha of potash is required.
  • Potassium (k) is not restricted under the Nitrate directive, nor is lime.
  • I hear the GrassOmeter device for measuring grass is getting closer to market but not yet available for purchase. I’ve used a demonstration model and a number of other dairy farmers around Ireland have the GrassOmeter and are testing with the new tool and reporting any problems back to Steven Lock and his development team.

    The GrassOmeter is operated via an app on the farmer’s mobile phone. The phone’s GPS system tracks the farmer’s movement as the farm is measured. Results are displayed instantly and uploaded to the cloud.

    The GrassOmeter uses four ultrasound sensors linked to a nine-point orientation sensor to measure both grass height and the topography of paddocks. It takes 40 height measurements per step, enabling hundreds of samples per field. Linked to the phone via Bluetooth measurements are recorded and displayed instantly.

    When you first get the GrassOmeter, you simply register and map your farm on the GrassOmeter website. Name your paddocks, enter your herd details and you’re ready to start measuring.

    The GrassOmeter is mounted on a pole and used a bit like a walking stick. The GrassOmeter knows exactly where you are on the farm and measuring starts as soon as you start walking. Measurements are recorded and a grass wedge is generated automatically.

    When you finish a walk, you have all the details on your phone and can go about making decisions.

    I was talking to a few farmers this week who are using the new GrassOmeter tool for measuring yield of grass.

    In discussion all recognise that it is a next generation measurement tool but until it is available to purchase with all updates completed they are slow to comment as to date it has been over four years in development.

    Kernal Capital, Enterprise Ireland, Glanbia, and the Irish Farmers Journal are investors in the tool.