Poultry manure can replace N, P and K

As well as being updated on various soil and fertiliser research, the recent Soil Fertility Conference also provided practical advice and experience from advisors. This ranged from the sensible use and performance of poultry manure, to the practical use of soil test results on farm over time, to the importance of quality product in the case of urea where wide tramlines are to be used.

I start here with chicken litter or poultry manure use. Most tillage farmers will be very aware of the benefit of poultry manure in crop production. Until recently, there was very little evaluative work done on the real contribution of such material to crop yields. Growers were at the mercy of the generic nutrient values for the product.

However, in recent years, Martin Bourke and Mark Plunkett of Teagasc have established trials to examine the potential of poultry manure to replace artificial fertiliser and to examine its consequences for grain yield. Martin presented these trials at the recent soil fertility conference, where he spoke about making the most of poultry manure. The level of research is broader than the results presented as some of the topics, such as the use of broiler litter, had only been examined in 2016.

High nutrient value

Poultry manure (layers) is a very useful source of nutrients. It is high in N, P and K and is now being made available as a high dry matter product to help reduce the overall cost of transport. It contains a lot of trace elements and the product Martin used in both years was either 87% or 89% dry matter and 35% nitrogen, which is deemed to be 50% available in year one, providing it is minded and not lost. Analysis of the material in both years showed a predictable level of nutrient variability.

The trial in year one aimed to evaluate the production value of poultry manure in situations where it was either ploughed-in or cultivated-in post-application. The trial plots were overloaded with both P and K and trace elements to help remove these as potential variables for individual plot performance.

In year one, individual treatments received either a combination of poultry manure (PM) plus ammonium sulphate nitrogen (ASN), or just ASN alone, as their source of nitrogen. The trial looked at the N replacement value of the PM where it was either ploughed-in or cultivated-in prior to planting. All treatments were deemed to have received 150kg N/ha and in year one all the treatments were about equal in terms of grain yield, ie 150kg ASN = 150kg ASN+PM ploughed-in = 150kg ASN+PM incorporated-in = 7.8 t/ha. In this trial, the zero applied-N plot yielded 4.3 t/ha. There was also no major impact on grain protein from the different treatments.

Additional treatments

Additional treatments were examined in 2016. The nitrogen rate was again set at 150kg N/ha and applied as either CAN, PM plus CAN (either ploughed-in or tilled-in) and PM plus urea (either ploughed-in or tilled-in). For CAN, 50kg was applied into the seedbed, with the remaining 100kg applied at early tillering. Once again, all treatment yields were broadly similar at 10.2 t/ha and the zero-N plot yielded 6 t/ha. Protein values were broadly similar too and there was no negative consequence from using urea.

Martin advised that poultry manure only be used on spring crops or on winter oilseed rape. He suggested that it be used to supply a maximum of 50kg N/ha, even on rape. It should be avoided on winter cereals as it may encourage diseases like mildew and the nitrogen that is not taken up by the crop in the autumn may well be leached, thus adding to cost. He also suggested that a spring application to a winter crop (where it cannot be incorporated) will give rise to volatilisation and N loss.

Where PM is being used, it is essential to know what it contains in order to help avoid waste and excessive rates. Analysis costs around €110 per sample.

These experiments showed that poultry manure successfully replaced the specified amount of artificial fertiliser. Martin commented that 4.27 t/ha of PM (68kg N/ha), plus 82kg N/ha as urea, cost €163/ha while 420kg 10-10-20/ha, plus 108kg N/ha as CAN, cost €225/ha. So it has scope to provide savings also.

Fertiliser advice

Advising on fertiliser input is not just a matter of having a soil test result and knowing the crop to be grown. Wexford Teagasc adviser John Pettit explained the challenges of trying to balance the major variables. What you need to put in relates to what has been taken out and so crop yields must influence the need for replenishment.

Among the major factors that an adviser must consider in this regard will be:

Ignoring any one of these will quickly lead to a drift in soil index levels and if deficiency is occurring then soil levels will drop and yield will also suffer. It is imperative that fertiliser regimes target the build-up of soil fertility levels up to the desirable Index 3 level for both P and K.

John recalled the early experiences on the Williamson farm in Wexford when it was in the BETTER farm programme. Despite applying what might be considered more than adequate P and K, soil levels fell after a few years. John said that this happened because the levels applied did not meet the off-takes of big winter cereal crops following the switch from spring to winter planting on part of the farm. When the current crop takes out more than was anticipated, this additional amount must be put back in to keep the soil in balance or to raise fertility, whichever is the objective.

Nutrient advice can be simple, John said, but the essential tools of current and old soil samples, farm/field yield records and fertiliser use history must be available to provide good advice. The challenge then is to choose the best-suited compounds to deliver the requirements for off-take, or better.

Lime remains a critical input to help get the best from all nutrients. On acid soils, this needs to be tested and applied every three to four years, as every fifth year is not frequent enough. This is also important for basic fertility. John explained how difficult and slow it is to build soil P levels. The experience on the Williamson farm showed that applying a surplus (over off-take) of 30kg P/ha over five years raised the soil P level by only 1 mg/L.

It was much easier to increase soil K levels. John said that every 0.81 kg/ha of surplus K increased soil K by 1 mg/L.

However, the ease with which either nutrient can be increased is influenced by the make-up of that soil, with the clay type being very important.

Fertilizer Association booklets

At the conference, PJ Browne from the Fertilizer Association of Ireland launched two new technical booklets in association with Teagasc. These are for use by farmers and advisers. One deals with soil pH and lime and explains its importance in terms of increasing the availability of nutrients in the soil and also helping to make better use of costly applied nutrients. The other deals with understanding major nutrient off-take and fertility building – a new P&K wheel.

Technically, lime is a nutrient and it gets used up or lost from the soil and so it has to be replenished regularly. It is perhaps the most important nutrient in that it affects the availability and utilisation of most other nutrients in a positive way.

Nutrients without the proper lime status will be less effective.

Lime is also important for the maintenance of good soil structure as it influences the whole soil biology complex, which is so important in the creation of a healthy, well-structured soil. This, in turn, helps drainage, workability and may even extend the working season.

The booklet explains what lime does, what optimum levels should be and it also explains why and how lime is lost from the soil. These are critical facts for those who work the land and try to live from it.

While many crops will still grow with insufficient soil pH levels, at current prices the return on money invested in lime is estimated at 7:1 over a five-year cycle. So spend €20 and the increased output will add up to €140, even where no other nutrient is applied. It’s basic common sense to lime.

The second booklet is a new phosphorous and potassium (P&K) calculator for grassland and tillage crops. Referred to as the P and K wheel, it can be used to get the maintenance P and K requirements for any crop at different yield levels. Separate tables in the publication tell how much extra nutrient can be added at the difference soil index levels for each nutrient to help build fertility to Index 3.

It is simple to use, based on a rotating wheel to view the rates through little windows. It also provides information on optimum pH levels for different land uses and also sulphur requirement. It also contains a table of available nutrients in the different organic manures, which is very useful.

This little booklet should be seen as being as essential to every farmer as diesel is to a tractor. It is designed to be left on the desk or table-top for regular use.

Spreading

The ability to spread fertiliser precisely takes on a new challenge where urea is to be spread at very wide bout widths. As the requirement for wider tramlines increases, so does the need for accuracy of spreader settings and for the quality of the fertiliser, according to Dermot Forristal of Teagasc.

Dermot explained that the accuracy of fertiliser spreading is always important and it is measured by a term called the coefficient of variation, or CV for short. This attempts to measure the accuracy or uniformity of the delivery of fertiliser rate across the spreading width of a machine. A low CV value (5%-10%) indicates good uniformity of rate across the spreading width, while a high CV (30%-50%) will have poor uniformity, inevitable striping and yield loss.

Dermot reported research that indicated a €38-€100/ha loss for high CV values, which dropped to €3.20/ha when the CV was in the 5%-10% range.

Fertiliser quality is important for spreadability and Dermot said that the most important quality parameters relate to the granules and include:

In general, larger granules are easier to throw further, but size distribution is also important. At its simplest, dust will not throw very far, while big dense granules could throw over 40m.

Density is an important characteristic. A fertiliser particle must have a certain mass to allow it to capture enough energy to be thrown a distance. Relatively large dense particles are more easily thrown, Dermot stated.

Imagine the difference between a table tennis ball and a golf ball. Both are broadly similar in size – one can travel well over 100m, while the other might not travel 10m while airborne. The density of many fertilisers is around one kilogramme per litre (1 kg/l) and this can be visualised in the size of a traditional 50kg bag of fertiliser. The normal density of urea is about 70%-80% of standard fertiliser at 0.7 kg/l to 0.83 kg/l and this requires a much bigger bag to hold 50kg. This alone makes urea more difficult to spread wide distances.

The ideal fertiliser for spreading is difficult to define, but certain principles apply when targeting larger widths. It is preferable that granules be rounded with a relatively smooth surface and large is preferable. Dermot indicated that at least 80% should be in the 2mm to 5mm size category. The granules also need to be strong and dense to help them resist the considerable impact that will occur when they are hit by the veins on the spreading discs.

All these things are important for the ballistic properties of a fertiliser and its spreadability. The figures for different fertilisers show the very broad range of physical characteristics that can exist between different products (Table 1). From this table, urea 1 would be very difficult to spread wide distances because the granules are very small and their low strength would allow them to break easily on the discs. Urea 3 was much more spreadable with relatively good all-around characteristics.

The type of spreader can also make a difference when spreading urea, largely because it can be so variable that it can challenge some spreading systems. Urea really needs a spreader that produces a nice triangular spread distribution pattern which overlaps comfortably between bouts to give a relatively uniform application across the full width.

Dermot said that machines which produce a more shouldered distribution pattern are more subject to the vagaries of field application (wind, etc). Such machines need a much tighter fertiliser specification to enable them to be spread well enough to do a good job.

Dermot advised growers that if they need to spread urea a considerable distance they must order a very specific spec which must then be checked on delivery. He warned about the challenges of trying to spread uneven blends of different ingredients as they can produce a banded application pattern. He cautioned even more about urea blends that contain other nutrients such as sulphur, phosphate or potash, because it may be easier to spread these elements a greater distance then the urea.