As commodity prices across the globe rise, it is important to keep those increases in your mind as you trade in straw this harvest and into autumn and winter.

Tillage farmers should not lose sight of the value of not just the straw for bedding and feeding, but of the phosphorus (P), potassium (K) and carbon (C) values within that straw.

Prices of P have doubled since last autumn, while K has increased in price by approximately 60%.

Muriate of potash (50% K) and 16% super phosphate are now both priced at approximately €450/t, so valuable nutrients are being taken away in straw bales.

Taking an 8t/ha (3.2t/ac) spring barley crop, it can be estimated that 3kg of P/ha are taken off in straw, while 53kg of K/ha are removed when straw is baled.

These figures vary between crops and yields. Table 1 below shows the crop yields and the offtakes of P and K.

Taking a price of €450/t for muriate of potash and 16% super phosphate, we can then work out the price per kg of each nutrient and the value of P and K taken away in straw.

P came in at €2.81/kg, while K came in at €0.90/kg. This equates to a total P and K value of €56.13/ha of P and K on at 8t/ha spring barley crop; €57.14/ha on a 10t/ha winter barley crop; €64.45/ha on an 11t/ha winter wheat crop; and €87.63/t on a 9t/ha winter oat crop.

Carbon is the up and coming commodity

Farmers are hearing more and more about C and the value of storing it in their soil.

Increased C levels mean increased soil organic matter content, but they also mean that the soil is sequestering carbon from the atmosphere and storing that C.

This C has a value and can be traded in a market if measured and calculated over a period of time.

The value of that C on the market is rising. C credits on the European Union’s Emissions Trading System have risen from €33.69/t on 4 January to €55.34/t on 23 August.

As we move forward, C could be an important commodity for farmers.

After all, the Straw Incorporation Measure (SIM) introduced by the Department of Agriculture was developed with the aim of storing C in the soil.

Table 2 shows the potential C storage value of a crop of straw. These calculations assume a C content of 40%, a straw offtake of 60% and a C retention potential of 20%.

Taking the same yields as used in the P and K examples above, the range in the potential value of C from these cereal crops is €21.12/ha to €29.04/ha.

Total accountable value

The total accountable value of P, K and C per hectare in straw can be seen in Table 3. It is important to remember that there are many benefits to straw incorporation that are very difficult to put a value on.

These benefits include improved soil structure and reduced diesel use, soil organic matter build-up, increased biological activity and release of nutrients and trace elements from the soil.

It is also important to remember that the P and K won’t be available to a crop straight away and may take some time to become available, particularly where soil microbial activity is low at present.