Science has come a long way in picking the time to seed and fertilise

MOST animals use lengthening or shortening daylight to work out the seasons for mating or migration. They sometimes get caught out by unseasonal weather, but mostly they’re right.

For farmers, though, knowing the optimum time to sow seed and fertiliser is a difficult art. Seeds sown too early may die or fail to thrive if they subsequently experience a prolonged cold, wet spell.

On the other hand, being cautious and sowing too late in the season can lead to low yields and poor quality grain, as well as a late and difficult harvest.

A mild spell in February could fool you into thinking spring has arrived early, but after a frantic spell of sowing you could see your work undone when winter returns with a vengeance.

Ancient farmers knew the importance of getting it right, as failure to do so led to hunger and famine. One of the reasons they set up rings of standing stones was to have an accurate farming calendar. Using the position of the sun and moon they were able to calculate the various seasons.

Later farmers used other tools, such as their knowledge of local weather folklore. Some even sat on the ploughed furrows with their trousers down to allow their bare bottoms to gauge the temperature of the soil. Thank goodness modern farmers take a more scientific approach.

I used a system called T200. Starting on New Year’s Day, the daily temperatures are recorded and added together. Freezing or minus temperatures are ignored. When the daily positive readings in degrees Celsius total 200, it’s reckoned that plant roots should be growing actively and capable of utilising fertilisers.

Another similar method is T100, where the daily temperature readings in the top six inches (15cm) of soil are added together from February 1. Again, negative readings are ignored until the total comes to 100, when the soil is deemed to be warm enough for plant growth.

Fertilisers are expensive so it’s important to get it right. Ammonium nitrate (AN) and urea, which provide the plants with nitrogen, have increased in price by 50 per cent in the past eight months, with AN now costing about £245 per tonne and urea up at about £295/t. This is more than can be explained by the weaker values of sterling and is largely down to tighter supplies of urea coming on to the market.

It’s important to ensure that crops are provided with adequate supplies of the main nutrients such as nitrates, phosphates, potash and sulphates as well as trace elements like manganese, copper, cobalt and selenium. Above all else, a fertile soil will be free-draining and not acidic – and that’s why lime needs to be regularly applied.

Nitrogen is important, as without it the machinery of photosynthesis cannot function – protein can’t be formed, so plants can’t grow. Maize, wheat and rice – the fast-growing crops on which humanity depends for survival – are among the most nitrogenhungry of all and demand more than soil in its natural state alone can provide.

Fortunately, man has developed industrial processes that capture atmospheric nitrogen and force it into a chemical union with the hydrogen in natural gas, creating the nitrogen fertilisers that modern crop varieties crave.

That nitrogen fuels bountiful harvests, without which human civilisation in its current form could not exist. Our planet’s soil simply could not grow enough food to provide the burgeoning world’s population with its accustomed diet. In fact, almost half of the nitrogen found in our bodies’ muscle and organ tissue started out in a fertiliser factory.

Potash is another vital ingredient in fertilisers in order to maintain good crop yields, although it’s not so important in grassland, as grazing animals return potassium to the soil in their dung and therefore potassium levels aren’t depleted as quickly as on arable land, where it is removed in the crops.

Fortunately, the UK is on target to have a £2.4 billion potash mine ontheNorthYorkMoors operational within the next five years. Sirius Minerals hopes to have the mine near Whitby opening in 2021 and producing 10 million tonnes annually, rising to 20m tonnes subject to council approval. The potash will be transported through a 23-mile tunnel to a processing plant on Teesside.

It’s reckoned that the growth in the world’s population, combined with the increase in biofuel technology, which leaves less land available for growing food crops, has led to a big rise in demand for potash.