Whether you run an arable or livestock enterprise, soil is a vital component of farming. So important in fact, that when the government introduced “Farming rules for water” they made soil testing a legal requirement. The requirement is to test your soil, on cultivated land, a minimum of every 5 years for pH, magnesium, potassium, phosphorus, nitrogen (although SNS can be used to calculate nitrogen in the soil instead).
Determining what nutrients are already within the soil is essential when considering what the crop needs and what fertiliser to apply. A deficiency in any of the elements listed above will reduce crop growth, quality, and therefore, yield.
Nitrate (as Nitrogen NO₃) is a readily available element in both organic and manufactured fertilisers and is arguably the most important for any plant or crop. However, Phosphorus, also found within most fertilisers, is becoming increasingly more polluting to the environment.
Farmers have been considering Nitrogen levels within their soils, fertilisers, and manures for many years, particularly if they are within an NVZ (Nitrate Vulnerable Zone). Whilst Nitrogen levels have been a top priority for farmers, Phosphorus levels have had less consideration.
Unlike Nitrogen – which is fast acting – Phosphorus reacts with other elements which are already within the soil. This chemical reaction transforms soluble P into an element which is insoluble and unavailable to the plant. Insoluble Phosphates can be supplied to soils at less frequent intervals and will slowly degrade to soluble P which plants can utilise.
Farming Rules for Water state that nutrients in addition to the required amount should not be applied. Phosphate levels in soils have been rising for some time now and some of this Phosphate (P) can escape into watercourses via soil erosion and run-off.
When a farm EA (Environment Agency) inspection takes place, soil test results are studied and correlated, and are taken as a priority, along with the nutrient management plan. Soil indices greater than 2 for P and K require little extra nutrient. pH level is significant in the result of any soil test, especially when phosphates are concerned. pH levels should be at approximately 6.5. However, the more acidic or alkaline the soil is, the greater the risk of phosphates being locked into the soil for a lengthy period, as soil P and K indices alter extremely slowly.
Additional phosphates applied, whether that be by manufactured compound fertilisers or organic manures, to a crop/plant that has no nutritive need for it, can be wasted. Factors like rainwater runoff from agricultural land and farm tracks can cause any soil bound with any excess phosphates to flow into nearby watercourses, thus causing a significant concern to the environment.
The main area of concern around watercourses and phosphorus levels is eutrophication. Eutrophication is a process in which a watercourse becomes increasingly overloaded with minerals and nutrients, eventually leading to an overabundance of algae and plants.
This oversupply of algae and plants, also known as algal blooms, will ultimately begin to perish and decompose. In the decomposing process large amounts of oxygen are consumed and carbon dioxide is released. This results in extremely low oxygen levels for all other plant life and fish.
It is important that farmers look at the guidelines, such as RB209 and Farming Rules for Water, or consult an agronomist for guidance and reliable direction to yield an economic response from their soil test results. Applying excess P may benefit the soil long term but will not be beneficial to the crop or financially profitable short term.
