All crops require optimum nutrition to grow well. Plants will extract naturally occurring nutrients from the soil but in order to produce crops of the highest quality farmers apply fertilisers. Wheat plants require the key nutrients of nitrogen, phosphorus and potassium. In addition they will require lesser amounts of other nutrients such as sulphur, magnesium, and manganese together with a range of trace elements.
Nitrogen is an especially important input for milling wheat as it is required to produce sufficient grain protein with the desired functionality. Crops derive nitrogen from three main sources – residual nitrogen in the soil, organic fertilisers and that which is applied during the growing season. Nitrogen inputs vary greatly but many milling wheat crops will require up to 300kg nitrogen during the season. This means that, depending on the expected soil nitrogen supply, farmers will apply 100 – 250 kg N during the season. Nitrogen is very soluble so it is only applied when it is unlikely to be washed away and when plants are able to absorb it from the soil. This is usually done using a number of critically timed applications. Some may be applied to the seedbed but the first application is usually in late February/early March, with the second in late April or early May. Additional nitrogen for bread making wheat is often applied at the end of May or in July as a foliar spray of urea solution.
Solid ammonium nitrate granules are the main form of straight N used on UK wheat. Alternative forms include urea, calcium ammonium nitrate or a combination of ammonium nitrate and urea.
Sulphur is another important element for milling wheat crops as it assists in the formation of strong gluten and also limits the formation of asparagines which is the precursor of acrylamide.
AHDB produce a range of technical leaflets about nutrient topics but the main source of information is the Fertiliser Manual (formerly RB209) the new edition of which will be published in 2017.
Many soils are relatively low in organic matter content. Farmers take steps to replace this organic matter by chopping and spreading straw after harvest. However, other sources or organic matter are often used including biosolids, composts and animal manures.
Biosolids, the treated form of sewage sludge, have been in use in the UK, US and European agriculture for over fifty years. They are a safe, sustainable, highly regulated and environmentally sound method of waste disposal; biosolid recycling represents less than 5% of organic material applied to land in the UK with just 3% of arable land in the UK treated with biosolids. Agronomic advantages from their use include improved soil nutrient (nitrogen, phosphorous, sulphur and magnesium) and organic matter content, increased crop yields and improved available water capacity and drainage.
Biosolids can be produced in cake, granular, pellet or liquid form and are spread over land before being incorporated into the soil or injected directly into the soil by specialist contractors. There is no obligation on farmers to use biosolids but a demand in excess of supply exists.