Can alternative products help cut back on typical N sources?

There are plenty of manufacturers of alternative fertilisers, biostimulants and biological products that claim their products reduce the need for conventional fertilisers but, in many cases, there is limited independent data to back those claims up.

There are exceptions, however, and with the high cost of conventional nitrogen sources, one expert says this could be the year to give them a try and assess performance on individual farms.

See also: How to offset high fertiliser prices in arable crops

Foliar nitrogen

Some relatively new foliar nitrogen products are starting to find favour among growers, but the most critical thing is applying them at the correct time.

The concept of applying foliar nitrogen certainly isn’t new, but in the past growers have been put off by the relatively high price.

However, with traditional N fertiliser currently at such a high price, depending on the time it was purchased, foliar N products are much more attractive and should return a margin over input cost.

Foliar products include PolyNPlus, Nitamin and EfficieN28 and are largely based on urea polymers such as methylene and triazone, which are created by reacting urea with formaldehyde in different ratios.

The products typically contain about 30% nitrogen from readily available and slow-release sources, with some offering additional sulphur or trace elements.

Niab’s southern regional agronomist and technical development lead Syed Shah has carried out work with PolyNPlus in trials and MZ28 on farm and says they have several advantages, including a low salt index, so risk of scorch is much lower than liquid N products.

They can also be applied with other products such as fungicides, so may save a pass with a spreader or sprayer.

However, the most interesting characteristic of these foliar products is their nitrogen use efficiency (NUE), particularly later in the growing season.

In Niab Tag trials, it was shown that NUE of soil-applied N in winter wheat significantly decreases the later it is used, as conditions generally become drier and roots become less efficient at taking up nutrients.

This means there can be a significant yield penalty where applications of traditional nitrogen are delayed, as well as risking nitrogen losses into the environment through leaching.

At the same time, the crop canopy is becoming larger and more suited to intercepting and absorbing foliar products, and PolyNPlus was shown to have a NUE of 100% when applied at growth stage 37-39.

This means a 25-litre/ha (8.75kg N/ha) application of PolyNPlus or similar product at T2 can replace 40kg/ha of soil-applied N in April or May in drier conditions.

However, it should be noted that if rain arrives soon after a later application of soil-applied N, the difference in NUE could be less significant.

Typically, a 25-litre/ha dose of PolyNPlus costs about £62, so where growers have paid £2/kg N and substitute 40kg/ha with a foliar application, they could save about £18/ha this year.

The product can also increase grain protein, but like with any applied nitrogen, results are inconsistent and dependent on conditions of the season.

Dr Shah says if growers want to reliably hit 13% grain protein, variety choice is a much more important factor, with cultivars such as Crusoe more efficient at converting N into protein compared with other milling varieties such as Zyatt or Skyfall.

This should be considered carefully by milling wheat growers next autumn if N prices remain high.

Foliar N – key points

  • Apply 140-180kg/ha of soil-applied N before GS32 to avoid yield penalty
  • 5 litres/ha foliar N at T2 or T3 can then replace 40kg/ha soil-applied N

Biostimulants

In independent trials, biostimulant products have not shown any positive yield effects, but they do increase root mass, so should help crops use applied fertiliser more efficiently.

Dr Shah has carried out work with products such as Nutri-Phite PGA (3:26:7) and Prosper Plus (4:30.5:15).

These products contain a small amount of nitrogen, phosphorus pentoxide and potassium oxide. Nutri-Phite PGA also contains trace elements manganese and zinc.

Also in the trials were Zonda and Bridgeway, which are amino acid-based biostimulants. Dr Shah says differences were probably not seen due to the full nutrient and fungicide programme applied to the trials, so plants never became stressed – a situation where biostimulants are claimed to be most beneficial.

However, improved rooting is observed when using the products and, in a year when growers will be looking to cut back on N rates, this could ensure crops make the most of lower amounts applied.

Biostimulants – key points

  • No clear yield benefit in independent trials (limited data)
  • Products tested did improve rooting, so potential to improve nitrogen use efficiency

Friendly bacteria

Another relatively novel type of product being used by crop producers is soil-applied bacteria, which provided a significant yield benefit in 2020 in Niab Tag trials.

Soil-applied SR3 from Kent-based biofertiliser company Plantworks contains four different plant growth-promoting bacteria, including Gluconacetobacter diazotrophicus, Bacillus amyloliquefaciens, Derxia lacustris and rhizobacterium species.

It is claimed that the bacteria in the product fix atmospheric nitrogen and can unlock soil-bound phosphorus.

Dr Shah applied the product to winter wheat alongside total N applications of 125kg/ha, 175kg/ha and 250kg/ha, and saw yield increases of 0.43t/ha, 0.55t/ha and 0.31t/ha, respectively.

However, the same effects were not seen in 2021, when cold and dry conditions prevailed through April and early May.

This led Dr Shah to conclude that more work is required to understand the effect of spray timing and environmental factors such as soil type, soil temperature and soil moisture.

Manufacturer advice is to apply the product with coarse nozzles or a dribble bar in early spring as crop growth resumes, ideally before a period of rain to wash the bacteria into the soil.

It should also be applied alone without herbicides and fungicides, and at least a week after any applied nitrogen.

Dr Shah says soil temperature should ideally be about 10C at application, and SR3 can lead to a saving of 20-30kg of bagged N given the right conditions.

For a cost of £15-£20/ha, it is again a product that could prove its worth in 2022. However, he doesn’t recommend it as a standard application, but encourages farmers to give it a try in tramline trials.

Soil-applied bacteria – key points

  • Bacteria product SR3 increased yield of winter wheat in 2020
  • Response in 2021 not seen, probably due to weather
  • Potential to reduce N input by 20-30kg/ha
  • Try in tramlines trials this year to assess on-farm benefit

Feeding biology

A final product that is worth a try to cut back on bagged N is QLF Boost, a liquid carbon fertiliser designed to feed soil microbes that help with nutrient cycling.

In 2020 and 2021, Dr Shah investigated the performance of QLF Boost in winter wheat alongside applications of 150kg/ha and 200kg/ha of N.

Results showed the addition of QLF Boost to 150kg/ha N produced the same yield as 200kg/ha, potentially replacing 50kg/ha of N.

Like with applications of bacteria, conditions need to be suitable at the time of use, and the product works most effectively on soils with an organic matter content of 3% or more.

It should also be applied when soil temperature is 10C or above and using a relatively high water rate. In wheat, the manufacturer recommends applying at drilling, then alongside spring N and fungicide applications.

As the cost of QLF Boost is relatively expensive (80p/litre), it may not pay for itself when nitrogen is at 70p/kg.

However, Dr Shah says assessing its performance in tramlines trials this year is a good idea and will help inform whether it will be useful for cutting bagged N use in future seasons if fertiliser prices remain high.

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