It’s time to maximize efficiency with nitrogen

With the first cuts well underway and nearly complete in some areas, attention is quickly turning to fertilizer applications to replenish valuable nutrients ahead of the second cuts.

There will be a desire to get the most out of all inputs given the high prices of fertilizer purchased this year, and farmers should be looking to make any gains, however small, in all possible areas, starting with maximize the efficiency of nitrogen use, says Alan MacKechnie, sales manager at Origin Fertilizers.

“Helping the plant achieve better nitrogen recovery has a quantifiable economic benefit. Not only is more of the applied nitrogen available to the plant to increase crop yields and protein, but losses through leaching and volatilization are significantly reduced.

“We need to manage what is under our control to make better use of any nutrition applied to the soil. Farmers should consider whether their fertilizer policy is the right one, because the most expensive fertilizer is the wrong fertilizer.

Tools such as the AHDB Cost-Benefit Calculator for Nitrogen Use on Grasslands can help and can serve as a useful guide for farmers who are undecided on fertilizer strategy.

AHDB’s calculator compares the cost of nitrogen applications with the feed value of grasses. This will give an indication whether it is more profitable to apply nitrogen fertilizer to grassland or to buy animal feed.

However, Mr MacKechnie said the calculator has limitations as it does not take into account the beneficial effect of sulfur in increasing nitrogen use efficiency and the importance of maintaining levels of other essential nutrients in the profile.

He added that there is a tendency to reduce smaller nutrients such as potassium and sodium in favor of direct nitrogen applications when prices start to rise, but there is a risk that an approach only Nitrogen-based inevitably contributes to plant stress.

“Potassium uptake increases when the plant is stressed, as the nutrient helps regulate the opening and closing of stomata and maintains cell turgor, which is critical in preventing plants from wilting early during stress.

“However, as high potassium absorption can increase the risk of hypomagnesemia (grass shift), sodium is an important nutrient needed to reduce this risk. If sodium levels are low, it replaces potassium in the saliva of cattle and once secreted into the rumen inhibits the absorption of magnesium through the rumen wall.

Silage removes many essential nutrients with each cut, so ensuring they are replaced will improve grass quality for subsequent cuts. Maintaining the correct nutrient ratios and applying what the grass needs will help alleviate weed lags and increase the palatability of the grass, by converting the sugars in the grass into more soluble carbohydrates.

“Grass should receive high nitrogen and sodium applications to increase dry matter yield, but nitrogen utilization and conversion to protein can be low under dry, cloudy weather conditions. Buffering capacity can be increased, slowing the fermentation process when nitrate levels are above 0.10% in a fresh herb analysis.

“High sugar levels, aided by properly timed sodium applications, will help increase the speed of the fermentation process. Higher sugar content translates to more food for bacteria, so the faster the pH drops.

Read more: Silage Management – Targeting High Quality Silage

In addition to the smaller nutrient profile, farmers will strive to get the most out of slurry applications. Therefore, ensuring the correct time and method of application should maximize the nutritional value of the applied product.

“Having the manure tested is essential to know what you are applying and this will allow you to assess what additional nutrients, if any, are needed. Slurry applications should take place immediately after harvest, with an application of inorganic fertilizer a week later in accordance with a nutrient management plan.”

The reason for this, he said, is to reduce the risk of denitrification, which occurs when covering inorganic nitrogen fertilizer in the slurry. It creates anaerobic conditions and means nitrogen is lost to the atmosphere as nitrous oxide. It is therefore crucial to leave a week between applications and to always apply the slurry first.

However, if slurry is not applied, an application of fertilizer immediately after the first cut is essential to maximize second cut yield.

“A blended fertilizer application based on soil testing can reduce the number of passes needed after harvest and ensure the fertilizer applied is matched to soil requirements,” MacKechnie concluded.