Without nitrogen, most of the world’s crops wouldn’t exist. Nitrogen is to corn, wheat and rice, what water is to fish. Yearly, more than 100 million tonnes of nitrogen are applied to crops in the form of fertilizer, helping them grow stronger and better. But issues arise when nitrogen run-off occurs, polluting air, water and land in the process. It is estimated that nitrogen discharge accounts for a third of agriculture’s greenhouse gas emissions.
“We’ve known for a long time that using nitrogen as fertilizer is great for farming to increase productivity but there's a whole range of threats resulting from nitrogen leaking into the environment,” said Mark Sutton of the Centre for Ecology & Hydrology in Edinburgh, who works with UN Environment Programme (UNEP) on the science of nitrogen pollution. “By considering nitrogen as a whole, it is becoming increasingly clear that nitrogen pollution represents a massive waste of valuable fertilizer and other nutrient resources. It means that smart nitrogen management can help reduce threats to water, air, climate and health, while contributing positively to farmers’ livelihoods.”
Here are three ways we can improve the way nitrogen is used in farming.
Using chemical fertilizers more holistically
Loss of nitrogen fertilizer through emissions means more pollution, lower yields and higher costs to farmers. To cut overuse and limit the amount of nitrogen run-off into air and water, farmers could adopt precision technology to calculate the best possible time and amount needed for crops to thrive.
“There are plenty of opportunities for reducing nitrogen losses from agriculture and recovering nitrogen which would otherwise be wasted,” said Sutton. “The first step is to improve the efficiency with which chemical fertilizers are used. This may mean tuning the timing of application or allowing reduced inputs by better matching to plant needs.”
Options for tuning fertilizer inputs range from using “leaf colour charts” or electronic colour sensing, where a deep green colour of leaves means fertilizer is not needed, to using improved fertilizer products that inhibit the main loss pathways.
Avoiding chemical fertilizers
Some farmers or companies prefer to avoid nitrogen fertilizer altogether. For this to be profitable, natural sources of nitrogen would need to replace the fertilizer. Sutton suggests planting legumes (such as beans, lentils or peas) in between other crops as a nature-based solution to convert nitrogen gas from the air to a form of nitrogen usable by plants. This method adds nitrogen to the soil, meaning there is no need for simulated nitrogen fertilization. There can be limitations to this approach, especially if soils are deficient in phosphorus, so research aims at increasing natural nitrogen fixation rates.
Mahesh Pradhan of UNEP commented: “One of the advantages of using biological nitrogen fixation is that it provides a natural ‘slow release’ form of crop nitrogen supply that matches to crop needs. In this way, the fraction that is wasted as pollution is expected to be much smaller.” There are still concerns however, when ploughing in a legume to benefit a later crop, as this may give a temporary peak of nitrogen pollution losses.
Better managing livestock waste
Good management of livestock manure is critical in reducing nitrogen pollution. Manure can be beneficial for soils and plants if applied at appropriate levels, but it can also lead to ground and surface water pollution if allowed to run-off.
In every 3786 litres of manure, there are 23 kilograms of nitrogen, 12 kilograms of potassium, 9 kilograms of phosphorous and 2 kilograms of sulfur. By better managing livestock manures carefully, farmers can retain those valuable nutrients and limit nitrogen pollution. For example, by keeping urine and dung separately and by covering manure stores, including a mix of urine and dung.
“If you can smell your dung heap, it means that you have already lost some goodness to the atmosphere,” said Sutton. In this way, reducing air pollution means more nutrients are available for farmers, reducing their need for expensive nitrogen inputs.