Legumes reduce the need for fertilizer, but farmers must plant them in advance

The American Farm Bureau Federation said on June 18 that 70% of the more than 5,700 farmers it surveyed could not afford all the fertilizer they needed for the 2026 crop year. One way to need less bought nitrogen is a crop, and a crop has to be planted in advance.

Farms.com reported on April 22 that legumes fix nitrogen from the air and add it to the soil, and that farmers who grow them in rotation, taking turns with other crops on a field, need less chemical fertilizer for the next crop. At this year's prices, that service is likely worth more. However, the saving goes to the crop that follows the legume, so the legume has to be planted in advance, and its size varies from field to field. The World Bank projected in May that urea prices would rise this year before easing in 2027. If they do, a legume planted now would deliver its credit to a later crop, after prices have begun to ease.

The shock shows in nitrogen prices. The World Bank said on May 14 that urea, a nitrogen fertilizer, climbed above $850 per metric ton in April, the highest level since April 2022. The bank's wider fertilizer price index also rose in the first quarter, its sixth increase in seven quarters.

The cost is forecast to show up in farm budgets. USDA's Economic Research Service, in a farm income forecast updated in September, expects spending on fertilizer, lime and soil conditioners to rise by $5.3 billion this year. That is 25 percent of the $21.2 billion increase it forecasts for all farm production expenses. Set side by side, the bank's price readings and the department's cost forecast point the same way.

The American Farm Bureau Federation said in its June analysis that, compared with USDA's earlier 2026 projections, fertilizer costs were revised 9% to 13% higher across major crops. Farms.com reported on May 11 that costs had risen by nearly one third since last fall, which made careful nitrogen management more important.

Planning numbers from a year ago pointed lower. Terrain, a Farm Credit publication, projected last year that urea would average $620 per ton for this year's crop, within a range of $610 to $635. The World Bank's April reading, published in May, sat above the top of that range, although the two are quoted in different units and may not describe the same market.

A credit for the crop that follows

The agronomy is not new. The FAO said in a World Soil Day release almost a decade ago that cereals grown after pulses, the grain legumes, yield on average 1.5 tonnes more per hectare than cereals not preceded by pulses. That gain equals the effect of 100 kilograms of nitrogen fertilizer, the agency said. It described the biological fixation of nitrogen as a natural process that would cost an additional $10 billion a year in synthetic fertilizers.

Yield studies point the same way, though unevenly. CIRAD said in a press release four years ago that a study published in Nature Communications pooled 462 field experiments across 53 countries. Introducing legumes improved yields of the main crops by about a fifth overall, and by less in Europe. At the far end, a trial reported in Scientific Reports found that maize yield more than doubled after velvet bean, compared with maize grown alone.

The limits start with where the nitrogen goes. The Government of Saskatchewan says in its guidance on legumes that most grain legumes can obtain between 50 and 80% of their total nitrogen requirements through biological fixation, and that faba bean will fix up to 90%. However, it says most of the fixed nitrogen leaves the soil when the grain is harvested, because the plant stores it in the seed. Cereals that follow still require less nitrogen fertilizer, the province says.

Rich soil blunts the effect further. The same Saskatchewan guidance says high soil nitrogen levels reduce fixation, because legumes use most of the available soil nitrogen before they begin to fix it from the air. On that reading, a legume on a field already high in nitrogen may fix less.

Age matters too. University of Minnesota Extension said in crop guidance four years ago that corn following alfalfa stands at least two years old, and at least half alfalfa, requires no nitrogen fertilizer on many soils. Credits for one-year-old stands of alfalfa or red clover are smaller, it said, and red clover earns less than alfalfa.

Cover crops, planted between cash crops, come with conditions of their own. The University of Tennessee Institute of Agriculture wrote in an advisory nearly five years ago that it recommended a nitrogen credit for a well established legume cover crop that has reached early bloom. There is "not a simple answer" on how much nitrogen a cover crop supplies, it wrote, because several factors influence availability. It also noted a risk: ending the cover crop late would delay planting and raise the potential for yield loss in cash crops such as corn.

Urea prices are projected to ease in 2027

The World Bank projected in May that urea prices would rise nearly 60 percent this year before easing in 2027, as Middle East exports recover and natural gas prices moderate. The American Farm Bureau Federation said in its June analysis that USDA projects fuel and fertilizer prices will drop that year as the Strait of Hormuz opens and resumes normal traffic.

A grower who seeds alfalfa now faces a wait. University of Minnesota Extension guidance says corn grown after alfalfa stands that are two or more years old, and that met its minimum share of alfalfa, requires no nitrogen fertilizer on many soils, and that credits from one-year-old stands are smaller. The World Bank projected in May that urea prices would ease in 2027, before a stand seeded now is that old.

Farms.com reported in April that legumes do not fully replace fertilizers but reduce dependence on imported inputs and soften price shocks. Because the saving goes to the crop that follows the legume, that suggests a cushion of this kind has to be planted before the shock it softens.

Farms.com reported in May that fields following alfalfa, or receiving common rates of livestock manure, often require little or no additional commercial nitrogen. That suggests a farm with such fields likely needed to buy less nitrogen this year. The American Farm Bureau Federation said in June that most respondents to its survey could not afford all the fertilizer they needed.

Urea prices will show which way this breaks. If urea eases in 2027, as the World Bank projected in May, a legume planted now would deliver its credit as prices ease. If urea instead holds at or above its April level into next year, that credit would arrive at shock prices.

The sources agree that legumes reduce the need for nitrogen fertilizer. The record, however, describes a saving that goes to the following crop and varies field by field, and the World Bank projected in May that urea prices would rise this year before easing in 2027. On that reading, farmers who wanted the saving this year needed legumes in the ground before this year's crop.