Nav: Home

Matchmaking for sweet potato? It's complicated

August 08, 2018

Some relationships can be complicated. Take the one between sweet potato crops and soil nitrogen, for example.

Too little nitrogen and sweet potato plants don't grow well and have low yields. Too much nitrogen, however, boosts the growth of leaves and branches at the expense of storage roots. That also leads to low yields.

"Carefully managing soil nitrogen levels is essential to obtain high yields from sweet potato crops," says Adalton Fernandes, an agronomist at the Center for Tropical Roots and Starches at São Paulo State University in Brazil.

Fernandes is the lead author of a new study that determined how much nitrogen is needed to maximize yields from sweet potato crops in Brazil.

The researchers discovered field history matters when trying to apply the optimal amount of nitrogen for sweet potato crops. Cover crops grown in the same plots prior to sweet potato crops affected how much nitrogen was needed.

Sweet potato plants grown in plots previously used to grow legume cover crops needed 35% less nitrogen fertilizer. Growing sweet potatoes after a cereal cover crop, however, was no different than growing them in a plot that had previously just had weeds.

"We show that growing legume cover crops, and incorporating them into the soil as they flower, is a simple technique that can reduce how much mineral nitrogen needs to be applied for sweet potato farming," says Fernandes.

Cover crops are often grown cyclically with economic or cash crops. They may be incorporated into the soil as green manure. They may also be left on the surface as living mulches.

Different cover crops bring different benefits to the growing relationship. Legumes, for example, can increase soil nitrogen levels. Beneficial bacteria in their root nodules pull atmospheric nitrogen into the soil. But they also decompose faster than cereal cover crops once terminated.

"That releases nitrogen into the soil earlier during the sweet potato growth cycle," says Fernandes. "We needed to know more about how different cover crops affect soil nitrogen availability for subsequent sweet potato crops."

Fernandes and colleagues used a study site in southeastern Brazil. The site is a good match for the tropical conditions and sandy soil typical of several areas where sweet potato is grown in Brazil.

In different plots, the researchers grew either one of two legume crops, a cereal crop, or allowed weeds to grow from seeds already present in the soil. When the legume and cereal cover crops were flowering, they were terminated. The plants were incorporated into the soil.

Subsequently, the researchers planted sweet potato in the plots. They tested how much nitrogen was needed to maximize yields.

When sweet potato was grown after legume cover crops, they needed about 110 pounds of nitrogen per hectare (roughly the size of a baseball field) for optimal yields. In contrast, sweet potato crops needed more than 168 pounds per hectare of nitrogen when grown after a cereal cover crop or after weeds.

"We show that there is no reason to use a cereal cover crop prior to sweet potato cultivation," says Fernandes.

Currently, recommendations of how much nitrogen fertilizer to use with sweet potato crops do not consider the history of cultivation in the area. That can result in farmers using more or less fertilizer than needed.

"We now better understand how much nitrogen is needed to maximize sweet potato yields in tropical regions," says Fernandes. "This will help manage the application of mineral nitrogen fertilizers during sweet potato cultivation."

In addition to maximizing yields, using less fertilizer also reduces costs for farmers. That's especially important in Brazil. Much of the sweet potato crop is grown on family farms with low technology use.

Fernandes is now pairing other species of legumes as cover crops. He is testing whether they may be more efficient at providing nitrogen for sweet potato crops. He is also exploring whether combining legumes and cereals as cover crops in the same area can provide different benefits to sweet potato farmers.
-end-
Read more about this research in Agronomy Journal. This research was funded by the São Paulo Research Foundation (FAPESP) and the National Council for Scientific and Technological Development (CNPq).

American Society of Agronomy

Related Nitrogen Articles:

Fixing the role of nitrogen in coral bleaching
A unique investigation highlights how excess nitrogen can trigger coral bleaching in the absence of heat stress.
Universities release results on nitrogen footprints
Researchers have developed a large-scale method for calculating the nitrogen footprint of a university in the pursuit of reducing nitrogen pollution, which is linked to a cascade of negative impacts on the environment and human health, such as biodiversity loss, climate change, and smog.
A battery prototype powered by atmospheric nitrogen
As the most abundant gas in Earth's atmosphere, nitrogen has been an attractive option as a source of renewable energy.
Northern lakes respond differently to nitrogen deposition
Nitrogen deposition caused by human activities can lead to an increased phytoplankton production in boreal lakes.
Researchers discover greenhouse bypass for nitrogen
An international team discovers that production of a potent greenhouse gas can be bypassed as soil nitrogen breaks down into unreactive atmospheric N2.
Bacterial mechanism converts nitrogen to greenhouse gas
Cornell University researchers have discovered a biological mechanism that helps convert nitrogen-based fertilizer into nitrous oxide, an ozone-depleting greenhouse gas.
Going against the grain -- nitrogen turns out to be hypersociable!
Nitrogen is everywhere: even in the air there is four times as much of it as oxygen.
Soybean nitrogen breakthrough could help feed the world
Washington State University biologist Mechthild Tegeder has developed a way to dramatically increase the yield and quality of soybeans.
Trading farmland for nitrogen protection
Excess nitrogen from agricultural runoff can enter surface waters with devastating effects.
Measure of age in soil nitrogen could help precision agriculture
What's good for crops is not always good for the environment.

Related Nitrogen Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Jumpstarting Creativity
Our greatest breakthroughs and triumphs have one thing in common: creativity. But how do you ignite it? And how do you rekindle it? This hour, TED speakers explore ideas on jumpstarting creativity. Guests include economist Tim Harford, producer Helen Marriage, artificial intelligence researcher Steve Engels, and behavioral scientist Marily Oppezzo.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".