Although the poultry litter added a lot of carbon over the years, that carbon tended to evaporate as carbon dioxide in the hot and humid region. So at the end of the experiment, the soil carbon didn’t change a lot.
Because carbon dioxide is a greenhouse gas, tracking soil carbon also gave the scientists insight into greenhouse emissions.
“Our results overall provide bases for developing guidelines for greenhouse gas emission predictions and for more realistic expectations of soil carbon improvement from applying poultry litter,” says Feng.
Soybeans planted in the fields grew better in the years after poultry litter was added to the soil. One year later, soybean yields were 8% higher. And three years later, yields got even better. They were 11% higher than in fields that received synthetic fertilizers.
“Left over nutrients from litter in the previous consecutive application can maintain higher soybean yield for three more years after stopping litter application,” says Feng.
Because a large portion of poultry production takes place in the Southeast U.S., this research on local crops and soils is especially valuable to farmers in the region.
“These results are useful for development of management practices that improve soil health and function,” says Feng.
These findings could be helpful to crop farmers deciding how to fertilize their fields. And poultry farmers can get a clearer picture of the value of the litter they produce.
Gary Feng is a soil scientist with the U.S. Department of Agriculture. This research was supported by the Mississippi Soybean Promotion Board.
Photo Caption: Scientists Gary Feng and Haile Tewolde test how fast water can infiltrate into soils that were fertilized by commercial inorganic fertilizer and manured by poultry litter. Credit: Gary Feng
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