|ACKROYD, VICTORIA - University Of Maryland|
|SPARGO, JOHN - Pennsylvania State University|
|DAVIS, BRIAN - University Of Maryland|
|GARST, GRACE - Former ARS Employee|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2019
Publication Date: N/A
Interpretive Summary: Soil phosphorus (P) levels in agricultural fields with a history of animal manure application may have excessive soil P because manures provide more P than nitrogen (N) relative to plant needs. Excessive soil P can result in losses that have substantial negative effects on the quality of surface and ground water supplies. Organic farmers may be able to supply adequate N to corn while maintaining or drawing down soil P levels by decreasing manure application rates when a legume cover crop is used. In a two-year study at three organic sites in Maryland, ARS scientists found that poultry litter application rate can be reduced by half and still achieve the same corn grain yield when used in conjunction with a legume cover crop. The legume provides most of the corn’s N needs while the poultry litter, applied at the half rate, provides additional N and sufficient, but not excessive, P. These results will be of interest to farmers, environmentalists, policy experts and others concerned with the health of the Chesapeake Bay and other estuaries impacted by agricultural losses of N and P.
Technical Abstract: On organic agricultural fields with a history of animal manure application, excessive soil P levels can limit fertility management options because manures provide a narrower ratio of plant available N:P than most crops require. Organic farmers may be able to supply adequate N to corn while maintaining or drawing down soil P by decreasing manure application rates when a legume cover crop is used. In a two-year study at three organic sites in Maryland, USA, we examined the combination of a winter annual legume cover crop (hairy vetch, crimson clover, and Austrian winter pea) at three levels of spring poultry litter (PL) application: 1) an N-based rate (sufficient to supply all the N needed by corn), 2) a P-based rate (replacing the P removed during corn grain harvest), and 3) a no-application control (0 PL). Cover crop biomass varied by site and by year, ranging from a low of about 2,000 kg ha-1 for Austrian winter pea in 2010 at a site in Queen Anne to a high of almost 5,000 kg ha-1 for Austrian winter pea in 2011 at a site in Eden. Cover crop N accumulation ranged from 60-155 kg N ha-1. Corn yields tended to be lowest in the control (0 PL) no-cover treatments, and similar in the N-based and P-based treatments no matter the cover crop treatment. Our results indicate that on sites with a history of PL application, PL can be applied at a P-based rate in conjunction with a legume cover crop, to successfully balance the need to support corn yield with the need to maintain or draw down soil P levels in accordance with environmental stewardship principles and local regulations.